Plastic Gears Are the Future (2017) | Hacker News Reader

Plastic Gears Are the Future (2017)

machinedesign.com

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.

It correlates well with people complaints about reccuring failure in recent german car brands. Maybe they're just cheaping out or maybe plastic is really not fit for the task.

Yeah, the article seems not much different than the way they were pushing plastic gears back in 1967 during the Space Age, when everyone was always thinking a more advanced "future" is right around the corner. Because it was happening in many ways.

Well, at the rate things were progressing until Nixon . . .

But plastics do not always mean progress, except maybe for plastic sales campaigns. By at least 1984 the timing gears on a regular Ford 302 V8 had become plastic, instead of the metal specified by the original engineering documents.

Naturally the joke is going to precede the punchline.

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".

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.

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.

Metal injection molding is the hot technology in consumer durables.

https://en.wikipedia.org/wiki/Metal_injection_molding

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.

As I understand it, the legendary Sturmey Archer bicycle gear hub used sintered internal components, as early as a century ago. Those hubs have extreme longevity. Of course a bike is not a super high power load, but still it's impressive.

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...

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.

Completely agree. You also run into strength issues at the layer interfaces if they’re not aligned properly in relation to your parts stresses. Fibers do nothing to help this since they don’t cross layers.

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.

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.

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

When I was a child I can remember my mother deciding the same thing when sewing machines began switching to plastic gears.

I agree. Seems a lot of new kitchen devices seems to fail by either some plastic gears stripping or coming loose from the shaft. My mom has 50 or more year old stuff that still works but the newer devices all break. Even very expensive ones.

To be fair the article is talking about new kinds of plastics that might actually be superior to metal gears in the future. The consumer grader plastic gearing of today who's primary advantage (AFAIK) is cost do kind of suck.

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.

It's a little disturbing how cheaply constructed the new Kitchenaids are, especially for their price tag. The ancient one that is a family heirloom weighs about 15-20 pounds more than newer models, and the base is cast steel. The moving parts have proper ball-bearings in them. I think you could set a bomb off next to it, plug it in and whip up a batch of pancake batter.

Wow, you seem to have some very detailed knowledge of plastic gears. It is almost if you copied and pasted text straight from the article.

Yeah, I read the article. I find the the title of the article does not match the content of the article (it's a bit click-bait, eh?) and that's what my own comment really was about.

Did you read the whole thing? Because it was about adding carbon fiber to the plastic to make it as strong as steel

metal gear to metal shaft first, then attach plastic gear for further reduction? Also the article mentions metal-core plastic gears.

I guess then - why not go all-plastic, or all-metal. I fear that if there's large differences in temperature, you're going to start having a really bad time.

You can for that matter pick a glassy self-healing core near the appropriately made metal shaft, continuous rubber as you fill out the radius, and coated harder (UHD) nylon at the outer, but who's to care to make it like that? Ship it with the dough hooks, maybe.

Or as you suggest, printing open-grid metal-inclusion ceramics could go swimmingly for the less green home refactory applications. There goes little Sigfried, recasting his molybdenum iWatch band with the concentrated symmetry-breaking solar from the shed.

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

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.

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

This is odly novel, in a silly way

Reply on news.ycombinator.com