Fair comment Timo. From my experience a majority of "traditional" Engineers pooh-pooed the introduction of "plastic" intake manifolds, thermostat housings, throttle bodies, etc, as they thought they would lead to high warranty costs due to poor durability. However history has proven the correct use of plastics in such applications as most cars have them as cost effective parts that keep products competitive and available to the budgets of many. I am sure that rubber tyres were laughed at by the wooden-wheel makers... just as steel was inferior to bronze for swords for hundreds of years. But in the right application, appropriately designed plastic parts are "right". I agree that brass is prettier for visible "classic" designs. And all to often, to copy a part in the "wrong" material will lead to early life failures. IMHO Plastic gears should be used in designs appropriate to the hardness, wear and friction properties, tensile and compressive strengths of the plastic. Not simply copies of designs that are suited to brass, steel or other material. And consideration of the temperature, lubrication, impact loading, speed etc. is necessary.
A friend sold his "Mini-mill" because it was full of nylon gears, and his milling, to correct feeds and speeds for the torque of the motor, materials, etc., simply could not take the duty he needed from the machine. But it had been fine when drilling previous models, that didn't have any milling. The gears were Mazak on earlier versions, but obviously just copied in nylon, and failed as expected, on the version he could buy.
Cheers!
K2
, but good enough for a plastic toy.
