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Internal threading

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bogstandard:
You will find that although threads are not listed under standard threading charts, doesn't mean that they do not exist.

A lot of specialist manufacturers use special threads, designed using standard thread formulae, to make unique parts. This helps them to keep control of spare parts, and charge what they want for them.

Once you have the OD, root dimension, pitch and thread angle, you can duplicate almost any specialist thread in existance, as long as your machine can give you the exact pitch.
 
On some German W+D envelope machines I used to work with, I made different sizes of taps for SAE (Society of Automotive Engineers) specialist superfine threads. Once you have they key to the threads used, you could very easily make up the special taps required. Thousands of squid to buy a new part, plus maybe weeks downtime waiting for delivery, or a few hours making a tap to repair the damaged part. You get a lot of brownie points with the boss if you can do that sort of thing.


This is one of those SAE taps, single flute, silver steel (drill rod) from many years ago. Plus of course, once you have the tap, you can make matching dies as well. They won't cut a lot of threads, but they get the job done at the time.




Bogs

Darren:
I used to make them out of the offending bolt with nothing more than a file.

If the bolt was high tensile even better, worked every time...

Eric, can you not use some of the threaded bar to make the tap?

Brass_Machine:
It is possible I imagine to use a scrap piece of lead screw. I saw someone had done it for 'plastic' anti backlash nuts. The machine in question is in the UK while I am stuck in the US.

Eric

DavesWimshurst:
Eric,
You didn't say if you had access to the feed screw from a micromill for comparison.  Transposing gears of 17 and 18 teeth (or 34 and 36) when used with a quick change setting of 12 tpi will give an accuracy of better than 1 part in 2000.  This should be close enough for a short anti-backlash nut but I wouldn't try making one without the screw to test the fit.  12 tpi is coarser than 2 mm so the lead screw should be geared to run slower but otherwise my setup shown here may work for you:



Hope this helps.
Dave

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