Distortion when moving a face on the Z axis

Draw a half circle 25 segements, draw a smaller half circle 25 segements
Try to move the smaller face up on the Z and it gets distorted.
Any ideas pse.

Can you show the hidden geometry?

You could force what you want by drawing the edges and then smoothing them after. Time consuming for some shapes, but for this, you just draw one radial line and then rotate-duplicate the rest.

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Autofold gets confused with some rounded shapes. Either draw in the radial fold lines as @RTCool suggests or make the shape using full circles then cut it in half after. Interestingly, once the shape is constructed beginning with full circles, it will continue to fold nicely after.

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yes.

let me guess, you’re trying to make sort of a truncated cone right ? or half cone.

using the method you are, the distorted face will pretty much always happen. It’s a flat face with many sides (2 arcs), and as you take the part up, SU will try to keep faces as faces, and it’ll do it as simply as possible, resulting in that.

So, what can you do ?

• well first you could manually triangulate the big face before moving, but hey, it’s not a great idea.

You have basically 2 solutions : pushpull - scale and follow me
other will probably come with more solutions, involving extensions (fredo’s pushpull I guess)

edit : or an @endlessfix special. often many solution to a simple problem

————

first solution, I’ll make the big cylindre. I know, in your case it’s half, but it’s the same.

then

I’ll select the top face, and use the scale tool. Pressing shift will allow me to scale it without distorsion, and as you see, I’ll scale it from the top of my curve, so the flat sides remains flat.

At this point, either I type in the ratio (0,5 for a 50% reduction) OR I type the new height of the curve (the dimension between the two red squares) AND I add the unit.

I just typed 25 cm so now my smaller curve is 25 cm high.

———

Or I could do a follow me.

all I need is the profile, and the path. like this. I’m starting / finishing with a straight line to make sure my final shape will be good, without it, it might look a bit angled.

then, select the path, follow me tool, select the profile, and bam !

left is without the small lines, right is with. follow me needs to start with a perpendicular line for optimal results. on the right one, I can just pushpull the back face so I end up with a proper half truncated cone.

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Thanks all for the quick replies.
I did know there was other methods but I just could not get my head around why this method did not work.
Now I know and will change my technique.

Eddy

Yes, you would think it would work, and agreed I don’t know why it doesn’t. I saw similar result trying to make a quick and dirty sink by pushing concentric rounded rectangles, and it didn’t quite work as you would think either.