topic Re: Mirror changes geometry in Fusion Support Forum

Mirror changes geometry

ICanSpinIt — Tue, 29 Sep 2020 20:48:22 GMT

I have had this issue before but since its recurring, why is this happening?

I mirror a part and when the part is mirrored it changes some of its geometry.

Part to be mirroredbad geometry after mirror

Re: Mirror changes geometry

jeff_strater — Tue, 29 Sep 2020 20:51:08 GMT

I suspect that what you are seeing is just a graphics anomaly, not really bad geometry. If you share the design here, I can take a look. We are starting a project soon to collect up these faceting problems, so it'd be good to know if this is another case, so we can add it to that project. Thanks!

Re: Mirror changes geometry

ICanSpinIt — Tue, 29 Sep 2020 23:07:40 GMT

I thought that's what it might of been. You can see the main body inside of the bad geometry but can also select the bad geometry..

I took the mirrored part and used it as a cutting tool in a basic block. The cut section still showed the bad geometry. When you do a section analysis and lower the face through the opening it does reveal the part as it is suppose to be...

The forum will not allow me to load the fusion file

Re: Mirror changes geometry

jeff_strater — Tue, 29 Sep 2020 23:24:34 GMT

you should be able to add the model here. See this article for how to info: How-to-share-a-Fusion-360-design . If nothing else, you can send me a private message with the link to the design.

Re: "but can also select the bad geometry", yes, this is correct. Selection happens on the graphics, so it stands to reason that you can select the bad geometry.

Re: "The cut section still showed the bad geometry". Again, the sectioning happens in the graphics, so yes, I'd expect to see that bad geometry here.

There are usually ways to fix this, most often with the level of detail control. If you are able to share the design, I can experiment.

Re: Mirror changes geometry

ICanSpinIt — Thu, 01 Oct 2020 14:59:00 GMT

@jeff_strater I have tried every trick I can throw at it to have a work around and changed all graphics settings, no luck. I even tried slicing it every inch to mirror just that section and when I do that the new sliced section changes its geometry.

When bringing the part into the manufacturing workspace Fusion cuts out the bad geometry as well.

Re: Mirror changes geometry

jeff_strater — Thu, 01 Oct 2020 18:23:56 GMT

Thanks for the model, @chickosr - I can easily replicate the problem. The good news is that this is, indeed, just a graphics/faceting issue. The bad news is that the usual, non-destructive method for working around the problem does not fix it in this model, so a more extreme work around is needed.

Some background on this, and why you see the "graphics effects" in other places. Fusion (or any 3D modeling application) will convert its precise, mathematical representation of a surface into triangles for display. All computer graphics systems use triangles for display. We call this process "faceting". In this case, the faceting has gone wonky. I can see this if I turn on the facet display:

so, really, the underlying geometry is fine, but the faceting is bad. But, the problem is: this faceting is used for other things inside of Fusion: STL export, and as you've seen, CAM.

So, this is, indeed a bug in Fusion, and I'll enter that bug.

The usual fix for this is to change the level of detail for the body:

and to choose one of the "fixed" levels:

but, that does not seem to fix it here. So, the only method I've found is to split the face, to force a different faceting. This is unfortunate, but does work. There may be other splits that will be less obtrusive, you can experiment with that.

screencast:

Re: Mirror changes geometry

ICanSpinIt — Fri, 02 Oct 2020 00:45:29 GMT

@jeff_strater Out of all the slices I never thought to try a 90 degree! Well it works so as long as there is a way to do some type of workaround...Fusions still the best👌
Thank you!

Re: Mirror changes geometry

ICanSpinIt — Fri, 02 Oct 2020 21:11:08 GMT

@jeff_strater

I played around more with the mirror issue. This is what I found out.

The original sketch was a DAT file that was positioned and scaled by me with the aid of an app.

That sketch profile had 200 points for each slice

it was 1 continuous spline..

What I think went on is that when I created the loft between each profile slice Fusion maybe lost which point was suppose to go where.

What I did was divided the sketch and made it have a top spline and a bottom.

NOT 1 PROBLEM after that with the mirroring or strange geometry!!

Re: Mirror changes geometry

jeff_strater — Sat, 03 Oct 2020 23:18:46 GMT

good to hear. Yes, a spline with 200 fit points can produce some bad geometry, and fewer fit points are almost always better.