Compound Lead Screw for American Pacemaker
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- Опубликовано: 2 окт 2024
- I begin the machining on the new lead screw that will be used in the American Pacemaker compound slide. This is a 3/4-5 left hand acme thread that will be cutting using the Monarch lathe. I unfortunately run into some machine issues during this process.
#manualmachining #acmethread #monarchlathe
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We had tons of folks have the same issue when cutting acme threads. Usually, the case was the part was slipping in the chuck. Either, it was twisting, or being pushed in/out. Not saying that's what your specific problem is but it's worth looking at.
That being said, I typically will cut flats on round stock I use for acme threading... This way I get a positive hard connection on the stock, and a stop against the jaws where the round becomes flat, so that you can tell if it is trying to move anywhere on you. Never had a problem doing it this way... Acme threads push a crap ton of pressure on the part and tooling, and even the tightest jaws can have issues holding it.
I am NO Machinist, but in my little mind, this possibility came up, so I agree with you.
The problem is the small diameter screw… it is not the lathe . It is pulling it in because the screw just started going up on your tool… it usually happens on the last 2-3 passes… you need following rest . I have also Destroyed a lot of screw like that …
I think you are spot on! I couldn't believe there was no steady to prevent climbing.
RPM reduced use coolant because final depth over load...
Correct,That is the reason.
It flexes away from the tool, which causes the thread walls to spread out on the far side of the tool, and to pinch in on the near side…. So it pinches the tool, and, like you said, it tries to climb up it.
I’m just a amateur but I had a similar problem with 3/4x8 tpi acme thread. I used a follow rest and the tool pressure was so high it destroyed the brass tips on my follow rest. Any ideas?
Correct me if I'm wrong but as I see it. The deeper the tool gets the load increases and the cross section/diameter of the part is significantly reduced. This will cause the stock to flex and the tool to dig in, Add in to that heat build up and you'll have this problem. My punt is a follower rest and coolant should see it do just fine.....
I'd prefer to see this done on this machine as problem solving is all part of why I got into this stuff.
Greta video as always
The root diameter that Adam was approaching is less than 0.55", which makes for a pretty flexible workpiece.. I think what is happening is that as the tool gets towards the mid length of the workpiece, the workpiece is deflecting upwards, which puts the tool below center, which then allows the workpiece to start to climb into the tool and thereby deepen the cut. The shallow taper on the flanks of the thread probably enhances the effect. In other words, the flanks of the thread on the workpiece can engage with the below centrer tapered tool and so make the workpiece climb further onto the tool. The effect may even be sucking the cross slide (or the topslide) forward into the cut. Some backward hand pressure on the tool post may avoid the latter possibility. A travelling steady would stop the workpiece from deflecting upwards in the first place and hopefully stop the whole cascade from starting. It is really good that Adam shares the things that don't work out as expected. That's where some of the best lessons come from. Cheers.
That's just under 14 mm whooo that's very thin. Think the original would be made in a different way then turning.
Agreed. A travelling steady is definitely worth a try, especially with an Acme thread since the top is flat.
Clear and articulated, should make top comment.
yea but he said he was just feeding 1/2000" ...?
Agreed, perhaps a follow rest or steady rest might be in order here.
Many years ago my father's engineering works in the north of Scotland, used to cut very long acme threads for a piece of whisky distillery machinery. Initially we had the same chattering and digging in problem that you have had Adam. We cured it with a travelling steady rest. Our lathe was a lot more worn than your Monarch.
A travelling steady / follower rest will fix the problem, that deep thread is weakening the work piece too much and its flexing. I was surprised you got as far as you did before the problem started! Great videos Adam, many thanks for sharing your hard-earned expertise.
So glad you did this video. Most would have scraped it and just shown the one that turned out perfect. Please update us on what you find out went wrong. No doubt we will all learn something new.
My sense is the problems you hare seeing is the result of thermal expansion:
1) Problem occurred on the final passes when heat has accumulated in the part.
2) The location of the bad cut is in the center of the part. Since it is confined between centers, the thermal expansion is causing the workpiece to bow - with maximum deflection in the center.
3) Cutting on the left edge of the tool also suggests thermal expansion.
As always a great video Adam.
I’ve always admired your self control and your ability not to curse. So I did it for you.
I suspect at least one word was seen, but not heard......
The old-style Abom79 video. Technical, frank, honest. More of these videos and less of the others, please.
