Thanks for the diagram and the explanation , I always attributed my parting problems to a a 72 year old Lathe with lots of wear. It will take considerable head scratching to figure a way to mount a rear tool post on my Lathe . 🤔 ! Inverted parting is out of the question since I have a threaded chuck and have already discovered the problems by trying to thread with tool inverted and Lathe in reverse 😉 . ( came close to a real disaster ) .
I also found out why the lathes that we had at school didn't have a reversing switch fitted to them. I convinced my Head of Department to have one installed and also found out how readily a screw mounted chuck will unscrew itself. Very exciting! Regards, Mark
Hi Preso, Nice machining on the solid tool post. If the video ran for an hour, I would still be watching for the entire time. Looking forward to the next installment. You and your family stay safe.
Thanks Michael. We here in Australia embraced the metric system back in the 1970's and we never looked back. It's a pity we cannot convince our North American friends to do the same. 😁 Regards, Mark
OH my you must have been watching me yesterday when I smashed my parting tool, bent the work and gave me a hell of a fright thinking I had broken a gear or something. I look forward to your solution
Gday Preso, I like the way you explained why the rear tool post is an advantage, makes sense, the interface for the TouchDRO looks better then the version I have, have a great weekend mate, cheers
Matty, I am using the beta version of TouchDRO. I believe that you can update your version of the app from Google Play Store. Mine updates automatically because Yuriy put me on the beta testing list. Regards, Mark
Great work Mark. Sound analysis is a primary element to success in design. Material selection is also critical. And isn’t cutting malleable iron simply a joy!
Yes, the iron stock was very nice to work with. The steel that I am using came out of a giant rectangular column that was part of a surgical operating table! The column was used to hydraulically raise and lower the table itself and it has yielded some much needed stock for my workshop. Having the means to cut it up is also nice. I have one of those little metal cutting bandsaws but it wouldn't be up to the task of cutting some 8" X 4" steel. Regards, Mark
I too had parting issues until I swapped to a GTN3 parting system w😊hen I instantly became a parting expert, now I can part anything that’s not hardened up to about 50mm on my Harrison M250. I thing a rear mounted GTN or other insert parting system would be the ultimate.
I have looked at that style of insert parting tool but I resisted buying one because I feared I would just smash it like the other parting tools I have used previously. However, I have designed the tool block so it can take that style of insert blade by rotating the tool block 180 degrees. If the HSS blade works the insert type will be the next upgrade. Regards, Mark
I guess your Myford has the tee slotted cross slide? I wonder why so few lathes have that feature? I think Hemmingway kits sell a version of the rear mounted tool post for Myford sized lathes. Regards, Mark
I never understood the point of the rear part-off technique, reasoning that the material couldn't possibly "know" which way the blade was oriented. Of course I was missing the crucial difference between a downward vs a lifting cut. Your analysis made the point with wonderful clarity. Thanks, and I eagerly await the rest of the series…
The ability of iron to absorb vibration was known to machine tool builders very early on in the Industrial Revolution. Your choice of using iron for the toolholder was very wise considering it was for a tool that is more susceptible to vibration in comparison to other tools.
I noticed the Whitelaw Engineering poster behind the DRO, I worked for the old fella when I was 15 and again for Rocky when I was in my mid 20's, that was 40 odd years ago.
I met Rocky Whitelaw. He was a good friend of my Head of Department and he introduced me to him about 30 years ago. I tried to get him to quote me a price on a four jaw chuck for my Colchester but it was like haggling for Persian rugs in a Turkish market. 😁 Regards, Mark
When I first got my 13" South Bend I was having a lot of trouble with parting off until I backed off the gibs on all axis and loosened the lathe up a bit. I know it sounds weird but it worked for me, lol.
That sounds counterintuitive but if it works that's great. I think that there is a lot of weird physics going on during parting off operations and my diagram is greatly simplified for clarity. Individual lathes will give different results with exactly the same tool bit too. Regards, Mark
That's good to know. Some of the cool kids on the block swear by solid tool posts (Robin Renzetti, Stefan Gotteswinter) so I am very keen to see if my version gives me some peace of mind when parting off. Regards, Mark
I made a rear solid parting post for my little Sherline lathe a few years ago, it worked very well. My "big" (10x22) lathe has a solid toolpost almost permanently attached instead of a compound, and it helped a lot too. Yours is much nicer :)
I do want to try using the rear tool post as a solid front mounted tool post. If it works as well as Robin Renzetti and Stefan Gotteswinter say it will I may make another to replace the compound. My only problem is the way the Colchester compound is mounted. It has a circular tee slot and two tee bolts. Removing the compound takes ages because you have to use a spanner to loosen the hex nuts and you can only swing the spanner a short way in the pockets on the side of the compound. It's my only gripe about the design of the Colchester Student. Regards, Mark
@@Preso58I didn't get down into the guts of the Colchester Student I used in school, but would a ratcheting box-end wrench with very short throw work under those constraints? I've got some cheap ones from GearWrench that advertise ratcheting action in just 4° of freedom. Wouldn't be quick in that space , but it would be easy.
I have had all of those problems when parting off, and now use a hacksaw ( unless it brass ). Your explanation of the problem was brilliant and has persuaded me to make my own rear tool post. Great video, can’t wait for the next part.
Thanks Chris. I also resort to either a small bandsaw or an angle grinder with a thin cutting disc. I can usually part off stock up to 25mm diameter in the lathe but after that I get very nervous. Regards, Mark
@@Preso58 Some sizes just seem to work. For instance, 25 mm and 1 inch (25.4 mm). Also, much of the world is held together by 6x1 mm and 1/4 (6.35 mm)-20 fasteners.
I found quite a long thread dealing with parting off on one of the machining forums and up until I did that research I mistakenly reasoned that all the deflection took place locally in the extended end of the parting blade. As it turns out, the movement takes place in all the parts right down to the bed of the lathe. That explains why I was seeing such large movements in the tip of the parting tool when it dug in or when it chattered. It's amazing what you can learn when you go down these rabbit holes. Regards, Mark
@@Preso58 I have a spare toolpost from when I bought the multifix so maybe I will repurpose that as a rear tool holder. My lathe does not have a 'boring table' so making a platform for the rear toolpost would have to be part of the job. Very useful thanks. Cheers
Always look forward to your videos. Informative, educational and well presented. Length is never an issue for me. Thanks for sharing your knowledge and experience.
Hi Mark! Every time I see you wipe away swarf with your hand I get a pain on the back of my head - right where my metalwork teacher used to hit me with the wooden brush when he spotted me using my hands for the same purpose! Great video, great explanations - even admitting to the odd "dumb ass" mistakes 😉
Mark, your metal work teacher was quite justified for reprimanding you! However he may have been more worried about litigation if you had cut yourself. I do have a little hook for clearing the birds nests on the lathe but it is true I am guilty of sticking my fingers where they don't belong. Regards, Mark
You will love how much easier it is to part off with this unit. I made the same conversion on my atlas craftsman lathe about a year ago. I found a source for the raw casting to make a T nut slotted cross slide and after that was installed the rear cutoff post was, added. I also set up a rear tool post at times when I want a second operation handy when making a part
Thanks. I have finished all the parts and it's installed on the lathe. Unfortunately, everything came to a standstill when our children came to stay for the Christmas break. I aim to start testing it out tomorrow. Regards, Mark
I used to have no end of trouble parting off and I've got a reasonable sized lathe, a Harrison M300. The cure for this was a "new" (good previously used) front spindle bearing. Turns out the tiny amount of pitting at the bottom of the front bearing shell allowed miniscule amounts of play. Before I changed the bearing, a rear toolpost was on the long term project list, after several snapped tool blades and damaged insert holders.
I wish I had the confidence to part off with power feed. I haven't had a dig in for quite a while but I am always expecting it. I am guessing your lathe has bronze split bearings? I believe the Gamet bearings in the Colchesters are hideously expensive. The other issue with parting off is having bell mouthed chuck jaws. That is also something I need to address. Regards, Mark
I had no idea that Tommy Emmanuel was also a machinist! Superb reasoning, dialog, and execution, thank you for sharing. I intend to try this out myself on a 8.7x30 import benchtop lathe as soon as I can locate some affordable grey iron.
On the glass scales I got I noticed that the extrusion has provision for double seal strips but only one pair were installed. I found a seller on aliexpress that sold the seal material by the meter and installed the second set. Very cheap peace of mind.
I have not checked to see if the Sino scales have the provision for a second set of seals. I know that the "good" scales have better sealing options. I fitted Sino scales to my Colchester lathe back in around 2004 and they are still performing perfectly. I don't use a lot of flood coolant on it though although I do have a pump fitted and it gets used occasionally (for parting off). Regards, Mark
Thanks for making this video. Parting has always been challenging for me, your animation has helped me understand why. The rear tool post amy be the answer. Looking forward to seeing the conclusion.
Not sure that anyone would design a lathe to cut slightly concave when facing. I would certainly want it too cut as straight and as flat as possible. I have your lathes bigger brother the Triumph, which was fitted with the rear toolpost before I got it. The main issue with it is the way it has been configured to take a special parting tool which I don't have. Having said that I have had no issues parting off any way. Been watching your videos for awhile now and have now subscribed, please keep the good work.
