I think the joint between the two pieces at 6:00 should be longer to accommodate 4 screws to increase rigidity. Use blue threadlock for necessary disassembly. The hole for the flexure is a great idea to reduce a stress riser.
I second Roy's suggestion to make the connection longer with 4 (or three) screws. The distance between the screws and rear end is not much, and that has to resist all the bending. It won't be near as rigid as you planned on.
You've got a relatively long moment arm of that adjustment screw vs the two flatheads on the little rear shelf holding that bottom adjustment member. Are you going to be bending the members or stretching the flathead screws? If the screws stretch or otherwise work loose you are possibly going to be rounding the shelf. Maybe the moment isn't enough to matter considering the small amount of bend, but I'd feel better with about twice that much shelf, and/or having the upper arm be the loose part.
Hi John and Tom. Three comments if I may. 1. The dial gauge vertical measuring axis should be coaxial with the front contact pad. As modelled your measurement will be scaled down by the ratio of distances (hinge to gauge)/(hinge to pad). 2. International Standard ISO8512-2 Surface plates - Part 2: Granite has an Annex B (informative) with a typical design example of a “datum gauge” of the Repeat-O-Meter type. It recommends that the four contact pads each has a contact area of “about 280 mm^2” which is a circle of about 0.75” diameter. This will provide local averaging in the same way that a gauge block is used to average local areas on a surface measurement. The ball in your model, and hence the final ground contact area, appears to be much smaller than 0.75”. 3. ISO8512-2 also suggests the pad spacing as 100 mm + 100 mm lengthwise and 75 mm across the width. Your model appears quite narrow. Widening the span of the two center pads will increase the size of the reference plane. Hope these comments are useful.
Just a nomenclature thought; an outfit where I once worked had a 'thing' about single 'parts' (as in a discrete individual object) being called a 'part'. Assembled collections of 'parts' normally sold/supplied together as a unit were always called 'assemblies'. Part numbers & assembly numbers were different animals, and if you didn't know the difference you spent a lot of time chasing the breeze. (Of course, many 'parts' were never available individually.) Probably depends more where your working than anything else... cool videos, Thanks!
John, Silly idea, but you might think about adding keys to the inserts for micrometers (and matching one in the frame). This will help to easily locate the adapter rings properly without having to remeber about rotating them into position.
well I guess I was pretty stupid to leave the other comments. only now noticing how long ago this was. anyway great series, thank you for finishing it.
John, thanks for the great video and the podcast, both are brilliant! I'm not deeply familiar with the current best design practices for CAD/CAM, how are you managing tolerance build up in this assembly? You've got bolts that look like they are locating as well as clamping the three plates together - is this all defined in your modelling dimensions or do you need to amend the exported code? Probably a daft question - the Haas might be dead-on, with miniscule variation part-to-part.
I had another thought regarding your flexure detail... The drilling / reaming and sawing add two additional setups - even if the sawing is not a precision operation. I take that back... you have to set up for the edge drill & tap for the travel limit arms. Consider making the flexure cut as a round-bottomed trough with a ball end mill.The actual flexure material remains identical as from your drilled hole method. The difference is that your saw cut is exchanged for a much wider end mill cut. If you are going to be decking the top face of the base body anyway you will already be setup. If, instead, you were planning on using CRS and only milling from the bottom for the feet you could also mill the flexure trough from the bottom. Other than moving the flexure hinge point to the top face of the base you would achieve the same results. I am not sure this is less work or less machining, but it does package your machining operations into fewer setups and eliminates the walk to the saw. Daen
John, Great collaboration between you and Tom. I would like to suggest tapping the holes made to push out the steel balls. You could now use a capscrew to push them out instead of having to go to a press.
You should keep the differential screw. Just use a thread insert with no locking goop on the exterior threads (can probably just burn it off) in the thick piece and then red loctite the thumb screw to the inside threads. I think that's a better alternative to the original which is two parts pinned together. If you need to disassemble it you can just torch it.