I ran into same issue on my Cincinnati 15”tray top. Put follow rest on and went smooth as butter 🧈
The cutting pressure gets so great on an Acme thread, that it overcomes the ability of the material to maintain a true Centerline. The workpiece rides upward on the tool bit and causes the bit to be below the Centerline of part rotation. When that happens the material strenght begins to overcome the cutting force of the bit and it all comes crashing down. It's not the lathe, it's the ability of the material to resist the necessary cutting pressures.
I would use 4140 H.T. and cutting oil to make that screw.
Totally, every pass, the force on the work gets a bit bigger because the profile of the cut gets a bit bigger, but the part's ability to stay straight gets a bit smaller because its cross section gets a bit smaller. The part is just insufficiently supported.
I am so appreciative of the fact that you are willing to show issues like this happening, a lot of people would not want to show problems/mistakes, This was a great thing to see that stuff like this happens to the best of us.
Thanks, Adam, for showing this! Those mortals of us out here learn WAY more from a professional having an issue than from a professional having an issue, chucking the part in the bin, and glossing it over!
That Monarch has been fed more than a few hot suppers, as AVE would say.. This might be the signal to take the old fellow down for some maintenance, give everything a once-over and address things that need it. Lord knows that with a little TLC, that fine old lathe should last another lifetime or two. Great content! It's really good that you take us along with you when things go wrong, and we get to see the frustration that even a pro experiences from time to time. This channel has always been about integrity and hard work above all else, and nothing has changed there. Cheers!
x2
I’m pretty sure as meticulous as Adam is that Monarch has been well maintained.
It's not the machine, Adam. As the minor diameter gets smaller, the workpiece is deflecting, then being gouged toward the bit at the resonant frequency of that section. A follower rest and cutting oil wil help.
I am engineer not a machinist so I am not qualified to give opinion on what might have caused this. However, I want to make a very broad guess to what I thought could be the problem. Noting that every prior pass you made was going perfect until suddenly it was not. The one thing that continuously was changing was the rigidity of the rod, getting slender and slender. This of course you would have accounted for but combined with some other thing, who knows what, it was the feather that broke the camels back. I am anxious to know the answer when you have found it.
I kept thinking "This would be a perfect application for a follow rest" all through the video.
@@MoraFermi exactly... not the lathes fault, just needs a proper support for the job...
Acme thread has a lot of surface contact as compared to a conventional Imperial 60 degree thread
You need a follower rest for ANY long slender shaft for ANY "heavy" (relative) cutting.
Also, cutting oil should help any threading cutting!
I was wondering if that little bit of runout might have caused it to want to kick out once it got thin enough.
I'm just now viewing this video for the first time. I actually see myself in my day to day work life so I can relate. I'm not an engineer but I don't ever recall seeing a 3/4-5 acme threaded bar. If anything I've seen 1" and larger. So I agree, it might be a rigidity problem .
Adam, that sucks...big time, but you never edit it out. That, my friend, is another awesome part of your channel.
Old broke-down machinist here. How infurating! Having a part go belly-up so close to completion! I used to run a 20-inch swing 8 ft gap-bed Nardini. The lead screw was buggered in that to the point that cutting single-point threads was pointless (pun intended?) :). As far as your situation, the deeper the tool gets into the thread, the greater the tool pressure gets, as there is contact on the point and both sides of the tool. Also, the root dia is decreasing giving the part more ability to flex, thus increasing the possibility for chatter. Once the chatter starts, the chatter vibration will be conducted to both your cross and compound-slides. That chatter may cause the slides to creep into the backlash zones thus moving the tool deeper into the part.
If that's the case I think I'd try using the slide-lock screws to try and prevent any creep. I think I'd also try a heavy duty cutting fluid. Perhaps Moly Dee or Tap Magic. I see the Mystic Metal Mover setting on the saddle, but I didn't see you using it.
We are all feeling your pain & frustration Adam. As others have said here, thank you for posting an honest video; you don't learn as much from success as from failure. Keep on doing what you do old bean. Nice to hear Abby.
totally agree, follower rest is missing in this picture.
That part is nowhere near long enough for a follower rest.
@@trainedtiger not the original factory made one, but the cross slide had plenty of space to mount a make shift one.
