Creating multiple parts from the same base design

[todd.trainnut]

I am trying to design a painting mask for painting model train wheels (what a nerd, right?). The problem is, not all train cars have the same size wheels, so I'd like to make a mask for 28", 33", and 36" scale wheels. My thought was to create a base blank design, then import that design into 3 different final designs where I would cut the appropriate sized hole for the wheels. I'm designing the mask in 2 identical halves that slide together (making 3D printing the mask easier).

Here's the blank design:

The problem I'm encountering is that once the base design is imported into one of the final designs, I can't cut the holes in it due to the link. I'd like to preserve the link so that if I need to change the geometry of the mask, I can just change the base design rather than changing all 3. Is what I'm trying to do possible?

I'm not very experienced with CAD, so it's totally possible I'm approaching this the wrong way. Thanks for your help.

[MRWakefield · Accepted solution]

Have you tried 'Insert Derive' from the 'Insert' menu? I think it should do just what you want.

[TrippyLighting]

Importing triangulated geometry is really not the best way to work with anything in a CAD software ... even for a nerd 😉

[todd.trainnut]

Oh hush. I got the design from a friend as an STL to print, decided to make some improvements myself, and didn't want to re-draw the whole thing.

[todd.trainnut]

That did it! Thanks for your help!