Instead of two separate bars on the top piece, it would be simpler to make the top bar in the top piece and the second adjustment bar in the middle piece. I like how the reamed hole simplifies the flexture on the bottom piece.
Nice work so far. As others have commented, I have reservations about how your 0.4" thick arm is attaching. By separating and reattaching with fasteners you have changed the load path. With the original single-piece design the bar was rigidly fixed to the body. All of the load from the adjusting screw was reacted with a bending moment between the bar and the main body at the point of attachment - at the depth of the saw cut. The bending moment acted through the full 0.4" thickness of the bar. The new design consists of a free floating body with counteracting forces balanced at the fulcrum of the two mounting bolts. The two counteracting forces are from the adjustment screw pushing down and the top of the bar pushing up into the body on the other side of the bolts. The entire loading is supported by the tensile strength of the bolts. Will your design not work? It will probably do just fine. But it is not as stiff. Others have suggested making the bar longer to accommodate four fasteners. I suggest making the bar full length. Mill a dado the full length of the upper body and just nest the bar in that. Your two "sandwiching" shoulder bolts could pass through the bar and secure it in the stack. The outsides of the top body would remain at full thickness. A second point which is probably a matter of semantics... you mention that the 0.4" thickness of the bar being greater than the 0.3" thickness of the upper arm will make the bar ridged and the arm will do all the bending. Remember Newton's third law: "For every action there is an equal and opposite reaction...". There is equal and opposite force exerted on both the arm and the bar by the adjustment screw. So both will bend. The thicker bar will just bend less than the arm under the same load. Instead of the thumb screw and locking nut, perhaps a differential screw would be cleaner. McMaster does not seem to carry them with the same thread on each end. But Maple-Ind.com does. The down side is that these are hex key driven so would require a tool - or attaching a knob somehow. Looking forward to the completed project. Daen
Just a suggestion to save stock: Make the top bar (at 4:32) the same thickness all the way to the back so you don't have to mill out so much material. The center block in the sandwich at the rear would then just be a bit thicker to maintain same overall dimensions. Of course saving that bit of stock only matter if you intend to make a lot of these...
John, I've been following you and Tom on this. Great design but my suggestion would be to switch the toolbar top and toolbar bottom as far as how they are mated. Since you want the bottom to be rigid that should be part of the one piece. The leverage on the two bolts will allow flexing in itself and since you want the top to flex when you turn the screw the top part should be bolted down. Just my two cents. Russ
Can't wait to see the machining. I have been modeling up a 10" version using Toms flexture and limit screw. Really dislike the bars. My version will use some tig welding to connect the bottom to the middle section.. the price of Rohn indicators is crazy since the video cam out, just like the baby bullet!. Dave
I think I'd be a little concerned about residual welding stresses possibly causing some random warpings in the unit over time unless you did some form of stress relief after welding. I'm not sure that it would really be a problem, but it makes me a little nervous on a supposedly stable and precision instrument.
Dave Strong Wouldn't weld. Welding causes random warping of areas due to heat differentials and then locking that warpage in place. That's why you'll never see any welds on and precision device, only press fits and fasteners
You rounded all of the corners on the "front end", but left sharp 90 degree corners on the back. I'd suggest breaking those corners as well. Something like a 1/4" radius. Other have mentioned it but I'll say it again-- the lower arm in the upper assembly should be longer to increase rigidity. In fact, you could extend that arm clear to the back end to create a fourth layer in the sandwich as it were. That would mean less stock removal on the top part on the arm end.
