# Edge to plane parallel mate removes 2 DOFs?

Question asked by Dara Kong on Jul 22, 2020
Latest reply on Aug 11, 2020 by Dara Kong

## MY SITUATION

I'm trying to mate two plates having two holes each. I need the holes to match/align, and the plates to touch each other. But I have two constraints : I need the fewer possible mates, an most importantly I need my assembly to have zero redundant mate (for complex motion analysis). The final assembly should look like that :

So I used a coincident mate between these two circles so there's only one degree of freedom (DOF) left :

After that, I usually use a plane-to-plane perpendicular mate to eliminate the remaining DOF being the rotation around the Z axis. But because my plates have round corners, I can't use this technique. Instead, I used an edge-to-plane parallel mate which is theoretically supposed to eliminate only one rotational DOF :

## THE ACTUAL PROBLEM / BUG

But it seems that SolidWorks thinks that an edge being parallel to a face removes two rotational DOFs instead of one! Here's a proof of that using motion analysis :

It's super annoying since I know for a fact that the edge can still rotate around itself, AND the edge can also rotate normal to the plane/face, so there should be 2 free rotations (around edge and normal to plane). And because a parallel constraint never removes any translation, my assembly should be fully defined without having any redundancy in my mates. But of course, here's what SolidWorks tells me when I try to add my coincident mate :

Finally, here are my questions about edge-to-plane parallel mates in SolidWorks :

1. Is this a bug or I'm missing something?
2. Should this kind of mate really remove 2 DOFs or just one like I think?
3. Is there a workaround for this?
4. Is there another way to achieve what I want?
5. Is it okay to have redundant mates for motion analysis?

The files are available for you to download if you need them...