I cannot recall where I had read about lathes being set up to cut concave. I believe the amount of angular displacement is tiny, usually around 0 to 0.02mm per 300mm. I also just checked and Dr. Georg Schlesinger wrote in a book called Testing Machine Tools that even toolroom lathes will have some concavity but it can be zero too. I think the point was that the facing cut should never be convex. Flat is preferable but concave is acceptable. I did get some photos of the original Colchester rear tool post and you are correct that it was set up to take some sort of proprietary tool holder for parting blades. Regards, Mark
Mark, I made one of these for my Bantam a few years ago, and have never looked back. I'm sure it'll work. My Dad owned a machine shop with turrets & capstans: parting was always done from the rear.
Excellent through analogy of lathe tool cutting forces and rigidity, or lack of it!. Great addition to any light duty lathe, Capstan and Turret lathes have obviously used rear tool posts, mainly for parting off, but for principally different reasons as I understand? Thanks for sharing. Best regards from the Black Country UK 🇬🇧. John.
Most CNC slant bed lathes use rear mounted and inverted tools but they are already massively rigid machines. I had to look up "Black Country" on Wikipedia! It was the one area that we didn't visit on our massive road trip around the UK. Oh well, there's always next time. Regards, Mark
@@Preso58 If you like canals, canal locks and crooked buildings ( caused by subsidence), and local beers, then it's the place to visit 👌. It had vast deposits of Limestone and coal, hence industry. I think many lathes have issues with parting off, due to high forces, and either poorly manufactured or worn cross and compound slides, but that's stating the obvious. Hope you chamfered the clearance hole at the bottom of the counterbore, this is missed by many design draftsperson, more critical on hardened items. Another feature on deep clearance holes, is to have standard clearance diameter on upper surface, then drill larger size from underneath leaving 2 or 3 diameters in thickness below, this prevents binding of the screw it is slightly bent, or threaded drunk. All the best Mark. John.
Interesting project. I liked your illustration at the start explaining why I can't part off successfully, unfortunately I cannot fit a toolpost at the back of my "Raglan Little John " lathe (c 1953) so it's the hacksaw for me!
A tip for you then lol swing your compound slide as far as you can to be square to the axis of lathe bed as long as you can turn the cross slide handles you are ok. If not get as close to 90 degrees as you can. Then make sure the compound is wound up to its stop, the loosen whatever gib screw locks you have and tighten the gibs fully so the slide is unable to move, do the locks up and you have a poor man's solid tool post and while you are about it tighten the cross slide gibs up to give a little friction as most of us probably have the cross slide a little too loose anyway and that's how I did it before I made my own rear parting off block which uses the tee slots on my cross slide.
Thanks Randy. I am hoping it gives me a bit more confidence with parting off. Maybe I am especially nervous about this process but I have witnessed some sensational dig ins and smashed tools during the time I was teaching metal machining. If you heard a big bang somewhere in the shop it usually meant a smashed parting tool. Regards, Mark
Hi Mark. Looking forward to the rest of this build. I’ve got a H&F 960B, roughly the same size as your Colchester. I’d love to add a rear tool post to that lathe. Great animation showing the mechanics of tool posts. One other factor is the direction of ‘lift’ of the work in a standard rear tool post. Probably not a lot in a modern lathe with precision headstock bearings…. Anyhoo, thanks for putting in all the extra work and time doing these videos. Regards Robert PS That Malleable CI makes nice chips…. the drilling looked almost like cutting steel.
That was the first time I had machined any malleable iron. It is very nice to work with and somewhat kinder to the tools than regular grey cast iron. Regards, Mark
I have a rear mounted parting tool holder for my 13'' lathe. Used it a few times, but find it just makes for a cluttered crosslide, and difficult to get measuring tools in to work piece. I now lock the gibs on the compound, as it doesn't get used much, and part with a standard parting blade mounted in a QC toolholder, and part off with power feed. Next job is to make a solid toolpost mounting, and do away with the compound.
Unfortunately, I don't have any locks on my compound. I have never been game to part off with power feed. I hope that I can have a bit more confidence with the new setup. I am going to start testing it out for real tomorrow. Wish me luck! Regards, Mark
Great explanation of the benefit of using a rear mounted parting tool. I recently acquired a Colchester Chipmaster that I intend to make a rear tool post holder for. I have an older samsung tablet that is now surplus, I may just use it with a touch DRO system on my lathe.
I have always admired the Chipmaster for it's streamlined shape. Almost Art Deco! My only advice if you are thinking of getting the TouchDRO system is to use glass scales with it. I started out with capacitive scales and I was a bit disappointed with their reliability. Regards, Mark
Another tool that seems to work well in a standard QCTP is a "spring cutting off tool holder" A la Armstrong. Winky's workshop channel has a good discussion "Better, Best ..." . This tool holder works for those of us who can't mount a rear mount tool post. Cheers.
I watched Mark Winquist's making of that tool. I actually modelled it in Autodesk Inventor so I could carry out some finite element analysis on the flexing forces involved. I sent him the results as verification that it would unload the cutting forces before they were transferred down into the compound slide. I believe that many metal planer tools were of the "gooseneck" variety which may have been the same as the Armstrong tool type. Regards, Mark
Ciao Mark,. A very nice project from the drawings to the machining, i liked so much the forces display, very clear!!And that block of steel Is huge!On My Colchester Bantam i have sometimes noise sometimes not, i really hate to cut with parting tool! Wait to see the finish and the test!! Ciao Mark, Alberto.
Thanks Alberto. I have finished the steel riser block and I just have to get to work on the tool holder itself. So far, so good! I feel confident it will be successful and if I can have the confidence to part off with power feed I will be very happy. Regards, Mark
@@Preso58 It will works of course, unfortunately in My Colchester Bantam i don have the T-nuts way like in your Student, but i will think at something similar in the future! 😀
Hi Mark, you have done a good explanation using those drawings. Like you, I have had a lot of issues parting and it was something that I did not like doing (broken tools, the part climbing up on the tool then being pulled out of the chuck etc.) . That was until I watched a parting video by Blondie Hacks. She has some good tips in that video and now I'm much more confident and my parting experiences are a lot better. But, that rear parting setup will give you a lot of rigidity and it will eliminate the 'dig in' potential. It will be good to see it in action. Have a Merry Christmas from us in NZ.
Thanks Jon. I have one of Eccentric Engineering's front mounted inverted parting tools and it's a good alternative to the traditional parting blade. However it does need to be set up exactly square to the axis of the lathe so it doesn't rub along the edges of the tool. That side loading will overheat the blade very quickly and it will still dig in. Flood coolant helps but it's always messy. The new version I am building has the tee profile so the there is a lot less side contact. I should know if it lives up to the hype by the end of next week. Regards, Mark
I have an admission to make. 2:25 I shrugged off this diagram of the cross section of the lathe parts and how they react under load as ........ 'we already know all this'. But I DID learn something here. And as usual I appreciate knowledge shared on your channel Mark. Look forward to the Part II. I imagine you'll have to make sure that gib on the back of the carriage that keeps the back from lifting up .... must be fitted properly or the entire carriage could pivot on the bed front way. where in the traditional parting set up it just pushes down into the bed front way
Bobby, I also learned something after I created that diagram. I used to think that all the bending took place in the overhanging parting blade. If that were the case the cutting edge would bend downwards and away from the part centre when parting off conventionally. However when you take into account the whole assembly of parts from the lathe bed upwards it's a different story. Regards, Mark
I used to suffer the same problems. I feel silly it took me 15 years to figure it out. The secret is p type (T shaped) cut off blades. Make absolutely certain they are 100% verticle. Jack them, shim them. Do what ever you have to do. Don't just trust the tool holders. Use a square or sweep them with an indicator. Stone them razor sharp. Set the hight with a presision tool. Take your pick. Don't eye ball it with your tailstock. You will be amazed how well they work. Parting off went from something I had all but given up on. I'd just go get the hacksaw. To something thats actually fun. The angle blades work too but setting them perfectly verticle is more of a pain. Start with the P type.
Thanks, I do all of the things you have suggested but I also find that power feed is more reliable than hand feed which seems counterintuitive. Also, lots of coolant is a must. I am still amazed at how non scary it now is to part off what I once considered to be difficult or impossible stock.
Love this, good timing as well. I used to enjoy parting off, lately been having problems. Something must have changed in my setup... im going to invert parting tool and try running in reverse.
I already have one of those tools and it's an improvement on the conventional parting blade. Eccentric Engineering sells a type called the FoR tool holder www.eccentricengineering.com.au/products/for-front-or-rear-inverted-parting-tool Mine is an older style that has the tapered blade and it resembles an conventional tool holder but with the blade inverted. It has a lot more overhang than the improved FoR type. The holder I am making will resemble the newer type. Regards, Mark
Mark I just don't understand , my parting off blade cuts like butter. Works great. I bought it last year. It's a Makita metal chop saw. 😜😜😜😜 I gave up years ago on parting off on my lathe. I believe I have that parting off curse also. If it could go wrong it went wrong. Lol.
I have looked at those high speed metal chop saws often and if I had the extra room I would definitely have one. I have one of the old style friction saws but it screams like a banshee and it throws grit and sparks hither and yon. Not especially workshop friendly. I am still hopeful that the rear toolpost will live up to the hype. Regards, Mark
Excellent video and it answers why my mini lathe starts then stops cutting as I try to provide a constant feed rate. It seems like putting the parting bit upside down and running in reverse would give some of the advatages of a rear mounted parting method. Your videos are aways interesting, useful, with good camera work, and editing. Thanks!
