Since finding the big C-channel piece that makes up the base of the machine, I've always planned to build the electronics into the base to give a nice, compact and clean machine. I'd been waiting for a power-supply to arrive before doing this, but last week it came so I got to work.
The electronics are currently mounted to a piece of plywood that hooks on a key at one end and has bolt holes to bolt to some 3D printed plastic standoffs. It fits into the base pretty nicely.
The plywood is a bit of an old shipping box; it had my address on it, hence the black tape. Undoing two nuts on the right hand side allows the plywood to come loose:
Running approximately left-to-right, you can see the Arduino running GRBL, the three stepper driver carrier boards, a solid-state AC relay for spindle control as well as the power-supply and finally the E-stop button. All the mains power is wired with 14 gauge household wiring connected with Marretts. The E-stop button cuts all mains power to the power-supply and relay, thus rapidly immobilizing the machine. The Arduino is unaffected by the E-stop, being powered from USB. In this way, the E-stop also functions as an optional operator stop, allowing you to de-energize the machine, reposition it manually or change tools and then start it back up, knowing that it won't starting moving or cutting with your hands in there.
Looking from the back, the USB socket for the Arduino is accessible, as is the scavenged spindle socket and power cable. In a subsequent revision I plan to replace these with panel-mount components, but I couldn't locate them locally last week.
The other, straightforward, addition was cable drags on all the axes. This has really helped to clean up the machine, giving me something that looks more like an actual tool than before. Hopefully I will be able to start using it for projects soon.