Re: Guitar Techs...how would you do this
You first need to find where that hole should be for a pot. It's hard to tell from the picture whether or not it is in the right place.
You can certainly use a drill bit to make the hole. You just can't plow right through the finish in one step with a freehand drill and a dull 3/8" wood bit and expect clean results, though. For good results, you need a drill in steps, use the right types of bits, and use truly sharp bits. You also want to score the finish at the edges of where you want the hole to be before you drill through the finish. Fortunately, there is an ideal bit that – if used properly – can both do the scoring cleanly, and actually finish out the hole as well. It's called a Forstner bit.
I would do the following:
1) Find the center using measurements and visual judgement, then mark it with a small dot using an ultra-fine-tipped permanent marker.
2) With a small punch, make a depression on the marker dot.
3) Place a piece of masking tape in the control cavity, over the spot where the hole will come through. Press it down firmly.
4) Drill a small pilot hole (1/16" or slightly larger). If you have good skill with a drill, you can skip this step.
5) A drill press is ideal for this step. Use a 3/8" Forstner bit, with the center point riding in the pilot hole (or, if you skipped step 3, riding in the mark left by the punch). Slowly lower the drill until the outside rim of the Forstner bit starts scoring the finish. Again, the bit must be factory sharp, or better! Do not use much pressure. At this point you are only lightly scraping finish away, but some wood will have to come out too, due to the curved top. Pause as necessary to prevent the finish and wood from overheating. Continue this until you have scored a complete circle in the finish.
6) Continue the hole through the wood. You can move a bit faster now, but you want to slow down near the end of the hole, basically going back to the pressure you used when you were scoring the finish. Finish out the hole at this pressure. Slowing down like this, in conjunction with the masking tape you applied earlier, helps to minimize grain blowout in the control cavity.
7) Remove the masking tape and neatly clean up the edges of all the freshly drilled areas with 400 sandpaper.
If you must use a hand drill for steps 5 and 6, make sure you are good at using one, and make sure you clamp your guitar down to your work bench first.
If you suck at doing any of this sort of work, and don't know how to finely control a Forstner bit, just use a reamer. But the above method is the ideal way to go IME.
