I originally discovered that none of the square, rectangular solids and cutouts that VEX designers made have axes in them. If you want to constrain a “square peg to a round hole”, (or a round screw to a square hole, or square shaft to a square hole) you have to create the missing axis, or center points in the solid. A pain, I know. It should have been done when the designers were first creating the solids, but oh well…
I had to go back, take all their parts in Inventor, or .STP format, (I work primmarily in Inventor, but am familiar w/ Pro-E & SolidWorks)
- make a sketch on the face perpendicular to the desired axis,
project existing geometry,
Create sketch lines that meet in the center (across corners of a square, from centers of unequal sides, etc.)
to find the geometric center,
then add a point. Add a inscribed circle also (good idea).
Pattern the sketch elements, particularly the points, circle and axis line.
Close the sketch,
start a new sketch at the other end of the proposed axis,
repeat above from (1.)
Then, add an axis along the centerline of the solid that can be used to constrain a cylindrical object (like a screw, which has built in axis) to the artificial axis that you’ve created in your square hole in the sheet metal, nylon bearing block, etc.
If it’s a patterned feature, like the sheet metal plates, c-channel, etc., just find the C to C and pattern the artificial, created axis or point.
Note: after you’ve done constraining your assembly, go back into the individual parts and turn off visibility of the "constraint construction"elements. Axis lines, sketch elements, etc.
Lots of work, but then you’ll easily and accurately be able to constrain round to square, and vice-versa.