Larry, I have an inverted parting tool that mounts in the front tool post. It is better than the conventional type in that it does lift clear when loaded but you still have to push it into the cut and they are no good for a threaded chuck (I have a LO taper on my spindle so I can run in reverse). I am hoping that the rear mounted tool will give me more confidence to part off using power feed.
Great explaination of the torque pivot and tool reaction. I'd not ever really considered it but might have to look at this on my home lathe. Really enjoy your video's Mark.
Thanks Brent. Maybe you can confirm this for me. Just from watching videos of slant bed CNC lathes, I assume the tools are rear mounted although not always inverted? I guess they use linear rails too. Keep up with the sexy CNC posts on Instagram! Regards, Mark
@@Preso58 Yes they can run either way but generally spindle rotation is the same on a CNC as a manual and the tool is somewhere in between from above and the rear so sort of inverted. Box slides are still quite common for CNC's. Not as quick a linear in most cases but great in rigidity. If you want to throw another variable into your parting equation.... look up y-axis parting. It does your head in to start with. This runs the spindle in reverse to what might initially seem logical but it puts the load directly into the toolholder rather than across it. It requires a very rigid setup to work for all the reasons you described.
Nice presentation on the forces involved Mark. It certainly shows that you were a teacher! I did a very similar thing to my Chinese lathe/mill last year and it works reasonably well. Especially if I use my shop made cross slide motor driver. I can control the speed and once I've got it cutting nicely I can concentrate on getting the lubrication of the tool with the suds brush to give a nice smooth parting off.
Putting a rear part off tool post on my Chinese lathe totally transformed the part off ability. I didn't arrange an upside down tool so I have to reverse the spindle. I was thinking if the tool is pressed down by the forces there is no further down than hard down. I thought it less likely to induce chatter.
I think that not having a compound slide under the tool will give you a massive increase in rigidity. I did initially think that inverting the tool was unnecessary but I was won over by not having to reverse the spindle to part off. I am hoping to have this operational by the end of the week. I have already machined the riser (video out next weekend) and it's just the tool holder to go. Regards, Mark
I find it worth the effort of making a physical model. You will see in the next episode how I can use it to verify that I am placing the features in the correct faces of the part. Regards, Mark
Tan-fastic! So sad to hear you have the same problem with those cheap scales, I always thought it could be rectified, Anyhow vert nice design, much need out there in hobby land. Enjoyed, cheers!
Hey Mark..........as a hobbyist myself, I to find myself to be in more of the coward category as well haha. I am actually in the process of making a router attachment for my tool post with a slitting saw to take care of that part. It will also permit more function later for grooving geometry and hole patterns. Something to think about for a later build cause I can see the possibilities as I am making this. Great build Preso! I look forward to the next vid.
Actually, Mark, your observations regarding force, vibrations, and such for parting apply equally to most all the operations on the lathe. If there were a good way to see what's happening on the back side, we should do most operations on the back.
You are correct in that all cutting operations carried out in the conventional front mounted tool post will tend to make the cutting edge dive into the work. There must be some other factors at play though when using parting tools. Perhaps because they are so slender compared to their stick out length or that they can overheat when buried so deep in a closely fitting groove. Whatever it is, it can lead to some spectacular catastrophic failures. Many CNC slant bed lathes are designed with the cutting tools on the back side of the lathe axis and many are fitted inverted so maybe there is a reason for that. Regards, Mark
I do somewhere in the back of my mind have a design for a parting tool that looks a bit like a steady rest - two roller points of contact and the third is the parting blade which is fed in by a lever action. Still mounted in the tool post but as there is two points of contact as support the forces are converted from a down force to a rotary force . One thing i have found that really helps with parting off is you can never have enough coolant - now that might be flood coolant or something like WD40 which i have extensively tested and found to be the best all round coolant for parting off - even on steel. Unfortunately for me I spent many years breathing in Kero fumes and as WD40 uses this as a base liquid even a small amount of it makes me sick, so I have had to find something else to use.
That sounds like an interesting concept for a parting tool. I have never seen one in the wild but I am guessing that having two floating points of support would help. Absolutely agree about coolant. I have flood coolant on my lathe but I hate using it. It makes such a mess. However excessive heat will make the blade jam sideways in the kerf or make the tool gall up which in turn gives you runaway heating. Regards, Mark
Gday Mark, Fantastic job with the illustration graphic and explanation. Design and machining of the base looks great...that ductal iron sure machines nice. See you in the next episode... ATB....Dean
Thanks Dean. Yes, that continuously cast ductile iron is nice to work with. I have never really machined it before and the guy I bought it from seems to have gone out of business which is sad. It must be tough selling small volumes of specialist materials here in Australia. Regards, Mark
G'day Preso. I enjoyed your analysis. I have a Ward 3A capstan lathe that has a rear toolpost. I assumed it was there for efficiency reasons given that these lathes were used to make lots of the same parts, but I wonder if it was also for the very reasons that you outlined. Which would also make it more efficient!
Thanks Rod. When I acquired my Colchester lathe we also took delivery of a medium sized capstan lathe. I cannot recall the make but it also had a rear mounted tool post. The capstan had all the turning tools and a couple of drill chucks. I actually "souvenired" the rear mounted tool post which had a rack and pinion mechanism for advancing the tool. There was no tool mounted in it but I am now thinking that it would have been for a parting tool. Interesting! Regards, Mark
It all goes in the bin. It is too hard to separate all the different materials but I do know that some people who machine mostly brass or aluminium will recycle the chips. Brass especially is probably worth collecting and taking to the scrap merchant. Regards, Mark
Great project ahead! Taking the cartoon, I'm also a coward 🙂 My excuse is I have a minilathe with a compound that acts like rubber when parting. Sure I can work on all dovetails and make all the modifications available on the web and on YT, but there's still not enough rigidity with so little metal mass. So, the rear tool post is a good alternative, the problem being that there's not enough room for it in the compound, although some designs do exist. It's amazing that a much flimsier Sherline parts much better than a minilathe (Clickspring is a good YT example of this).
I must say that I have seen some impressive feats of parting off in small lathes. I am sometimes jealous that I balk at even small diameter work. Clickspring makes everything look easy so he doesn't count!😁 Regards, Mark
@@Preso58 LOL. I agree, and Chris (Clickspring) is really out of this world :-) I was absolutely overwhelmed by the extent of his research and painstaking recreation of the Antikythera mechanism and the tools to make it.
Hi Mark Where did you buy that piece of malleable cast iron in Australia. I live in Perth. I have Harrison M250 which has only 3 screwed holes on the back of the cross slide. Looks like I will have to take it to pieces and drill and tap on the milling machine. Look forward to the drawings
David, I got that piece of malleable iron from Mancave Metals last year but I have been told that the website is down and it's possible that the business has folded. I guess that trying to run a specialist metal supply business in Australia is hard. Try Edcon Steel www.edconsteel.com.au/store/products/steel/cast-iron/round-bar/3d I haven't bought anything from them yet but apparently they will sell cut to length stock and the prices seem good. I will make the drawings available when I have finished the build. Regards, Mark
Good stuff. Here in Missouri metric bolts are about 50¢ or $1 a piece (expensive) and SAE bolts are $1.49 a lb (cheap) for grade 5. I've wondered often if opposite was true in metric countries. Can you shed some light on this?
I don't pay a lot of attention to the prices but here in Australia, imperial fasteners are still available but they are considered to be "legacy" stock. The range is limited at big chain hardware stores but there are some local online stores where you can get just about any thread type, imperial or metric. I think the prices would be roughly the same. The dominant "hardware" imperial thread type is usually Whitworth. UNF and UNC can be had at motor accessory shops but again, the range is limited and you generally have to buy in packs of three or five which drives me mad. You always need two, four or six! Regards, Mark
32:30 I had to laugh. You and Mr. Pete have neighbors that do things while you're making videos. You with Mr. wood chipper and Mr. lawn mower with Mr. Pete.
Yes, my neighbour does like his wood chipper and he is retired like me so he has more opportunities to use it. I have seen Mr. Pete discussing his lawn mowing friend! Regards, Mark
how does lift on the slide tighten anything? isn't it effectively just resting on the ways and that works because normally all the forces are downwards
The cross slide will lift if you are parting off with an inverted tool from the rear. As it does so it will close the clearance in the dovetail. This also increases the drag between the cross slide and the gib strip. I am guessing that the saddle will also lift at the rear (slightly). My lathe has a shear on the rear way which does stop the saddle lifting clear. Regards, Mark
I think you missed movement points on your setup that could provide movement before the tip of the tool; from the bottom up they are: 1. Ways for the saddle; this only affects if the bed is extremely worn causing parting blade to “twist” to the right. 2. Ways for the Cross-slide; worn or loose. 3. Compound Rest rotating joint; loose or contaminants between the surfaces. 4. Ways for the Cross slide; loose or worn. 5. Toolpost rotating joint; loose or contaminants between the surfaces. 6. Quick change or Lantern post; QC could be loose, have contaminants between the mounting surfaces or locking mechanism, or loose/worn QC dovetail, plus either style can have loose/worn tool mounting surfaces/screws.
