I know this is more of a mechanical question than electronics, specifically, but some older electronics did involve a fair amount of mechanical aptitude as well (VCRs probably being the most complex and impressive example in my opinion)

What types of plastics are easier to 3D print a replica of? If I'm wanting to get a 3D printer for that purpose, what specs should I look for in terms of ability to 3D print gears? I can get measurements with calipers and use a 3D scanner app since I could just get a ballpark value and manually shape it up in software to match my measurements before actually printing it.

An alternative would be, of course, to glue a gear or lever back together, assuming it's cracked in half rather than the teeth being stripped off. Can I tell what kind of plastic it is by simply attempting to glue it with Krazy Glue / super glue? If I were to do a 3D "scan by pictures" I'd do it before trying to glue it.

It's a more general question, rather than for a piece of equipment that's in front of me right now. If I get a 3D printer it's because I also have ideas for things to make with it as well, not just for repairing things.

 

You can print simple and complex gears on a 3-D printer. But the devil is in the details.
What is the load, torque, size, pitch, geometry, etc.?

I have had an Ender 3D for two years now. This is a basic entry level printer. Today I repaired a toddler's trike by printing this wheel axle end cap shown as white in the photo. Even though the design was moderately complex I think I got it done in about 15 minutes. It fitted the first time, no iterations, which is not the usual case.



There are many occasions for fixing broken items by printing parts on a 3D printer.
I have printed gears for paper shredders which require a lot of torque.

The most basic and common material for 3D printer filaments is PLA. This has universal good qualities for 3D printing but it is not strong. The next step up for strength is ABS. There are many other materials available and I have yet to try anything other than PLA and ABS. If you want to be a perfectionist you can print metal parts.

 

Yeah, if it can print usable gears for a paper shredder, that's more torque than most of the things I would be trying to fix. Generally, it would be mechanical repairs on things like tape/CD/DVD players, and I'm guessing I would want ABS for that sort of thing. The last question I suppose would be what level of precision was required to match the gear pitch of the original part, though I suppose I could "over-print" and then adjust it down with an x-acto knife depending on the situation.

The mechanisms in VCRs in particular use some pretty clever mechanics to have fewer separate motors for things. It's almost like a Rube Goldberg machine, and it makes me want to do something with a marble toy or game that does a lot of cool motions with fewer motors than others might use. A 3D printer would make that a breeze, even if the "standard" gears are still Lego or Vex Robotics: The printer would be for the weird "gear/levers" or gears that have slots in them for other lever "fingers" to ride in.

 

No. You don’t have to overprint. You just need to make accurate measurements and keep trying until you get it right.

Basic resolution on my printer is 0.2mm.
When I try to print a solid shaft it tends to come out about 0.2-0.4mm too large. On the other hand, a hole turns out about 0.2-0.4mm too small. I have to allow for these in the design stage.

 

I moulded and cast smaller gears with the Smooth on system. Vacuum drawing makes a big difference.