Precision Mechanics

[@forrestaddy9644]

Adding... I think Tom deserves an extra-big "atta boy." Cooking up demonstrations and making visual aids takes a ton of time. He's done this for all his hundreds of videos and got little thanks for it. Tom, if you weren't 950 miles away, I'd buy you a pizza and even help you eat it. That's how grateful I am for all your good works.

[@oxtoolco]

Hey Forrest, Thanks for keeping us all honest around here. Your comments and insight are always on point. This humble mechanic thanks you. All the best, Tom

[@forrestaddy9644]

oxtoolco Any time, Tom, BS is my name and nit-pick is my game.

[@PracticalEngineeringChannel]

Very cool. Really enjoying this series.

[@fredgenius]

28:06 - the equation for metric threads is far simpler, just pitch a - pitch b. I designed bed corner adjusters for my 3d printers using this principle, M4 is 0.7mm pitch, M6 is 1mm pitch. Difference is 0.3mm, so 0.3mm per 360° rotation of the adjuster wheel. Very cool!

[@billlee5307]

Priceless information for anyone designing fine adjustment into a device. Once again I have to say that this video alone would have saved me many days of head scratching back when I was designing and fabricating research instrumentation. Before I learned about differential screw mechanisms I used to go to swap meets and buy beat up old micrometers and use them for projects that required fine adjustment. I know the following remark betrays my prejudices and I in no way want to diminish the incredible power of software based design, but it is great to see design done in the shop with physical objects. Many thanks Tom!

[@ErosNicolau]

I can't afford a shop. Not even a small one (living in a block apartment and the noise would be too much). But I love to watch and learn. And I know I'm watching the right people when, after a while, I get goose bumps finding out I can anticipate the same solutions to the problems they propose as the ones they find themselves. Thank you, Tom!

[@TheMadJestyr]

This is the kind of thing that makes me look forward to your videos. So many idea's floating through my head right now.

[@ydarg1]

Tom, i consider you one of the smartest people on youtube. thank you again for a great lesson

[@FredMiller]

One of the best videos on the subject I have ever seen. Thank you for the tutorial!!! Fred

[@rcoray]

Never cut a single chip. Never miss a single video. Your content is great...except the 3rd vid on lapping

[@josephwilson6651]

Sneaky? How about alternatively derived, I say your "Tomiszims" are just one of the reasons I enjoy your productions.You have a truly unique mindset.Thank You for the adventurous journey in machining, and satisfying culmination thereof!!!

[@MikeBramm]

Another great video, Tom. Thanks for showing the various steps to getting finer and finer adjustment. The trick of using differential threads is awesome. An easy way of thinking of the differential movement is that the 1/4-28 thread is moving ~0.03571" per rotation, while the 10-32 thread is absorbing 0.03125" per rotation, making the resulting movement ~0.00446" per rotation, or about ~0.001" for every 90 degrees of rotation.

[@ROBRENZ]

Great video Tom, looking forward to seeing the final design and execution. Best, Robin

[@arnljotseem8794]

Differential screws, never heard of them before now. Wicked cool. Thanks for the knowledge transfer. Keep them coming Dr. Ox

[@Landrew0]

This is a clever concept for achieving precision, if I understand it correctly; one screw unscrews, while the other one screws in, so it actually moves at a rate corresponding to the difference in the amount of travel between the two different thread pitches. The part I don't understand is how it could work without one them being a left-hand thread.

[@arnljotseem8794]

When you screw the big bolt in, it wants to push the parallels apart since the top parallel is threaded. However, since it also screws onto the small bolt the push on the parallels is reduced by a less amount since it also screws down onto the smal bolt with smaller pitch.

[@oxtoolco]

It is a bit of a mind bender. One is threaded into the other and fixed. Thanks for the comment. Cheers, Tom

[@georgeyork8975]

i know i am late in the game but this has intrigued me to build my own repeatometer etc. So if I am not mistaken, the top bolt is threaded into the bar and the lower 10-32 is threaded into the lower bar as well? Thanks!!!! Geo

[@ianjoubert7505]

Thank you mr Lipton, very educational episode! You might just as well build your own repeat o meter, as you are almost half way. Oh and thank you very much for the metric, screen shots, it really makes it easier to understand, and at the same time get to know the imperial sizes!! Ian South Africa

[@warpigs330]

One of my favorite videos you have made. I would love to see more design iteration like in this video. It really gives a good sense of the reality of designing a product and what problems you have to solve along the way, and how you solve them. Thanks for the excellent videos.