I've had that same issue, your lathe is fine . . . Your part is climbing up your tool. The part is getting less and less ridged and the insert less sharp. Your taking a bug cut even if not deep because of the surface contact of that big insert. As the part climbs its digging into the left side, the tool is aligned but the part isn't. Clock your insert to a fresh face when you're close to depth. Let part cool well and keep it cool. Use coolant or at least oil. I was told use a follow rest but I find they are more trouble than help. Don't give up on that lathe, stick-stay and make it pay . . . Except the challenge.
I think this makes a lot of sense.
Was going to say the same thing.. I thought this fella knew what he was doing, but after the wheel valve video and this.. I'm not so sure now.
He hasn’t done acme threads got awhile. I find when I go a few years from a certain job, I don’t do it very well
For awhile
Makes a lot of sense Andy. I'd like a look at the insert under a microscope to check for wear. I'd do exactly as you suggest and rotate the insert when you start to see the chips changing in appearance. The point about decreased rigidity is also well made, there must be a point on pretty well any thread where the length of the part, the decreasing diameter of the core and the ability of the tool to cut cleanly ( it's sharpness? ) gang up on you. In some of Adam's close-up shots you can see a small burr developing on the outer edge of the thread. To me this is an indication that the tool is deforming rather than removing some of the material. Also note the chip form changing with successive cuts ( i.e 25:00 compared with 34:30 )
It's a long shot, but is the tool clamped flat to the bottom of the holder along it whole length? Even a few microns gap could allow a resonance to develop.
Heat build up could also contribute as, if the part is held very rigidly, the heat could cause buckling.
Just cutting tool surface area, part just climbed the tool once it had so much traction, slower speed and coolant to lubricate and you're fine. Happens all the time with Acme thread cutting, you can cheat a little by moving half and half with the compound and the cross slide when you get over half depth to balance the cutting forces off the right side and shift some to the left side.
@@ralphgesler5110 Yeah it would do it just the same on any lathe.
Had the part climb on a few threads I've cut, cut pallets of rods I've threaded on a manual so I'm not exactly green at it.
I think it's definitely what he is having problems with.
I'm wondering if the tool point is not on center with the lathe center, IE the shank is one inch and Adam normally uses a three quarter. Any deflection would then dig in.
I'll toss my comment in as well. Others have said it and i have found the same, the work is climbing the tool, period. You've removed enough material now that 2 things are happening;
1, the work has become more flexible
2, the tool has more contact area as it gets deeper into the work.
Add those 2 and you ceate a situation where the drag coefficient increases with every .002 you are moving in.
Get/use the follower rest as they are designed to eliminate this exact scenario.
I've ruined enough threads with the same process on my 10EE that has less than .0003 lash in the nut/screws. It's not the lathe my man.
A good machinist not only makes junk parts from time to time, but is willing to be humble and ask others for advice. Sometimes we just can't see the forest through the trees.
Keep making chips and keep learning !
Well Adam...These are the moments to separate the wheat from the chaff...I watched the process closely....Your first thought was also mine...it is a long and thin workpiece...and the further away from the chuk...the less support you have....But as your are gentle on it and taking only 2 thou a pass...then you would have noticed a deflection more early. Esp. on carbide inserts because on thread cutting inserts you have a 0 degree cutting angle...and the deeper you dive in, the more cross-section you get when cutting threads...
But hey... turn around and look from the other side. Nothing dramatic happened...you invested your time and a bit of steel....I would love to find out the real issue of that....maybe the ancestors did it right with high speed cutting steel, because there was nothing else available....
Give it a try and use some of that hss cutting steel for that acme thread...
Best regards from Germany!!
Good to see professionals showing things that go wrong, whatever or whoever the problem. Enjoy your videos and like it better with your new video photographer...Keep up the good work
.
Every time I have seen Acme anything it's usually really messing with a Coyote. Kidding.
Same, damn coyotes
Meep, Meep 😉
😂😂
...HECK- THE PROBLEM ISN'T THE ACME PRODUCT(S): THE PROBLEM IS THAT THE WRITERS ARE AGAINST THE COYOTE!!!
THE COYOTE CAN'T POSSIBLY WIN AGAINST THAT KIND OF A HANDICAP- NOBODY CAN!!!
Indeed! Meeep-meep!
The material is getting so small on the minor dia for its length. The material is flexing and trying to climb over the tool. Trust me, the machine is fine
I tend to agree with you.
My understanding is like this - "While the tool is normally cutting, it is pulling the rod towards itself. / By default the rod always wants to roll up on top of the cutting tool.