I agree. My diagram was greatly simplified for clarity. There are lots of sources for flexing and movement and with lots of measuring devices it would probably be possible to map the forces more accurately. Regards, Mark
Hmmm... You can aply this concept of forces, fulcrums... to any work on the late, not just parting. Parting is just extreme load cos of wide cutting with. So.. it will be better to run spindle in reverse, and have all tools upside down. As a bonus, you will get chips that go directly down, not spraying around.
That was one of the bonus features of the inverted front mounted parting tools that I bought from Eccentric Engineering. Having the chips form underneath also allows for cutting oil to make it into the bottom of the groove. Regards, Mark
Interesting- not so sure about your fulcrum points- I think there are many, wherever movement can happen. The 'dig-in' is more likely due to the tool rake pulling the tool in. It is not a single point cutter! The rear post just has more rigidity, and the slide is operating in a different position, where there is likely less wear. A popular solution is to have the tool holder slightly flexible, with a pivot point above the tool. This means any movement both reduces the cut and the rake. Typically, this starts a cut with a high pitched sound, as the tool finds the balance between bending and cutting, and then settles into a good cut. I certainly intend to make a rear post- not just for the rigidity, but it is needed for almost every part, and it can be set up once and left, always available. Might experiment with the flex though- conveniently this will be below the tool in this configuration, so necking the support in the Y directions should do the job..
Thanks. My diagram was greatly simplified for clarity and I agree that there is no single bending centre. One thread that I had read on a forum was comparing the bending action of the rear toolpost design with the older style of gooseneck tools that had a slot to allow for the bending forces to disengage the cutting edge of the tool. I watched a couple of videos by Mark Winquist (Winky's Workshop) where he made a replica of that type of tool and had good success with it on an older (I think South Bend) lathe. I should have the entire build finished by the end of the week. I feel confident it will be an improvement and my ultimate goal is to be able to part off using the power feed. Regards, Mark
@@Preso58 Yes, I watched that too. With a rear post the required bend point is below the tool, so much easier to arrange. I intend experimenting with this- there will be an optimum load deflection for a given tool type- possibly different for different materials.
If I need to accurately measure with calipers I try to zero them with the same force (by feel) that I will be using for the real measurement, and try to zero them when measuring at roughly the same place on the shanks. At least in my head this should remove most of the flex in the material as well as the slack in the bearing surfaces.
Hello to Sweden! Thanks for the feedback. Measuring with calipers, even good ones like Mitutoyo is a challenge at times but until I get a set of digital micrometers I'll take the convenience of being able to zero them out and measure the difference. Regards, Mark
I am running the beta version of TouchDRO. I just checked on Google Play Store and the latest version is 2022-11-26. My version updated automatically since I am registered as a beta tester but you should be able to go to Play Store and update manually. The new version does have some pretty cool tools in it including probe and rotary encoder support for rotary tables. Regards, Mark
Yes, the rear holder comes from most home shop lathes have or used to have chucks that threaded on the spindle. The chuck would come off the spindle if you tried cutting in reverse.
Almost. I have a tool that I can use front mounted with an inverted blade. You do have to reverse the spindle and I find it better than the conventional parting tools. As some people have identified below, you are still pushing the tool with the leadscrew though. Regards, Mark
Hello Mark, I've made the same rear tool post for my Emco Unimat 8 (lower size) and I'll make another one for my Myford ML 10. Parting off on small lathe is not a peace of cake , but whith these tool-posts it's Ok . Important point, is to lock all the movements you don't use. What is the software you use for the analysys? Regards - Didier
Didier, I can lock the saddle on my lathe but often I don't bother when I am using the front mounted inverted parting tool holder that I have. It is "almost" as good as a rear mounted inverted tool but you are still pushing the tool into the work instead of pulling it as you can do with the rear mounted tool. I used Corel Draw for the animation. I used it a lot when I was teaching Graphics at school. It has some very good tools to allow for CAD like drawing but it is strictly 2D. Regards, Mark
@@Preso58 Mark, on my both lathes I made anti backlasch nuts, and with that I have no problem in parting. The pressure is constant , and I have no wobble and looseness. I never used Coreldraw but it seem atractive
Simon, I already have a front mounted inverted parting tool and it is a big improvement on the conventional type. You do still have to push the tool into the work though. I prefer it to the Chinese style of insert parting tool since you can sharpen the HSS blade to a very fine edge. I find the tip radius on the inserts to be a disadvantage on soft materials like brass and aluminium. Regards, Mark
No, the cheap tablet is still running. It was very sluggish to start up though and my wife pensioned off her old Samsung so I snatched it up real quick. Regards, Mark
If you are referring to the aluminium trays that cover the tee slots, I did not video their manufacturing. I saw the idea on someone else's mill on Instagram. My primary reason for wanting them was so I wouldn't lose small parts and tools down into the tee slots. It also makes the clean up a bit easier. They are just made from 2mm aluminium sheet. The corners are not welded. There are some ribs fitted underneath that locate in the tee slots. The ribs are made from some composite decking material. Regards, Mark
Hey Preso. Long time stalker/watcher of your channel, and another denizen of god's country in SEQ. Quick question, where did your get your bar stock for this job? Love your work mate. Cheers Tom R
The big chunk of malleable iron came from a now defunct web store called Mancave Metals. However you can purchase cut lengths of "Durabar" from Edcon Steel www.edconsteel.com.au/cast-iron/ The riser block and tool holders came from some big chunks of good quality steel that were salvaged from a donated surgical operating table! It was full of cast iron, hydraulic cylinders, carbon fibre and electrical gear. A real treasure trove. Regards, Mark
Is this same as upside down tool and changing direction of rotation ? I admit I have thought about doing this, but ever since I switched to a solid tool post without the compound I've not have a lot of issue parting.
It's slightly better than having an inverted parting tool at the front of the lathe in that the leadscrew is pulling the tool into the workpiece instead of pushing it. Also, for those that have a screw on chuck it means that you don't have to cut with reversed spindle direction. Regards, Mark
Here is a link to the 2D drawings. I would suggest you check your centre height very carefully and compare it to the drawing that I used. The position of the slot in the tool holder doesn't include much adjustment and depending on what type of parting blade you have it may need adjusting. I made an extra tool holder for a carbide insert blade and it did need shimming. www.dropbox.com/s/66uvsurxhoin8g4/COLCHESTER%20REAR%20TOOL%20POST.pdf?dl=0 Regards, Mark
Hi Mark brilliantly presented video. Coming on nicely. Not sure if you watched my build on one of these. My idea was to be able to fit different blades in the holder , so I made it slightly adjustable up & down. Probably the best add on I have made. Works brilliantly as I am sure yours will. Regards. Steve. P.S My drawing was on the back of a fag packet.
Steve, I did watch your build and it motivated me to move my version up the list of jobs to do. I want to be able to fit a carbide insert tool on the other side of the riser for harder materials. I will wait to see how the HSS tool works though. Regards, Mark
Unfortunately, no. I will have to do some additional work to match the hole pattern which holds the compound slide down. It has a radial tee slot and two bolts but I think it can be done. Regards, Mark
Thanks for the diagram and the explanation , I always attributed my parting problems to a a 72 year old Lathe with lots of wear. It will take considerable head scratching to figure a way to mount a rear tool post on my Lathe . 🤔 ! Inverted parting is out of the question since I have a threaded chuck and have already discovered the problems by trying to thread with tool inverted and Lathe in reverse 😉 . ( came close to a real disaster ) .
I also found out why the lathes that we had at school didn't have a reversing switch fitted to them. I convinced my Head of Department to have one installed and also found out how readily a screw mounted chuck will unscrew itself. Very exciting!
Regards,
Mark
Hi Preso,
Nice machining on the solid tool post. If the video ran for an hour, I would still be watching for the entire time. Looking forward to the next installment. You and your family stay safe.
I Love this Video. The Language is English (little Problem) but you are using the Metric System. This is great to me.
Michael from Germany
Thanks Michael. We here in Australia embraced the metric system back in the 1970's and we never looked back. It's a pity we cannot convince our North American friends to do the same. 😁
Regards,
Mark
OH my you must have been watching me yesterday when I smashed my parting tool, bent the work and gave me a hell of a fright thinking I had broken a gear or something. I look forward to your solution
Yep, it's happened to me too. I was convinced I had torn the side out of the tee slot in my compound slide.
Regards,
Mark
Great creation Mark. Excellent content. Superior workmanship. I'll Be Back ! Nuff Said.
Gday Preso, I like the way you explained why the rear tool post is an advantage, makes sense, the interface for the TouchDRO looks better then the version I have, have a great weekend mate, cheers
Matty, I am using the beta version of TouchDRO. I believe that you can update your version of the app from Google Play Store. Mine updates automatically because Yuriy put me on the beta testing list.
Regards,
Mark
Great work Mark. Sound analysis is a primary element to success in design. Material selection is also critical. And isn’t cutting malleable iron simply a joy!
Yes, the iron stock was very nice to work with. The steel that I am using came out of a giant rectangular column that was part of a surgical operating table! The column was used to hydraulically raise and lower the table itself and it has yielded some much needed stock for my workshop. Having the means to cut it up is also nice. I have one of those little metal cutting bandsaws but it wouldn't be up to the task of cutting some 8" X 4" steel.
