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Originally Posted by Andy A.
As an aside, I noticed the other day that aluminum gears were available, and cheap! Is there any marked difference between an aluminum gear and say a nylon equivalent? Any practical experience with them?
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For what it's worth, 188 managed to break a couple aluminum ones last year.... Actually, I ended up misjudging the loads on the gears a little, and ended up with too much torque on one particular pair of gears. (This was, mind you, in a very powerful transmission.) The aluminum gears above it (i.e. spinning faster, with less torque) in the transmission have worked perfectly, without so much as an unsightly mark on the teeth, after two regionals, the championship and an off-season event. For reference, the failed gears (26 & 84 T, 20° PA, 3/16" FW, 0.7 M, 2024-T4) were spinning at 3500 & 1000 (free) rpm, respectively, with around 1.2 HP driving them. The gears of the same size and composition (and the 32 P, 20° PA ones, which are very similar) at 5500 (free) rpm and above were undamaged and still function as intended. We actually bought nylon ones as spares for the upper stages, when we replaced the broken gears--thinking that the aluminum might have been unsuitable for those too--but as it turned out, they were never needed. Without knowing too much about the exact plastic properties under load, I would simply note that the tensile yield point is much lower for the nylon than the aluminum--a definite warning sign.
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Originally Posted by sanddrag
Care to give the source?
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Both of the following stock aluminum gears, and can (theoretically) cut custom sizes of stock pitches, including the ever-popular
0.7 module at PIC; also, be wary of the stamped 5052 aluminum gears at SDP/SI--I don't think they're too precise:
SDP/SI
PIC Design