If your drilling, reaming the base flexure no need to bandsaw cut the top. Just make it wide enough to slot with a reasonable endmill (assuming your doing that setup anyway why not) Or just skip the dril, ream from the side op entirely and just ball mill the flexure slot from the top entirely. But I assume Robbin has some smart-guy reason with residual stresses etc that you want to do the drill, ream op. :)
John, if you are going to start selling these which it appears that is your eventual plan, loose the Nylon spacer. Make that out of brass, copper, or something more aesthetically pleasing the to eye. Remember the AVE video where critiqued your Bridgeport collet duhickie, same same on this with the nylon spacer. You are making what is potentially a hi dollar piece of measuring equipment, make it look like one too + plus you have a cnc lathe so no excuse not to other than "other" production. Also does the thing need handles? ( Don't know? Is it a temperature thing? ) Seems to me as big as the surface gauges are handles are just over kill, unless of course it is a temperature issue with your hands. All in all awesome! Can't wait to see finished product.
You use a differential screw pitch device practically everyday. That's how a micrometer thimble works. 25 tpi rod with a 20 tpi nut gives an effective movement of .01" per turn of the thimble.
Interesting bit of info...I'll definitely keep that in mind for a future project using an electronic edge finder to use on a surface plate. If the pivot point and the indicator center are equal distances from the thumbscrew you would get .020 per turn. Heaven forbid I might have a metric and imperial combination located who knows where in the equation...thanks for twisting my brain lol!
No, most machinists either end up tool broke, or divorced because they spend too much time making their own tools. I might be a bit biased, but my Dad was the best machinist I've ever known, and his tools all sucked. I've been in the trades for 40 years and all my tools suck by comparison to today's standards. I don't think I can blame anything I've ever done wrong on the tools I was using at the time.
I've been wondering why you don't use the difference in thicknesses of the two bars you spread with the thumb screw? You can within a a minor range use it as a lever, with the thicker one yielding less, than the thinner one. I imagine a thread in the upper one, with a ball bearing ended thumbscrew like these: www.thorlabs.de/navigation.cfm?guide_id=131 lower one only acts as an arm. If the lower one only has 1/3 of the thickness, you effectively have a somewhat smaller than 1/3 of the deflection on the upper arm, as compared to the lower one. The ratio of displacement won't be linear to the ratio of thicknesses, but it'll be monotonous at least. It's tricky to explain, but please, if I'm not making sense, or missing a point let's discuss!
the factory repeat-o-meter flexure would have been done with a slitting saw on a mill. It's on an angle to clear the milling head, they can run several at the same time and once they made the cut they can test it's movement and repeat the cut to make sure it's just the right amount of flexy. I can guarantee you without even seeing the original that it was done with a slitting saw.
I think you will find that the Nyloc is not enough to keep the nut in place on the thumb screw. I would expect to pin, setscrew or stake the nut into place.
@@Trent-tr2nx based on personal experience Nyloc nuts do not resits loosening/shifting over them when they being rotated or are improperly tightened. Think of Nyloc nuts as anti vibration not anti rotation. Red loctite and/or jam nuts do a better job of anti rotation than Nyloc in my experience.
I don't see the reason for the nylon nut holding the adjustment screw. I get that you want to spread the two bars apart - but why? Why not just pull them together instead? Or if it's imperative to spread the bars, thread the upper bar and not do anything to the lower one.
Love the collaboration improvements! Nice work!
Enjoying the iterative design improvement process! Tom knows his stuff.
Looking good John. Can't wait to see some grinding footage.
Is there enough room to turn the indicator face parallel to the length of meter? Seems like the thumbscrew would interfere
I think the joint between the two pieces at 6:00 should be longer to accommodate 4 screws to increase rigidity. Use blue threadlock for necessary disassembly. The hole for the flexure is a great idea to reduce a stress riser.
I second Roy's suggestion to make the connection longer with 4 (or three) screws. The distance between the screws and rear end is not much, and that has to resist all the bending. It won't be near as rigid as you planned on.
You've got a relatively long moment arm of that adjustment screw vs the two flatheads on the little rear shelf holding that bottom adjustment member. Are you going to be bending the members or stretching the flathead screws? If the screws stretch or otherwise work loose you are possibly going to be rounding the shelf. Maybe the moment isn't enough to matter considering the small amount of bend, but I'd feel better with about twice that much shelf, and/or having the upper arm be the loose part.