[@timmallard5360]

Awesome video! Tom you are making baby nap time very enjoyable for this engineer! These principles of precision are fascinating and make us all better metal workers!

[@grahamspinks4801]

The description of the differential screw I found very interesting. I was looking for a way to hold a collet chuck in my pillar drill so that I could use it for light milling. The idea I came up also used two threads of unequal pitch to draw the arbor into the taper. Excellent video.

[@martinszinbergs2073]

Very nice video. Thank you for sharing your knowledge and showing a design process. I'm particularly happy that you showed how you made some prototypes and tested the ideas. Very important for this type of work. Very cool to see.

[@squelchedotter]

Thanks for also giving the values in microns!

[@renderbrandt]

Differential screws are awesome, never knew about them, or thought about it, but it makes so much sense!!!

[@homeworkshopengineering]

I’m a little late to the party but knowledge like this doesn’t go out of date. Some fantastic elements to apply here. As someone just starting to try this video stuff, I really appreciate the work that goes into these.

[@AronGreen]

Man, I listened to the first minute of what you had to say, and thought it would be interesting to see you review/dissect the mechanics/precision of some home/hobby grade "precision equipment" - I'm thinking like 3d printer, or cnc machine. A lot of people don't understand the tolerances of their machines, and I just think it would be interesting to see you dissect one at that level.

[@gandersson6121]

really cool stuff Tom! sneaky screws are the best screws :)

[@xmachine7003]

😂😂😂😂😂😂😂😂😂

[@raincoast2396]

Being an obsessive/compulsive type personality, this fine measurement series is fascinating. Especially like the fine thread, within a fine thread, differential screw. Thanks Tom.

[@paulwomack5866]

Differential screws are often used to get the progression rate of a fine pitch with the robustness of a coarse pitch

[@rogerkimball2098]

When you finish this project, let the gentleman who calibrated your surface plate borrow it. Of course, if it performs better or equal you may not see it again. Your videos are really cool and show a wide range of interesting topics! Keep it up!

[@oxtoolco]

Hi Roger, That may happen as I will have them back to calibrate my plates in a year or so. Thanks for the comment. Cheers, Tom

[@finnna8352]

Excellent part on the Differential screws. I never heard of that before. Thank you.

[@fredgenius]

Thanks Tom, great video. I found a use for the differential threads, I just finished making 3d printer bed adjusters using 0.7mm and 1mm pitch threads so the net difference is 0.3mm. Working perfectly!

[@larrysperling8801]

interesting stuff tom. i" learnt "a lot of new words today, and thanks to you and google i may even be able to use some to impress my buddies. the world beyond tenths is like looking for quarks to me. i really enjoyed the machining and the creative setups as always. i will forever remember the differential screw. thanks for another great video.

[@bigb0r3]

There are some great tips in here. Loved the ball bearing /screw combination; that can have soooooo many applications. Detent applications are common for ball bearings but I don't recall seeing a ball bearing applied like that.

[@johnbodmer5645]

Good ideas Tom. Thanks for the video.

[@ebenfourie9057]

Fantastic video Tom, always interesting watching your stuff and I learn several new things from each video. Thanks for posting this.

[@myenjoyablehobbies]

Very enjoyable, watching your design work, from the drawing board to the final product.

[@makingsense2268]

That is super awesome. Thanks, Tom!

[@MrJugsstein]

Tom really liked these 2 videos. I always enjoy the thought process. and the info on flextures. Will

[@SuperKingslaw]

You are an amazing teacher. Thank you!

[@literoadie3502]

I was trying to do the math and I was putting the actual pitch values in the equation, whereas you really meant just the TPI values and I was getting crazy results!

