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Bobcad v6 thread milling

deepsix11

Plastic
Joined
Jun 3, 2019
Hello every one . This is my first post here on practical machinist . I'm a cnc programmer at the age of 26 so some experience but not a whole lot . one of the things that I have never really done is thread milling . I have the capability of doing it with my bobcad package . its easy if the the thread is one that's in the CAM library how ever there is a thread I have to do 1"-20 UNEF , its not in the library and I'm wondering what resource I can reference for the fields circled in red . or what page of the machinists hand book do reference to figure it out with math's . I appreciate any and all responses.


thread question.JPG
 
The thread height you can get from the Machinists Handbook or I'm sure Google will find it for you.
I'm attaching a picture of the relevant page for you. Thread height is simply the difference between the major and minor diameter (see attachment)
The question is, does Bobcad want that value per side or does it want the total difference?

The thread pitch is easy. How far does a screw go for each revolution? That's it's pitch.
So for a 10-32 thread, we know it travels 32 times in an inch (it's right there in the name!), so divide an inch up 32 times and theres your answer 1 / 32 = .03125.
A 1/4"-20 thread has 20 turns per inch, so divide an inch up 20 times...

What confuses me is your "Threads Per Revolution" box. Is that a trick question? There's always one thread per revolution :) Maybe that's for multi-start threads or something? I dunno..

Capture.jpg
 
If BobCAD was smart it would calculate the thread height for you based on the thread standard selected by the programmer.

If you are stuck, look up any 20 TPI thread in its library. The value will be very close but not exactly what you need. I'm not sure why it even requires it, possibly for the clearance diameter for internal threads because I do not see any options for multi-pass or other strategies.
 
If BobCAD was smart it would calculate the thread height for you based on the thread standard selected by the programmer.

If you are stuck, look up any 20 TPI thread in its library. The value will be very close but not exactly what you need. I'm not sure why it even requires it, possibly for the clearance diameter for internal threads because I do not see any options for multi-pass or other strategies.

that suggestion worked thank you
 








 
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