Regards,
Mark
I too had parting issues until I swapped to a GTN3 parting system w😊hen I instantly became a parting expert, now I can part anything that’s not hardened up to about 50mm on my Harrison M250. I thing a rear mounted GTN or other insert parting system would be the ultimate.
I have looked at that style of insert parting tool but I resisted buying one because I feared I would just smash it like the other parting tools I have used previously. However, I have designed the tool block so it can take that style of insert blade by rotating the tool block 180 degrees. If the HSS blade works the insert type will be the next upgrade.
Regards,
Mark
Hi Mark, Thanks for addressing this tool I want it for my Myford Super 7 .
I guess your Myford has the tee slotted cross slide? I wonder why so few lathes have that feature? I think Hemmingway kits sell a version of the rear mounted tool post for Myford sized lathes.
Regards,
Mark
I never understood the point of the rear part-off technique, reasoning that the material couldn't possibly "know" which way the blade was oriented. Of course I was missing the crucial difference between a downward vs a lifting cut. Your analysis made the point with wonderful clarity.
Thanks, and I eagerly await the rest of the series…
The ability of iron to absorb vibration was known to machine tool builders very early on in the Industrial Revolution. Your choice of using iron for the toolholder was very wise considering it was for a tool that is more susceptible to vibration in comparison to other tools.
That is a great analogy of the functional differences from front to rear Mark
Thanks for sharing
Cheers
I noticed the Whitelaw Engineering poster behind the DRO, I worked for the old fella when I was 15 and again for Rocky when I was in my mid 20's, that was 40 odd years ago.
I met Rocky Whitelaw. He was a good friend of my Head of Department and he introduced me to him about 30 years ago. I tried to get him to quote me a price on a four jaw chuck for my Colchester but it was like haggling for Persian rugs in a Turkish market. 😁
Regards,
Mark
@@Preso58 Born with a silver spoon in his mouth that man
When I first got my 13" South Bend I was having a lot of trouble with parting off until I backed off the gibs on all axis and loosened the lathe up a bit. I know it sounds weird but it worked for me, lol.
That sounds counterintuitive but if it works that's great. I think that there is a lot of weird physics going on during parting off operations and my diagram is greatly simplified for clarity. Individual lathes will give different results with exactly the same tool bit too.
Regards,
Mark
I made a very rigid traditional post and it aided my parting, I had heard of this before, I think it is time to revisit it. Thank you.
That's good to know. Some of the cool kids on the block swear by solid tool posts (Robin Renzetti, Stefan Gotteswinter) so I am very keen to see if my version gives me some peace of mind when parting off.
Regards,
Mark
Hello Mark,
A very interesting video... Great explanation of the benefits of a rear parting tool...
Take care.
Paul,,
I made a rear solid parting post for my little Sherline lathe a few years ago, it worked very well. My "big" (10x22) lathe has a solid toolpost almost permanently attached instead of a compound, and it helped a lot too. Yours is much nicer :)
I do want to try using the rear tool post as a solid front mounted tool post. If it works as well as Robin Renzetti and Stefan Gotteswinter say it will I may make another to replace the compound. My only problem is the way the Colchester compound is mounted. It has a circular tee slot and two tee bolts. Removing the compound takes ages because you have to use a spanner to loosen the hex nuts and you can only swing the spanner a short way in the pockets on the side of the compound. It's my only gripe about the design of the Colchester Student.
Regards,
Mark
@@Preso58I didn't get down into the guts of the Colchester Student I used in school, but would a ratcheting box-end wrench with very short throw work under those constraints? I've got some cheap ones from GearWrench that advertise ratcheting action in just 4° of freedom. Wouldn't be quick in that space , but it would be easy.
I have had all of those problems when parting off, and now use a hacksaw ( unless it brass ). Your explanation of the problem was brilliant and has persuaded me to make my own rear tool post. Great video, can’t wait for the next part.
Thanks Chris. I also resort to either a small bandsaw or an angle grinder with a thin cutting disc. I can usually part off stock up to 25mm diameter in the lathe but after that I get very nervous.
Regards,
Mark
@@Preso58 Some sizes just seem to work. For instance, 25 mm and 1 inch (25.4 mm). Also, much of the world is held together by 6x1 mm and 1/4 (6.35 mm)-20 fasteners.
Mark, good proof of concept 💡 excellent explanation 👏
Thanks Mark, that was extremely useful. When you understand the physics the reason for parting tool snatching becomes very clear. Cheers
I found quite a long thread dealing with parting off on one of the machining forums and up until I did that research I mistakenly reasoned that all the deflection took place locally in the extended end of the parting blade. As it turns out, the movement takes place in all the parts right down to the bed of the lathe. That explains why I was seeing such large movements in the tip of the parting tool when it dug in or when it chattered. It's amazing what you can learn when you go down these rabbit holes.
Regards,
Mark
@@Preso58 I have a spare toolpost from when I bought the multifix so maybe I will repurpose that as a rear tool holder. My lathe does not have a 'boring table' so making a platform for the rear toolpost would have to be part of the job. Very useful thanks. Cheers
Always look forward to your videos. Informative, educational and well presented. Length is never an issue for me. Thanks for sharing your knowledge and experience.
Hi Mark! Every time I see you wipe away swarf with your hand I get a pain on the back of my head - right where my metalwork teacher used to hit me with the wooden brush when he spotted me using my hands for the same purpose! Great video, great explanations - even admitting to the odd "dumb ass" mistakes 😉
Mark, your metal work teacher was quite justified for reprimanding you! However he may have been more worried about litigation if you had cut yourself. I do have a little hook for clearing the birds nests on the lathe but it is true I am guilty of sticking my fingers where they don't belong.
Regards,
Mark
@@Preso58 that was 40 years ago, the school doesn’t have lathes or metalwork machinery anymore, a sad loss in my opinion.
You will love how much easier it is to part off with this unit. I made the same conversion on my atlas craftsman lathe about a year ago. I found a source for the raw casting to make a T nut slotted cross slide and after that was installed the rear cutoff post was, added. I also set up a rear tool post at times when I want a second operation handy when making a part
Thanks. I have finished all the parts and it's installed on the lathe. Unfortunately, everything came to a standstill when our children came to stay for the Christmas break. I aim to start testing it out tomorrow.
Regards,
Mark
I used to have no end of trouble parting off and I've got a reasonable sized lathe, a Harrison M300. The cure for this was a "new" (good previously used) front spindle bearing. Turns out the tiny amount of pitting at the bottom of the front bearing shell allowed miniscule amounts of play.
Before I changed the bearing, a rear toolpost was on the long term project list, after several snapped tool blades and damaged insert holders.
I wish I had the confidence to part off with power feed. I haven't had a dig in for quite a while but I am always expecting it. I am guessing your lathe has bronze split bearings? I believe the Gamet bearings in the Colchesters are hideously expensive. The other issue with parting off is having bell mouthed chuck jaws. That is also something I need to address.
Regards,
Mark
I had no idea that Tommy Emmanuel was also a machinist! Superb reasoning, dialog, and execution, thank you for sharing. I intend to try this out myself on a 8.7x30 import benchtop lathe as soon as I can locate some affordable grey iron.
Excellent job, Mark. That DRO is a fine piece of kit. TOP. Looking forward for that end-result, this will be interesting.
Thanks Mark! This is brilliant. Especially the explanation to understand what is happening under load.
On the glass scales I got I noticed that the extrusion has provision for double seal strips but only one pair were installed. I found a seller on aliexpress that sold the seal material by the meter and installed the second set. Very cheap peace of mind.
I have not checked to see if the Sino scales have the provision for a second set of seals. I know that the "good" scales have better sealing options. I fitted Sino scales to my Colchester lathe back in around 2004 and they are still performing perfectly. I don't use a lot of flood coolant on it though although I do have a pump fitted and it gets used occasionally (for parting off).
Regards,
Mark
Thanks for making this video. Parting has always been challenging for me, your animation has helped me understand why. The rear tool post amy be the answer. Looking forward to seeing the conclusion.
Hello Mark, good analysis of the forces that are generated in machining and how to take advantage of them in your interest.
Good explanation, years ago we found this out just by accident and really never understood why the rear mounted post worked so much better.
Not sure that anyone would design a lathe to cut slightly concave when facing. I would certainly want it too cut as straight and as flat as possible.
I have your lathes bigger brother the Triumph, which was fitted with the rear toolpost before I got it. The main issue with it is the way it has been configured to take a special parting tool which I don't have. Having said that I have had no issues parting off any way.
Been watching your videos for awhile now and have now subscribed, please keep the good work.
I cannot recall where I had read about lathes being set up to cut concave. I believe the amount of angular displacement is tiny, usually around 0 to 0.02mm per 300mm. I also just checked and Dr. Georg Schlesinger wrote in a book called Testing Machine Tools that even toolroom lathes will have some concavity but it can be zero too. I think the point was that the facing cut should never be convex. Flat is preferable but concave is acceptable. I did get some photos of the original Colchester rear tool post and you are correct that it was set up to take some sort of proprietary tool holder for parting blades.
Regards,
Mark
Mark, I made one of these for my Bantam a few years ago, and have never looked back. I'm sure it'll work. My Dad owned a machine shop with turrets & capstans: parting was always done from the rear.
That's good to know!
Regards,
Mark
Making a rear tool holder is something I'm thinking about for a long time. All I have to do is get to it.
Thanks Michel.