[@tridium-go6hw]

Good stuff Tom. One of the benefits of your design (for me, at least) is that, since the flexure can be disassembled at will, there is a lot better chance of a home shop machinist getting through the fabrication without destroying it. If I were building the original design I would have to save the saw cut as the last op, and I would still probably wreck it before getting the limit straps in place. and the differential thread idea is brilliant! Regards, Dan

[@lyntonr6188]

Another excellent video tom. Thank you.

[@essentialvision6025]

Great information Tom. I've learned a lot from these videos on the Rahn instrument.

[@toddk.5873]

These are really nice videos Tom. Thanks for sharing.

[@mudnducs]

Miss your videos Tom. Glad I have your books

[@pitu72ger]

excellent subject and presentation. Dan Gelbart has also nice video on flexures.

[@Sharklops]

As an overtravel mechanism, would it work to have two or three dowel pins bridging the gap set into slightly oversize holes in the ends of the two pieces? Or even maybe a tongue and groove cut into those ends instead.

[@RRINTHESHOP]

Great ideas, Love the differential screw.

[@RGSABloke]

Holy shit Tom, that was very I interesting/brain challenging. Just about to look up my Black Book to get the inside on these differential fittings. Great series, thanks for sharing. Kindest regards. Joe.

[@chrismayhew4531]

Thanks Tom, that was fabulous. Have added this to my "mint" playlist for future reference!

[@jmwarden1]

Tom, that was a very informative video that just blew me away with the differential screw. Wow, what resolution.

[@outsidescrewball]

Hmmmm.....maybe I snoozed during a discussion, the flex is a cantilever so I would assume the original remaining material of the saw cut was calculated that it could flex "X" to assure a correct reading, if I am correct in my assumption, how do you calculate the attached flex part the your design uses?

[@PixelSchnitzel]

That was tremendously educational! Thanks!

[@denny9931]

Machinist magic! Thanks so much for enlightening me. That really comes handy.

[@nothermarkgnomex]

Very neat! I like to see alternatives explored with reasons why. I have one concern. When you tap the flexure and the base then the screw threads set the any spacing when then two parts are put together. I have been bit by that in the past. Is that what you want in the end?

[@mearloo]

Tom, fantastic video. Is there any need to create a vent hole in top portion of the differential screw to avoid air/lube compression ? or are the threads course enough to let air/lube to pass? (i assume some oil could be added to the threads to help any friction)

[@aserta]

A drop of weld on the tip of the screw also works. I've done that with an adjustment screw for an indicator base. I don't remember what filler i used tho. Hasn't lost its tip in 10 or so years i've done it.

[@Gkuljian]

I hadn't seen that equation for differential screw pitch before. It's remarkably similar to the equation for parallel resistance, except in the case of right/right pitch there's a minus sign. Now I've got to make something with one of those setups. Cool.

[@robmckennie4203]

Just a layperson here, but is there a reason you wouldn't want to lock the adjustment on that over-travel fastener with a jam nut? You could easily mill some clearance for it on slot side of the flexture, and just use a nice low profile nut. It wouldn't even take much torque to lock it in place, just a light snug. Personally I love field stripping my tools, I think it'd bug me if I had something glued in place

[@arjenvld]

This video could and should be a guideline on when and how to use the "educational" tag! excellent video

[@ckvasnic1]

Me Wizard... Great Video! Especially love the differential screw. I am going to use that somewhere... Someday!

[@rlsimpso]

Excellent information. That differential screw and parallel flexure mechanism would be a great improvement to the adjustment on a cheap comparator stand I have. Great, another project to do before finishing another project.

[@daki222000]

cool stuff. how did you get the differential screws in place is what dazzles me! they are threaded in both pieces(?!), cheers.

[@89sirmonk]

possibly drill holes in the flats of bolt head (at the flecture) and you can turn it by inserting a wire, pin, or Allen wrench.

[@piccilos]

Great info, we need a more "Tom's improvements" series. Go over random shop tools and redesign them. :)

[@Paddington60]

Hi Tom, I keep wondering about swapping the locations of the screw and indicator. If the indicator were to be located between the screw and the pivot point wouldn't there be lees movement? I guess the repeat in the name is a bit of a clue as to the desired function, not just a small amount of movement from the adjustment screw. Hummmm . . ..