When the rod becomes thinner it is less able to resist that pulling action and so it moves toward the tool which results in excess material being removed.
When the rod was thicker it was better able to resist deforming towards the tool.
The work piece has a changing resonant frequency so be sure to listen to it when it starts to appear.
It's telling you that vibrational waves are present and they can rapidly get into phase with each other to sing loudly together to vibrate the work piece violently. "~ original answer by RocketMan.
Looks like a future series rebuilding a monarch😁
just want to say thank you for showing when things go wrong sometimes
wish more youtubers would dare to do it
Hello Adam, the Monarch is ok, it's just too much tool contact for the distance away from the chuck so the material is flexing as you are getiing deeper, the material is becoming thinner so it's more flexible and riding up on the tool, this will happen on any lathe, now that you know you will figure it out......... looking foward to your solution.
This is one of those things that's always boggled my mind and something I've questioned on Keith's channel. This is a relatively short screw, how are the lead screws that a 8 feet long or longer made? This little one clearly flexed so I can only assume the larger ones are cut with a series of dies
@@maggs131 follow rest.
@@strangefruit8776 I was wondering if there was such a thing and why I've never seen one used
@@maggs131 . Where I worked at we made a 4 acme thread that was 36" long rod . You still have flex . You just to get feed and speed right . The part was made on CNC 35 y mazak. Alot of things come in to play tool pressure . A lot programers will rough the thread out with a grooving tool then chase it to the thread profile with the right threading insert .
@@aaronmcclain1279 kind of like the way the tap made the nut?
I'm an Adam too, also born in '79, and I love this channel. Your a good bloke mate, sharing all you hard earned knowledge. I've got a mini mill, but I'm busting for a small lathe too. Thanks for sharing your experience with us on thread cutting, keep it up👍👌🇦🇺
David Vic and others are right, follower rest. I worked for one of the largest North American valve manufacturers back in the 90's, I cut 1000's of valve stems all Acme. Mostly in SSTL. On an Engine Lathe ALWAYS used a follower rest. Your lead screw has a pitch to diameter ratio that leads to easy flexing given that length. Nothing wrong with your machine, just your setup.
Yup +1.
Namely the cross slide angle.
@@waxore1142 the cross slide isn't adjustable, the compound is set correctly for a left hand acme thread
But that won't help if the problem is in the lead screw or the gears.
@@markshort9098 it is adjustable. Two bolts, one on each side. Its basic geometry. The further in it goes the more to the right it goes and the more it's pressing on the right side of the thread. Until it pops out and does what it did.
Adam, Just before the tool dug into the material I was thinking that your minor diameter at the time was getting pretty small to be unsupported in a 10 inch long part. I'm guessing you're at about 1/2 inch making it essentially turning a 1/2 " shaft with a huge amount of tool pressure caused by the blunt nose of the acme tool. This is asking for trouble without support such as a follower rest IMO.
Exactly. I predict that if he machines this screw
exactly the same way on another lathe, no matter how new, he’ll get the same result.
Adam, you probably know this but for the viewers at home, there is a downside to using oversized stock. the outer part of the barstock has fine grained, homogeneous crystal structure but the inner core (typically barstock bigger than 2-1/2" or so) of larger barstock will have a lot of sulfide inclusions and larger grains because it is both the last part of the bar was to cool, as well as receiving less rolling forces to break up the original cast grain structure.
Useful info, cheers
Rorschach, thanks for that comment. I had been wondering if material homogeneity might be a factor here.
Yes, but! He was getting even chip control and smooth cutting when facing the bar, which on a gross basis would suggest fairly uniform grain structure across the diameter. I know what you are describing is real and have seen that before in mild steel cold rolled barstock, but that doesn’t seem to be the case here.
@@Zircon10 this was free machining steel which is riddled with inclusions precisely to make chipbreaking easy. Free machining steels should NEVER be used on any highly loaded or critical component because it's propensity to crack anyway. I'm not sure that material was a good choice for this part.
@@Rorschach1024 Well as a metallurgist with 35 years of industry experience I’ll have to disagree with you re strength and fatigue resistance of Stressproof. Niagra LaSalle manufactures it and here is what they have to say about it: “STRESSPROOF was designed to meet, in one bar, the need for greater strength, elimination of heat treatment, better machinability and improved fatigue and wear resistance. It has a tensile strength of 115,000 psi, yield strength of 100,000 psi and an elongation of 8% minimum (7% above 2”). It is used in many applications including: Arbors, keyed shafts, spindles, gears, pinions, piston rods, sleeves, lead screws, racks, motor shafts, splined shafts, link pins, mandrels, boring bars, collets, bushings, drive shafts, armature shafts, rotary pump shafts, gusher pump shafts, kingpins, oil and water pump shafts, wrist pins.”
