At the core of a command module block (CMB) is a part that I call the frame.  It holds everything together and allows the CMBs to attach to each other.  The frame is sized to fit a variety of elements, such as switches and potentiometers, but is no larger than it needs to be.  It also provides mounting features for a circuit board on the bottom and a cover on the top side.

I thought the frame would be an easy design . . . then many iterations later, realized that it's quite tricky to get right.   In fact I've accumulated a whole bin full of past designs that didn't quite work for one reason or another!

But behold, the latest version!  I think it's pretty promising, but has lots of testing ahead of it.  I've been churning some out over the past couple days.

The frames connect together in rows or grids.  After printing several, I was able to test their fit. 

So far so good!  They fit together just fine.

The next step will be installing heat set inserts.  The inserts provide mounting points for the circuit board and top cover.  They also allow you to more permanently fasten two CMBs together using a single screw.

If all continues as planned in the coming couple weeks, I'll install the circuit boards and front covers.  They're being fabricated as you're reading this.