Unusual transplant: 12-string guitar tuners save a mandolin

Issue 138 April 28, 2011

Unusual Tuner Transplant

unusual tuner transplant

12-string guitar tuners saved this Martin mandolin

This 1950s Martin A-style mandolin recently came into our shop for a tuneup, presenting an oddball repair challenge.

At age 60-plus, this mandolin was still in good shape, but its tuners weren’t working well, which is usually the case with such old machines.

After taking them apart and cleaning the pieces, we lubed them with a small dash of Tri-Flow. That helped, but they still didn't work smoothly enough to rely on in a performance. New tuners were needed.

So here was a puzzle.

The spacing between string posts on these tuners was .922" — unusual for a mandolin.

Unusual Spacing between String Posts

We now carry replica tuners with the perfect look, but they don’t have this oddball post spacing and the slightest mismatch between posts and holes prevents a tuner from working smoothly.


Maybe these tuners were exclusive to Martin, or maybe Martin took whatever the tuner manufacturers offered. In any case, we didn't have a replacement, and a web search turned up no modern replacements that would fit.

My shopmate Gene noticed our 12-string tuners had this same .922" post spacing. Gene suggested we perform a transplant.

The 12-string tuner screw holes lined up with the holes in the peghead, too! And the string posts were plain and straight like the mando tuners (it’s just that there were too many of them).

If we were to chop off two of the gears, these guitar tuners would fit this mandolin perfectly. An excellent solution!

An Excellent Solution

Next to each string post hole you see a pair of small gouges to accommodate protrusions on the bottoms of the old tuners. The new tuners don’t have these protrusions, but they neatly cover up these scars.

Check it Out!

Golden Age Mandolin


Golden Age A-style Mandolin Tuners are designed for vintage-style mandolins. Improve your tuning without giving up authentic looks. Bright finish, or relic.

Take a look at all 6 varieties.

I removed the posts and scribed a line where I wanted to make my cut,

Removing String Posts

then used a .015" gauged saw to cut through the plate.

Gauged saw

I then followed up with a 3 corner file to smooth out the edges,

Smooth out Edges with 3 Corner File

then re-assembled them for their new life as mandolin machines.


The diameter of the new posts was about .005" larger than the old, so the pegholes needed to be reamed just the slightest bit — about half a turn with our standard size reamer. This was quick and easy, and the result was invisible. (Martin hadn't installed peghead bushings, so there was no problem with a mismatch between post and bushing.)

Reamed the Pegholes

The screws fit the old holes — no need to plug and drill new holes. Easy!

Posts and Bushings

This old Martin’s back in business and staying in tune better than ever. I’ve got to hand it to Gene for his resourceful thinking on this project. A tuner transplant — why didn't I think of that?!

Finished Tuner Transplant

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