Notice lead screws are specifically called out as an application. Beyond that many of these parts are loaded well beyond what a cross slide lathe screw will see and applications like piston rods and wrist pins will see far more fatigue cycles than would be seen in a lathe feed screw.
I had a very similar issue, which was greatly remedied by replacing the half-nuts. I came to that solution by discovering that they would sometimes be pushed out of engagement under heavier cutting pressure. And to prevent it, I’d hold the threading lever in position.
A general purpose tool, cutting at virtually a single point, will exert significantly less force on the work piece than the Acme thread tool, which has a wide cut. Once you had reduced the diameter of the work piece to the extent that it could flex in the centre due to the force applied by the tool, your problem started.
If I am correct, you will get the same problem on the new lathe, if you use the same set up and lathe speed settings, feed rate, etc.
Hi Adam. I don't know if you found your problem or not but I have found in the past that when the work piece is getting closer to your minor the heat of the piece can cause it to grow just a hair and may push slack in your tailstock and cause weakening of the support from the tailstock and allowing slight movement of the work piece. Keep up the great work and videos. I love 'em.
I think the rod has become thin enough to flex and it is riding up on the cutter. Could you add a back and top rest to take out the whip?
This is a few months old I noticed, You handled yourself WAY better than I would have.
I would have yelled at the Lathe, the material (probably something that rhymes with Chuck). ...... Then edited the
Incident.
Miss Abbey in your videos. You both bring a synergy to the channel, and it is way cool seeing the success you have achieved with the new Machines!
Bad ass really. I like how you never stop learning and getting better at your craft. I attempt to do the same. KUDOS.
I really appreciate when people show the projects that, for one reason or another, failed to turn out as planned. It gives hope to hobbyists like me to see that even the machinists that I look to for advice still scrap a part now and then. On the brighter side, sometimes mistakes can be the greatest teachers. Looking forward to the next video.
I am very happy you posted this video. I enjoy it when things don't go perfectly, and look forward to an analysis video once you have figured out what happened. That will be brilliantly helpful.
Sorry about the problem, though. The Monarch is my favorite and I'm sad it shat the bed.
I can't wait for a cross-slide tear down and inquiry.
I agree with the idea that when You get close to the finish, the material flex and the tool got pinched.
You will probably have the same issue in the Viktor-lathe. It starts earlier or later depending on the stiffness of the material!
Use a follower rest an You will be fine.
Thanks for Your videos! Most valuable for us with a home shop.
Say hello to Abby as well!
PS. Lubricant might be of use as well! DS
You probably need a follow rest. The part is getting thinner and thinner, it seems like the threads are pinching the tool insert on the last passes and the part is being pulled upwards near the tailstock.
Thanks for showing us this anyways, there are not many youtubers that will show when things doesn't go their way.
EDIT: Would it help to go over with a V profile insert first and finish with Acme insert? That may relieve some of the tool pressure against the screw.
Same approach as the Acme tap you used in the bronse Acme nut video.
Appreciate your honesty when having a problem. You didn't have to upload this.
I don't think it was the lathe that moved, I think the bar flexed.
Wow! at around 36:40 when you run your cut out to the end, you can really see the far end at the centre really moving around.
I actually put the playback speed down to 0.25 speed and as the tool comes off the end of the cut the work piece drops over a millimeter (excuse the metric, I don’t know any better).
It's not the machine, it's too much flex in that thin workpiece..
Plus no lubricant.
On my Colchester the combination of wear in the different components caused mine to do the same when cutting big threads like that. Did not matter if i tried .001 or .002 cut just to much tool pressure and wear to get it done. So same conclusion was to move to another known better less worn machine. You will get it done on the knew one for sure.
Two suggestions: Use cutting oil. Use a follower rest.
Nothing wrong with that Monarch. Just needs a follow rest. The Diameter of that minor and that shaft length is flexing half way. Damn close to the finish line. I was hoping you would make it.
The rod is bending and binding on the threads. its squeezing the cutting tool between the threads.
long rod is getting thin from threads, it bends easier.