Hey John, great video to see how you took Tom's input! You cant go wrong with any of Robin's advice either!
Hi John and Tom. Three comments if I may.
1. The dial gauge vertical measuring axis should be coaxial with the front contact pad. As modelled your measurement will be scaled down by the ratio of distances (hinge to gauge)/(hinge to pad).
2. International Standard ISO8512-2 Surface plates - Part 2: Granite has an Annex B (informative) with a typical design example of a “datum gauge” of the Repeat-O-Meter type. It recommends that the four contact pads each has a contact area of “about 280 mm^2” which is a circle of about 0.75” diameter. This will provide local averaging in the same way that a gauge block is used to average local areas on a surface measurement. The ball in your model, and hence the final ground contact area, appears to be much smaller than 0.75”.
3. ISO8512-2 also suggests the pad spacing as 100 mm + 100 mm lengthwise and 75 mm across the width. Your model appears quite narrow. Widening the span of the two center pads will increase the size of the reference plane.
Hope these comments are useful.
Just a nomenclature thought; an outfit where I once worked had a 'thing' about single 'parts' (as in a discrete individual object) being called a 'part'. Assembled collections of 'parts' normally sold/supplied together as a unit were always called 'assemblies'. Part numbers & assembly numbers were different animals, and if you didn't know the difference you spent a lot of time chasing the breeze. (Of course, many 'parts' were never available individually.) Probably depends more where your working than anything else... cool videos, Thanks!
great design, Tom
On the upper arm, where the indicator comes in, why not recessing the base of it so it is easier to adjust with the screw?
Awesome stuff John!
John,
Silly idea, but you might think about adding keys to the inserts for micrometers (and matching one in the frame). This will help to easily locate the adapter rings properly without having to remeber about rotating them into position.
I really like your version of the flexture. Obviously not the best for production, but it looks really slick and stylish
well I guess I was pretty stupid to leave the other comments. only now noticing how long ago this was. anyway great series, thank you for finishing it.
Really cool... thanks! Suggestion for the logos: much smaller... perhaps electro-etched... don't forget the year the tool was made.
John, thanks for the great video and the podcast, both are brilliant! I'm not deeply familiar with the current best design practices for CAD/CAM, how are you managing tolerance build up in this assembly? You've got bolts that look like they are locating as well as clamping the three plates together - is this all defined in your modelling dimensions or do you need to amend the exported code? Probably a daft question - the Haas might be dead-on, with miniscule variation part-to-part.
I had another thought regarding your flexure detail... The drilling / reaming and sawing add two additional setups - even if the sawing is not a precision operation. I take that back... you have to set up for the edge drill & tap for the travel limit arms.
Consider making the flexure cut as a round-bottomed trough with a ball end mill.The actual flexure material remains identical as from your drilled hole method. The difference is that your saw cut is exchanged for a much wider end mill cut. If you are going to be decking the top face of the base body anyway you will already be setup. If, instead, you were planning on using CRS and only milling from the bottom for the feet you could also mill the flexure trough from the bottom. Other than moving the flexure hinge point to the top face of the base you would achieve the same results.
I am not sure this is less work or less machining, but it does package your machining operations into fewer setups and eliminates the walk to the saw.
Daen
I'd definitely make that thumbscrew a bit shorter like the original. Looks like it might interfere with the dial face depending on dimensions.
John,
Great collaboration between you and Tom. I would like to suggest tapping the holes made to push out the steel balls. You could now use a capscrew to push them out instead of having to go to a press.
details, details, details :)
Doesn't the screw have to be right on top of the ball so you don't have a cosine error?
I really like the rounding. Square corner tools are literally a pain in the hand. How about a small radius for those two back corners, too?
You should keep the differential screw.
Just use a thread insert with no locking goop on the exterior threads (can probably just burn it off) in the thick piece and then red loctite the thumb screw to the inside threads.
I think that's a better alternative to the original which is two parts pinned together. If you need to disassemble it you can just torch it.
