I was thinking how surprising it was, that your video about differential threads seemed to have skipped the opportunity to point out one of the main places that many of my fellow RU-vid shop students might discover that they possess and regularly use a great example of differential threads... And then, just as I was about to start typing a comment to that effect, I saw the tap handle you put on screen, right at the end! I actually own an identical one, no less. Anyway, the subject matter of today's class reminds me of when I first figured out the trick to disassembling that style of tap handle. In any case, now I'm hoping to come up with an idea for something I can make or modify to have extra-fine adjustability. Thanks, Mr. Pete!
Interesting use of these in bone surgery. Bones heal better if there is slight compression across the fracture (or deliberate cut). So screws with differential thread pitch are often used, especially in smaller bones such as in feet where not much room for fixation.
I am currently fabricating a telescope mount that requires precision leveling screws. This looks like a perfect application! Thanks. Great presentation, just like all of of yours!
This was great! I’ve been thinking about differential threads in the back of my mind for some time now, as a way to make very fine measurements, to precisely position something, and as an alternative to geared stepper motors for small ranges of motion. This brought it all together for me, very, very well-done as always! (What a beautiful little tool that mini-boring head is, by the way! 👍)
Made no sense to this 71 year old mind until the demo. Wow! That makes it easy to comprehend! The closer the pitches, the finer their difference until they match and there would be no movent. You are still an excellent teacher!!
Interesting tidbit: Differential screws depend on the difference in lead so a 1/2-20 screw has a lead of 0.05" but a 1/2-20 LH has a lead of -0.05". When you put these on the same shaft just as you did, the leads still subtract: 0.05 -(-0.05) = 0.10. In other words, they double. This is used in a lot of scissor jack applications such as bumper jacks and some machinist jacks. I think your use of different leads is far cleverer than just using the more obvious LH / RH combination.
Hi, Lyle I had a former Master Machinist for a machine shop teacher in college. No PhD, just a lifetime of mechanical and machining experiences. We had to cult multi start threads, internal and external, as well as differential screws to his specification, as far as movement per revolution. It was quite a challenge, especially using the old and very clapped-out South Bend lathes that were in the shop. (I cheated the process by using my Le Blond lathe at home) I got way better results than others in my class. About 10 years ago, the college shop was closed down, and I managed to purchase the very large, 16-inch lathe Boyd and Emmes. It was still in perfect shape, and still had the war production tag on it, June of 1941. It is one hell of a large machine, and very heavy. It hadn't aged at all from when I ran it 40+ years before. I am hoping to see you again at the Bar Z Bash in June, I think it might be my last visit there, as my health is failing, I just don't have the endurance I once did, and I am struggling to keep up with the usual farm chores. I really appreciate seeing your continuing progress presenting all the good old days of my High School machine shop teaching. I am kind of sad, that all that great knowledge will never come again in our public schools. Kids these days just don't seem to want to work with their hands, and most all the Industrial Arts shops are now closed. Tim
I do not know if I will make it to California, I have very little endurance and tire out very easily. Young people do not want to work with their hands or get dirty. I watched a Videos the other day, where they were talking about tool and die makers in the auto industry. Almost all those work as overseas as they cannot find anyone interested to learn the trade .
Right. If you run a single bolt through two nuts, their relative distance won't change as you turn the bolt. And you wouldn't need two different diameters either, because you wouldn't need to feed one thread through a differently threaded hole for assembly. You could just screw the both through the first nut and then start the second nut on it.
Thanks, Mr. Pete, this is something I never paid mind to before! I have seen the reverse used where the threads speed up the movement of the pitch, sometimes used in vises.
@@homemadebuilder113 it's not the same as a turn buckle. This would be one bolt or shaft moving the piece twice the normal distance per revolution. God bless you!
Almost 40 years ago we made something like this in Mr Nordofts class at Beloit WI Memorial HS. He was a fine instructor just like you Mr Pete. (He let us sneak out the back door when the bell rang 7th hour)
They say old dogs can't learn new tricks. But the old dog shop teacher has tought this old dog some information that will be added to the book of tricks. I will have to study up on the math though. Awsome Mr. Pete. In the language of young people you are the GOAT. GREATEST OF ALL TIME. THANKS FOR YOUR EFFORTS.
