Curve bevel distortion

I add a bevel circle to a curve. My curve is a angular inverted U with two 90deg corners at top, shaped like a door frame.
When I add the circle to the curve that starts and ends like a circle but at the corners it becomes a tilted circle and consequently an ellipse in between them.
What I would like is to retain the profile (circle) geometry along the path. As an example imagine 3 pieces of pipe cut at 45 deg and welded at two corners.
Can I get that with a curve? (I know how to do it with mesh) Btw same thing happens if I use the curve as a modifier on a mesh object.

Hey, change it (BezierCurve) from ‘3D’ to "2D’, that should fix it.

Hey you too. Thank you, it worked.
But I do not understand why 3D deforms… so if all the segments of a mesh are not coplanar, you cannot extrude a profile along a curve?? why not?

I’m not sure I can explain that - but I understand what you are saying. 2 things that I know - when your ‘Resolution U’ is set to ‘1’ no matter what handle type you have it will end up at a 90 degree angle, 2D or 3D. Just add a default BezierCircle and change the resolution to 1, you will see what I mean. Some things are best modeled using a mesh, but that does not mean they can’t start off as a curve. Moldings & trim are fine examples, easy to do with this method but I convert them to a mesh so I can ‘miter’ them.

Allow me to complicate the issue a little. :slight_smile: I am attempting to avoid the same distortion in a 3D curve than cannot be 2D. The above solutions have not fixed it in this case. Any further suggestions?

Alternately there’s a shear tool in Blender. You could use it on a cylinder mesh object. If I recall it’s one of the view based transformation tools, so you need to be in orthographic and viewing the cylinder side-on for it to work.

Part of the problem with the curves is how Blender handles the radius for them. There’s no separate X and Y relative to the end face (or bevel profile), so it can’t correct in the way that would be needed for those “bevel cut” type corners. But at least there’s some level of work-around.

And another alternate to this alternate is with the knife tool. You can use the constraint and cut-through options to bevel cut the cylinder mesh as needed to change the extrusion direction. And it also needs to be in orthographic view and side-on to work correctly.