topic Re: Patch mode issue in Fusion Support Forum

Patch mode issue

igor.blokhin2003 — Fri, 15 Sep 2023 22:25:51 GMT

I'm learning patch mode now and have some difficulties. After some patch operations when I want to to edit previous sketches and patch them again, I see something like this, surface doesn't conect to its sketch and make holes between itself and connected surface. I know holes between surfaces can be fixed by stich operation, but i want to prevent them to appear. What can I do?

Re: Patch mode issue

jhackney1972 — Fri, 15 Sep 2023 23:05:58 GMT

It is hard to tell without the model, please attach it. If you do not know how to attach your Fusion 360 model follow these easy steps. Open the model in Fusion 360, select the File menu, then Export and save as a F3D or F3Z file to your hard drive. Then use the Attachments section, of a forum post, to attach it.

Re: Patch mode issue

igor.blokhin2003 — Fri, 15 Sep 2023 23:11:23 GMT

Sure, here is the file. Hope you can help me

Re: Patch mode issue

jhackney1972 — Fri, 15 Sep 2023 23:20:02 GMT

You model is created in Direct Modeling Mode which makes it rather hard to edit and troubleshoot. Can you show a screen capture where on the model you are seeing the problem you posted in your first post, I do not see it?

Re: Patch mode issue

jhackney1972 — Fri, 15 Sep 2023 23:26:00 GMT

Here is the model you attached with all sketches patched and stitched together.

Re: Patch mode issue

igor.blokhin2003 — Fri, 15 Sep 2023 23:57:10 GMT

This part is on the first screen. But honestly i see it everywhere. Surfaces just don't fit to their sketches.

Re: Patch mode issue

igor.blokhin2003 — Sat, 16 Sep 2023 00:07:30 GMT

I see this in your file too. You can even create another patch surface using the sketch line and the actual surface line created with that sketch, it's crazy.

Re: Patch mode issue

TrippyLighting — Sun, 17 Sep 2023 20:28:05 GMT

Neither is this a bug nor is it crazy!

When creating a patch, you are creating a NURBS surface. The shape of a NURBS surface is controlled by a rectilinear grid of control vertices (CVs). Regardless of the shape of the NURBS surface, that grid is ALWAYS rectilinear.

The ISOcurve analysis tool with curvature combs shows this clearly. It does not exactly show the location and density of control vertices, but it follows the UV coordinates of the CV grid.

That means that usually, only one of the boundary curves is naturally aligned with one edge of that control grid. The other edges are created by trimming. That is a process hidden from the user.

I used the Untrim command in the Surface tab to bring back the untrimmed NURBS surface created by the patch.

Imagine that you are trying too stretch a very stiff table cloth over a frame of welded together, curved tubes. If the curvature is too high, the stiffness of the table cloth does not allow for the table cloth to touch the frame in some areas. This is what you are seeing.

That is the reason why in professional vehicle design no one works with boundary patches. 4-sided lofts are the predominant tool.

Re: Patch mode issue

TrippyLighting — Thu, 21 Sep 2023 14:22:08 GMT

@igor.blokhin2003 If my last post answered your question, please click the Accept solution button 😉