This video showcases the kind of excellent explanation that Mr. Pete is renowned for- THANK YOU! As a Land Surveyor (hobby machinist).....no doubt my Total Stations utilize differential threads in the horizontal/vertical adjustment screws.
This video proves that in the 17th and 18th century, brilliant engineers and craftsmen had skills that are Really amazing, ALL without the Internet!! All they needed was to wait a little while for the Dummies to Catch up!!!!
Lyle; You mentioned multi-start threads and the difference between pitch and lead. I make custom pens and the cap and nib end of the pens are often either 2-start, 3-start, or 4-start threads. The purpose of these is to multiply the distance that each turn of the cap takes in closing the pen. This allows the pen to close rapidly, but keeps the chance of the threads loosening to a minimum. Keep up the good work, I learn something on each one of your videos!
Here’s an interesting example, Randy - some Cessna aircraft use beautiful, ground four-start threads on their elevator trim jackscrews. As with the pen caps, the object is to convert small rotary motions into large linear translations; it’s also required to have high strength in tension/compression. The four-start threads do that very nicely.
We use those daily on extrusion dies, it sets our gap in the die to maintain consistent adhesive coating. The gap is set using differential bolts of various sizes depending on the die being used. An example of one of our bolts, has threads of 3/8-26 & 7/16-20 which comes out to .012" per revolution. Have had to make a few of those in a pinch to get us thru the run. We mostly order them from a supplier due to the cost of labor in house vs. the amount of bolts we go thru.
Excellent video on a little known topic. Woodworking hand-screws (two jawed wooden clamps) are usually made with two long steel screws that are right hand thread over half of their length and left hand thread over the rest with corresponding swivel nuts lodged in the jaws so that as the screws are turned the jaws move together or apart quickly.
I built a STEM (scanning tunneling electron microscope) and needed very fine threads for adjustment. I used violin bridge tuners because they were very fine, but now that I've seen this I can easily go back and differentially thread some rod with (already small) watchmaking dies and get even finer results. I actually enjoyed the math part. Thank you Mr. Pete!
Very interesting video - thanks for posting! This brings to mind the head-to-block studs on my Willys L-134 flathead engine - that have two different thread pitches for another reason. The block side threads are 7/16-14 for maximum root strength, while the head side threads are 7/16-20 for precision while torquing. A common mistake is to replace them with 7/16-14 hex cap screws - which will not stay torqued for very long under use.
Absolute gold! Without a lathe and now long in tooth I'll probably never practically apply what I've learned here to anything that I build, but suffice that I'm smarter this eve' than I was over morning coffee.
I had come across differential threads only once in 40 years of machining and fitting on a very old machine tool . It seemed like magic back then and still amazes me today .
Thank you very much for teaching this! It is just the knowledge I needed to solve an issue with a problematic microscope stage. You always present such interesting topics. I especially appreciate the math examples which make quick use of the information very easy!
Thank you sir for the lesson. As always your show and tell does a great job explaining the idea! I do like introduction of the math along with your functional parts. Teaching shop as you do machining and manufacturing examples is great, these simple parts clearly getting the point across. My only experience with this in my past, that was machining parts for a instrument maker who a shop made parts for. Cheers to you. I spent 40 years, a better part of my career working in many small independent job shops 2-5 years then move on. I only recall seeing parts like that at one shop.
I was looking at building a bracket to align two telescopes, so they can be used as high powered binoculars. Optics need serious precision as being 2 thousandths out is perceived by the eye. I came across differential threads when doing research and your 2nd example might be perfect for my purpose but scaled down a little. It needs to be something that can hold itself in place for long periods as well.
Mr. Pete, you are the best! I've been a machinist and machine designer and somehow this mechanical concept escaped my attention. Needless to say, I will file this away in case I ever need to build myself something that requires extremely fine adjustment.
