FRETS.COM Thumbnail Article
Please click on the small images to see the large views.

Tuner Bearing Replacement
© Frank Ford, 2007; Photos by FF
I don't know exactly how this damage occurred, but the tuner bearing support was worn or broken completely through. This tuner is original equipment on a Martin guitar made in 1867, so repair is a much better option than replacement.
My challenge was to replace this bearing post without disturbing the cracked button or taking apart any more of the assembly than necessary .
I started by using my flush cutting end nippers to cut the protruding bit of the worm gear support rivet.
With the post and gear removed I was able to push out the bearing out, revealing the rectangular mounting hole.
Next I measured the diameter of the bearing area so I could fabricate a new bearing.
After making a brass section with a long "foot" the same width as the length of the rectangular mounting slot, I drilled the length to the same diameter as the bearing, and rounded off the piece on the milling machine.
I'd made this part in a long section so I could slice it and have several identical sections. That way, I could experiment with my fitting technique, and not worry about messing up.  I used a .010" slitting saw.
Here's my batch of little bearing "blanks."
I sliced the foot of the bearing with that same slitting saw blade, splitting it right up to the hole.
After "improving" the shape by filing, I finished the part with 600 grit abrasive paper and buffed it to a high shine.
I knew I'd have to hammer the little rectangular tab to rivet the bearing onto the plate, so I spent some time making a little anvil to support the part.  I used a piece of 1/4" hot rolled steel scrap and filed the shape to match the bearing.
Bending the bearing "open" so I could wrap it around the shaft put a fair strain on that brass, so I annealed it with my propane torch.  The heating process also gave the brass something of an oxidized patina.
Once I had the bearing bent around the shaft and squeezed back into shape, I used regular soft solder to fill the saw kerf and solidifiy the piece.
With the bearing in my little shaped anvil, I was able to hammer away with my small ball pein to form the backside rivet.
All done.  The new bearing is as solid as the others, and the worm shaft is well supported. I hope it can last another 140 years.
Here's the final view. 

Back to Index Page