Reproducing tiny plastic gears for vintage 'gear'

[Jeff_Birt]

I love the 4-pen Alps printer/plotter mechanisms that were used by dozens of manufacturers back in the day. Repairing then and keeping them working is a struggle. The #1 failure is the pinion gears on the stepper motors. Being a simple spur gear, it was possible to commission getting a large number made at a reasonable price. These brass gears will last a lifetime.

The second most common failure is the Y-Axis (paper) anti-backlash gear set. This is a set of two interlocking gears that are spring loaded to reduce backlash on the Y-Axis. The outer gear is pressed onto a steel shaft and cracks (like the plastic pinions do.) Being quite complex machining replacements if not practical commissioning a mold is far too expensive.

Thankfully now we have relatively inexpensive 3D printers that use a UV curable resin. I picked up a low cost one recently, on sale, and have spent the last two weekends trying to reproduce this gearset. I finally got what looks to be a workable set after about 10 tries. It took a while to get familiar with printing with resin as it is unlike FDM (filament) printing.

Attached are a few pictures with a ruler for scale. The resin used is no ideal for this application but does produce very good detail and is inexpensive enough to experimentation. I also have some 'ABS like' resin which I'll try next if the design proves feasible. It is tougher and will make a better long-term replacement.

I'm excited about being able to reproduce small mechanical parts for out old calculator and pocket computers. This opens up new possibilities.