You need to get a Round Tuit! 😄
Regards,
Mark
Excellent through analogy of lathe tool cutting forces and rigidity, or lack of it!.
Great addition to any light duty lathe, Capstan and Turret lathes have obviously used rear tool posts, mainly for parting off, but for principally different reasons as I understand?
Thanks for sharing.
Best regards from the Black Country UK 🇬🇧.
John.
Most CNC slant bed lathes use rear mounted and inverted tools but they are already massively rigid machines. I had to look up "Black Country" on Wikipedia! It was the one area that we didn't visit on our massive road trip around the UK. Oh well, there's always next time.
Regards,
Mark
@@Preso58 If you like canals, canal locks and crooked buildings ( caused by subsidence), and local beers, then it's the place to visit 👌. It had vast deposits of Limestone and coal, hence industry.
I think many lathes have issues with parting off, due to high forces, and either poorly manufactured or worn cross and compound slides, but that's stating the obvious.
Hope you chamfered the clearance hole at the bottom of the counterbore, this is missed by many design draftsperson, more critical on hardened items. Another feature on deep clearance holes, is to have standard clearance diameter on upper surface, then drill larger size from underneath leaving 2 or 3 diameters in thickness below, this prevents binding of the screw it is slightly bent, or threaded drunk.
All the best Mark.
John.
Great illustration!
Interesting project. I liked your illustration at the start explaining why I can't part off successfully, unfortunately I cannot fit a toolpost at the back of my "Raglan Little John " lathe (c 1953) so it's the hacksaw for me!
A tip for you then lol swing your compound slide as far as you can to be square to the axis of lathe bed as long as you can turn the cross slide handles you are ok. If not get as close to 90 degrees as you can. Then make sure the compound is wound up to its stop, the loosen whatever gib screw locks you have and tighten the gibs fully so the slide is unable to move, do the locks up and you have a poor man's solid tool post and while you are about it tighten the cross slide gibs up to give a little friction as most of us probably have the cross slide a little too loose anyway and that's how I did it before I made my own rear parting off block which uses the tee slots on my cross slide.
Outstanding Video, very enjoying to view your work and the Idea of the need for Solid Tool Post. :)
Nice job Mark, nice addition to your lathe.😊😊😊😊😊 Merry Christmas
Thanks Randy. I am hoping it gives me a bit more confidence with parting off. Maybe I am especially nervous about this process but I have witnessed some sensational dig ins and smashed tools during the time I was teaching metal machining. If you heard a big bang somewhere in the shop it usually meant a smashed parting tool.
Regards,
Mark
Wonderful analysis on this Mark. No argument from me on your approach. Looking forward to next video and chips!
Shakespeare said it best, “parting is such sweet sorrow”.
Hi Mark.
Looking forward to the rest of this build.
I’ve got a H&F 960B, roughly the same size as your Colchester.
I’d love to add a rear tool post to that lathe.
Great animation showing the mechanics of tool posts.
One other factor is the direction of ‘lift’ of the work in a standard rear tool post.
Probably not a lot in a modern lathe with precision headstock bearings….
Anyhoo, thanks for putting in all the extra work and time doing these videos.
Regards
Robert
PS That Malleable CI
makes nice chips…. the drilling looked almost like cutting steel.
That was the first time I had machined any malleable iron. It is very nice to work with and somewhat kinder to the tools than regular grey cast iron.
Regards,
Mark
I have a rear mounted parting tool holder for my 13'' lathe. Used it a few times, but find it just makes for a cluttered crosslide, and difficult to get measuring tools in to work piece. I now lock the gibs on the compound, as it doesn't get used much, and part with a standard parting blade mounted in a QC toolholder, and part off with power feed. Next job is to make a solid toolpost mounting, and do away with the compound.
Unfortunately, I don't have any locks on my compound. I have never been game to part off with power feed. I hope that I can have a bit more confidence with the new setup. I am going to start testing it out for real tomorrow. Wish me luck!
Regards,
Mark
Great explanation of the benefit of using a rear mounted parting tool. I recently acquired a Colchester Chipmaster that I intend to make a rear tool post holder for.
I have an older samsung tablet that is now surplus, I may just use it with a touch DRO system on my lathe.
I have always admired the Chipmaster for it's streamlined shape. Almost Art Deco! My only advice if you are thinking of getting the TouchDRO system is to use glass scales with it. I started out with capacitive scales and I was a bit disappointed with their reliability.
Regards,
Mark
Another tool that seems to work well in a standard QCTP is a "spring cutting off tool holder" A la Armstrong. Winky's workshop channel has a good discussion "Better, Best ..." . This tool holder works for those of us who can't mount a rear mount tool post. Cheers.
I watched Mark Winquist's making of that tool. I actually modelled it in Autodesk Inventor so I could carry out some finite element analysis on the flexing forces involved. I sent him the results as verification that it would unload the cutting forces before they were transferred down into the compound slide. I believe that many metal planer tools were of the "gooseneck" variety which may have been the same as the Armstrong tool type.
Regards,
Mark
Ciao Mark,. A very nice project from the drawings to the machining, i liked so much the forces display, very clear!!And that block of steel Is huge!On My Colchester Bantam i have sometimes noise sometimes not, i really hate to cut with parting tool! Wait to see the finish and the test!! Ciao Mark, Alberto.
Thanks Alberto. I have finished the steel riser block and I just have to get to work on the tool holder itself. So far, so good! I feel confident it will be successful and if I can have the confidence to part off with power feed I will be very happy.
Regards,
Mark
@@Preso58 It will works of course, unfortunately in My Colchester Bantam i don have the T-nuts way like in your Student, but i will think at something similar in the future! 😀
I like watching your work and it gives me good vibes with my shake hands to do my small work.
Hi Mark, you have done a good explanation using those drawings. Like you, I have had a lot of issues parting and it was something that I did not like doing (broken tools, the part climbing up on the tool then being pulled out of the chuck etc.) . That was until I watched a parting video by Blondie Hacks. She has some good tips in that video and now I'm much more confident and my parting experiences are a lot better. But, that rear parting setup will give you a lot of rigidity and it will eliminate the 'dig in' potential. It will be good to see it in action.
Have a Merry Christmas from us in NZ.
Thanks Jon. I have one of Eccentric Engineering's front mounted inverted parting tools and it's a good alternative to the traditional parting blade. However it does need to be set up exactly square to the axis of the lathe so it doesn't rub along the edges of the tool. That side loading will overheat the blade very quickly and it will still dig in. Flood coolant helps but it's always messy. The new version I am building has the tee profile so the there is a lot less side contact. I should know if it lives up to the hype by the end of next week.
Regards,
Mark
I have an admission to make. 2:25 I shrugged off this diagram of the cross section of the lathe parts and how they react under load as ........ 'we already know all this'. But I DID learn something here. And as usual I appreciate knowledge shared on your channel Mark. Look forward to the Part II. I imagine you'll have to make sure that gib on the back of the carriage that keeps the back from lifting up .... must be fitted properly or the entire carriage could pivot on the bed front way. where in the traditional parting set up it just pushes down into the bed front way
Bobby, I also learned something after I created that diagram. I used to think that all the bending took place in the overhanging parting blade. If that were the case the cutting edge would bend downwards and away from the part centre when parting off conventionally. However when you take into account the whole assembly of parts from the lathe bed upwards it's a different story.
Regards,
Mark
Great video production/discussion/demonstration/build…interesting
Thanks Chuck. Let's hope I can put the hacksaw away for good.
Regards,
Mark
I used to suffer the same problems. I feel silly it took me 15 years to figure it out.
The secret is p type (T shaped) cut off blades. Make absolutely certain they are 100% verticle. Jack them, shim them. Do what ever you have to do. Don't just trust the tool holders. Use a square or sweep them with an indicator.
Stone them razor sharp. Set the hight with a presision tool. Take your pick. Don't eye ball it with your tailstock.
You will be amazed how well they work. Parting off went from something I had all but given up on. I'd just go get the hacksaw. To something thats actually fun.
The angle blades work too but setting them perfectly verticle is more of a pain. Start with the P type.
Thanks, I do all of the things you have suggested but I also find that power feed is more reliable than hand feed which seems counterintuitive. Also, lots of coolant is a must. I am still amazed at how non scary it now is to part off what I once considered to be difficult or impossible stock.
top marks for the graphics Mark!
Corel Draw is great!
Regards,
Mark
Love this, good timing as well. I used to enjoy parting off, lately been having problems. Something must have changed in my setup... im going to invert parting tool and try running in reverse.
I already have one of those tools and it's an improvement on the conventional parting blade. Eccentric Engineering sells a type called the FoR tool holder www.eccentricengineering.com.au/products/for-front-or-rear-inverted-parting-tool Mine is an older style that has the tapered blade and it resembles an conventional tool holder but with the blade inverted. It has a lot more overhang than the improved FoR type. The holder I am making will resemble the newer type.
Regards,
Mark
Great video Mark! Looking forward to part 2. Gonna relay this to my chum he also has a student
very very good video, excellent explanation of the different parting pros and cons thank you sir for sharing
The theory is solid. Thanks for sharing.
Mark I just don't understand , my parting off blade cuts like butter. Works great. I bought it last year. It's a Makita metal chop saw. 😜😜😜😜 I gave up years ago on parting off on my lathe. I believe I have that parting off curse also. If it could go wrong it went wrong. Lol.
