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helix extrusions (by Alex B)
Folks,

Has anyone mastered helix extrusions for modeling things like bolt threads ? Can't seem to figure out how to constrain them correctly. I see I can do the height, which turns out to be arbitrary and may not necessarily connect the surfaces, or can make it worse by having surfaces overlap. Would be cool if anyone has an example. Thanks!
Wed Jan 8 2020, 12:55:14
(no subject) (by Paul)
There are currently 2 ways to drag a helix. 1) you can drag a point on the axis of revolution to change the length. You can also add a constraint to set the length. 2) you can drag points off-axis to change the angle of revolution. It's rather hard to set the angle. You need to drag a point around many times to get a large number of threads, and then it's strange (but possible) to add a constraint to entities on opposite ends. Or you might constrain a point on the end to one of the primary planes.

There is a related open issue here:
https://github.com/solvespace/solvespace/issues/488
The idea being to add a pitch parameter in the text window for helix - number of mm per rev. Then you could just constrain the length in the drawing and the rest would follow.
Wed Jan 8 2020, 13:21:11
(no subject) (by Alex B)
Understood, thank you for the quick reply!
Wed Jan 8 2020, 13:35:12
(no subject) (by Alex B)
Was able to constrain opposite sides, but the end result is all messed up even with NURBS. I will attach the model tonight, maybe some people will have suggestions.
Thu Jan 9 2020, 14:11:07
(no subject) (by Alex B)
This is the model I'm struggling with...
Thu Jan 9 2020, 23:04:57, download attachment helix_test2.slvs
(no subject) (by Paul)
You have the "force NURBS to triangle mesh" checked in g005-extrude. I have not been able to make it work without that. However, the holes in the helix seem to be fixable. I changed the thread sketch to be just the triangle part that forms the thread - changed all the other lines to construction and then added a single line to close the triangle. The I added another extrusion (circle within a circle) to replace the portion that was previously created along with the thread. I don't know why, but the resulting file was too big to attach here (6.7M) so I zipped it.

Not sure if this is good enough for you. Forcing to triangle mesh is OK for some uses and not for others.
Thu Jan 16 2020, 23:45:10, download attachment helix_text2a.zip
(no subject) (by Alex B)
Paul,

both export to STL and naked edge analysis are still unhappy. I'm not on the super latest though, maybe it works fine on yours ?
Fri Jan 17 2020, 12:14:34
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