Help identifying and duplicating this thread.

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Torch
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Re: Help identifying and duplicating this thread.

Post by Torch »

Ok, maybe I'm really missing something here. With a V-thread, there is a tiny bit of flat at the root, but for the most part one v-thread tool can cut a range of thread pitches by cheating on the depth in favour of hitting the pitch diameter. It was my understanding that trapezoidal threads are not so forgiving, and the single point tool form had to be pretty much bang on.

Are you saying I can just get a 30° tool, and go a little deeper so long as I hit the correct pitch diameter?
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Bill Shields
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Re: Help identifying and duplicating this thread.

Post by Bill Shields »

I have always done acme threads groove up the middle first then front flank then back flank with a tool that is less then a thread form wide.

But then I have been known to do things the hard way..
Too many things going on to bother listing them.
Torch
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Re: Help identifying and duplicating this thread.

Post by Torch »

Bill Shields wrote: Thu Mar 24, 2022 9:38 pm I have always done acme threads groove up the middle first then front flank then back flank with a tool that is less then a thread form wide.
Ok, my first thought was "that would simplify the grinding process". My second was "Wait, what?"

How does that work? Do you have the compound set parallel to the ways instead of at 14.5°, using the carriage to control depth and the compound to shift left and right? If you are creeping up on the final dimension, how do you know if you need more depth or more width?

I'm so confused now...
Torch
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Re: Help identifying and duplicating this thread.

Post by Torch »

Two separate go/no-go gauges, one with narrow threads and varying diameters, the other with varying thread widths?
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Harold_V
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Re: Help identifying and duplicating this thread.

Post by Harold_V »

Cutting the three features independently isn't a bad idea, assuming one can measure the major diameter, which can be used as a guide.
One thing to be careful of. When one single points threads, the tool should be advanced towards the side of the cut that is loaded by the screw. In a right hand thread, the trailing cut isn't so loaded. Drag on the carriage will ensure that you don't get a drunken thread. If the carriage has a lock, it can be set with enough friction to prevent floating--or the hand wheel can be gently restrained while the cut is taken. Don't trust to luck.

H
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Torch
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Re: Help identifying and duplicating this thread.

Post by Torch »

Makes sense. But then, most of the advice you give does.
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Bill Shields
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Re: Help identifying and duplicating this thread.

Post by Bill Shields »

Groove up the center.
Compound set parallel to screw axis.

Feed in X cutting on front flank

When at depth on front flank, retract to starting od and move cross slide BACK to new starting position and repeat.
Too many things going on to bother listing them.
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Bill_Cook
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Re: Help identifying and duplicating this thread.

Post by Bill_Cook »

As for the thread profile, A cutter without sharp corners will go farther between sharpenings. A grinding wheel even more so, assuming the threads were ground.

It's a dirty trick to leave you with maybe about 1/2 the effective thrust surface of an acme thread. The angle of the flanks make it even worse. I can see why the nut wore so badly.
BC

If there was only one way to do each machining job, the smell of sulphurized cutting oil smoke would have fewer fond memories.
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