I have looked at those high speed metal chop saws often and if I had the extra room I would definitely have one. I have one of the old style friction saws but it screams like a banshee and it throws grit and sparks hither and yon. Not especially workshop friendly. I am still hopeful that the rear toolpost will live up to the hype.
Regards,
Mark
Excellent video and it answers why my mini lathe starts then stops cutting as I try to provide a constant feed rate. It seems like putting the parting bit upside down and running in reverse would give some of the advatages of a rear mounted parting method. Your videos are aways interesting, useful, with good camera work, and editing. Thanks!
Larry, I have an inverted parting tool that mounts in the front tool post. It is better than the conventional type in that it does lift clear when loaded but you still have to push it into the cut and they are no good for a threaded chuck (I have a LO taper on my spindle so I can run in reverse). I am hoping that the rear mounted tool will give me more confidence to part off using power feed.
Great explaination of the torque pivot and tool reaction. I'd not ever really considered it but might have to look at this on my home lathe.
Really enjoy your video's Mark.
Thanks Brent. Maybe you can confirm this for me. Just from watching videos of slant bed CNC lathes, I assume the tools are rear mounted although not always inverted? I guess they use linear rails too. Keep up with the sexy CNC posts on Instagram!
Regards,
Mark
@@Preso58 Yes they can run either way but generally spindle rotation is the same on a CNC as a manual and the tool is somewhere in between from above and the rear so sort of inverted.
Box slides are still quite common for CNC's. Not as quick a linear in most cases but great in rigidity.
If you want to throw another variable into your parting equation.... look up y-axis parting. It does your head in to start with. This runs the spindle in reverse to what might initially seem logical but it puts the load directly into the toolholder rather than across it. It requires a very rigid setup to work for all the reasons you described.
Nice presentation on the forces involved Mark. It certainly shows that you were a teacher! I did a very similar thing to my Chinese lathe/mill last year and it works reasonably well. Especially if I use my shop made cross slide motor driver. I can control the speed and once I've got it cutting nicely I can concentrate on getting the lubrication of the tool with the suds brush to give a nice smooth parting off.
Putting a rear part off tool post on my Chinese lathe totally transformed the part off ability. I didn't arrange an upside down tool so I have to reverse the spindle. I was thinking if the tool is pressed down by the forces there is no further down than hard down. I thought it less likely to induce chatter.
I think that not having a compound slide under the tool will give you a massive increase in rigidity. I did initially think that inverting the tool was unnecessary but I was won over by not having to reverse the spindle to part off. I am hoping to have this operational by the end of the week. I have already machined the riser (video out next weekend) and it's just the tool holder to go.
Regards,
Mark
Heck the mock up was impressive.
I find it worth the effort of making a physical model. You will see in the next episode how I can use it to verify that I am placing the features in the correct faces of the part.
Regards,
Mark
Tan-fastic! So sad to hear you have the same problem with those cheap scales, I always thought it could be rectified, Anyhow vert nice design, much need out there in hobby land. Enjoyed, cheers!
Hey Mark..........as a hobbyist myself, I to find myself to be in more of the coward category as well haha. I am actually in the process of making a router attachment for my tool post with a slitting saw to take care of that part. It will also permit more function later for grooving geometry and hole patterns. Something to think about for a later build cause I can see the possibilities as I am making this. Great build Preso! I look forward to the next vid.
Good to see another of your excellent educational videos. Cheers!
Actually, Mark, your observations regarding force, vibrations, and such for parting apply equally to most all the operations on the lathe. If there were a good way to see what's happening on the back side, we should do most operations on the back.
You are correct in that all cutting operations carried out in the conventional front mounted tool post will tend to make the cutting edge dive into the work. There must be some other factors at play though when using parting tools. Perhaps because they are so slender compared to their stick out length or that they can overheat when buried so deep in a closely fitting groove. Whatever it is, it can lead to some spectacular catastrophic failures. Many CNC slant bed lathes are designed with the cutting tools on the back side of the lathe axis and many are fitted inverted so maybe there is a reason for that.
Regards,
Mark
Nice work, thank you.
I do somewhere in the back of my mind have a design for a parting tool that looks a bit like a steady rest - two roller points of contact and the third is the parting blade which is fed in by a lever action. Still mounted in the tool post but as there is two points of contact as support the forces are converted from a down force to a rotary force . One thing i have found that really helps with parting off is you can never have enough coolant - now that might be flood coolant or something like WD40 which i have extensively tested and found to be the best all round coolant for parting off - even on steel. Unfortunately for me I spent many years breathing in Kero fumes and as WD40 uses this as a base liquid even a small amount of it makes me sick, so I have had to find something else to use.
That sounds like an interesting concept for a parting tool. I have never seen one in the wild but I am guessing that having two floating points of support would help. Absolutely agree about coolant. I have flood coolant on my lathe but I hate using it. It makes such a mess. However excessive heat will make the blade jam sideways in the kerf or make the tool gall up which in turn gives you runaway heating.
Regards,
Mark
Super nice project 👍👍😎👍👍. Cheers
I am certainly the coward. #hacksaw Looking forward to this series. Cheers friend.
Great content interested in the subject
Gday Mark, Fantastic job with the illustration graphic and explanation. Design and machining of the base looks great...that ductal iron sure machines nice. See you in the next episode...
ATB....Dean
Thanks Dean. Yes, that continuously cast ductile iron is nice to work with. I have never really machined it before and the guy I bought it from seems to have gone out of business which is sad. It must be tough selling small volumes of specialist materials here in Australia.
Regards,
Mark
G'day Preso. I enjoyed your analysis. I have a Ward 3A capstan lathe that has a rear toolpost. I assumed it was there for efficiency reasons given that these lathes were used to make lots of the same parts, but I wonder if it was also for the very reasons that you outlined. Which would also make it more efficient!
Thanks Rod. When I acquired my Colchester lathe we also took delivery of a medium sized capstan lathe. I cannot recall the make but it also had a rear mounted tool post. The capstan had all the turning tools and a couple of drill chucks. I actually "souvenired" the rear mounted tool post which had a rack and pinion mechanism for advancing the tool. There was no tool mounted in it but I am now thinking that it would have been for a parting tool. Interesting!
Regards,
Mark
I’m excited to see the rest of the video. I have a question at this point. What do you do with all the chips? Recycle? Trash? Something else? 19:15
It all goes in the bin. It is too hard to separate all the different materials but I do know that some people who machine mostly brass or aluminium will recycle the chips. Brass especially is probably worth collecting and taking to the scrap merchant.
Regards,
Mark
Great project ahead! Taking the cartoon, I'm also a coward 🙂 My excuse is I have a minilathe with a compound that acts like rubber when parting. Sure I can work on all dovetails and make all the modifications available on the web and on YT, but there's still not enough rigidity with so little metal mass. So, the rear tool post is a good alternative, the problem being that there's not enough room for it in the compound, although some designs do exist. It's amazing that a much flimsier Sherline parts much better than a minilathe (Clickspring is a good YT example of this).
I must say that I have seen some impressive feats of parting off in small lathes. I am sometimes jealous that I balk at even small diameter work. Clickspring makes everything look easy so he doesn't count!😁
Regards,
Mark
@@Preso58 LOL. I agree, and Chris (Clickspring) is really out of this world :-) I was absolutely overwhelmed by the extent of his research and painstaking recreation of the Antikythera mechanism and the tools to make it.
Hi Mark Where did you buy that piece of malleable cast iron in Australia. I live in Perth. I have Harrison M250 which has only 3 screwed holes on the back of the cross slide. Looks like I will have to take it to pieces and drill and tap on the milling machine. Look forward to the drawings
David, I got that piece of malleable iron from Mancave Metals last year but I have been told that the website is down and it's possible that the business has folded. I guess that trying to run a specialist metal supply business in Australia is hard. Try Edcon Steel www.edconsteel.com.au/store/products/steel/cast-iron/round-bar/3d I haven't bought anything from them yet but apparently they will sell cut to length stock and the prices seem good. I will make the drawings available when I have finished the build.
Regards,
Mark
I fall in the category of "it's on the to-do list for 30 years"
Nice work
Good stuff. Here in Missouri metric bolts are about 50¢ or $1 a piece (expensive) and SAE bolts are $1.49 a lb (cheap) for grade 5. I've wondered often if opposite was true in metric countries. Can you shed some light on this?
I don't pay a lot of attention to the prices but here in Australia, imperial fasteners are still available but they are considered to be "legacy" stock. The range is limited at big chain hardware stores but there are some local online stores where you can get just about any thread type, imperial or metric. I think the prices would be roughly the same.
The dominant "hardware" imperial thread type is usually Whitworth. UNF and UNC can be had at motor accessory shops but again, the range is limited and you generally have to buy in packs of three or five which drives me mad. You always need two, four or six!
Regards,
Mark
@@Preso58 thanks.
very smart man. Enjoyed video
32:30 I had to laugh. You and Mr. Pete have neighbors that do things while you're making videos.
You with Mr. wood chipper and Mr. lawn mower with Mr. Pete.
Yes, my neighbour does like his wood chipper and he is retired like me so he has more opportunities to use it. I have seen Mr. Pete discussing his lawn mowing friend!
