Another way to determine thread lead.

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tornitore45
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Another way to determine thread lead.

Post by tornitore45 »

I have a tiny chuck, probably off some kind of Dremel tool.
Too small a hole to get a good feeling with the thread gauge.
I threaded it onto a soft wood dowel but the thread imprint was still too fuzzy, shallow and too chancy to get a good read.
So I chucked to dowel in the late with the nut threaded on. Set my dial travel indicator and unscrewed four turns
Indicator moved 0.101" making it a 40 TPI

This is weird The thread is a 17/64 or 6.75mm 40TPI
Anyway the mandrel I made fit perfect. I need it to extend the reach with a small drill
Mauro Gaetano
in Austin TX
pete
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Re: Another way to determine thread lead.

Post by pete »

In case someone doesn't know? 40 TPI is generally known as a constant pitch series Model Engineer thread and still fairly common in the UK at least with those Model Engineer's that haven't gone metric. But it has a 55 degree thread flank angle. There's also two more that I know of, 32 & 26 constant pitch tpi. I seem to remember that 26 tpi was a standard at one time used on Bicycles and I think early motorcycles in the UK. The 17/64" diameter X 40 tpi however isn't. The closest 40 tpi M.E. thread would be 9/32". Probably almost everybody here already knows there's lots of manufacturer's that purposely use proprietary threads and sizes because were then forced into using factory replacement parts. In a high volume parts production situation I very much doubt any non standard thread count, diameter or flank angle adds much to the costs for the custom tooling since the bigger tooling manufacturer's will make whatever you can dream up. But that was a clever method of figuring out what thread pitch it had to be when a pitch gauge won't quite fit and one I need to remember.
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Bill Shields
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Re: Another way to determine thread lead.

Post by Bill Shields »

.275 x 40
Too many things going on to bother listing them.
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