Question about printing materials.

With a RepRap which material could we use to print working gears that could handle the stress of say a motor running at 3k rpm with about 90-150Nm of torque?

Probably more likely ABS would be better than PLA as PLA needs much less heat to get soft. At those speeds I would expect heating of the gears to take place potentially causing them to fail or warp

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Experimenting in 3D in New Zealand

This was my fear as well NelsonRap but I also fear the strength, or lack of it, with ABS. I am used to dealing with brass, steel, and aluminum gears and they all dissipate heat pretty well and are strong but plastic I don't know if it would hold up to ~110 Nm of Torque at 3k rpm. That is a lot of torque when you think finger tightening is ~2 Nm of torque.

If your extruder can handle it, you can try polyarbonate.
Richrap tested it and wrote about it here.

I suppose it means you need a very thick gear but that will reduce efficiency I think.

If plastic gears are not available off the shelf at that rating then printed ones are likely not going to work because they will be weaker and made from less suitable materials.

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[www.hydraraptor.blogspot.com]

This is an interesting question. Straight off, I'd say PLA can be ruled out as it doesn't take much of a temperature rise to soften it.

I'm not primarily a mechanical engineer, I've spent most of my time with electronic circuitry and software, so I'd wecome a critique of this thinking...

But according to my initial calculations, I'd say this application is right out of the realm for any kind of plastic gears. Here's my thinking:

Power = rotational speed x 2pi x torque
= 50 rev/sec x 2pi x 150Nm = 50kW

Assuming 10% engagement loss (probably optimistic?), that would mean 5kw needs to be conducted away. I don't see that happening by air convection! I'd assume you'd need an oilbath and forced circulation through a heat exchanger. Even then you'd need the conductivity and heat tolerance of metal gears.

Does anyone have a realistic estimate of typical engagement losses of plastc gears under various lubrication schemes?

any thougts?

Derek
[RepRapKit.com]

derekd Wrote:
-------------------------------------------------------
> This is an interesting question. Straight off,
> I'd say PLA can be ruled out as it doesn't take
> much of a temperature rise to soften it.
>
> I'm not primarily a mechanical engineer, I've
> spent most of my time with electronic circuitry
> and software, so I'd wecome a critique of this
> thinking...
>
> But according to my initial calculations, I'd say
> this application is right out of the realm for any
> kind of plastic gears. Here's my thinking:
>
> Power = rotational speed x 2pi x torque
> = 50 rev/sec x 2pi x 150Nm = 50kW
>
> Assuming 10% engagement loss (probably
> optimistic?), that would mean 5kw needs to be
> conducted away. I don't see that happening by air
> convection! I'd assume you'd need an oilbath and
> forced circulation through a heat exchanger. Even
> then you'd need the conductivity and heat
> tolerance of metal gears.
>
> Does anyone have a realistic estimate of typical
> engagement losses of plastc gears under various
> lubrication schemes?
>
> any thougts?
>
> Derek
>
Spot on. The issue is that plastic can do it but not pure plastic and it seems we can only get pure plastic filaments (where to get polycarbonate filaments from beats me). Normally, from other plastic pieces I have toyed with, the plastic has metal shavings or some sort of crystals in it to toughen it up but that scheme leaves us out.

... print moulds, so you can cast the gears with 2K-resins or low-temp metal alloys - Fields metal 71°C, Roses metal 98°C.

Or lost cast moulding with low density PLA objects and 'normal' metals in moulding sand ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Maybe you could design a gear that has vents and cools itself as it spins, kind of like the brakes on a car?

..or possibly a gear that is assembled from several parts that would increase the strength? Kind of like building it out of glued and/or keyed wedges so that their's more strength where it's needed?

Definitely not as easy as using a suitable material, but it would be an interesting project to try.

These guys sell polycarbonate. I would think that it would be your best bet. [www.protoparadigm.com]

Plastic gears are normally made out of low friction plastics I think. HDPE, nylon and Delrin for instance. HDPE is definitely printable. Nylon is reported to be but might poisonous you. Not sure about Delrin. I think it certainly smells bad if you heat it.

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[www.hydraraptor.blogspot.com]

a_shorething Wrote:
-------------------------------------------------------
> Maybe you could design a gear that has vents and
> cools itself as it spins, kind of like the brakes
> on a car?
>
> ..or possibly a gear that is assembled from
> several parts that would increase the strength?
> Kind of like building it out of glued and/or keyed
> wedges so that their's more strength where it's
> needed?
>
> Definitely not as easy as using a suitable
> material, but it would be an interesting project
> to try.

That would be interesting but not sure it would do any good in an enclosed environment like a gearbox.

gtg252b Wrote:
-------------------------------------------------------
> These guys sell polycarbonate. I would think that
> it would be your best bet.
> [www.protoparadigm.com]
> pby/filament_material-polycarbonate/


Ewwwwwweeee, 24 dollars for a half a pound? WOW. Still, very nice to finally see someone selling it and it earned my bookmarks for future testing.

Thank you.

nophead Wrote:
-------------------------------------------------------
> Plastic gears are normally made out of low
> friction plastics I think. HDPE, nylon and Delrin
> for instance. HDPE is definitely printable. Nylon
> is reported to be but might poisonous you. Not
> sure about Delrin. I think it certainly smells bad
> if you heat it.

Found this @ [iplasticsupply.blogspot.com]

Quote

Nylon vs. Delrin (Acetal)
Nylon and Acetal (or brand name Delrin) are the two most popular plastic mill shape materials sold.

The East Coast of the US prefer Nylon, while the West Coast prefers Acetal. Nylon was invented by Dupont in 1935, while the Delrin was invented by the same company in the early 50's. The Nylon product made great in-roads throughout the manufacturing sector, and is a wonderful material for endless applications. The one down side, which was exploited by suppliers on the West Coast, is Nylons moisture absorption. The Delrin material has a very low moisture absorption rate, and Nylon has a rather high moisture absorption rate. The moisture absorption can cause a part size fluctuation that may affect final part size or part tolerance. The Acetal resins are much more dimensionally stable, but a bit more brittle.

Both materials machine well, and can be worked on/with most common machine tools. Both have very good mechanical properties and can be used for things like gears, slides, housings, and many more. They both are considered 'self lubricating' for parts replacing metals requiring grease.
For more differentiation, review our data sheets for each material.
Compare with other materials at www.iplasticsupply.com

Just ran across this post.
Both the Nylon 6/6 and Acetal (Delrin) are FDA approved as standard sheets and rods.
The Acetal when heated to burning will release formaldhyde fumes - not good. Stay under, and it is extremely safe and non-toxic. Many parts on machines for food processing are made from this Acetal stuff. Liked the post about Nylon versus Delrin.
Thanks

Has anyone tried to extrude delrin? A Google search puts it at 175 Celsius for the melting point. I was wondering if it was safe to recycle the material by making filament in a filabot or other filament maker.

I would rather go with Nylon for now. Taulman makes Nylon filament, already tested it and deemed it safe as noxious fumes and gases stayed well under recommended maximum values even in a sealed chamber. I have ordered a spool of this filament and will try it out. It wasn't really cheap at 34€/pound (the price quoted by Taulman himself was 19$/pound, but being in Europe and all...).

I will prefer Nylon......