Single point threading

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Mr Ron
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Re: Single point threading

Post by Mr Ron »

I don't think anyone has addressed the way to set the compound at 29.5°. The degree marks on the compound are not precise enough to read 1/2 a degree. I made a template that I can place between the side of the compound and the face of a chuck. That ensures the same 29.5° every time. How do others do it?
Mr.Ron from South Mississippi
whateg0
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Location: Wichita, KS

Re: Single point threading

Post by whateg0 »

Mr Ron wrote: Tue May 08, 2018 10:17 am I don't think anyone has addressed the way to set the compound at 29.5°. The degree marks on the compound are not precise enough to read 1/2 a degree. I made a template that I can place between the side of the compound and the face of a chuck. That ensures the same 29.5° every time. How do others do it?
I usually just set it for 29. The markings should be good enough for that. If I want to be really exact, I can setup a sine bar on the compound and a DTI and get it that way. In fact, I should someday, compare the two and see just how close the markings are on my machine. The problem I have is actually that the line on the cross slide is buried below the compound and when setting it, is almost impossible to see. I was thinking about putting another mark off to the side, maybe 30 degrees away, that I can see.

Dave
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GlennW
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Re: Single point threading

Post by GlennW »

It doesn't need to be exactly 29.5 or exactly anything. It just needs to be slightly less than the half angle of the thread profile.

The threading tool geometry is what dictates the thread profile.

The object of the game is to have the leading edge of the threading tool do nearly all of the cutting while the trailing edge just cleans up the thread flank.

I use somewhere around 28-29 degrees unless I am cutting BSF threads, then it's 27 degrees as they are 55 degree threads.
Glenn

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Harold_V
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Re: Single point threading

Post by Harold_V »

GlennW wrote: Tue May 08, 2018 12:52 pm It doesn't need to be exactly 29.5 or exactly anything. It just needs to be slightly less than the half angle of the thread profile.

The threading tool geometry is what dictates the thread profile.
What Glenn said. The only exception is if the setting exceeds the half angle, at which time the tool no longer dictates the profile of the trailing flank---which will be generated with the proper angle, but with minor steps. That's the very reason why I choose a simple 29° setting, which assures the trailing flank is in contact with the tool with every pass.

One should understand the reason for the setting, regardless of thread profile, to be less than half angle. Armed with that knowledge, you'll choose the proper setting for any thread form.

H
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