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raymus.houston
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Unexpected toolpath result from Threadmill Operation - Pitch Diameter Offset

I have programmed for several parts where I have used the threadmilling operation with some single tooth threadmills and it performed as expected in simulation and on the machine. When it comes to the pitch diameter parameter, I am working with models drawn to the minor diameter so it has always worked for me to subtract the tapdrill/minor diameter from the major diameter of the thread I want to mill with only minimal radius comp adjustments at the machine needed when it is actually run for the first time.

 

Now I have a part that I am using single tooth threadmills for a few threads and they are simulating fine as described above, but I also have a 20 tooth 20TPI threadmill that appears to be giving me bad simulation results. I am trying to mill a 1-20 UNEF-2B thread. The model feature is drawn to a Ø0.9515 inch minor, so I used a pitch diameter offset value of 0.0485 inches to get to the Ø1 inch major. When simulated, the thread appeared to be cutting too deep (see attached image below) since the modeled chamfer at the top is Ø1.0115 inches at its max. When I set the pitch diameter offset to 0 it looks closer to the correct size, but I don't understand why it is working differently with this particular threadmill. Is this a bug?

 

When it comes to sharing this file, it is a customer supplied model, so I am not comfortable publicly sharing it on this post.

 

This is an image of what the simulation looks like with 0.0485 inch pitch diameter offset. Notice how it is cutting beyond the top chamfer max diameter which is Ø1.0115 inches.

Zero pitch diameter offset.PNG

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