We use milling instead of drilling to avoid issues like splintering, especially with delicate woods like mahogany, which will splinter without proper backing. Milling also allows us to handle various hole sizes using a single milling bit, eliminating the need to switch tools multiple times during the process. Each bit of attachment hardware has hole patterns from 2 to 6 holes.
The code I'm using is what we're currently using with Mach4, and successfully running for 10 years. We're about to pull off the old controller and put on a Centroid controller. We have about 600 different drum patterns and G-code job files. Since wooden drums dimensions are not particularly accurate our automation probes the drum to make sure it's reasonably close it then launches the drilling job and uses the results of the probe to accurately place the holes. Which is why you'll see Pythagorean theorem and some Euclidean geometry in the gcode that's calculating the position, and why the numbers cannot be hard coded and offsets set manually in the machine.
My C# automation of Centroid is almost done but I wasn't prepared for the differences in GCode, I assumed GCode worked pretty much the same from machine to machine. I'm a programmer and my GCode experience is only with the automation and processing of the shells for our custom drum line. The initial GCode was provided by someone using CAD/Cam software that created the GCode. I just adapted it into my drum design software that I wrote.