I'm doing my first big organized bike ride in a couple weeks - the STP (Seattle to Portland). I was thinking it might be fun to do a 3D printed part or two for my bike. I had originally considered a 3D printed belt-drive - but the more I looked at it - the less realistic it seemed.
A more realistic idea was a shifter. Specifically - a friction shifter. The first version took an afternoon to design / print - and surprisingly worked pretty well.
While friction shifters don't "click" into gear like index shifters - they have several advantages.
A slightly bent derailer or worn cables / housings will cause an index shifter to miss shifts (resulting in that click that won't go away). A friction shifter is much more tolerant of minor problems like these. This is why shifters on touring bikes have a friction mode.
My bike is a 1x7 (no front derailer) - so it's been pretty well tested at 7 speeds. This shifter should work for front and/or rear derailers - and pretty much any number of cogs.
The files for this project are published on Thingiverse. See there for printing tips.
The shifter takes about 1.5 hours to print - and only needs a few non-printed parts:
2x #10 Nylon Lock Nuts
2x #10 x 1" Bolts
3x #8 Washers (yup - they fit)
The screw works as a friction adjustment and allows for a large amount of wear before anything needs to be replaced.
I've put about 150 miles on this shifter design (about 80 so far on the last version) - with very few signs of wear.
Expect a few friction adjustments in the first mile or two - then again around mile 50 (probably less frequently after that).
How long will it last? I have no idea - but I suspect a good while - maybe 1000's of miles?
I've done a fair amount of "hardening" to the design and should hopefully stand up to normal use.
Of course - if you're really concerned about reliability - you can always print a backup.