Ukelele Friction Tuner Replacement Washer

Disclaimer: I AM NOT a luthier (craftsperson who makes and repairs stringed instruments) and this is probably NOT a very good repair. If your ukelele breaks, talk to somebody who knows about fixing instruments, not a computer scientist who has a uke and a 3D printer.

I have a ukelele with probably little monetary value, but sentimental value and practical value to me. It's probably on the high-end of "souvenir ukes", in that it's really rather playable (as far as I know, which isn't much), but has "Hawaii" printed on it along with some wooden dolphin cutouts glued on the body, and fishing line around some of the tuners to use to hang/display it. A piece broke, and this is the replacement piece I printed to keep it playable longer.

This model may also serve as a reasonable introduction to some basic OpenSCAD concepts, since the .scad file is heavily documented, both for easy customization, as well as for instruction.

On this particular uke of mine are what are known as "friction tuners" for the strings: there's a tuning key for each string that just goes straight through to the front of the uke head directly turning, to tighten and loosen each string, no gears involved. All that holds the tune with these particular tuners is the friction between a slope on the base of the plastic tuning key/knob and a rather special-looking (and I'd guess nylon) washer sandwiched between that key and the back of the headstock. That washer on one of the tuners (G, not surprising to me since I had the hardest time keeping that string in tune) just cracked into two pieces, so I measured a combination of the key surface that was now easily accessible, and the other washers still intact, to design a quick and easy printed replacement.

So here it is - the replacement part I needed for my friction tuner.

Note: After looking around at search results for "uke friction tuners" it does appear that there are a wide variety of designs, and thus the highly adventurous could probably use this as a starting point to re-design/replace both of the plastic parts of the tuner, to potentially provide a nicer tuning experience.

Note #2: This was one of my first 3D prints, and especially published 3D prints. I don't use ABS anymore, nor MakerBot Desktop, and so don't need a raft anymore, etc. but fortunately most of the detail there probably doesn't matter. The model still should work.

Print Settings

Printer Brand:

MakerBot

Printer:

MakerBot Replicator 2X

Rafts:

Yes

Supports:

No

Resolution:

0.2mm layer height

Infill:

50%

Notes:

I printed this in ABS (blue Octave 1.75mm, if you're curious), because that's what I have/can print. Not sure the importance of the material here, other than that I think the original was nylon or at least that nylon seems like it would have been the "ideal" thing, if fully smooth.

One semi-important note: to avoid a "ridge" in the resulting print, make sure that "Fixed shell starting point" is unchecked (or the equivalent in your slicer if you use something other than MakerBot Desktop). If you let it start all the shells at the same angular position, you'll get a ridge on that inside "bearing" surface, instead of some very small randomly-distributed bumps. I suspect, but did not test, that having a ridge might "feel weird" or wear the tuner down in an undesired way.

If you can get away with not using a raft, or maybe just using a brim (presumably depends on your printer and material), that would be ideal, since on these little parts it can be hard to remove the raft sometimes, especially if your nozzle-buildplate spacing isn't perfect. (I can only remove the raft if I print with my right extruder, not my left, for example)

It would probably be nicer, and smoother, with a smaller layer height.

I set the infill fairly high because this is a small part that will bear some degree of compressive load. Might be unnecessary, you're welcome to experiment.

Post-Printing

Remove raft, smooth bottom

If you had to use a raft, remove it. Same for a brim.

If the bottom isn't nice and smooth, you probably want to sand it, or at least file it. (This is the part that will be against the headstock of the uke.)

If you have a way, you can try smoothing the inside bearing surface a bit. It's an awkward shape to sand, though, so I didn't, and it still works fine for me.

Remove tuner screw and install

Unscrew the screw that tightens/loosens the tuner's tension (not the tuner itself - you can probably leave that mostly fully wound) so you can slide the key off the peg. Then, slide your new washer in place (I'm assuming your old one broke away like mine) then put the key back on. Tighten screw to personal preference and tune your uke!

How I Designed This

I made this with OpenSCAD, and have included a very-highly-commented source file so that you can "make one to order" custom for your needs - since I have no idea how common the particular model of tuner I have is.

When measuring, it may help to refer to the OpenSCAD preview, a capture of which I've included in this "thing" - the shape consists of a truncated cone (the yellow solid) with a smaller, "upside-down" truncated cone, and a cylinder, subtracted from it (the green inner surfaces). You can make all the measurements required from just the key on the broken tuner, as well as the outside of one intact washer: shouldn't need to remove an intact washer to measure.

You can see an original washer in one of the pictures I uploaded, on an adjacent tuner to the one with the printed tuner.

Disclaimer

I am NOT a luthier (craftsperson who makes and repairs stringed instruments) and this is probably NOT a very good repair. If your ukelele breaks, talk to somebody who knows about fixing instruments, not a computer scientist who has a uke and a 3D printer. I have no idea if this will damage your uke, cause your cat to start plotting revenge against you, etc.

As they say, "for novelty purposes only". (That said, if your needs are similar to mine and you find this suitable, I'd love to see your "make" of it!)