Instead of two separate bars on the top piece, it would be simpler to make the top bar in the top piece and the second adjustment bar in the middle piece.
I like how the reamed hole simplifies the flexture on the bottom piece.
Nice work so far.
As others have commented, I have reservations about how your 0.4" thick arm is attaching. By separating and reattaching with fasteners you have changed the load path. With the original single-piece design the bar was rigidly fixed to the body. All of the load from the adjusting screw was reacted with a bending moment between the bar and the main body at the point of attachment - at the depth of the saw cut. The bending moment acted through the full 0.4" thickness of the bar.
The new design consists of a free floating body with counteracting forces balanced at the fulcrum of the two mounting bolts. The two counteracting forces are from the adjustment screw pushing down and the top of the bar pushing up into the body on the other side of the bolts. The entire loading is supported by the tensile strength of the bolts.
Will your design not work? It will probably do just fine. But it is not as stiff.
Others have suggested making the bar longer to accommodate four fasteners. I suggest making the bar full length. Mill a dado the full length of the upper body and just nest the bar in that. Your two "sandwiching" shoulder bolts could pass through the bar and secure it in the stack. The outsides of the top body would remain at full thickness.
A second point which is probably a matter of semantics... you mention that the 0.4" thickness of the bar being greater than the 0.3" thickness of the upper arm will make the bar ridged and the arm will do all the bending. Remember Newton's third law: "For every action there is an equal and opposite reaction...". There is equal and opposite force exerted on both the arm and the bar by the adjustment screw. So both will bend. The thicker bar will just bend less than the arm under the same load.
Instead of the thumb screw and locking nut, perhaps a differential screw would be cleaner. McMaster does not seem to carry them with the same thread on each end. But Maple-Ind.com does. The down side is that these are hex key driven so would require a tool - or attaching a knob somehow.
Looking forward to the completed project.
Daen
Is this repeat-o-meter part2 ?
If you don't already have a feature in the way, have Fusion calculate the center of mass X position and put the handle there for balance!
Just a suggestion to save stock: Make the top bar (at 4:32) the same thickness all the way to the back so you don't have to mill out so much material. The center block in the sandwich at the rear would then just be a bit thicker to maintain same overall dimensions. Of course saving that bit of stock only matter if you intend to make a lot of these...
John, I've been following you and Tom on this. Great design but my suggestion would be to switch the toolbar top and toolbar bottom as far as how they are mated. Since you want the bottom to be rigid that should be part of the one piece. The leverage on the two bolts will allow flexing in itself and since you want the top to flex when you turn the screw the top part should be bolted down. Just my two cents. Russ
On the top part: dont make the fixed part lose. Better make the indicator holding part to screw on. This way you can even tweak your design easier.
Can't wait to see the machining. I have been modeling up a 10" version using Toms flexture and limit screw. Really dislike the bars. My version will use some tig welding to connect the bottom to the middle section.. the price of Rohn indicators is crazy since the video cam out, just like the baby bullet!. Dave
I think I'd be a little concerned about residual welding stresses possibly causing some random warpings in the unit over time unless you did some form of stress relief after welding. I'm not sure that it would really be a problem, but it makes me a little nervous on a supposedly stable and precision instrument.
Dave Strong
Wouldn't weld. Welding causes random warping of areas due to heat differentials and then locking that warpage in place. That's why you'll never see any welds on and precision device, only press fits and fasteners
You rounded all of the corners on the "front end", but left sharp 90 degree corners on the back. I'd suggest breaking those corners as well. Something like a 1/4" radius.
Other have mentioned it but I'll say it again-- the lower arm in the upper assembly should be longer to increase rigidity. In fact, you could extend that arm clear to the back end to create a fourth layer in the sandwich as it were. That would mean less stock removal on the top part on the arm end.
Really cool project, can't wait until you finish. (Also first!)
