Arc is missing a constraint

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peetervois
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Joined: Sun Oct 18, 2020 7:29 am

Arc is missing a constraint

Post by peetervois » Sun Oct 18, 2020 9:55 am

Hello, I am pretty new here with FreeCAD but I found that (my version 0.18) is probably missing a arc constraint. The FreeCAD tells me that the sketch is fully constrainted but the Arc in matter of fact has unsolved freedom. By changing the angle in Constraint.a from 30 to 60 makes the arc length to be different. You will see the outcome from attached pictures. It may be possible that I am doing something wrong. I also found that that there is a discussion of sidedness or something going on which may be very similar matter. I was trying to make a construction line to define the centre of arc sidedness with an angle but that fails because the sketch is fully constrained.
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Screenshot_2020-10-18_12-44-06.png
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Screenshot_2020-10-18_12-43-34.png
Screenshot_2020-10-18_12-43-34.png (203.17 KiB) Viewed 215 times
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peetervois
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Joined: Sun Oct 18, 2020 7:29 am

Re: Arc is missing a constraint

Post by peetervois » Sun Oct 18, 2020 12:15 pm

The reason may be that I have used 2 tangent constraints. I shall use only one, then I can make constraint for the center location. Although I was using tangent constraint, the freedom for the center location was left more than one position, and I think one more freedom must be left to solve.
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Kunda1
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Re: Arc is missing a constraint

Post by Kunda1 » Sun Oct 18, 2020 12:32 pm

Please update to 0.19 and retest
https://github.com/FreeCAD/FreeCAD/rele ... g/0.19_pre
(most of us on the forum use 0.19 now as it is far more advanced and stable than 0.18, due to some technical and time constraints 0.19 release has been delayed.)
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chrisb
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Joined: Tue Mar 17, 2015 9:14 am

Re: Arc is missing a constraint

Post by chrisb » Sun Oct 18, 2020 1:16 pm

I can indeed not reproduce in 0.19, but I see that your sketch is poorly constrained: You must not use tangency and coincidence on the same points. And you should not use 90° angles, use orthogonal instead. As it is advised to minimize the number of dimensional constraints I would recommend to use symmetry instead of the 0.5mm expression.

For further explanations see https://owncloud.gwdg.de/index.php/s/eZ ... 9/download.
You need at least FreeCAD 0.19.23300 to edit my current sketches.
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