Having trouble with creases not working as expected in SubD

Rhino SubD
1

hi there … i’m trying to figure out why i can’t get this to work but after a couple of hours trying different quad structures i’m at a loss.

so what i want to achieve here is basically the green square with all crease edges being straight lines but for some reason the left edge wants to bulge out in a curve instead of being straight. i might just have tunnel vision but i can’t see how this quad structure is flawed.

Screenshot 2023-03-19 at 15.32.54
Screenshot 2023-03-19 at 15.32.541132×1002 165 KB

the only way i can get it to work is by continuing the crease upward like so:

Screenshot 2023-03-19 at 15.43.11
Screenshot 2023-03-19 at 15.43.11693×845 82.5 KB

which is not really what i want for the model. would love to understand why this happens since i’m getting much better with quads/subds as i clean up my models and convert them from nurbs to subd but i stil have many things to understand about the inner workings … this being one of them :blush:

any ideas anyone ?

2

Can you post a model or a part of it?

3

dear @chris16

are you aware that there is a difference between creasing a SubD-Vertex and a SubD-Edge ?

image
image1819×1257 103 KB

left to right

  • no creases
  • creased edges
  • creased vertices and creased edges (3 of 4)

if you need more help, please post a file.
hope this helps - kind regards - tom

4 Likes
4

hey thx Tom for your quick reply … unfortunately i can’t post the file since it’s a production file of one of my guitars. i’ll try to cut out a piece and post it.

i am aware that you can crease vertexes and edges separately … sort of :joy: … meaning i don’t really understand yet why you’d do one or the other … guess i’ll have to read up on that but couldn’t really find anything on it in the docs or web.

EDIT … ok here’s a cutout of the model:
creaseDebug.3dm (3.1 MB)

5

Modeling strategies vary… I’m not such a big fan of creases and I’d suggest to use move the edges closer together where you want sharper edges. Or use the new sharp command in Rhino 8 WIP.

Also the corner in your model is not really a corner since it has 4 adjacent faces. A simple corner has 3 adjacent faces…

I’m not sure which of the edges should be creased, maybe you still need to post a full model.

image
image1920×847 141 KB

creaseDebug.3dm (100.7 KB)

Here’s a second option which leads to a nicer corner, no matter which of the edges are creased:

image
image1920×908 145 KB

creaseDebug_corner.3dm (93.2 KB)

2 Likes
6

ah yes of course … adding edges is agreat idea. i’m also not a fan of creases but for manufacturing sometimes i need a really crisp precise edge somewhere, in this case this is the junction of the guitar’s neck and body so a crisp edge is kinda mandatory. but really many thx, this got me ‘unstuck’ and i can now move on and experiment further instead of bangin my head against the wall :slight_smile:

i didn’t even know Rhino 8 WIP was available, that’s cool and diving into that is a perfect occupation for a sunday.

1 Like
7

example:
000

1 Like
8

hey thx, that’s also a great technique i hadn’t thought about