If your drilling, reaming the base flexure no need to bandsaw cut the top. Just make it wide enough to slot with a reasonable endmill (assuming your doing that setup anyway why not)
Or just skip the dril, ream from the side op entirely and just ball mill the flexure slot from the top entirely. But I assume Robbin has some smart-guy reason with residual stresses etc that you want to do the drill, ream op. :)
John, if you are going to start selling these which it appears that is your eventual plan, loose the Nylon spacer. Make that out of brass, copper, or something more aesthetically pleasing the to eye. Remember the AVE video where critiqued your Bridgeport collet duhickie, same same on this with the nylon spacer. You are making what is potentially a hi dollar piece of measuring equipment, make it look like one too + plus you have a cnc lathe so no excuse not to other than "other" production.
Also does the thing need handles? ( Don't know? Is it a temperature thing? ) Seems to me as big as the surface gauges are handles are just over kill, unless of course it is a temperature issue with your hands.
All in all awesome! Can't wait to see finished product.
You use a differential screw pitch device practically everyday. That's how a micrometer thimble works.
25 tpi rod with a 20 tpi nut gives an effective movement of .01" per turn of the thimble.
Interesting bit of info...I'll definitely keep that in mind for a future project using an electronic edge finder to use on a surface plate. If the pivot point and the indicator center are equal distances from the thumbscrew you would get .020 per turn. Heaven forbid I might have a metric and imperial combination located who knows where in the equation...thanks for twisting my brain lol!
Funny, all of mine are straight forward male and female threads, does this mean they must all be cheapies?
No, most machinists either end up tool broke, or divorced because they spend too much time making their own tools.
I might be a bit biased, but my Dad was the best machinist I've ever known, and his tools all sucked. I've been in the trades for 40 years and all my tools suck by comparison to today's standards.
I don't think I can blame anything I've ever done wrong on the tools I was using at the time.
I've been wondering why you don't use the difference in thicknesses of the two bars you spread with the thumb screw?
You can within a a minor range use it as a lever, with the thicker one yielding less, than the thinner one.
I imagine a thread in the upper one, with a ball bearing ended thumbscrew like these: www.thorlabs.de/navigation.cfm?guide_id=131
lower one only acts as an arm. If the lower one only has 1/3 of the thickness, you effectively have a somewhat smaller than 1/3 of the deflection on the upper arm, as compared to the lower one. The ratio of displacement won't be linear to the ratio of thicknesses, but it'll be monotonous at least.
It's tricky to explain, but please, if I'm not making sense, or missing a point let's discuss!
the factory repeat-o-meter flexure would have been done with a slitting saw on a mill. It's on an angle to clear the milling head, they can run several at the same time and once they made the cut they can test it's movement and repeat the cut to make sure it's just the right amount of flexy. I can guarantee you without even seeing the original that it was done with a slitting saw.
I think you will find that the Nyloc is not enough to keep the nut in place on the thumb screw. I would expect to pin, setscrew or stake the nut into place.
Why?
@@Trent-tr2nx based on personal experience Nyloc nuts do not resits loosening/shifting over them when they being rotated or are improperly tightened. Think of Nyloc nuts as anti vibration not anti rotation. Red loctite and/or jam nuts do a better job of anti rotation than Nyloc in my experience.
@@franklimaunderstood. thanks for the information!
Round those back corners! All the other corners are nice and round, but the back looks like it was cut right off the bar!
differential screw math. (1/ coarse TPI)-(1/fine TPI) == difference per revolution. 1/((1/course TPI)-(1/fine TPI)) == effective TPI. 1/28-1/32 == 0.00446428571428571428" or 1/(1/28-1/32) == 224 TPI. I'll see you Saturday!
Looking forward to the build, by the way " Sometimes its time to shoot the engineer and get on with production" just kidding. Keep them comming. Greg
interesting video.
I don't see the reason for the nylon nut holding the adjustment screw. I get that you want to spread the two bars apart - but why? Why not just pull them together instead?
Or if it's imperative to spread the bars, thread the upper bar and not do anything to the lower one.
here are some very precise adjustment screws:www.newport.com/f/ajs-high-precision-adjustment-screws