lapping a thread

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refinery mike
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lapping a thread

Post by refinery mike » Wed Jan 27, 2016 6:52 pm

I needed a special hardened bolt. So i machined it and hardened and tempered it and then polished it up. Now here is the question. To polish the threads i split a nut and put the thread in that nut and then ran it back and forth with 600 lapping paste in it. Then i clamped the split nut in a vise and tightened it to clamp the nut tighter, and ran the thread back and forth a few more times. Is this an acceptable practice to lap threads. or how would you clean up threads after heat treating. I do not have tools to grind the threads.

mikeehlert
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Re: lapping a thread

Post by mikeehlert » Wed Jan 27, 2016 7:02 pm

I would likely do the same. Might be a good idea to use a couple nuts as the first ones wear will affect thread form. Not sure it it would pass a profilometer check in an Aerospace QA department but it sounds like it would work.

GK1918
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Re: lapping a thread

Post by GK1918 » Thu Jan 28, 2016 6:47 am

Absolutely, we usually do this with the lathe in back gears and run a class nut back and forth, just slit a nut on
one side and squeeze the nut as needed....

Carm
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Re: lapping a thread

Post by Carm » Thu Jan 28, 2016 7:42 am

refinery mike wrote:(snip) Is this an acceptable practice to lap threads. or how would you clean up threads after heat treating. I do not have tools to grind the threads.
If the method produced what you needed within time frame and cost, sure.
Start requiring specs/tolerance, mating part made by someone else (and not in your hand) and other methods may need examination.

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refinery mike
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Re: lapping a thread

Post by refinery mike » Thu Jan 28, 2016 10:33 am

Thanks for your replies. I could find nothing on the net about thread lapping except for lead screws in fancy machines. It worked fine for this project. But like mentioned i had the second hardened part that i could keep trying until it ran smoothly. Thanks again!

Carm
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Re: lapping a thread

Post by Carm » Thu Jan 28, 2016 11:22 am

refinery mike wrote: But like mentioned i had the second hardened part that i could keep trying until it ran smoothly.
Mike, better to get a Gr.2 nut or better yet, brass.

hanermo
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Re: lapping a thread

Post by hanermo » Mon Feb 01, 2016 8:54 am

You used abrasives to average the two parts .. and that is not lapping, technically.
For non-precision use, not meant for sale, sure, a fine solution.

All sorts of similar options, while maintaining better threadform, could be used.

You could bias the lap alongside the axis, rather than squeezing it.
The lap could be slit longitudinally, and the two parts leveraged in or out.
Etc..

As it works for what you wanted to get done, its a great solution, easy to do, and works fine.

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