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How to define a custom thread path

Question asked by Paul Millhouse on May 29, 2018
Latest reply on Jun 6, 2018 by Dan Pihlaja

Hi all, I've been wrestling with the Swept Cut feature for a few days now and still am not getting quite what I want.


In my past experience making custom threads (using Pro/E), the machinist likes to see two things in the drawing: the thread profile and the thread path. This is because he/she will make a cutting tool according to the profile and use this to follow the thread path on the lathe with whatever settings are required to get the desired pitch.

In SWX the closest thing to a thread path I've been able to find is a Helix/Spiral defined by Height and Pitch (even though the pitch will be constant), wherein I alter the diameter at a given height. This is not only unnecessarily complicated but it doesn't give you much control over the ultimate thread path.

This option is similar to a custom thread path and a step closer to what I'm used to, but there are some inherent flaws:

1. You can't define the geometry at the intersection where the diameter of the helix changes, as depicted below:

2. With Cut-Sweep the cuts can't overlap each other. This seems logical until you think about how the threads will ultimately be formed on a lathe. The cutting tool will actually be wider than the pitch as shown below. Lets say you want your threads to end in a conical fashion. When your cutting tool is coming down (or up) the "ramp" the material behind (or in front of) the form tool will be higher than the thread depth. You really need to allow some "overlap" (i.e. the cutting profile to be wider than the pitch) to overcome this. I'll try to draw something up to illustrate (assume pitch is 1.1 and I haven't drawn the spacing to scale I'm just showing two different threads):

Your cutting profile needs to be wider than the pitch in order to get the desired thread width.



Hence there seems to be no way that I've found, with a conical-tipped screw and variable thread diameter, to model the part the way you actually want it to be machined.


Now below is a screen grab of my ultimate part. This is pretty close to what I want except the teeth should actually be a bit thinner and the bottom flats a bit wider. However I can't model this without running into the problems mentioned above. How in the world do I model this part using the ultimate desired geometry?

Only thing I can think of is to do two cut-sweeps using the same helix but, c'mon SWX there's gotta be a better way.