Plastic Gear

[Ksplice]

Hi,

i have a question regarding fits for plastic gear shafts within a plastic housing. Are there standards for fitting a plastic gear shaft into a plastic slot.
we are making a gear box with plastic gears inside of it. The tolerances of the slots which the gear shaft fits into have tolerances of +.0012/-.0008. the part is plastic and
these tolerances are really hard to hold on a plastic part.

thanks

 

[MikeHalloran]

Tight tolerances on plasic parts are often a waste of time and money.

If you are rotating a round shaft stub inside of a slot, the bearing area is zero, so one or both parts will wear until the bearing area becomes finite, and the pressure on the area goes below a threshold under which wear is minimal.

It might be better, given that you really want to locate the gears, to start with a finite area and negative clearance, and allow controlled flexure of the bearing. Think two bearing sectors mounted on cantilevered flexures, all molded together of course.

That may or may not be appropriate for your actual problem, since you have given only hints about its nature and severity.



Mike Halloran
Pembroke Pines, FL, USA