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Cutting depth on a standard acme thread 3/8's 10

expressline99

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#1
Acme General Purpose Threads
Am I understanding correctly that I need to feed in on my cut .060 to get proper thread depth on 3/8's 10 acme? External threads. Major Diameter max is .3750 . Minor Dia. Max is 0.2550 Basic height of thread is .0500 since it's a 10(or coarser) pitch from the way I read it clearance should be up to .010?

Thanks,
Paul
 

4gsr

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#2
Paul,

My calculations say the nominal thread depth is .060" The root width is .0332" Maximum. Not saying the thread depth could be .050", it could. Also remember that most threading tools for 10 pitch Acme has a point width of .032". This is based off of the internal thread internal root width. On external threads, the root width will vary according to the OD of the thread. Oh, then you have to throw in the class of thread fit you are cutting. 2G, 2C, 3G,3C, they all affect the root width, depth of thread, and of course the pitch diameter of the thread. Believe me, Acme and Stub Acme threads along with all of the modified versions of the Stub Acme threads will drive you to drinking quickly trying to figure them all out!

For most of us trying to cut and make replacement lead screws and nut for our machines, stick to 3G and 3C class of fits. Anything marked 2G or 2C will have too much slop to use as a machine nut or screw.

To answer your question, yes, you will have to go to at least .060" deep. At .060" deep, side step the cutting tool to get the proper root width along with the correct measurement over wires to qualify the pitch diameter of the thread.

See my down load for calculating thread parts.

http://www.hobby-machinist.com/resources/thread-program.2496/

Ken
 
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expressline99

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#3
Hi Ken, Oh I got your program as soon as you told me about it. I'm just figuring it out. Are the Gagemaker numbers referring to one of their machines setup numbers?

Oh and on all those versions of Acme. I'm sticking strictly with General Purpose at the appropriate tolerance standard. Is 4g or 5g even used on machining equipment?
 

4gsr

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#4
Yeah, the Gagemaker dimensions are for setting their instruments for making gages only. I really need to take that out since very few here even know what Gagemaker is all about or even can afford their equipment. I know I can't even pay for one piece if it to start with! Companies that can afford their equipment can tie us $20K in one purchase! For just one set of internal and external gages. Definitely not for the home shop environment!
 

4gsr

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#6
Thread depth for general purpose acme is .5 P

In practice it may need to be more depending on the tool used.
That's your basic thread depth to start with. BUT, you have to add .010" to the resultant for the correct depth, to get the proper clearance in the thread. The exception to this is if your cutting a Centralizing thread like a 3C fit.

Ken
 

expressline99

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#7
The .5p + .010 is what I thought I understood with the numbers. Just having little experience makes me second guess and reconfirm.

Paul
 

Ulma Doctor

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#9
i have not cut acme threads single point. this thread is very interesting.
thanks for asking the questions Paul.
looks like i have some(read: tons of) learning to do :)
 

Wreck™Wreck

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#11
That's your basic thread depth to start with. BUT, you have to add .010" to the resultant for the correct depth, to get the proper clearance in the thread. The exception to this is if your cutting a Centralizing thread like a 3C fit.

Ken
I have no idea what you are on about, please explain.
 

expressline99

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#12
OK so I made a plug gauge to get some practice. Certainly worked out better than the first test on some garbage stock I had. Before you begin to get on me for the knurling I know it's a fail. I lost track of where I was and it's what it is. I did 3 wire measuring(size .0550 for 3/8's 10 tpi) at .401 Should have been about .406. I will probably make another one closer. It's 1.5" of thread the relief cut at the beginning was cut in .070 (.140) deep. I did run into trouble and broke the first one as I was not supporting the end with a center. I knew better as the overhang was too far. It did flex on me quite a bit. So I did a lot of spring cuts after each pass. I was cutting .005 per pass after the first pass at .010...at the end it was .003 cuts. Lots and Lots of cutting fluid to keep things smooth. After all was done I did knock down the burs with a file lightly while turning on the lathe. This is a right hand thread. I need a left and will also make that next. After which I'll make a set for 7/16's 10's right after I finish the next one.

Then new screw for both the cross feed and compound feed.


Paul