
Plastic Gears Are the Future (2017) - peter_d_sherman
https://www.machinedesign.com/materials/plastic-gears-are-future
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nimbius
Speaking as an automotive mechanic in a small chain of Midwest shops, this has
been an automotive punchline for 30 years. It started with chain primary shoes
in Harley Davidson's going to plastic and is seen today in BMW water pump
assemblies.

None of them, not one, is equal or superior to a sintered powder, stamped, or
forged metal gear. Even aluminum in low torque applications will grossly
outperform plastic, for example in sunroof gears. I'll believe the hype when I
start seeing these as drive/bull gears in things like chainsaws.

~~~
upofadown
The plastic gears discussed in the article are more expensive than metal so
chances are the sorts of plastic gears you are encountering are different. The
article could of been more informatively titled "Ridiculously expansive
plastic gears are the future for some niche applications".

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nullwasamistake
Plastic gears are quiet and lubricate themselves. but they're inferior in
nearly every other way.

The materials mentioned are as much the past as the future. High tech polymers
like Delrin and nylon have been in use for decades and saturate their markets
already. These "future" gears have been around forever.

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spqr0a1
You'll find a lot of sintered metal gears these days; Nearly universal in hand
power tools for example. They have similar cost advantage as plastic in
reduced manufacturing expense compared to machined gears but retain the
improved strength and dimensional stability of metal.

~~~
swsh
In terms of a general statement, its a bit misleading to state that sintered
metal gears retain the improved strength of traditional metal gears. They are
a lot stronger than plastic gears, but in the majority of cases (particularly
in hand power tools), they do not have the strength of traditional machined
gears.

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Animats
Someone else on here reads Machine Design?

One of the interesting ideas mentioned is putting some chopped carbon fiber
into the plastic to give it more tensile strength and hardness. That's being
used in 3D printing now. See the current issue of Machine Design. Finally,
decent tensile strength from hobbyist-type FDM 3D printing.[1]

[1] [https://ultimaker.com/en/blog/52718-our-complete-
solution-3d...](https://ultimaker.com/en/blog/52718-our-complete-
solution-3d-printing-with-high-performance-plastics-and-composites)

~~~
dymk
Long, aligned strands of carbon fiber add rigidity. Chopped up, small bits at
random angles does not.

3D printed "carbon fiber" PLA (which is small chopped up bits like you said)
actually does not a lot to increase the strength of the plastic. Parts just
break around the individual CF bits.

IMO, it's primarily a marketing gimmick. And it chews up your hotend _very_
quickly during extrusion compared to normal PLA, because the material is so
abrasive.

If you want stronger prints, you're better off printing in ABS or nylon.

~~~
defterGoose
The samples I got from Markforged refute your point. They are identical parts,
one in plain nylon and one in their chopped CF nylon. The CF filled one is
noticeably stiffer. I'm not sure anyone is making the claim that the CF filled
parts are comparable to traditional composite parts.

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justinator
Although I can see plastic gears being an alternative choice in some
applications, their downsides seem to be many:

* Less load-carrying capacity compared to similarly sized metal gears.

* Molded gears cannot hold the same high tolerances that metal gears can.

* Plastic is less dimensionally stable when compared to metal and this results in dimensional variations due to temperature and humidity conditions.

* Material cost is significantly higher than that of base metals and can vary widely due to fluctuations in the cost of base chemicals.

* Difficulty in attaching plastic gears to metal shafts.

That last point seems especially problematic.

~~~
klyrs
As somebody who's used a 30 year-old kitchenaid and blown the gears on a brand
new kitchenaid on the same recipe... the future sucks

~~~
slavik81
The Professional KitchenAid mixers (i.e. the ones with bowl-holding arms) are
all metal gears, with an electric controller to protect the motor from
overtorque. The tilt-head models are mostly metal gears, but have a single
kevlar gear that's designed to break to protect the motor from overtorque.

Stripping the plastic gear in the mechanics is like blowing a fuse in the
electronics. It's possible it was a bad component, but it probably means
you've overloaded the circuit. If you need more torque, buy the models with
the bigger motors designed to handle it. The main trade-off between the
various mixer models is basically price vs max torque.

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hurrdurr2
Reminds me of the one plastic part they substituted in for the Omega
Speedmaster watch for the second gen movements.

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westmeal
Plastic gears are garbage, I had them on a Pontiac with pop up headlights and
the gears broke pretty much immediately. Replaced them with metal gears
instead and it never had problems after that.

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kjar
I have not worked with nylon, but have with PETG (no gears yet). I wonder how
they compare.

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keiru
This is odly novel, in a silly way

