1/2 hp motor driving PLA gears? Crazy?

I have need of a somewhat light weight winch. It needs to be able to pull about 500 lbs of force.

I've been pondering how large the gears would have to be to print them out of plastic. They would need to be involute gears because I'd like to build a two speed transmission using them.

Nylon?

How crazy is this idea?

Have you played around with this?

[www.rushgears.com]

You could maybe start with the derlin numbers to at least get some idea. Maybe sandwiching the gear between metal sheet could discourage delamination too.

It's not that hard to cast the pla gears into aluminium after printing if you need something stronger.

PLA gears have a tendency to destroy themselves - the teeth heat up a bit, and become tacky, increasing friction and causing further heating, until you have a large blob of semi-molten gears that get thrown around. I've never printed with nylon or abs, but you'd have more luck with those (even if it still didn't work.). Like konwiddak said, just cast them if you want to use printed pieces.

Thanks for the info.

Instead of aluminium, you could also cast it in bronze as it is better suited for gears. Don't know the exact requirements of doing so, but two guys I know tried that out.

I'm actually planning on running PLA gears with 1kw electric motor. The load would not be great, the machine is planetary ball mill and the gears are only supposed to make the sun gear setting to rotate counter-clockwise, the load is carried by an axial arm made out of steel, but the speed would rise to 3-5 revolutions per second. I live in cold climate country so the heating shouldn't be an issue. Previously I tested gears made out of plywood and they worked surprisingly well for nearly 10 hours of testing, but the noise was absolutely unbearable. The diameter of the involute gear is about 300mm and there are 3 smaller gears about 100mm in diameter. The gears should be helical with 10 degree angle, width 20mm. Should the half-life of the PLA gears be calculated in minutes, hours or days?

Edited 1 time(s). Last edit at 09/02/2014 12:14PM by Reprint.

This guy seems to have made it work... don't know about the lifetime, though:

[www.youtube.com]

I would be more concerned with the shaft hole wallowing out before the teeth failed, and how long that would depend on the shaft size.

As mentioned, you could cast them. That doesn't mean you have to cast them from metal, there is plastics that would hold up far better than PLA.

What about greasing the gears to reduce friction and therefore heat?

Would white lithium grease react with PLA?

Spray graphite?

I am designing a gearbox right now and need to get some white lithium grease for my car anyway...

Some discussion on this aspect here: [forums.reprap.org]

Andy

Edited 1 time(s). Last edit at 09/03/2014 04:55PM by ajayre.

To paraphrase Earl Scruggs, just because it's possible play any type of music on a banjo, that doesn't make it a good idea.

[www.ewp.rpi.edu]

This indicates that PLA can be used for gears for some extent. It is certain that they're not supposed to be used in high torque reduction gears where loads on gear heads rise to significant levels. And of course they might not hold up for thousands or tens of thousands of hours.

I'm interested in lubrication too. Silicone oil and grease seem to be tested and working with PLA.

Quote
Reprint
[www.ewp.rpi.edu]

I'm not sure I'd put much stock in this study. Only one aspect of gear design (contact stresses) is examined, and even at that, the tooth profiles are nothing close to real involute gear teeth. The line contact present in real gear teeth will produce much higher contact stresses than with the surface contact analyzed in the paper. Bigger issues might be tooth bending stresses, wear, delamination, heating, etc., as people have mentioned.

Have you considered printing it with Delrin? It's extremely tricky to print with, harder to do so than ABS even from what I hear, but it's qualities may make it the best suited material for printing gears.

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"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus