Why does the boolean fail on this after following video where such worked?

Hi, V5.
followed a video, helix touches edge of 7.9mm dia cylinder,
orient perp to curve the profile of the thread (I have a 1 x 1.5 triangle, helix is 1.5 apart (pitch).
sweep1 then cap.
then to overlap thread to cylinder, make cylinder the correct diameter 8mm
scale2D cylinder from centre to become 8mm dia.
run boolean union…fail !
boolean fail on overlapping screw thread following video.3dm (539.8 KB)
file attached.


Hi Steve- the thread is self-intersecting, I imagine that is what causes a problem here.


but overlaps are good for boolean surely ?


Steve overlap between two objects is good for boolean. Internal surfaces in a closed solid is going to give you problems with a boolean.

If you increase the cylinder in your file by a small amount ( i used 8.038) to expose a very slight amount in the thread like this it solves the problem.

Then I split the two objects against each other and joined.

If your tolerances allow this then that would be a quick fix otherwise you might need to go back and fix your sweep to get rid of the overlapping surfaces.

For what its for that will suffice. :slightly_smiling:
I wonder if it would fail if the exact junction of the V profiles met at the cylinder wall, I shall dabble and find out.


I would expect you to have problems. If the edges meet perfectly then that is the time to use split, join, trim etc IMO.