LCS change position when MasterSketch evolves

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alexanderthomas
Posts: 8
Joined: Wed Jan 19, 2022 1:34 pm

LCS change position when MasterSketch evolves

Post by alexanderthomas »

Hello,

Thank you for this forum, it is of great help. I am seeking help from you on a problem in my assembly.

I am using FreeCAD 0.19 with Assembly 4. I have several parts that need to move relatively, so I built a MasterSketch in the assembly model which acts as a constraints solver. Several LCS are attached to edges of this sketch, which are then used to import parts in the model on these precise locations. It works fine, as showed in numerous tutorials: when I change (or animate) my Variable (an angle), the sketch evolves and parts move accordingly, it's good.

My problem is that, at a certain point (when my Variable exceeds a certain value), parts completely change position and end very far from where they should be. I have identified the problem: some LCS attached to the MasterSketch also change position (to precisely where parts end up).
For instance, an LCS attached to one segment of the sketch now appears on another segment (therefore, moving the parts attached to this LCS in the assembly). This LCS is still attached to "Edge6", but the name "Edge6" now seems to designate another segment. It only happens when my Variable exceeds a certain value, moving some segments below some others.
I guess it has to do with FreeCAD naming the segments (Edge1, Edge2, Edge3, ...) of the sketch automatically in a certain order, maybe from one side to the other. The problem is the same if I attach my LCS to points (Vertex).

Do you know how to deal with this? Ideally, I would like to give kind of "labels" to segments of my MasterSketch, so that they are always correctly "identified" and can be used to attach an LCS quite confidently.

Thanks in advance!
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Zolko
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Joined: Mon Dec 17, 2018 10:02 am

Re: LCS change position when MasterSketch evolves

Post by Zolko »

alexanderthomas wrote: Thu Jan 27, 2022 9:32 am This LCS is still attached to "Edge6", but the name "Edge6" now seems to designate another segment.
yes, this is the dreaded topological naming problem (TNP). This is a long-standing FreeCAD issue.
try the Assembly4 workbench for FreCAD — tutorials here and here
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