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Symmetric contraint not working

MikeHenry

Alibre Super User
I'm trying to use a symmetric constraint to center the slots in this part about the X axis but GM 2014 won't let me, claiming that it is unable to find a solution. This problem crops up for me intermittently - what am I doing wrong?

BTW, I've temporarily solved the problem in this part by adding a dimension between the X-axis and the slot center on one side, but I'd like to find out why the symmetriuc constraint doesn't work.

Mike
 

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DavidJ

Administrator
Staff member
Interesting - symmetric constraint doesn't seem compatible with shapes. [EDIT - that's not right]

I can think of alternative workarounds, but I don't see why the constraint shouldn't apply to shape tool (at least the anchor point).

[EDIT - I had another look. If I replace your second 'distance from edge' dimension (D14) with a vertical constraint between slot centres, I can remove D16 and apply symmetric constraint without problem. I think the software isn't smart enough to realise that the two linked distance from edge constraints fix the geometry so that symmetrical constraint can be applied. Constraining the slot centres to a reference line also works. ]
 

MikeHenry

Alibre Super User
Thanks David. I've played around with your suggestions and it looks like the act of symmetrically constraining has the effect of making the D14 dimension redundant, which then causes an over-constraint condition. If D14 is deleted then the symmetric constraint can be applied and the second "edge to slot" dimension (D14) is set equal to the 1st "edge to slot" dimension (D13). IOW, to make two slots symmetric about a reference line or axis, only one of the slots can be dimensioned perpendicular to the symmetric line or axis. The dimension on the other slot will be automatically fixed at that of the 1st and there is no need for the vertical constraint you mentioned.

I can see situations where one would want the "edge to slot" dimensions for the two slots to be different while imposing a symmetric constraint about a perpendicular line, so this constraint "specification" seems needlessly restrictive to me, though it's easy enough to deal with once you realize what is going on.
 
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