Well, it's small.  Too small.  I thought that skateboard bearing looked huge...

I had messed with the number of teeth on the drive sprocket earlier.  The design is parametric so the tooth count, being bound to the fixed parameter of the tape hole interval, scaled.  Max part depth is somewhere around 4mm right now.

Not all of my math in OpenSCAD was done correctly, so not everything scaled correctly when I put it back.  I go through cycles of just trying numbers, and then figuring out the math to produce them and some of that hard coded stuff stuck.

I have some work to do still.  Math...  I'm taking a break and will be back at it this weekend.