That makes a lot of sense. Since the minor dia. is getting thinner with every pass. And the problem seemed to get worst with every pass.
We had this problem on a engine lathe at the machine shop where I worked, were the tool would not follow in the same path, we took it apart and the half nut was packed with chips.Cleaned it all up and it worked fine.
I suspect that, with the loss of material from threading, the piece is bending, turning a catenary. (Bent like a two-person jump rope.) That would make it behave like it's "thicker" in the middle; it would account for "the tool getting sucked in" and "cutting very heavy," etc.
That really sucks Adam. Abby is becoming an awesome Videographer.. I look forward to see you the new lathe up a running. Brother you are s machining GOD. The issues with the Monarch lathe can't be you...the work you do is freaking amazing....thanks...Denny
Travelling steady rest. Your Monarch is one of the best. Please don't fault it.
I use to make 2 1/2 inch 316 stainless square thread, going left and right thread Level winder screws for fishing boat drums, sometimes 6-7 feet long. With a traveling steady, never had a problem.
You're a damn fine machinist and i've learned a great deal from you and really enjoy your videos.
Small inner diameter makes shaft flex. Do first square thread, then change acme insert and finish it. It helps digging and if you have some play in lead screw too.
This is looking like a perfect time to use a follow rest. Actually I’m surprised you were able to get as far as you did with that small of a diameter.
This is the BIGGEST reason why I watch Adam.....he shows EVERYTHING - goods/bads/etc....my heart did sink when I heard that noise though!!!
In my view, as someone who owns a lathe or two, is that you simply need a follow rest... The tool pressure is too high for that diameter at that length between the chuck and the center... As you said, its the rigidity, but its not the lathe`s fault, its more of a lack of proper approach... In my view, acme threads should always have a follow rest, as should any longer threads done on a lathe... It simply avoids you a lot of trouble with deflection and climbing parts and what not... Hell, a follow rest is a great side kick for parting off some rudely unpleasant materials... Sure, it may be a bit tough on the bronze jaws, but just freshen them up with a mill every now and again, they are expendable bearing surface...
All the best!
P.s. you said that you checked it before the screw up pass with a nut, and i think i saw a wiggle in the tailstock ram when the shot was happening, its entirely possible that you didnt fit the center snug enough and that allowed for chatter which turned into an instant disaster at that diameter without a follow rest...
Gotta keep in mind, you’re turning something that’s 30-40x the diameter. With a very blunt tool nose.
Not the machine, you need a follow rest. The part is climbing up the tool tip.
Maybe even less SFM? Chatter is usually related to speeds and feeds. It’s a harmonic vibration.
I have the same problem with my monarch 20c, the tool post height was designed for positive rake tools, and most tool posts and tool holders wind up below center line with negative rake tools and a bit of flex and then the part rides up on top of the insert
An offer to the gods of machining! Thank you for sharing this unfortunate moment Adam! Greetings out of Belgium!
Worked for a company that made lead screws and Ballscrews for 23 years, when we were single point cutting such a large acme we would rough it out with a v form tool first, then cut 5he whole form after and using a spring pass every 10 or so full cuts. Also normally would use a travelling steady to stop the work piece flexing.
It is adversity and that is always something that has to be overcome. It's human to doubt your lathe, but this is one of the best lathes in the world. And there is no place in the drive train but the shear pin to fail. That's the only place I would investigate.
I was surprised from the start that you don't use cutting oil. It would improve the quality of the thread, after all it is for a lathe.
Man that sucks after all that work. Sorry bud. Thanks for sharing, even the failures as it is a part of the machining world.
100% right on with your thoughts though. Looking @ 36:30 - 36:43 you can actually see the piece flexed, and climbed on the tool.
Maybe a follow rest would help on such a small shaft?
I tip my hat to you for showing the mistakes as they happened. As many others have said, numerous variables were involved in the failure. Some in the machine and some in the operator. Not a ding by any means on your abilities, or the eccentricities of the machine, it's just some times the process gets overwhelmed by tiny compounded problems. Be thankful the dig in did not lead to a "grab and fling" (been there, not fun)
This is more interesting to watch than when things go smooth. I love to hear you think through your troubleshooting process... there's so much to learn hearing a professional talk through what they're thinking. Thanks for the informative videos!
I believe that the thread is squeezing the cutting tool on the sides because of lack of support. This is clear because it happened on the middle of the thread and only after you had enough depth. Use the follow rest before you take the thread rod out so that you can quick check. Anyway I believe its already late.
