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How do you invert what is deemed as solid vs empty for a sketch?
blob_fight
Member Posts: 9 ✭
If a sketch has two closed loops, one more inside of the other, sometimes onshape will misidentify what sections would be solid vs empty. E.G two concentric circles, a donut, the center hole is deemed as solid and out ring is empty, but I want vice versa. Deleting the inner holes and remaking them usually doesn't work once onshape has deemed an inner hole as solid it's very hard to do anything change this paradigm.
Best Answer
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wayne_sauder
Member, csevp Posts: 551 PRO
It is not surprising that the system struggles to maintain tangency on the spline. It ought to give an error, but it doesn't for some reason. The curvature is really poor. I would suggest finding a different way to model it. There have been plenty of discussions on the subject of curvature on the forum; do a search.
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Answers
If it doesn't guess it correctly, you can clear the selection and manually choose which ones to include.
Yes, that's exactly what I want to do, but I couldn't find a way to do.
It's in the extrude dialog - press spacebar to clear all, then just click the regions of your sketch on the screen.
That's what I tried first, but it won't let me select the face of the outer ring in this dialog. Only the inner circuits are shown with a grey region, and outer is always white, I suppose that's the core issue. Once the sketch has deemed the inner circuit(s) regions to be grey and the outer region to be white, it's very hard to ever get the outer region to be anything but white. I suspect the issue be arising from a corner case of the outer circuit, it involving an offset spline (from an inner circuit spline) and perhaps tangent lines to this offset spline. Maybe Onshape can't figure out the outer circuit is closed, it really seems to struggle and lag with offset splines.
If I make all the inner circuits construction geometries the outer circuit still stays white. If I delete one of the inner splines, it will fix the outer circuit. Deleting the other inner spline won't. The two inner splines are made exactly the same specs as each other. (mirrored splines offset seemed be even more of an issue for onshape)
Share your doc URL and a pic of what you're trying to do.
I've figured out that it's certain combination of angles of the tangent lines coming off of the offset splines. Top left image: it won't make the outer circuit a closed loop. Top right image: move the top point a bit and then it's happy, but if you move the bottom point it might not be happy any more. Bottom left image: it's happy. Bottom right image: move the top point a bit and it's no longer happy, but if you move the bottom to create the right angles it might be happy. I think I had even managed to happen on angle for the bottom tangent lines where I could adjust the top right tangent line angle to as low as about 26.3 degrees, but 26.25 or lower would make it unhappy, but then below 10 degrees or so would make it happy again. This was with all 3 other tangent lines staying fixed.
https://cad.onshape.com/documents/395059ab1164105aa0cf3db6/w/d0ae55d99c45e8f4bb38651a/e/cad709ef3b97109e98592856?renderMode=0&uiState=66df7a022d1f32292b7f24a4
@blob_fight
It is not surprising that the system struggles to maintain tangency on the spline. It ought to give an error, but it doesn't for some reason. The curvature is really poor. I would suggest finding a different way to model it. There have been plenty of discussions on the subject of curvature on the forum; do a search.
Interesting, that would explain a lot. So maybe I could offset the spline, and then do some techniques to smooth this offset.
One thing that still doesn't make much sense is, when I delete the inner spline, why would this sometimes fix the outer connection, why would this subtly change the offset spline if that is what is happening?