Not sure if this is helpful but it is something I have used a fair bit in the past. Curious if someone has found another way?
Drilling holes at 90 degrees to the Z-axis is a two setup job on the CNC (one setup to do the main milling, second setup is taking the part and putting into the vice at 90 degrees, zero off some x,y,z, position on the part, etc etc.) Basically alot of CAM and setup work. If the hole placement is not super critical but it needs some sort of locating I have got into the habit of creating a little pocket that is the width of the hole and at the right depth for the bottom edge of the hole. This little pocket can be machined in the first setup and allows me to easily locate the position using the drill bit and I just manually drill out the hole.
