Don’t know if this would help, but I made a thread-generator in Grasshopper. You can find it here:
Some pros and cons:
(1) It needs some minor updates, which I’m hoping to do soon.
(2) As input, it needs a thread axis (specified by two end-points) and a thread-profile.
So, once you have the thread profile (tapered or straight), it will generate solid objects that represent the thread. But that does mean you need to create the thread-profile yourself (as a curve).
(3) Right now, the “Tolerance” input says “mm” but is actually in whatever units your document is using. I need to fix this.
(4) There are standard tolerances for thread-fits, and you would need to account for those in the positioning of the thread-profile relative to the thread-axis, as well as the numerical input for the tolerance.
(5) On extreme cases, this GH script will fail.
If you find any bugs or have suggestions, let me know. I mostly created this GH script as a way to learn Grasshopper, and for creating custom threads. But in theory, there is no reason it couldn’t be used for creating standard threads.
Sincerely,
–Anthony K. Yan
P.S. Based on how a tapered thread is cut on a lathe, I think it is impossible to make a geometrically-perfect tapered-thread using Sweep1 and/or Sweep2. So instead, the thread-generator uses Loft.
The reason Sweep1 and Sweep2 fail is not obvious. This is geometrically subtle (unless you are a mathematician and/or engineer). Here’s the short “explanation” that isn’t an explanation, unless you understand the problem already. On a lathe, the thread profile is always in the plane of the lathe axis. That’s because the thread-cutter is always in the plane of the lathe axis. The lathe-axis is unique and global.
However, Sweep1 and Sweep2 orient the thread (sweep shape) based on local geometry of the rail(s). Even if you use Sweep1 with “Roadlike” orientation, you will get sweep-shapes that are not in the plane of the lathe axis. “Roadlike” means the thread-profiles are in planes that are parallel to the lathe axis, but do not always contain the lathe axis.
Sorry if this explanation is obscure as all heck. If there is interest, just ask, and I will make some example files and images to show the problems with using Sweep1 and Sweep2.
P.P.S.
Thread relief is usually cut before the threads are cut. Generally, the thread relief is a cone (either Boolean subtraction or intersection with a cone). I think most of the threads I see use a thread-relief of 45 degrees. But personally, I like to use a 60 degree cone (120 deg included angle) which is the same angle as in the thread-profile. I’m not an engineer, so not sure why one relief-angle would be better than another.
P.P.P.S.
I wasn’t aware of the RailRevolve command. I’ll have to try it. I think it does the right thing for making straight threads. Will have to try it and/or think if it works on tapered threads.