topic Re: Getting compute error when trying to mirror a body in Fusion Support Forum

Getting compute error when trying to mirror a body

joanpecas — Wed, 10 Feb 2021 18:41:47 GMT

Hi everybody. Well, I'm new to Fusion 360 so I do apologize if I'm asking something obvious.

I'm working on the design of two simple, symmetric parts (https://a360.co/3aQjaml). Due to their symmetry, I designed half of the parts and when I wanted to mirror them to get the other halves, so I defined the symmetry plane but when I tried to perform the mirroring I got a "compute error". The text of the error is not very explanatory, it just encourages to "adjust values or change the geometry". Tweaking a bit I noticed that the issue is in the process of mirroring itself, but of joining the parts with their mirrored counter parts, since if instead of mirroring with the "join" option I mirror it with "Generate new body" option, the mirroring results successful but I cannot join both bodies later since I get a "Failed to Boolean bodies together".

I've been googling about those issues and learnt that they may be due to something in the geometry disliking Fusion 360. I read about a "Validate" option that materializes under the "Inspect" menu after deleting the design history but it didn't find any issue in my bodies. Since I'm an absolute novice I'm aware that my design must be a compilation of bad practices... but I'd like Fusion 360 to tell me what is what he doesn't like. Now I run out of ideas, I'm thinking in redoing from scratch, doing a mirror after every step to find which one is offending Fusion 360...

Any tip before resorting to brute force?

Thanks in advance,

Jose A.

Re: Getting compute error when trying to mirror a body

g-andresen — Wed, 10 Feb 2021 19:40:55 GMT

Hi,

Because you have made a surface element into a solid by thickening it, a plane surface is missing in the transition between the mirrored bodies, which would be necessary for connecting the bodies.
I would do it differently.

Watch the screencast and follow browser and timeline

günther

Re: Getting compute error when trying to mirror a body

joanpecas — Thu, 11 Feb 2021 08:15:46 GMT

Thanks so much for your detailed reply. Well, that's something I didn't know, so if a solid body is generated by thickening a surface, the resulting sides (the ones perpendicular to the growth direction) are not considered planar surfaces. That changes all!

I did the design by means of a 3d-sketch instead of by extruding the profile of the part as a 2d-sketch because its topmost plane is not parallel to the XY plane, but tilted 4º, and didn't know how to achieve this with the 2d-sketch approach. In addition, the topmost of both parts should be aligned, since they are supposed to hold a planar object on them.

I'll think how to achieve this without relying on a 3d-sketch.

Thank you very much!

Re: Getting compute error when trying to mirror a body

g-andresen — Thu, 11 Feb 2021 10:45:28 GMT

Hi,

A simple but somewhat rustic way is to "cut" so that a plane surface for mirroring is created.

Screencast

günther

Re: Getting compute error when trying to mirror a body

g-andresen — Thu, 11 Feb 2021 17:54:07 GMT

Hi,

In the screencast I have created another variant.

Perhaps this one goes in the desired direction.

günther

Re: Getting compute error when trying to mirror a body

joanpecas — Fri, 12 Feb 2021 08:38:11 GMT

Thanks so much for your replies! Good point, from the second one, I see that if you cut a thickened surface, you get a planar face in the cut! However, the second approach in your third post is exactly what I needed, much neater than the 3D sketch which required a lot of steps and dealing with the particularities of thickened faces... and what's more, allows me to get exactly the result I wanted. Awesome! The key is the use of the move and the shell features, which I didn't know could be used in that way. I've learn a lot in this thread! 😁

Thank you very much!

Jose A. Pérez