[@peteferguson7024]

Great content, I feel like I should be prepping for a midterm though :) . With the new knowledge I quickly tried to figure out how to get you a one-one turn with the tenths indicator you had even though you were close with the P(effective) of 224 as set up. With 0.0008" total indicator travel for a 360 degree turn you would need at P(effective) of 1250 which could be done with none standard hardware but that was not your point... so with standard gear it looks like that 224 is a good result that can easily be achieved. Just messing with some combinations and an formula, it appears the P(effective) increases as the individual TPI(s) increase and the difference between them decreases. With a custom set of hardware, 80 TPI and 79 TPI, you can get to 6320! Great lesson Tom, Thanks

[@dtec30]

Will you be making your own dial gauge ? For the repeat o meter

[@Gary3247]

Instead of the bolt in the milled slot, use 1 or 2 metal dowels press-fitted into one side projecting out into larger holes on the other side. The size of the larger holes would dictate how much lateral movement you have. This would be simpler to produce. I hope this makes sense.

[@matman7546]

Gary3247 exactly what I was thinking

[@johnroberts4789]

Great visual demonstration!

[@rjkee5157]

That was a very interesting video. Thanks

[@daque1960]

I wonder if you could use two flexures of different thicknesses so the the weaker one would not move anything useful but would bend more than the other one in the opposite direction. The effect would be most of the movement from the screw effect the stronger flexor less and give an effective higher tpi on the screw. I am probably not describing my idea very well ...

[@ElectraFlarefire]

Quite enjoying this series and hope to see lots more about it. I really don't like nycnc's style, so this is the only side of the story I get to see.

[@RobertSzasz]

I wonder if there are monolithic interferometer on IC modules available. It would be neat to see something like the repeatometer with a dual flexure and interferometer sensing.

[@FredMiller]

I can't remember who did it but there is someone on KZbin that did and showed exactly that. Sorry I can't help more....

[@MattOGormanSmith]

and while you're at it, add accelerometers and gyros so you can make an automatic map of your surface plate :)I couldn't find a suitable module with a quick google, but I'd be worried by the fact that surface plates are not optically flat. This could be corrected with a polished transfer pin of some sort I guess.Now I'm curious what accuracy you could get from an iphone with 3 balls glued to it. Assuming 16 bit resolution, one tick on the gyro would represent about 0.00012" across a 4 inch base.

[@RobertSzasz]

With drift and noise? You would be measuring everything except the surface flatness. With the setup in a smart phone expect .5° angular resolution of the gravity vector. The 16bits is almost always assigned to measure +-5g where for angular resolution you want +-1g (and a hair) I brought up an interferometer because there have been huge leaps in single chip integration of optics which has driven costs through the floor. It should be 'easy' now to have a module capable of measuring a few mm or travel with sub um precision for under $100. Resolving Less than .1mm over 10cm by measuring acceleration is..... hard. (Remember you are sensing the magnitude of acceleration along 3 orthogonal axis)

[@ProtoSimTechnologies]

Never heard of a differential screw. Very interesting. Thanks for the video, and the explanation of how they work ;-)

[@mxcollin95]

Great video Tom! I had never heard do differential screws before. Lots of interesting content in this one. 👍

[@wither8]

This and the last episode were both great. Your indepth analysis of the subtleties behind the mechanics of the tooling and design improvements were both damned interesting. You should do a whole series of "Tom Redesigns [foo]" where foo = industry standards like the Kurt vice (which is no doubt fairly good, but has it's flaws, i.e., overtorque will lead to canting your workpiece vertically, rather than keeping it flush).

[@douglaslodge8580]

Great series.

[@djberg3483]

thanks again Tom, very cool stuff to learn!

[@lookcreations]

A very informative feature again. I would live to see your solution to increase the sensitivity of a 1/10000" indicator so we lesser mortals could look to build the meter for home shop use and negate the hi-end indicator requirement. Keep up the great series . All the best. mat

[@intagliode]

Great video Tom! I see a lot of people in the US talking about 10ths of an inch as such a small amount. As soon as you converted it into microns. Its a sausage in a corridor measurement. I found the differential thread part really interesting. Project should have been a build off against SMW instead of a collaboration. Keep up the great work!

