3D constraints: How to fix only center of circular edge?

Roy Klein Gebbinck

I am looking for a way to fix the center, and only the center, of a circular edge or face.

Imagine a vertical cylinder that has to have a flexible radius and flexible height, but does need to have a fixed location. If you fix the bottom face, you only fix the Z-location of that face. Fixing the cylindrical face locks the XY position of the cylinder, but also its radius. Fixing the circular edge of the bottom face leads to a combination of these two results.

The only solution I can come up with is adding a dummy solid with a concentric constraint. But I would prefer to not have to use dummy solids. Is there another way to do this?

Dmitry Ushakov

Hello Roy,

I agree with you that dummy solids are bad. But why don't you use dummy (=construction) lines and circles for that?

Best regards,

Dmitry

Roy Klein Gebbinck

'Why don't I' you ask? I simply did not know that this was possible. I can't find any mention of this in the Help. All I can find in the Release Notes is: "3D CONSTRAINTS: Rigid Set and Fixation constraints can now be applied to entities of any kind." No mention of DmConcentric3d there.

But it is good to know that this is possible. Mind you it is confusing that you have to select the 3D sub-entity first and then the 2D entity. Also the 2D entities must be fixed with the DmFix3d command, and not with the 2D GcFix command. Using GcFix leads to buggy behavior.

Dmitry Ushakov

 You are right - it is a kind of undocumented functions, which, however, was already discussed in another thread of this forum. We plan to legalize it in the next non-maintenance release. Moreover, we plan to allow application of 3D constraints to all relevant non-ACIS entities (lines, circles, arcs) independently on the sequence of selection of arguments for a constraint. And it is not recommended to create loops between 2D and 3D constraints - the behavior is undefined in that case.