topic Why can't this edge be chamfered? in Fusion Support Forum

Why can't this edge be chamfered?

GRSnyder — Thu, 08 Oct 2020 22:54:54 GMT

I thought I knew most of the factors that arouse the interest of the chamfer police, but this edge looks pretty clean to me:

True, there are several curved and angled surfaces involved here. However, if the cutout is created by cut-extruding Sketch2 from the same face (rather than split-facing and offsetting), the edge chamfers just fine. Strange, because the edge profile should be identical, although the edge walls are angled slightly differently.

The error message is Fusion 360's usual "Something bad happened but I don't know what or how to fix it." 🙂 Specifically, "Error: The fillet/chamfer could not be created at the requested size. This might be occurring at the ends of the selected edges. Try adjusting the size or using multiple separate operations. Check that the selected edge chain ends at a sensible position, and if not try selecting more edges."

Re: Why can't this edge be chamfered?

jeff_strater — Fri, 09 Oct 2020 01:47:15 GMT

Not completely sure. However, putting a fillet on that same edge, I think, gives us a clue:

there is something very funky going on near that vertex.

[edit] I've sent this off to the modeling kernel folks to look at. Will update if I hear anything interesting back.

Re: Why can't this edge be chamfered?

GRSnyder — Fri, 09 Oct 2020 03:31:37 GMT

Thanks, @jeff_strater. Yes, it definitely seems to be that corner - if you shave 1mm off that edge, then it chamfers fine. That's good enough for a workaround, but it still seems a bit suspicious given the simplicity of the construction.

Re: Why can't this edge be chamfered?

richard.hallT2EK9 — Fri, 09 Oct 2020 14:25:56 GMT

There does seem to be something odd near that corner .. attached is the (zoomed-in) shading there ..

Can I ask how this was created ? thanks

Re: Why can't this edge be chamfered?

GRSnyder — Fri, 09 Oct 2020 19:16:28 GMT

@richard.hallT2EK9 wrote: There does seem to be something odd near that corner .. attached is the (zoomed-in) shading there. Can I ask how this was created ? thanks

I'm a bit unclear as to what you're asking since you seem to have the Fusion 360 file already. (If not, it's attached to the OP above.) So here's what I know...

This is a simplified test file that I made after experiencing this problem in another project. The main mass is first created as an extrusion. Then the top face is split by projecting a curve from a different sketch and the face is offset negatively into the body to create the detent.

Some points:

The face to be split must be generated from a spline. An extruded arc does not show the problem, nor does a face generated by revolving an arc.

In the sketch that splits the face, the problem edge must not be vertical.

The exact workflow of splitting a face and then offsetting the split portion does not need to be followed exactly. For example, you can project the splitting profile onto the face and then use Patch and Thicken to generate a cutting body, then use a Boolean operation to reproduce the shape. The problem edge still won't chamfer. (You will need to adjust both the splitting path and the cutting body slightly to allow the projection and avoid near-coincident faces, however, just to make this procedure work mechanically.)

If you just extrude the detent profile with the Cut option, then all edges are chamferable. Of course, the shape is slightly different, too.

Re: Why can't this edge be chamfered?

richard.hallT2EK9 — Fri, 09 Oct 2020 19:58:17 GMT

Apologies @GRSnyder I had imported Jeff's SMT file for the body and hadn't swapped back to the full model, so I assumed it was a history-less part. There appears to be an issue with extending the inner side wall in order to create sufficient geometry for the full chamfer to be created and then trimmed against the pre-existing geometry. I am awaiting feedback from the relevant developer. Sorry again.