Printed these for my kids after they got frustrated with their commercial kids' gear toy.
They work smoothly as long as you get the tolerances right.
I use a -0.1mm size compensation in Simplify3D or Slic3r for these, which seems to do the job.
I had trouble with my Inland Green filament when printing the 1-inch and 2-inch gears. The center axle hole tended to shrink and become oblong, making them not turn well. Larger gears printed fine in the green, and other colors worked fine for the 1-inch and 2-inch gears. Still not quite sure what the cause of that is.