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Another Mirroring Issue
S1mon
Member Posts: 3,039 PRO
I found another basic mirroring issue. Feature Mirroring a sketch doesn't update correctly. I've reported this as an issue to support.
If a reference for a sketch changes, it's not seen as "dirty" by the mirror, and it produces an incorrect result. I created this simple model and Loft 1 was fine. Then I moved Sketch 2 (the upper circle). Sketch 4 (side curve) updated correctly, but its mirrors fail (no longer connects to the right place on the upper circle), which causes the loft to fail because the guide curves don't connect anymore. Going in and editing Sketch 4 will fix the mirrors and the loft, so this is likely a dirtiness issue.
If a reference for a sketch changes, it's not seen as "dirty" by the mirror, and it produces an incorrect result. I created this simple model and Loft 1 was fine. Then I moved Sketch 2 (the upper circle). Sketch 4 (side curve) updated correctly, but its mirrors fail (no longer connects to the right place on the upper circle), which causes the loft to fail because the guide curves don't connect anymore. Going in and editing Sketch 4 will fix the mirrors and the loft, so this is likely a dirtiness issue.
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Comments
Sorry, I thought I had clicked Public, but it should be now.
https://cad.onshape.com/documents/42decfc43f748663ccd16459/w/da1b9ade01794d5aa16d9a3c/e/bb6df2aceaf8ad8ac3f80598
I just tried using the pierce relationship on another model (that I didn't want to make public) and at first I thought you had a good fix. Unfortunately it seems to still be a dirtiness issue. Even with the pierce relationship moving the reference will cause the mirror to fail. I've added V2 to the document with the pierce relationships. If you modify the "50" dimension back to 40, this model will be fine. If you go into sketch 4 and tweak a spline handle, it will be fine.
https://cad.onshape.com/documents/35110b7fa7200960f00b3422/w/99a60bd4b6feec92f1b83c30/e/34c67fecaa503e6d03da2954
In the real non-public model that I'm working on, I just added another angled plane on the other side, and created another spline with the same constraints.
In the public model, I've added a branch which implements your projected curve idea. This does work. I usually shy away from using projected curves because with anything other than a line, a projected curve will end up with a zillion internal points and have bad quality. In this case, it is quicker to model and rebuild with a projected curve/part mirror instead of recreating the sketch curve with the same constraints.
I also avoid building 1/2 models for class-a surfacing because it's difficult to maintain G3 across the mirror plane in many CAD tools unless the surface is built in one piece. You generally never model the hood, windshield or roof of a car in a 1/2 and mirror it - you model the curves in a way that their CVs are all symmetric so that things are clean across the mirror plane.