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Gear drives and design

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Aviacs

Well-Known Member
Joined
Mar 16, 2019
Messages
912
It seems that the sticking point for amateur built gear drives primarily includes TV "black art" (ignorance) at the theory/development level; and hardening/distortion/post finishing at the practical level.

Let's ignore the first for now to see how feasible some approaches to the second are.

Steel gears for automotive apps are hardened for 2 reasons:
1.) smaller gears with stronger sections & teeth than non-hardened equivalents
2.) wear resistance.

c955 aluminum bronze is as strong (tensile) as a high strength gear steel such as SCM415 or, say 4140. 95Ksi tensile.
It is used sometimes for gears, or more specifially wormwheels for higher stress applications (lots of shear and tooth face sliding pressure) in combination with a hardened steel worm where c954 or other lesser materials fail.

Hardened steel spur or bevel spur gears from automotive apps are widely available.
Strictly from the materials standpoint, what are the limitations & considerations to running a hardened steel spur gear in a 954 or 955 aluminum bronze ring gear for power transmission? (Think Marcotte.) Assume designed for the app in terms of tooth strength & engagement: how will it fail, and how fast compared to 2 hardened steel parts? How much larger (%) or not would the components be? Was the ring gear for Marcotte thermally hardened? As opposed to say, being machined from a prehard (4140 or 4142 prehard, or ETD150, e.g.? ) & perhaps only stress relieved? Nitrided? or?

Alternately, ETD 150 at 150ksi tensile would offer huge strength increase, still machinable, but without further hardening (nitirding?), how would it fare in terms of wear, running with a hardened steel pinion?

There are materials for which cost is the primary inhibition to commodity use for apps in which they *might* be suitable.
So the quesion is, sort of, **** the raw materials costs, are there any likely that could yield as "good" (reliable) a 2 gear mating system in which the driven component could be machined & put in service without further hardening, other than perhaps thermal stress relief? Or is that quixotic on the face of it?
Obviously (i hope) the assumption includes "enclosure, & provision for lubrication typical to the app"

Thanks!
smt
 
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