One problem I always run into with rotary motion: gearing. Finding gears of the right diameter, thickness, and thread pitch is always such a stumbling block for me. Most sites that sell gears to fit their motors have a small selection, and sites that sell gears are very hard to navigate (only to find out they don't sell in quantities <1,000 units). I end up having them laser cut out of HDPE online. Wish there was an easier solution.
This was PRECISELY the problem that led me to get a 3D printer. I have successfully printed many gears using PETG for my projects. Now, they are physically bigger than metal gears for the same strength, but that hasn't been an issue in my applications. Using the wishbone-style gear teeth with 3D printing is remarkably sturdy. Of course the other way is: buy motors with (metal) gears that are close to your need - then you only need to 'transform' that motion a little bit.
I also can cut involute gears on the (mini-) lathe or mill. You want to practice this skill because being off just a little means you have a useless part. I have found 3D printing more convenient and forgiving.
Belt drives are also very annoying. Naming conventions are inconsistent and obtuse. Parts materials differ, and a whole lot of stuff seems to be custom.
in Servos and steppers, there are also weird mixes of metric and standard sizes - e.g. Nema 34 motors often have 1/2" (12.7mm) shafts with 5mm keyways. No idea why.
Finding gears or pulleys for my purposes has 100% of the time resulted in some machining and lathe work to take off the shelf parts and make them work for my applications.
The key, if you can, is to choose a NEMA standard motor, there are tons of suppliers you can get a nema gearbox from. They get pretty small, but if it's amaller than the smallest nema size I'd go to a place like stock drive components which stocks thousands of gears.
The challenge is that gear tooth geometry is often more than 2d, so laser cutting may not be the best solution for longevity. For a quick and dirty prototype it's certainly fine.
standalone gear boxes also seem to be really really expensive
what i would really love is a set of compatible gears that work from the same shank and would allow easy construction of 1:2 or 1:4 or 1:8 and i could compose. maybe some 1:1 bevels too
Stock Drive Products and Berg are the classic US small gear, bearing, and accessories suppliers. I've used those two. KHK (Kohara Gear Industry Co., Ltd, Japan) is now active in the US.
The classic Boston Gear Gearology course is no longer online at Boston Gear, but there's a copy here.[1] This gives a quick overview of the minimum you need to know about specifying gears.
It really comes down to the fact that gear shaping/cutting machines are quite specialized machines. Therefore demand a higher cost to buy (machines cost) and setup (tooling cost).
For example a single gear shaper cutter is on average $700-$1000, and that's for a pretty standard and brand new cutter.
So without taking into account actual time to set up the machine, program it, and feed it material. You are already having a high overhead. So the only real way to deal with that cost is in volume or cost.
But when looking at the hobby market, volume is out of the question (who wants to buy >1000 of one gear for a personal project) and cost is out of the question ( if it's so expensive, I might as well 3D print or laser cut or waterjet some)
If you watch enough tool teardowns (AvE, etc), most gears are sintered metal or plastic. I'm sure large industrial applications use machined gears but it looks like consumer-prosumer space goes for much cheaper fare.
standard gear cutting arbors aren't that expensive, but are often for standard module gears and the gear form is an approximation that applies to a given range of gears.
I came here to say exactly the same thing. I'd love to find a kit or gearbox than can gear up/down a simple stepper motor for Arduino projects. The HDPE laser cut is a good idea though, I'll give that a try.
Inkscape has a plugin for gear teeth pitches. I no longer have the link to it (or the install because it was 13 years ago), but I was able to cut a whole bunch of HDPE gears. THe next hard part was getting hubs to match with them. :|
