There are several ways to approach this depending on the amount of time and the tooling available to the operator. Here are two relatively safe ways to go about it.
Drill press method:
- Cut 3/8" dowel rod to fit existing holes.
- Option: Cut plugs to fit holes.
- Glue plugs into holes.
- When glue has cured, clamp neck to drill press on suitable backer to prevent tear out.
- Bore new hole for tuner.
- Repeat location and clamping sequence for each hole.
Notes: This is exacting finish work. Care should be taken during layout to locate the centers of the new holes. Use either a brad point or Forstner bit. Regular twist drills will wander. Center punch the layout mark on the plug to help locating the bit before clamping. Plugs are better than dowel rods because the grain runs perpendicular to the bit. The grain in the dowel plug runs parallel and has a tendency to cause the bit to run off course. However, if care is taken it won't be much of a problem. Using a hardwood backer board beneath the headstock will help to prevent tear out.
Low tech method:
- Clamp neck into vise or to the bench
- Using a half inch diameter tapered reamer, ream existing hole from the rear to the front.
- Stop reaming before penetrating the front.
- Ream from the front to the rear.
- Penetrate through the hole.
- Repeat for each hole.
Notes: The hard part about using a hand reamer is maintaining a straight line through the hole. If a visual aid, like a machinists square or a simple horizontal or vertical line on the wall depending on how the workpiece is mounted will make it easier to stay on line. It is important to use the reamer on both sides for the same reason as using a hardwood backer board when using the drill press to bore a new hole. Even with a reamer there some significant tear out can happen. When both sides have been reamed, pass the reamer through the hole several times to make sure the hole is clean and round.
There are other ways to accomplish this task. These are two of the safest.
Respectfully submitted.
