Mating Problem with Dovetails

Although I am a newcomer to Solidworks, I have mated hundreds of
different parts to one another in 50 and 60 part assemblies, without
many problems. For some reason, that now shatters my confidence, I am
unable to assemble a simple male dovetail to a simple female dovetail.
Is there an unknown factor involving dovetails that I am missing? I am
attempting to mate a 60 degree male (slide) part, to a 60 degree
female (housing) part and without any success at all. I am attempting
to mate the back flat face with back flat face , and beveled male
slide to same bevel female housing, I have tried in different sequences
with same result.
I would appreciate any help that would be offered.
Erika

 

Erica,

As Keith pointed out, check that the angles are the same. To add to this,
they must be EXACTLY the same out to 8 decimal places. If they aren't
Solidworks (or any other similar program) can't resolve it.


Mark

 

@a75g2000cwd.googlegroups.com>,
says...

Erika,

I use a dovetail slide in an optical assembly and found
that SWX chokes on the two plane-to-plane mates.

Try this:

Make a plane-to-plane mate between the "60 degree" beveled
faces. Then make a coincident mate between the "flat" plane
of the housing (female dovetail) and the **EDGE** of the
slide (male dovetail) where the "60-degree" and "flat"
faces of the slide intersect (assuming a sharp edge).

Now the slide is constrained (I wish SW Corp would call
them constraints instead of mates!) in 5 DOF, with only the
"sliding" direction free. You can drag the slide with your
cursor only along its direction of travel, or you can add a
distance mate of a point on the slide to an end face on the
housing to finish the job.

HTH,
Art

 

Thank you kind Sirs,
I learned an important lesson today. For some reason I developed a bad
habit of sketching to line/length, rather than entering exact angles,
and my angles were indeed off by a foot, and it is more than evident
that they need to be on the money. I edited all male and female
sketches to 60 degrees, and everything, including the gib mated like
velvet.
Hugs to all of you.
Erika

 

Why bother trying to mate the dovetails at all?

1. In the real world and in your model the male and female parts will
never exactly be line to line.
2. If you try to mate the angled portions there is inherent ambiguity
in where the dovetails are with respect to each other based on the
roundoff error in the angles.

So instead of mating the angled portions, create a centerline plane on
the male and female portions and mate that to center the two to each
other. Then you will be using three orthogonal mates to locate the
feature.

 

My model is an IGES download from a vendor. After checking,
I found the two angles were in error at the 3rd & 4th
decimal points (which I rarely have displayed), enough to
cause the problem.

Keith and Mark are right about having the angles exactly
the same. In that case the two plane-to-plane mates work.

From a kinematic standpoint they shouldn't work, because
each one consumes 3 degrees of freedom, leaving a "7th" DOF
(which doesn't exist) to control sliding motion. I suppose
that SWX ignores the conflict when the angles match
exactly, and only constrains 5 DOF.

Art