It’s climbing the tool. It’s too long and skinny without enough support.
I ran a 25ftx46in lathe. Lots of 5”x250” bars. Chatter is usually a combo of rigidity and speeds/feeds.
Just too much tool pressure for such a long and relatively small diameter thread; its climbing up the tool. Traveling steady and cutting lubricant might be your best option.
"Life is what actually happens, when you had made other plans."
Thank you for sharing this specific part of the project.
I don't know 0.1% of what you do about cutting metal, but I'd have tried adding a follow rest next.
Adam Your best video ever!! When a machinist of your high caliber has a problem machining a part, it reassures us amateurs, that things don't always go as planned and we should not get discouraged. Thank You
I'm happy that you posted this video considering it was a fail. It shows that even a great machinist such as yourself can be done in by a mechanical mishap. Made me feel a bit better about some of my pieces. 😁 I'm just a hobby machinist and have learned a lot from you. Look forward to your next video. Thank you.
It's good to see your camera "person" is back on the job.
I feel like the primary issue is either with the timing of the lead screw, or with the halfnuts being worn. The cut at 26:45 was cutting HEAVILY on the left side of the tool, as shown by the bevel on the left side of the chip and the chip curling to the left rather than the right like in the majority of the passes. Then, in the cut at 30:45, the tool was way to the right of the previous pass, so much so there was a visible step at the bottom of the threads behind the cutter. Part deflection eventually added to this to ruin the part, but I believe it would have gradually gotten worse as the threads got deeper, not happened all at once. My bet is that the halfnuts have some strange wear patterns that occasionally cause the cutter to engage a few thousandths to the left of where it should; maybe a groove in the righthand side of the halfnut threads, worn in by all the righthand cuts I'm sure they've driven? In any case, I always enjoy watching your videos, even (or especially) those that show things going wrong; shows that mistakes happen to the best of us. Stay Abom strong and keep machining on!
Hi Adam. What a shame and I know exactly how you feel as it was going very well up to that point. I am not sure if I have mentioned it before but I worked for Seco Tools here in New Zealand for 28 odd years and gained a lot of knowledge about the application of carbide etc. I am a fitter and turner by trade but am now retired so I understand a bit about machining. When an insert is made, one of the last operations is a light honing of the cutting edge to give it strength as a sharp edge would soon fail. The hone level depends on the application of the insert so for finish it would be a very light hone and of course the opposite for roughing inserts, a heavy hone. Your threading insert will have a very sharp edge and I wonder if the sharpness has caused it to be pulled into the workpiece, especially on a long slender thread getting worse from every pass. Maybe consider taking a diamond hone and just break the edge a little. Too much of course will apply a lot of tool pressure and may introduce chatter. Anyway, that's my suggestion for what it's worth. I enjoy your film clips as they are so exacting and straightforward. Cheers, and keep up the good work. Ps Love your new shop!!!! Ian
I had a similar thought, I was thinking that since this is a brand new insert that's nice and sharp that it may not have been exactly centered and that made it want to dig in once it got thin enough to have some flex to the part. While this is unfortunate, the amount of info and suggestions in the comments here are awesome and I'm learning a lot just from reading everyone else's suggestions.
I like watching you work and that you take the time to explain things.
Edit: It is unfortunate that not everything works out. If this happened to me I would let the part cool down then start using oil to finish the threading. Because the part is so long and thin and possibly too hot, I would creep up on the feed like you did as well. I have been there where you get panicked and instead of taking a step back you started running the cross feed in, instead of using the top slide to feed. I look forward to your success because you got this.
When I was in college I had the task of making a 1"-2 Acme thread male & female. I actually made a double start 1"-4 male & female. The instructor was so impressed he gave me 100% anyways even though it was not a 1"-2 thread. He even gathered the other students and showed them then added it to the display case where only the best projects made it in. Our grading system was either 100% or fail.
I incorporated all of the various machining process we were do do into an 8 lb slide hammer gear puller with a 2 jaw & a 3 jaw head, reversible with locking nut. Also included heat treating.
I retired at 42 & I do miss the work. Thank you Instructor Ted Begman - Delta College
just do metal working diy from home like abom does
Your lathe is fine! Acme shaft is to flimsy being that long and is rolling up on your tool follow rest will correct that problem
Funny how he cut the new one without a follower rest and it worked just fine
If you have the tool holder at 14 degrees, every time you give it 5 thousandths in, the tool loads a little bit to the right. This gradual increase may be overloading the cut and manifests itself in the central part of the piece, which is the one with the least support.
