I have a cylinder plus a square helix made from running a square around a rail. (Helix is planar capped.)

I can take a box and perform a Boolean Subtraction on both…

… and it works perfectly.

I then move the square helix down into the cylinder

to attempt a subtraction of the helix from the cylinder concentrically with the outer surface.

This fails.

If I move the square helix up or down concentric with the cylinder it still fails.

If I scale up the edges of the square helix outside the cylinder diameter …

The subtraction still fails.

Now, if I break concentricity… And perform the subtraction … it works fine.

Appreciate any thoughts about why I am not getting the subtraction when the solids are concentric?.

Thanks! Best regards,

Bruce