[@oxtoolco]

Sausage in a corridor gave me a great laugh. Thanks for the comment. Cheers, Tom

[@intagliode]

metalhead2508 sorry tenths of a thou.

[@davecope3322]

Brilliant! Thanks Tom.

[@dejanira2]

Fascinating, The amount of time you have used to do the machining and design must be outrageous. Still I enjoy the knowledge that is provided.

[@imajeenyus42]

Great demo of the differential screw! Was playing with something similar recently, they're really neat things. You might know them already, but Thorlabs sells stock adjuster screws in various sizes (1/4"x80tpi is popular) along with drills+taps. Not the cheapest, but maybe handy to have.

[@oxtoolco]

Hi Lindsay, Somebody else sent me a link. I didn't realize they were so cheap from Thorlabs. Used to New$$port pricing I guess. Thanks for the comment. Cheers, Tom

[@therealstubot]

Tom, I hope at some point you'll be discussing the efficient setup of differential thread systems. In my experience, there's a good bit of clocking of the internal thread in order to get the outside thread synched with the start of the internal thread. In this application, would you spread the flexure to the maximum point, then get the internal threads lined up with the start of the lower screw? Or what process would be employed to get the thing together and not under tremendous stress? Is there a way to do it that isn't trial and error?

[@oxtoolco]

Hi Jeff, It was actually pretty easy in this case since they are the same hand thread. I just turned the 1/4 inch screw a little as the #10 entered and all was fine. I was more worried about the angle change between the two limbs. It turns out it wasn't a big deal over the distance I moved. Thanks for the comment. Cheers, Tom

[@12345NoNamesLeft]

When does the high quality video kick in ?

[@OldIronShops]

love this. this is a great example oh combining simple machines to make a much more complex one. it's one of the things I love about this trade. (note must add this to the build list.

[@slarti42uk]

I was pondering on the reason for the angled cut in the original. I was wondering if it was to give a more accurate single point for the rotation of the floating arm. The thinnest single point at the bottom of the cut. With the shim flexure, you can't be sure where it's flexing. Now comes the "but why?" Why would you need to know the distance between the foot on the floating arm and the pivot point?? Is there some math involved for working out the movement, or just the direct reading?

[@oxtoolco]

Hi Steve, Its really just a displacement under the indicator. The support base needs to be far enough away to not be in the hole the front foot is seeing. Thanks for the comment. Cheers, Tom

[@eideticgoone7035]

I came up with another simple way to increase the sensitivity of the indicator to the adjuster screw by making the lower limb thinner than the upper. After viewing the first video. I could hardly stop thinking about the differential screw. While calculating pitch multiplication factors, I noticed something in Rahn's design which can be further exploited for precision. Notice that both the upper and lower limbs are free to move relative to the base under the force applied by the adjuster screw. This means that the spreading distance from the adjuster screw is distributed between the two limbs in accordance to their springiness. If in the original, assuming the spread is equally distributed between the upper and lower limbs, the upper limb moves about half as much as the change in screw length. Since the indicator measures from base to upper limb, this effectively doubles the thread pitch since the upper limb only moves up by half the spread of the screw. My big idea (in my mind) is that one could further increase sensitivity by making the lower limb springier by making it even thinner. For example, to make an effective screw pitch 4x as fine, make the lower limb 1/3 the thickness of the upper. 1/3 thickness should move 3x further under the same screw force. For a total movement of 4 units, (1 upper + 3 lower) the upper would only move 1 unit. As long as the elastic properties of the limbs is not exceeded, the thinner the lower spring, (or thicker the upper) the greater the thread pitch multiplier. Your proposal (previous video) to make these limbs bolt together in the previous video, makes it easier to try out this idea. Thanks again for this awesome follow up video. I'm vary curious what you think of this.

