[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]

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.