Used a 1/2 inch harbor freight end mill, 15mm/s feedrate, 1mm depth, 65% step over. Next time I do one of these, I will oversize the slot so it can be cut with the 1/2 inch bit and still fit the t-slots, and I’ll also put the two boards together and cut the slots for both at the same time (just set the depth to 31mm). I might also speed it up some – either faster feed rate or deeper cuts. But I shouldn’t need to do this again for awhile.
The only thing left is dressing the bed.
These t-slots are awesome! They take 1/4-20 carriage bolts, which are cheap and readily available. I couldn’t find a 1/4-20 knob with a trapped nut, so I remixed my own. Here’s what I used: