Differential threads...

[Chuck Pressure]

I thought I would share with you a neat little project that I made at work on the cnc lathe this week. I guess I would call it a “Differential thread micro-adjuster Gizmo!” My company needed to make a test/calibration stand with a high degree of linear adjustment.
Differential threads use two different thread pitches to obtain fine adjustment, this part has a 1”-28 ID and OD thread and a 1-1/2”-27 OD and ID thread, Both threads are right hand. Since 1/27th = .0370 and 1/28th =.0357 the difference between the two is .0013, which is the amount of distance this thing moves in 1 revolution! It’s pretty cool! The two threads offset one another except for the difference in pitch. On a clockwise rotation, it is pushing 1/28th while simultaneously pulling 1/27th. I attached a couple of pictures; assembled and disassembled…I’ll try to post more pics as the project progresses. Note that the 1” section can’t rotate because of the cap screws and slots.

[Ken_Shea]

Intriguing Chuck,
While I am grasping the concept I can't quite wrap my head around the mechanics.

And I don't see a single thread

Thanks for sharing

Ken

[Chuck Pressure]

Ken,
Sorry, the threads are pretty hard to see, they are really fine pitch and where a real pain to measure the pitch! Couldn't post a higher quality pic!

[jkeyser14]

I've read about differential threads before, but haven't been able to get my head around them. It would be something nice to see in person in order to help understand I guess.

[Geof]

Originally Posted by jkeyser14 I've read about differential threads before, but haven't been able to get my head around them. It would be something nice to see in person in order to help understand I guess.

At your local auto parts store, or Home Depot, you should be able to find studs that have a NF thread on one end and a NC thread on the other. If you screw a nut on each thread then hold both nuts and turn the stud you have a differential thread.

[Ken_Shea]

Geof,
That helped some, that was what I had in mind when I stated I was grasping the concept.

Chuck,
With regards to the piece with the slot/s, they hold it from turning as you mentioned but are the slot/s also the travel freedom ?


Ken

[Chuck Pressure]

Ken,
All the slots do is to keep the center piece from rotating but still free to move along the thread axis, I guess they would also act as travel stops as well, although total travel is probably only 1/8" or so......Next week I'm going to make an support bracket for a .00005 digital test indicator!

[Geof]

QUOTE "Next week I'm going to make an support bracket for a .00005 digital test indicator!"


Don't blow on it while taking a reading. Come to think of it; stop all traffic in surrounding States.