Last weekend, I found my old label gun- one of those standard doohickeys that embosses that adhesive plastic tape. It had gotten lost in the miasma of home because it didn't work; it was unable to advance the tape. Without obvious screws or pins, I had no reasonable way to disassemble it, so I'd never tried to fix it. This is not a new device; I remember cheerfully using it irresponsibly at the age of 5, so it's at least 15 years old. I noticed, for the first time, a friction lock, holding the two halves of the machine together. If that was held by a plain friction lock without glue, maybe the rest of it was as well? Using a screwdriver in ways it wasn't intended, I found this to be the case, and separated the machine into its two halves- I only broke one of the three friction locks in the process.
A label gun is a really clever device. A plastic hook (the entire thing is plastic, actually, except for the spring on the lever) connects to the end of the spring on the lever, moving it in while the lever goes up but out while it's being pressed down, which goes nicely with the polarity of the ratchet gear the hook is intended to catch. The hook had moved and wasn't catching the gear- partially because the gear had also shifted out of position. That gear connected to the more finely toothed wheel that grips and advances the label tape itself. Farther down on the lever is a small plastic peg, which pushes the embossing wheel. The letter selector is just connected directly to the embossing wheel as might be expected, so turning it directly turns the letter into position; there's a small piece of plastic on a thin, semi-pliable plastic board that acts as a spring, and that piece of plastic catches the notches on the wheel, providing the "click" that tells me when I've got a lever in place. The embosser wheel for the "cut" setting has the only other metal part of the device, a fairly dull blade.
It's fascinating engineering. There's nothing in it that is entirely non-obvious, but given the problem of inventing a way to emboss plastic tape, would I have approached it the same way? I probably would have designed the embossing wheel differently, and I might have made the mistake of building it more like a typewriter- which would result in an unworkably large and unreliable device, probably requiring pressure by a finger on a key that can be done with the entire hand with the lever on the label gun. (The embossing pressure is more significant than might be expected.) I possibly would have made the tape advance mechanism more reliable, likely by having an exposed advance wheel directly- but then, would I have thought of the possible faults of the current ratchet system (the hook moving out of position) had I not seen it?
Disassembling things is fun. Even simple devices can be surprisingly clever.