I've found the easiest way to work with gears is to 3d print my own. That way you can (semi-)easily match them to the shaft diameters and to each other, and you can sometimes make them integral to the things they're driving, if those things are 3d printed too.

That's on my list to try!

I made a rotational-to-linear translator with adjustable linear depth using 1/4" HDPE and a gigantic OMAX waterjet cutter. The pitches were perfect to within 0.0001", but the design was five layers of gears, some were planetary, others slid on cams. Trying to connect planar gears is very effing hard when you can't use a pass-through collet (e.g., the pinion has to be FLUSH but yet allow rotation).

I doubt you can get 0.1 thou tolerance out of a water cutter.

Sorry, I was off by one decimal place.

http://info.omax.com/precision

Average of ±0.003" (±0.08 mm) and up to 0.001” (±25 µ)

About the same as a laser cutter.

You set it to cut very slowly and it angles the head to account for motion and material deformation (you need to program the type of material).

I would suspect GP is referring to precision as amplified through the gear chain

I print a lot of 3d gears too, but the one I couldn't manage was a fine pitch worm gear (I purchased the worm, and tried to print the gear) to drive a heliostat. Technically, I was able to print it and mount it, but tiny imperfections led to accuracy problems. I've had excellent results with larger herringbone gears.