Hi all.

Can someone please help me figure out how to twist this cylinder in such a way that the flat on the internal diameter stays flat and does not develop a bulge as it progresses up the bore.

thank you.

Hi Guy, I'm not sure that I'm understanding what is the bulge that you're trying to get rid of.

Is it maybe from the lateral shearing type of shaping?

Is something like this attached version any better?

- Michael

Hi Michael.

Maybe what I'm seeing is some sort of shading illusion or just the curve of the helix. The bulge is highlighted in blue.

Yes it's just optic effect! :)
Your surface has only "straight lines" propagated!

Hi Guy,

re:
> Maybe what I'm seeing is some sort of shading illusion or just the curve of the helix.

Well the surface isn't flat it does have a curved shape but it's normal for a shape made up entirely of lines to have a curved silhouette like that:





It's similar to the silhouette of a hyperbolic paraboloid surface:
https://en.wikipedia.org/wiki/Paraboloid#Hyperbolic_paraboloid

You'll get a curved shape like that if you traced a curve on the surface at an oblique angle instead of in the locally linear direction.

It doesn't mean there is a bulge in the surface though.

For how to avoid it, I don't think you can avoid it if you want to have a helical shape, it's just fundamental to that type of surface.

- Michael

Ahh thank you both. I love this program by the way.