Author Topic: NPT Thread Milling  (Read 5766 times)

Offline Dave Otto

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Re: NPT Thread Milling
« Reply #15 on: April 02, 2016, 01:11:04 AM »
Maury,

I do find it interesting; but when I look at code I just as well be trying to read Russian.  :lolb:
I can understand G code and even write a little when I have too; but when you start adding code to the mix my little tiny brain checks out.

Question; if you were using a single point tool did you taper the stock before you threaded it? I understand that if you use a multi tooth thread mill designed for pipe threads that it will generate the proper taper in one pass but not so for a single point cutter?

Dave
« Last Edit: April 02, 2016, 01:15:03 AM by Dave Otto »

Offline kvom

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Re: NPT Thread Milling
« Reply #16 on: April 02, 2016, 02:51:17 AM »
Dave,

If you think about a tapered spiral in 3 dimensions, you'll realize that at every point it increases its radius.  G02/03 codes can't work in 3 dimensions, so in the this case the spiral is composed of short straight lines.  For each the Z changes such that each time around the total is one thread pitch.  At the same time the distance of each point from the center of rotation increases such that the slope of the spiral equals the required taper of the thread.  All my posted code does is compute the endpoints in 3 dimensions of each of the lines and outputs them as G01 X Y Z.

There is no need to taper the stock as long as the thread mill can cut the full depth of the thread at its deepest point.  Even if that isn't possible the thread can be cut in several passes of increasing depth.

The same program logic could be employed to cut straight threads just by eliminating the radius adjustment.

Offline maury

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Re: NPT Thread Milling
« Reply #17 on: April 02, 2016, 01:39:38 PM »
Tim, you outsmarted me. I'll give that a try if it ever happens again. it'll save me a few hours of boring tool zeroing.

Dave, I use 5/16 Dia brass tubing with 1/16 wall thickness from ENCO. All I do is face the ends, cutting it to length. THere is no need to taper the tube. I did find it may give a nicer thread if you file a 30deg chamfer on the end of the tube, but it's not necessary. The modification I made to KVOMS program to start the thread 1 turn above the stock takes care of that.  The only cleanup I do is to remove the burrs with a wire brush.

My tool has 10 flutes. It's just a standard 60 deg V tool. I started using it at 900 rpm, and moved it up to 1200. The swarf is just dust now. When the thread starts out the cutting depth is fairly deep, but the finish is nice, so I do it in 1 pass. If it becomes necessary I may modify the program to use 2 passes, but I want to get some history first.

I can understand that if you have not been a programmer in your past life the code can be quite intimidating. The learning curve on the environment is the most intimidating thing to me, as I have always been a hardware developer, not a (software) tool developer. I can tell you this is the simplest environment I've ever seen. If you need help I can work with you. If you want, I can email you some G code. Just email me your tool diameter.

maury

"The trouble with socialism is that you eventually run out of other people's money."... Margaret Thatcher

Offline kvom

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Re: NPT Thread Milling
« Reply #18 on: April 02, 2016, 04:30:55 PM »
With my single-point carbide thread mill I cut 5/16-18 straight threads in brass at 4000 rpm and 5 ipm.

Using my multi-tooth NPT cutter 1/16-27 is cut at 4000 rpm and 15 ipm.

You could take Maury's version and cut any size NPT thread by varying the parameters.  If we were to make the program accept parameters from the command line you'd only need the Java runtime environment on your machine and no program changes needed.

Offline kuhncw

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Re: NPT Thread Milling
« Reply #19 on: April 04, 2016, 05:51:39 PM »
Maury,

I would like to see your thread milling code, if you don't mind posting it.

Thanks.

Chuck

Offline maury

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Re: NPT Thread Milling
« Reply #20 on: April 06, 2016, 12:48:44 AM »
KVOM, another idea I had, is to make a Mach3 Wizard to do this. Don't know if its possible to use Java runtime within Mach, nor do I have any idea of how to do it. Just know it would be neat.

Chuck, I am attaching to code files. Hope they help. If you have any questions, just post.

maury
"The trouble with socialism is that you eventually run out of other people's money."... Margaret Thatcher

Offline kuhncw

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Re: NPT Thread Milling
« Reply #21 on: April 06, 2016, 02:34:44 AM »
Thank you, Maury.

Chuck

 

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