Looking at the inner workings of my retired Canon Pixma MX340 multi-function inkjet, I understood many details to be results of making very domain-specific optimizations for mass production. Such details wouldn't be useful doing anything else, and time and effort required for such work wouldn't make sense for hobbyist-level projects.

On the other hand, I also found the design reflected a priority for easy serviceability. Something I do aspire to in my own projects. I know serviceability hasn't always been a design priority in my own projects and it shows. Some people who had build their own Sawppy rover got confused or encounter problems in assembly or repair. By not putting any effort into serviceability, I have implicitly assumed I'll always have my workbench and that wasn't always true. Fixing my Sawppy rover in the middle of Maker Faire Bay Area was a huge pain.

With that experience I now recognize effort went into making the MX340 easy to service. Every fastener is a Philips-head screw, the vast majority of which can be turned by a #2 Philips driver. Nothing is glued down, welded, or hydraulic pressed. Everything can be taken apart and reassembled.

This is the result of deliberate decision by Canon and they had allocated the engineering time to improve serviceability. Some of which is quite elaborate: look at this mechanism securing the shaft that hosted the rotary quadrature encoder. This assembly could have been press fitted into the stamped sheet metal chassis. Simple, reliable, cheap. But that's not what Canon did.

They designed this plastic bearing carrier so I could turn its arm...

... and lift the entire assembly out of its stamped sheet metal chassis. No tools required.

Why did Canon decide to invest this engineering effort? I assume there must be a monetary payoff. Perhaps this reduces their costs to service devices under warranty? Whatever their reason, my teardown experience indicate it is a very rare thing among consumer electronics manufacturers. It makes teardown projects like this one so much easier and more rewarding. I chose not to reassemble the paper tray sheet feed gearbox to see exactly how it worked, but because it was easy to non-destructively take it apart, I could have done so and that's is a luxury I don't take for granted. Up to this point, and as I proceed forward.

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