Filling Tuner Screw Holes -- How To Make Skinny Dowels

Sometimes, vintage guitars with very high quality necks like Harmony Sovereigns have problems with the tuners. Now, the OEM tuners on Harmony guitars are not of good quality. But they should hold tune consistently. One problem is wobbled out or striped screw holes. How can any tuner work correctly if the mounting screws cannot be tightened? The following suggests a solution for this problem. This procedure should also be done on all screw holes when new tuners are installed. We always fill all screw holes and re-drill using the tuner plate screw holes as drill bit guides.

Recently I saw a guitar tech filling tuner screw holes with a roughly 3/16 inch dowel sharpened in a pencil sharpener. Egads what a great way to ruin a pencil sharpener. Those machines are only designed to cut white or red cedar which is very soft. Mahogany? Maple? NO!

Then the guy pounded the sharp dowel into the tuner hole. Egads! I say again: EGADS! That is a great way to split a vintage gear head. On an el cheapo guitar, that gear head may well be made of poplar (for example Harmony H160) or even bass wood (many vintage Chinese imitation guitars). Those woods are especially easy to split.

The screw hole should be filled with a dowel sized to fit the entire depth of the screw hole, not just the top 1/16 inch. And there is never any justification for drilling out the screw hole so as to fit a 1/8 inch dowel. And it should fit snugly because all glues appropriate for guitar work do not fill gaps effectively. And it is never appropriate to 1) fill the hole with glue or 2) glue the screw into the hole. There is a special place in hell for those who glue tuner screws into the gear head. Egads!

So, how to make a properly sized dowel to fit those tiny little tuner screw holes?

Steps follow:

Preparatory step: Remove old tuners and use naphtha to clean out the holes. Do not enlarge the holes.

  1. Using a small plane, straighten one edge of a piece of 1/8" thick mahogany scrap. Scrap should be approximately 10" long. We use mahogany tops and backs from wrecked guitar bodies to fill mahogany gear head screw holes. Alternatively, Woodcraft sells small mahogany sheets good for this purpose.
  2. Cut a 1/8" by 1/8" strip from the scrap.
  3. Use a block plane to shave off the corners from the strip. Precision not required here, just minimal reduction.
  4. Chuck the strip in any drill capable of slow speeds. I use one of these new fangled battery drills.
  5. Fold a small piece of 220 grit sand paper in half, grit side in. (150 and 120 and 100 grit papers are too thick.)
  6. Turn on the drill and gently squeeze the strip in the sand paper.
  7. Sand until the dowel is reduced to 1/16" or less as needed.

Cutting the strip is almost impossible free hand. Clamp the mahogany sheet or scrap to a work bench under a metal straight edge.

You might think you can cut the strip with a knife of some kind. That usually results in a broken strip. This operation actually requires sawing as opposed to slicing. The image below shows the secret to cutting break free 1/8" strips. The tool shown is a veneer cutter. These are available from Woodcraft and other wood worker suppliers. Sorry about the blurry picture. I am but an egg when it comes to photography.

Run the veneer cutter along the scrap against the metal straight edge. It will take multiple passes to cut through.

Here is the square 1/8" by 1/8" strip chucked into my new fangled battery powered drill. I have made so many of these little dowels that I no longer bother to shave off the corners as suggested above. Afte a few broken strips, you get a feel for it.

Just about ready to sand the dowel.

Finished dowel. A further step not shown here is to sharpen the dowel to a point. That allows it to go into the screw hole to at least the depth of the mounting screw. No need for pounding! Fit the dowel to the hole properly and the glue. Hide or PVA will hold as it should. The dowel below is 1/16" diameter.

After drying over night cut off the dowel with a flush cut saw. I highly recommend the Kugihiki (12F24) saw sold by Woodcraft. You can also use a very sharp chisel, but that takes a lot of skill to avoid digging out a great swath of finish. Therein lies the dark side of guitar repair work.

©2018 D.R. Hanna