One of those 'AhHA!' things. Once you see it, it seems so trivial, but you realize someone was pretty clever when they dreamed this up. Thanks for sharing.
Thank you Mr Pete. That was some mighty good teaching! Makes me wish I could have been in your class. You already mentioned the example's that I am familiar with.
Hi Mr. Pete, Great video. I always appreciated differential threads in precision instruments. You mentioned the difficulty in making fine pitch threads. Think of the micro screws in watch movements. Some are .25mm pitch or just under .010 inches, or 100 TPI. Cant imagine making those! I have a watch apart now waiting for parts. With my 68 year old eyes I use a microscope and can hardly see the tiny screws unaided!
Design engineer here... I used a differential thread in an assembly fixture to precisely align parts under a microscope. I actually went much smaller, drilling and tapping a #10-32 thumbscrew with a #4-40 through hole. Six thousandths and change per revolution (with off-the-shelf tools!) The 4-40 stud was fixed, the 10-32 thumbscrew was the operator input, and the nut threaded on the thumbscrew was the actuator.
I didn't quite understand the point or how it worked exactly until you demonstrated it. It's one of those things that makes perfect sense when someone tells you about it but hard to imagine how anyone came up with the idea.
I love this instructional videos that you make. Hope you make more. I have differential threads on my Veritas handplanes fine adjustments for advancing and retracting the iron
@@mrpete222 looking closer i noticed that on my little block plane the two threads are not differential but, i would say, incremental. In fact the big thread is right handed and the other is the opposite. So they add to each other, i think for space issues
Always interesting stuff Mr. Pete. If one was 18 (1/18=0.0556") and the other 20 (1/20=0.050") the difference would be 0.0556" - 0.050" = 0.0056" or the equivalent of 180 TPI. wow.
Always enjoy your videos. General Electric CF6-80A accessory gearbox thrust link uses differential threads for adjusting length, except one is RH and the other is LH.
Thanks Mr. Pete. It reminds me how a Chinese windlass works, where the rope is unspooled from one drum, put through a snatch block, and is wound back on to another drum that is co-axle with the first.
Planning on fabricating a microtome for cutting extremely fine sections of objects to view under a microscope - this could be just the solution I have been seeking! Thank you!
NOW i Know ! never heard of them. But how good is that, and your Example was a great teaching device. Learn something new every day. Cheers Dave from Australia
This is the best basic demonstration of the concept I have seen. 2 threads the same pitch (such as 1/4-20 and 1/2-20) would provide no movement per rotation. I had to think about that but it made the concept more clear to me.
If 2 threads of the same pitch produced a movement, then threads wouldn't work at all, because a single thread is indistinguishable from 2 threads of the same pitch + diameter. Simply running a nut onto a bolt would split the nut in half!
@@cogentdynamics Yeah, exactly. It must be the case that 2 threads of the same pitch have no differential movement, otherwise you wouldn't be able to thread a nut on to a thread, because the front of the nut would be jacked away from the rear of the nut!
You have shown me something that blew my mind. I believe that this thing could be used very well in the machining industry and the reloading and firearms industry. I’ve been in the light line and heavy line repair industry for 30+ years and never saw one in use but I’ve seen some laying around the shop that were used and damaged and never knew what they were called or for. Thank you Mr Pete!
genius.... I will be pondering the property behind this for some time. This kind of thing is like magic to me. Not in the sense of a lack of understanding but because of the high degree of cleverness :)
I have a variety of micrometer drives used to adjust lens translators in my optics lab. They are all "differential thread" type. I knew that meant they provide very tiny movements, but I didn't know how it works, And the arithmetic you showed made no sense either until I realized, in the example you made, the large thread is pushing the part away, while the small thread is pulling it back, hence the need to subtract the leads. Very clever, and thanks for the lesson.
Lyle, your pink paint reminds me. Back in the 70's, my dad made bolo ties, and the ends of the cord had sexogonal ends which he painted red, white and blue. He couldn't find small enough containers of paint for that, so he used nail polish. It worked out well. The paint held up nicely.
