I'm finishing up the teardown of my old Canon Pixma MX340 multi-function inkjet. After completing my exploration of the print carriage encoder, I looked over my workbench and saw: Hey, the automatic document feeder (ADF) gearbox is still intact! I'll take it apart now.

Since I don't expect to need to know how to mass-produce a paper feeding mechanism, I'm not going to spend too much time to understand exactly how all the mechanisms work together.

Mechanically, a stepper motor drives at least three shafts, each turning a set of soft rubber rollers. I wonder if these gears are all specifically designed for this device or if they might be standard parts from a catalog. If the latter, I would love to browse through that catalog.

As with the rest of the device, everything came apart nicely now that I recognize the system of clips Canon engineers use to ease disassembly and repair.

The ADF lid is likewise an assembly of injection-molded parts held together with easily disassembled mechanisms. Within this assembly I noticed several freewheel mechanisms implemented with a coil of metal, now that I understand what I'm looking at.

I appreciate precision ground metal shafts, much more satisfying in the hand than an injection-molded plastic shaft. I keep thinking it would be cool to reuse them in another project, but due to their precision nature they're typically tailored to a specific purpose and not easily reused elsewhere. They usually end up just as toys for me, roughly analogous to fidget toys but with no moving parts. When my projects need metal shafts, I end up having to cut new ones tailored for my project. My shafts are not as precise as these mass-produced units, but good enough for their own respective purposes.

Next up: the original finish line of my teardown, the main circuit board itself.

This teardown ran far longer than I originally thought it would. Click here to rewind back to where this adventure started.