A little bit about plugging holes again (as it’s something that comes up pretty regularly when you work with guitars).
Much of the time, you can shove a length of something handy into the hole and forget about it. By that, I mean you can plug a hole with a dowel (or toothpick, skewer, or whatever). Most of the time it’s fine. Plug it and patch/touch-up a little over the damage. Great.
Sometimes, you really want to make a wooden plug to fill a hole, though. Especially if you need to re-drill close to the plugged hole.
So what’s the difference between a dowel and a plug you’ve gone to the hassle of making for yourself?
A dowel (or the smaller substitutes, mentioned above, that can work for tiny holes) will have its grain running along its length. And that’s as it should be. That’s what gives it its strength.
The problem is that plugging a hole with a dowel leaves you with that lengthwise grain being mostly perpendicular to the wood around it. This clumsy image shows what I mean.
From a touch-up point of view, this means you’ve got the dowel’s end grain to deal with (and end grain looks different under transparent finishes).
However, the bigger issue is that, if your drill bit overlaps the dowel, it can get pulled into the dowel’s grain and can wander. That’s not good if you’re doing something that requires precision.
Like a vintage-style Strat tremolo bridge replacement.
This Strat bridge is being replaced with a newer unit. The owner had hoped it’d retrofit the same six bridge screws but, alas, no. The screw spacing is different. So, plug ‘em and re-drill ‘em.
Yes, but some of the new holes closely overlap the old ones. Even using a drill press, I know that I don’t want to take the risk of a wandering bit on something that needs this much accuracy.
So, I cut some plugs.
My smallest plug cutter is a little larger than the existing screw holes, so I first drilled these to widen them a little.
Drilling the holes wider also has the added benefit of cleaning them up a little. The’ve had a tapered/conical screw in there for a while so they’ll have threads and (probably) a slightly tapered shape. My newly widened holes will have clean parallel sides.
Perfect for accepting my plugs. Splodge on a bit of wood glue and tap them in. It’s good to try line up the grain of your plugs with the grain of the instrument for extra safety (just make a guess if the guitar’s got an opaque finish — you know which way it usually goes).
A great trick I learned from Dan Erlewine* is to shave down the tops of the plugs straight after installation. That way, the curing action of the glue will pull them just a teeny bit below the surface of the guitar. Just the right amount for a little finish touch-up. Sorry for the slightly out-of-focus image. I can't afford a photographer so I'm making do. 😉
I really like this Stew Mac brace-carving chisel for jobs like this. I can get a nice flush cut, even in the centre of the guitar body where the handle would usually prevent me getting an ordinary chisel flat. By the way, I just checked and it looks like Stew Mac don’t do this particular chisel anymore but they now have a number of similar ones in different sizes.
And that’s it. You obviously still have to be careful when drilling but things are much more likely to go well if you don’t have dowel grain to worry about as well as everything else.
* It's probably fair to say I learned most of what I know from Dan Erlewine. Thanks, Dan. And, dammit, I want my face on a pint glass. 😉
This article written by Gerry Hayes and first published at hazeguitars.com