Thread pitches and change gears

[DLF]

I have a thread pitch table for the G0602/G0755 that @WobblyHand mentioned which gives the possible thread pitches which are available using the stock gears. The example of 19tpi given can be achieved using stock gears to within .08%. The gears required would be the 100 , 127,48, and 46 t. with a gear box setting of IIIA.

I offer this only as an example of what can be done with creative use of existing tools. It more than likely would never be needed.

As to what degree the actual pitch has to match, that is a good question and the answer was given by @Asm109 above. Metric and inch threads can be interchanged for some threads. The 10-32 inch thread fasteners will thread into an M5-.8mm nut. OTOH, an M5-.8mm fastener may or may not fit a 10-32 nut, depending on thread class. I suspect the difference is more about the difference in diameters rather than the pitch difference of .79% though. For this example, the threads will be a mismatch of 1/5th of a thread after 25 threads or .78". For a 1/4" nut, the mismatch would 4.9% of a thread.

My expectation is that if I could get the threads to match within 1%, It would probably make a workable fastener.

I looked it up in the Machinery's Handbook. The thread classes chapter talk about pitch diameter, not pitch deviation. A bit counterintuitive.

Anyways, my take on this is that one would be able to get away with some pitch error if the thread diameter is cut smaller, or larger if ID, to allow for a looser fit between the mating parts.

And for my lathe only a handfull of odd threads can not be cut perfectly, so it's not the end of the world.

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[RJSakowski]

I looked it up in the Machinery's Handbook. The thread classes chapter talk about pitch diameter, not pitch deviation. A bit counterintuitive.

Anyways, my take on this is that one would be able to get away with some pitch error if the thread diameter is cut smaller, or larger if ID, to allow for a looser fit between the mating parts.

And for my lathe only a handfull of odd threads can not be cut perfectly, so it's not the end of the world.

Sent from my SM-G973U1 using Tapatalk

Exactly. Thread classes are about differences in pitch diameter not pitch. A .001" clearance fit on the diameter would allow for a .00029" mismatch due to differences in thread pitch. How many threads this represents will be determined by the thread pitch. Using the 32 tpi example, the pitch is .03125" and a 1% difference in pitch would be .0003125" so it would be approximately one thread for each thousandth clearance. (If I did the math right!)