Photodiode Holder for Bantam Tools Desktop PCB Milling Machine

We wanted to add vacuum on/off control to our Bantam Tools Desktop PCB Milling Machine. While there are a few different ways to accomplish this with CNC machines in general, sensing current didn't seem like a good plan as there weren't any good places to sense it from. However, it turns out there are a series of LED lights visible from the back of the machine, with one corresponding to spindle on/off.

This little holder slots into a channel milled in the back of the mill. You just need a phot