topic Re: cannot select face to construct offset plane after merging face in Fusion Design, Validate & Document Forum

cannot select face to construct offset plane after merging face

Anonymous — Thu, 13 Sep 2018 08:44:18 GMT

I imported a simple stl and converted it to brep. After merging some of the triangles on the face, I found out that the merged face cannot be selected to construct offset plane, is this expected behaviour? and why?

Thanks.

Re: cannot select face to construct offset plane after merging face

TrippyLighting — Thu, 13 Sep 2018 12:18:32 GMT

As opposed to a triangle which is flat by definition, the merged fence is probably not flat and thus cannot be selected as a face to be sketched on. I think most users don't realize that merging faces can modify the faces.

Re: cannot select face to construct offset plane after merging face

Anonymous — Fri, 14 Sep 2018 04:15:57 GMT

when merging the face, I choose 'chain select' and see that all coplanar face is selected, which mean all the faces are on the same plane, why is it that the merged face is not on the same plane anymore?

Re: cannot select face to construct offset plane after merging face

Anonymous — Fri, 14 Sep 2018 04:42:43 GMT

my screencast showing what I meant

Re: cannot select face to construct offset plane after merging face

TrippyLighting — Fri, 14 Sep 2018 10:08:38 GMT

Can you provide a link to the model on Thingyverse ?

Re: cannot select face to construct offset plane after merging face

jeff_strater — Fri, 14 Sep 2018 14:24:55 GMT

most likely, the faces you chose are not precisely co-planar, down to the precision that Fusion uses. In that case, the merged face will not be planar. I verified that if the faces are indeed coplanar, they will be merged into a plane (I did this by using Split Face to split an already planar face into four pieces). So, as @TrippyLighting suggests, share your model, or the original mesh so others can take a look at it.

However, a better question is: Why do you feel it is necessary to merge these faces? What do you hope to gain by doing so? Since you started with a mesh model, are you trying to end up with a precise BRep model? If so, using Merge is not the approach I would recommend. This design looks simple enough that it could probably be more easily re-created by using Mesh Section and Fit Curves to Mesh Section, IMO, that to struggle merging faces.

Re: cannot select face to construct offset plane after merging face

Anonymous — Mon, 17 Sep 2018 04:59:40 GMT

https://www.thingiverse.com/thing:1773900

this is the stl model on thingiverse.

I'm total beginner on fusion 360, and have no idea what mesh section and fitting means. I'll look into it, and hope to learn more, thanks for the suggestion.

Re: cannot select face to construct offset plane after merging face

jeff_strater — Mon, 17 Sep 2018 16:02:55 GMT

thanks for sharing the stl object, @andycjw. I took a look at it, and my guess was correct: All the faces that you merged were not co-planar. If you use Measure on the extreme vertices of that face, you can see that there is a tiny non-planar distance (in global X axis):

Regarding using mesh sections, here is a screencast where I show the basic idea. You just create a section, then can fit curves (in this case it is all lines) to that section, which can then be used to create a solid model. This can be useful if you need precise geometry for other operations, or if you need to make large changes to the model. The screencast is below.

I also realize that, if you want to continue with the Mesh -> Brep approach you started with, you can just dispense with the Merge. There is no real need to merge those faces. If you want to create a sketch, just select one of the triangle facets to sketch on. Also worth a try.

screencast: