Printing replacement gears and knobs that actually last: material and orientation

Gears: print in PETG or nylon (not PLA for anything near heat or under constant load), 100% infill or 6+ walls, teeth in the XY plane (lay the gear flat) so layer lines do not run across the teeth. Model from measurements of the broken part plus the module (tooth size): count teeth, measure outside diameter, module = OD / (teeth + 2). Knobs: ASA for appliances, a heat-set insert and set screw, D-shaft hole printed 0.2 mm undersized then reamed. If it is a timing gear in a printer or an appliance that will cost $300 if it fails, buy the real part; everything else, print it.