Sourcing or making small miniature threads

C

Cadillac

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I recently acquired a old brown and sharp vernier height gauge. The height adjustment screw mechanism has a hourglass shape in the threads from use. When the threaded adjustment nut gets to that point it will skip threads if any pressure is applied. Also the thumb screws have bends in them which look terrible.
191F3317-C854-4195-B3E1-B8F22AFE5B2F.jpeg
While trying to remove the threaded rod adjustment from the height gauge arm the thread spun off and broke.
Now I think I can bore out the piece in the arm and rethread without to much hassle. But my thread gauges don’t go that small/fine of a thread. The smallest screws I have are 4-40. I would like to make all new hardware for the gauge.
So my questions are can you buy threaded rod and screws in these miniature sizes? Where?
Do you need miniature tooling to cut these threads?
Does a typical modern lathe have the capacity to cut these threads?
Are procedures the same as normal size threads?
Any info or tips on cutting miniature threads would be appreciated.
 
I can, and do 40 tpi on my 1340GT for compensators, but when I need to make small diameter screws for firearms or something similar I use dies to cut the threads. For what you want to do I would get some of that threaded rod that Cooter suggested.
 
If you wish to produce threads that conform very accurately to the Unified Screw Thread standards as published great care must be taken.
The root and crest radii, PD and flats are a product of the lead.

In this illustration H is the theoretical sharp V which you can not produce.

P/8 Is the width of the flat at the crest of the external thread, the lead ÷ 8, for instance a 40 TPI thread has a lead of .025", .025" ÷ 8 is .003125"

P/4 is the width of the flat at the crest of the internal thread, .025" ÷ 4 = .00625"

3H/8 is the distance from the major diameter to the Pitch Diameter, in the case of a 40 TPI thread this is .025" X 3 ÷ 8 =.00937"

The major diameter of a #4 screw is .013" X 4 + .060" = .112", this yields a PD of .093" (I have rounded the fourth decimal place)

This is the Thread Form regardless of diameter or lead for 60 Deg. Unified Screw Threads.

 
Thanks for the responses guys. I should of checked McMaster thanks cooter. So would anyone know what pitch the thread is on height gauges like this. The thumbscrew and rod are the same pitch and my gauges don't seem to go with them. The OD on the threads is .0984.
 
Your adjustment screws may well have a non-standard thread. I ran into this issue when trying to find a replacement screw for an adjustable parallel. Your first step should be to somehow get an accurate measurement of the thread pitch. Can you securely mount a dial indicator so the stem makes contact with a flat area of the screw head? If so, try doing the setup and measuring how far the screw advances per turn (or per several turns).
 
For what its worth micrometers use 40 tpi threads. This means one rotation causes a linear movement of .025". I would hazard a guess that your height gauge would use 40 tpi.
 
The size is right for a 3-48 UNC or 3-56 UNF thread (0.099" nominal). If I had to guess I'd go with the UNF thread.

Sent from my Pixel XL using Tapatalk
 
Doing alittle investigating I think I've found the size. Going off OD measurement and wag I think it's a 3-56 unf.
 
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