Tuning Machine Gear Issue

[Tom Haywood]

I'm stumped. This problem is occurring on an American Conservatory bowl back which a customer really wants to play for sentimental reasons. Somewhere in the past the headstock split through some of the tuner holes on both sides - two splits running from just above the nut to the top of the headstock. The original repair, probably done in the 1940s, was done with small nails and was coming apart. The tuner holes were in good shape except for being slightly separated along the cracks. I wicked HHG into the splits and pressed it all together tight and level. The old tuners (4 on a plate) were cleaned and mounted and worked fine, except for one closest to the nut. Ultra-light strings are on the mandolin. The tuner in question worked fine until the string was almost in tune. Then the cog would lift off the plate until the the gear was not firmly in the channel, causing the string to slip. A set of SM Golden Age Restoration tuners were put on, and after a couple months of playing the same problem is occurring. There are no grommets in the holes, and the posts appear to move slightly under tension as they should. I wonder if the steep angle of the headstock combined with modern strings has something to do with this, but maybe it is something simpler. Anybody seen this problem before or have any ideas?

[HoGo]

You have bad headstock holes. Most likely the one hole is not aligned well with the rest and under tension it causes wear on the plate.
I'd recommend plugging all the holes and redrilling with proper sized drill (usind precise drilling guide) so all post are held perfectly upright and turn loosely.

[Tom Haywood]

Thanks Adrian.

[pops1]

If all the other tuners are working good, you might first plug and redrill the hole that is giving you the problem.

[HoGo]

If all the other tuners are working good, you might first plug and redrill the hole that is giving you the problem.

I'd prefer doing all at once as if one hole is that much off, I bet others are not close to perfect either and the plugging and drilling one or eight holes doesn't make that much difference but the result may...