Sorry my english.
Oh thank God! Adam IS human! LOL! I have watched a TON of your videos and I think this is the first time Ive seen you have a failed part. That gives me hope that I too can do this! Keep the great content coming!
This was my thought. I don't wish for Adam to struggle, but it was humanizing and might have lifted him up a little higher to see how he handled it. Me personally, part ruined=cussing and breaking more stuff.
A great start, I was glued to the screen as I knew from Instagram the screw failed this time. Shame but it gives the rest of us something to digest while you get set for another try.
Looking forward to seeing the next stage. In sure you'll work it out.
I'd say it was tool pressure causing the work to bow. As it bows it tightens the shoulders of that deep thread onto the tool causing it to dig in and trying to ride up on the tool. Probably need a follow rest to keep it from bowing. Don't think it was entirely the lathe's fault. Backlash would contribute for sure but probably a secondary issue.
I think you nailed it, the piece is long and whippy with deep threads, a recipe for pinching. At first I thought the tailstock may not be good and tight causing the piece to ride up.
Nothing wrong with machine.
It's the job flexing.
No cutting lube??
From the UK. ALL the best.
Should use a traveling steady to hold the thread from vibrating no matter the lathe.
Lube!
I never cut any threads without oil/lube except brass
With that small of a diameter and as course the thread is it may be time ti break out the follow rest.
Life is filled with tiny injustices. While the cuts were not consistent with the .005 or even the .002, I'm not sure why it decided to climb when the material thickness became flexible, but my "I have less machining experience in 55 years than you did by age 10" opinion is that the large diameter of the starting material may not have the ideal grain structure by the time it reaches your minor diameter.
Basically, I would like to see you start with a much smaller diameter material.
I am looking forward to seeing the new precision lathe, it can't hurt to have a nice tight machine.
Please consider this advice as an uneducated guess. But blaming the material gets you and the lathe off the hook! ;)
Thanks for showing failures as well as success.
Hi From Australia. Great video!
I noticed a small "Edge" in the bottom of the cut about half way through the cutting. That suggested to me that the half nuts were not fully engaged. Maybe there is slack in the cams that engage them, maybe dirt? or just wear. My Lathe a VDF has detents as well to keep the nuts engaged. One trick I have used is to shift left and right when working down to depth. near the end I revert to plunging straight in maybe at a reduced speed.
Maybe the Monarch knows you’re not going to use it much cuz you have big toy Pacemaker so it screwed up your lead screw. 😂
Yeah, the last few passes are almost always disappointing. I have only done them on a CNC and the only thing I did was use a slightly steepr rake angle by one degree and it made a big difference. It also seems there is so much side contact it does not take much to have it dig in. I was making shafts out of 400 series stainless, by the way. They were shafts for large refrigeration valves. I sure miss machining. It has been 18 years since I have done it. Keep up the great work Adam.
Great video! it's even more interesting if something doesn't work out as it was planned!
One of the best explaining lathe lesson I saw. You are a great professor.
I think it’s pushing the bar away from the tool and nipping the thread together on the tool side grabbing the tool
A follow rest would solve this...
Most common mistake is live center loosing, but to me it is not easy to cut the Acme tread that long when it reaches the full depth. It needs the follow steady rest to do it.
He said he had checked it with the nut I believe and that a little more needed to come off. If so he must have removed the center to check, maybe not quite correct when the center was put back?
Are the gibs tight on compound and cross slide and do you have a little pressure/drag on the carriage clamp? As you come down in diameter the bar flexes more, if there is any play in the carriage and slide they can dive below center and the bar wants to climb up on top of the tool. Small diameter brass is especially bad that way. A follower rest would help bar flexing, and using some resulphurized thread cutting lubricant would cut down on friction that exacerbates the situation. I’ve been on a well worn South Bend and lack of rigidity is a big problem when cutting threads. Everything has to be tightened up to prevent the tool from moving up/down in the vertical plane. Also, the deeper you get with the thread the less rigid the bar becomes and it’s not a one-to-one relationship…stiffness decreases to the 4th power of the diameter. All the more reason for a follower rest. That chatter we all heard in the problem section is a sure sign of lack of stiffness.
3:24 ...... that makes alot of sense and I never thought of that before. Thanks for the tip!