[@oxtoolco]

Hi Goone, It may have some merit. One reason I constructed the analog of the Rahn was to see what effect the two limbs spreading had on the sensitivity needs for the knob. There is certainly some effect but hard to quantify. The other purpose of the screw is to actually unload the indicator from the contact point when not using the device. It needs a bit of travel to do that as the preload of the indicator is something like 1mm. Thanks for the comment. Cheers, Tom

[@Sketch1994]

Hi, First of all thank for all the information you provide us about all these different subjects, and I have a question. What is the best way to go about roughing a granite plate that is very out of flat(at least 0.02mm/4cm of angular error with the pivot of indicator taken into account or a max indicator error of almost 0.05mm/4cm). I half tried my DIY lapping compound which consists of burnt sandpaper of different grits and ground honing stones but my shoulders are getting worn way faster than the granite(in fact it took me 3,5 hours to correct 0.01mm/4cm of reading)

[@Sketch1994]

PS: Check out Dan Gelbart's videos on flextures. This man is a genious and he uploaded a small part of it in a small series of videos(one of them about flextures).

[@oxtoolco]

Hi Sketch, Diamond is your best bet. It stays sharp for a really long time and will cut nearly everything. Its what the guys that resurface granite surface plates use. Start with some 40 micron and go from there. Hope this helps. Thanks for the comment. Cheers, Tom

[@MakinSumthinFromNuthin]

Brilliant Tom!, thanks for sharing! Regards, MSFN

[@coleyoung500]

hey Tom I was wondering if you could do a video on what's In your tool boxes I and probably a few other people would find that interesting

[@forrestaddy9644]

VERY fine discussion of alternatives. I went overboar:d with my concerns with the fine Vs differential thread business. There are lots of alternatives: if 1/4 - 28 against 10 - 32 is too slow. 5/16 - 18 against 10 - 24 = 0.014"/rev or 5 degrees per 0.0001"; against 10 - 32 = 0.024"/rev or 8 degrees etc until awash with too many choices. Suggestion for drilling or punching spring steel sheet for flexure: chuck a wood dowel in the drill press on max spindle RPM, force it against the drilling site until friction heat draws the spring temper to machinability (wood smoke for 10 seconds?). Spritz with water to limit heat migration.

[@oxtoolco]

Dang it! Now I have to go try that out in the shop. I usually resort to carbide end mills for blue scaleless spring steel. The 510 phosphor bronze is a good alternative and can be drilled easily. Thanks for the comment. Cheers, Tom

[@forrestaddy9644]

oxtoolco The usual precations for drilling thin stuff. I love them Uni-Bits.

[@Watchyn_Yarwood]

You just made differential threads cool! A p.s. to Andy Coakes, I am out in the boonies of Arkansas on an investor owned telephone co-op with a self-build PC that's 8 years old and I can play the video at 1080p just fine! Think you may have problems on your end.

[@JeffCowan]

Incredible content.

[@samsmith9764]

Fascinating video, thanks for posting

[@chronokoks]

Tom looks like you should have worked for the semiconductor industry.. it doesn't get more precise than that (except the IBM machine that can mess with single atoms)!

[@deeremeyer1749]

Single atoms? Does IBM make a desktop "Hadron collider" now?

[@douro20]

Well, the guy is a Berkeley engineer.

[@ddistrbd1]

Was it difficult to drill and tap the 1/4-28 screw ? .

[@williamsquires3070]

Now, see if you can calculate the thread pitch needed so the angular displacement of the screw (bolt) head = ang. displacement of the indicator dial! :) More to the point; could you make such a thing using differential screws with commonly available thread pitches?

[@hardwareful]

30:00 ok you got me :-) I wonder however: the threads aren't smooth, how bad is the "rumble" noise still present in the differential screw arrangement?

[@ggordon4127]

yes I agree where can you fine a really fine screw these days?

[@PatFarrellKTM]

Why did you thread the holes in the flex-plate? Normally, don't you want simple thru holes in the fixed piece, and threads in the piece you connect to?

[@oxtoolco]

Hi Pat, They are not threaded. I just tapped one side with the flexure in place so I could remove the goofy clamp I had on the other side. I drilled clearance holes through the bronze plate before I tapped the holes underneath in the steel. Thanks for the comment. Cheers, Tom

[@maxheadflow]

Stick / slip.. Pretty much the difference between static and dynamic friction.. Really like the dual tread arrangement..

[@workshop_from_nothing]

why not drill the saw cut faces and press a dowel pin in and have the other side a semi slip fit just a tinny bit lose to create the range of motion but once the two parts get x degrees out of alignment it binds up