Regards,
Mark
@@Preso58 Thanks for the reply.
how does lift on the slide tighten anything? isn't it effectively just resting on the ways and that works because normally all the forces are downwards
The cross slide will lift if you are parting off with an inverted tool from the rear. As it does so it will close the clearance in the dovetail. This also increases the drag between the cross slide and the gib strip. I am guessing that the saddle will also lift at the rear (slightly). My lathe has a shear on the rear way which does stop the saddle lifting clear.
Regards,
Mark
I think you missed movement points on your setup that could provide movement before the tip of the tool; from the bottom up they are:
1. Ways for the saddle; this only affects if the bed is extremely worn causing parting blade to “twist” to the right.
2. Ways for the Cross-slide; worn or loose.
3. Compound Rest rotating joint; loose or contaminants between the surfaces.
4. Ways for the Cross slide; loose or worn.
5. Toolpost rotating joint; loose or contaminants between the surfaces.
6. Quick change or Lantern post; QC could be loose, have contaminants between the mounting surfaces or
locking mechanism, or loose/worn QC dovetail, plus either style can have loose/worn tool mounting surfaces/screws.
I agree. My diagram was greatly simplified for clarity. There are lots of sources for flexing and movement and with lots of measuring devices it would probably be possible to map the forces more accurately.
Regards,
Mark
Hmmm...
You can aply this concept of forces, fulcrums... to any work on the late, not just parting.
Parting is just extreme load cos of wide cutting with.
So.. it will be better to run spindle in reverse, and have all tools upside down.
As a bonus, you will get chips that go directly down, not spraying around.
That was one of the bonus features of the inverted front mounted parting tools that I bought from Eccentric Engineering. Having the chips form underneath also allows for cutting oil to make it into the bottom of the groove.
Regards,
Mark
Interesting- not so sure about your fulcrum points- I think there are many, wherever movement can happen. The 'dig-in' is more likely due to the tool rake pulling the tool in. It is not a single point cutter! The rear post just has more rigidity, and the slide is operating in a different position, where there is likely less wear. A popular solution is to have the tool holder slightly flexible, with a pivot point above the tool. This means any movement both reduces the cut and the rake. Typically, this starts a cut with a high pitched sound, as the tool finds the balance between bending and cutting, and then settles into a good cut.
I certainly intend to make a rear post- not just for the rigidity, but it is needed for almost every part, and it can be set up once and left, always available. Might experiment with the flex though- conveniently this will be below the tool in this configuration, so necking the support in the Y directions should do the job..
Thanks. My diagram was greatly simplified for clarity and I agree that there is no single bending centre. One thread that I had read on a forum was comparing the bending action of the rear toolpost design with the older style of gooseneck tools that had a slot to allow for the bending forces to disengage the cutting edge of the tool. I watched a couple of videos by Mark Winquist (Winky's Workshop) where he made a replica of that type of tool and had good success with it on an older (I think South Bend) lathe. I should have the entire build finished by the end of the week. I feel confident it will be an improvement and my ultimate goal is to be able to part off using the power feed.
Regards,
Mark
@@Preso58 Yes, I watched that too. With a rear post the required bend point is below the tool, so much easier to arrange. I intend experimenting with this- there will be an optimum load deflection for a given tool type- possibly different for different materials.
If I need to accurately measure with calipers I try to zero them with the same force (by feel) that I will be using for the real measurement, and try to zero them when measuring at roughly the same place on the shanks. At least in my head this should remove most of the flex in the material as well as the slack in the bearing surfaces.
I realized that I have probably not commented on many of your videos, so I just wanted to say that I love your work and your video,
Best from Sweden!
Hello to Sweden! Thanks for the feedback. Measuring with calipers, even good ones like Mitutoyo is a challenge at times but until I get a set of digital micrometers I'll take the convenience of being able to zero them out and measure the difference.
Regards,
Mark
Hi Mark, What version of the Touch DRO software are you running? Mine doesn’t seem have the same features. Thanks , Terry
I am running the beta version of TouchDRO. I just checked on Google Play Store and the latest version is 2022-11-26.
My version updated automatically since I am registered as a beta tester but you should be able to go to Play Store and update manually. The new version does have some pretty cool tools in it including probe and rotary encoder support for rotary tables.
Regards,
Mark
So I'm guessing you'd get the same affect by inverting your tool on the normal side and reversing Spindale direction
Yes, the rear holder comes from most home shop lathes have or used to have chucks that threaded on the spindle. The chuck would come off the spindle if you tried cutting in reverse.
Yes, but you still have the slack in the feed screw and nut issue.
Almost. I have a tool that I can use front mounted with an inverted blade. You do have to reverse the spindle and I find it better than the conventional parting tools. As some people have identified below, you are still pushing the tool with the leadscrew though.
Regards,
Mark
Hello Mark, I've made the same rear tool post for my Emco Unimat 8 (lower size) and I'll make another one for my Myford ML 10. Parting off on small lathe is not a peace of cake , but whith these tool-posts it's Ok . Important point, is to lock all the movements you don't use.
What is the software you use for the analysys?
Regards - Didier
Didier, I can lock the saddle on my lathe but often I don't bother when I am using the front mounted inverted parting tool holder that I have. It is "almost" as good as a rear mounted inverted tool but you are still pushing the tool into the work instead of pulling it as you can do with the rear mounted tool. I used Corel Draw for the animation. I used it a lot when I was teaching Graphics at school. It has some very good tools to allow for CAD like drawing but it is strictly 2D.
Regards,
Mark
@@Preso58 Mark, on my both lathes I made anti backlasch nuts, and with that I have no problem in parting. The pressure is constant , and I have no wobble and looseness. I never used Coreldraw but it seem atractive
Would you not get the same relieving effect by reversing the direction of the lathe spindle and inverting the tool?
Simon, I already have a front mounted inverted parting tool and it is a big improvement on the conventional type. You do still have to push the tool into the work though. I prefer it to the Chinese style of insert parting tool since you can sharpen the HSS blade to a very fine edge. I find the tip radius on the inserts to be a disadvantage on soft materials like brass and aluminium.
Regards,
Mark
Hi Mark...I noticed that you are now using a Samsung Tab for the DRO application. Did the original cheapie Tablet bite the dust?
No, the cheap tablet is still running. It was very sluggish to start up though and my wife pensioned off her old Samsung so I snatched it up real quick.
Regards,
Mark
Hi I really enjoy your channel did you do a video on making your mill table covers
If you are referring to the aluminium trays that cover the tee slots, I did not video their manufacturing. I saw the idea on someone else's mill on Instagram. My primary reason for wanting them was so I wouldn't lose small parts and tools down into the tee slots. It also makes the clean up a bit easier. They are just made from 2mm aluminium sheet. The corners are not welded. There are some ribs fitted underneath that locate in the tee slots. The ribs are made from some composite decking material.
Regards,
Mark
Thank you. I really look forward to your videos. I am a 73 year old newbie and trying to learn as much as possible
I like it!
Hey Preso. Long time stalker/watcher of your channel, and another denizen of god's country in SEQ. Quick question, where did your get your bar stock for this job? Love your work mate. Cheers Tom R
The big chunk of malleable iron came from a now defunct web store called Mancave Metals. However you can purchase cut lengths of "Durabar" from Edcon Steel www.edconsteel.com.au/cast-iron/
The riser block and tool holders came from some big chunks of good quality steel that were salvaged from a donated surgical operating table! It was full of cast iron, hydraulic cylinders, carbon fibre and electrical gear. A real treasure trove.
Regards,
Mark
Is this same as upside down tool and changing direction of rotation ? I admit I have thought about doing this, but ever since I switched to a solid tool post without the compound I've not have a lot of issue parting.
It's slightly better than having an inverted parting tool at the front of the lathe in that the leadscrew is pulling the tool into the workpiece instead of pushing it. Also, for those that have a screw on chuck it means that you don't have to cut with reversed spindle direction.
Regards,
Mark
Is chattering a 'machine cry' when lathe tell us that we push it beyond it can do?
Mark: Any chance you would share the drawing. Looking at adding a rear post to my 1334 standard modern .
Dave H
Here is a link to the 2D drawings. I would suggest you check your centre height very carefully and compare it to the drawing that I used. The position of the slot in the tool holder doesn't include much adjustment and depending on what type of parting blade you have it may need adjusting. I made an extra tool holder for a carbide insert blade and it did need shimming. www.dropbox.com/s/66uvsurxhoin8g4/COLCHESTER%20REAR%20TOOL%20POST.pdf?dl=0
Regards,
Mark
Do you have an update on when the next video will be available? Thank you Sir!
Hi, it's due out tomorrow. 11am AEST.
Thank you sir!!!
Hi Mark brilliantly presented video. Coming on nicely. Not sure if you watched my build on one of these. My idea was to be able to fit different blades in the holder , so I made it slightly adjustable up & down. Probably the best add on I have made. Works brilliantly as I am sure yours will.
Regards.
Steve.
P.S My drawing was on the back of a fag packet.
Steve, I did watch your build and it motivated me to move my version up the list of jobs to do. I want to be able to fit a carbide insert tool on the other side of the riser for harder materials. I will wait to see how the HSS tool works though.
Regards,
Mark
Is your cross slide already equipped with the same mounting hole pattern at the front position?
Unfortunately, no. I will have to do some additional work to match the hole pattern which holds the compound slide down. It has a radial tee slot and two bolts but I think it can be done.
Regards,
Mark