Concrete Volume Knob w/ Arduino

I wanted to build a concrete volume control knob for my computer. I had found some done with paper molds and although they seemed to work well I was looking to do something that was overly complex so I made my own 3D printed designs.
I also wanted to do something a bit different (again, think too complex for my own good) and wanted a free floating button in the center of the knob to mute the volume.
I ran through several designs before I came across one that worked well. The mold takes the form of several pieces which allows for the center button, a curved top and an easier removal from the mold pieces.
I smoothed out the mold interior surfaces with some primer filler and some light sanding. I used some light Vaseline as a release agent. Once dried (slowly) I coated with a few coats of poly to finish.
Here's a note, when you fill the mold with concrete make sure you vibrate it enough to remove as many air bubbles as possible. Gently and repeatedly bang the mold on a hard, flat surface to help accomplish this.

Notes:

For the inner support ring (if you choose to use) I omitted top and bottom layers and used a 15% honeycomb fill. The idea was that the concrete slurry would work through the honeycomb and better lock everything together. The first few attempts at removing the center blank caused the concrete button to break into several pieces. I redesigned the center blank with a slight angle to reduce initial release stresses, added the optional inner ring to help keep it together, added a removal push template and changed the order of removal. I had first taken the button out of the outer mold and then tried the button blank and now I leave it in the outer mold and remove the button blank first. Works great now.
I also change the bottom piece to incorporate a built in push release hold so you can use that or the push plate itself depending on what order you want to do things...

Instructable

Like my design, how about a cup of coffee?