Author Topic: Cheapest 3D printer Suitable for Gears?  (Read 894 times)

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Offline ksquaredTopic starter

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Cheapest 3D printer Suitable for Gears?
« on: November 07, 2013, 09:50:24 PM »
Would anyone be kind enough to tell me the cheapest 3d printer suitable for printing gearing?

It would be incredibly useful if I could simply print custom gearing solutions - even if I have to print the gears individually but I don't know how well suited a typical low-end printer would be for this.

To summarize, I'm fairly indifferent about the material properties, owing to budgetary concerns, if I can get something hard enough at room temperature of sufficient precision to act as a well-(good)-(okay, half way decent)-meshing system.

Particular Case Details:
--The gears need be 2-3 inches in diameter, and they will bear only a very light load (much less than 1 foot pound), so the material need not be strong or machinable.

--The tolerances need only be sufficient for the teeth to mate robustly, preventing any hang. Unfortunately, I do not have a sense of what tolerances will allow gears to mate properly.

--(If the machine is precise enough to print a hole to statically mate with a shaft of a specified dimensions due to friction, excellent. If not, I can probably improvise a tiny shaft hole with adhesive.)

--Because this may be used in close proximity to pavement, a melting temperature in excess of 100F is desirable but not required.

--Because any given element will interact kinetically only with other elements that have also been 3D printed (except a metallic shaft), compatibility with external resources is not required.


I would be grateful for anyone who can shed some light on this!
« Last Edit: November 08, 2013, 01:07:32 AM by ksquared »

Offline jwatte

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #1 on: November 08, 2013, 03:13:47 PM »
WIth the cheap plastic fusion printers, either it works, or it doesn't.

You can find a $300 machine (in a kit) that prints in PLA, which is a fine plastic (I use it for some bike parts, keeping mud guards in place etc.)
The minimum size (filament width) is said to be 0.4 mm, but there is some expansion so I'd plan on the minimum thickness being thicker. Also, at very small thicknesses (under 2 mm) you get significant risk of delamination and fragility.

Going up to a $2,000 printer that still does plastic fusion, you don't get better mechanical properties -- you get faster printing, better material handling, larger print area, etc.

You'd need to use another printing model -- lithographically cured resin, or laser sintered metal -- to get significantly better material properties.

So, I'd suggest getting the $300 printer, and seeing if it works for you. It can realistically print about 3.5"x3.5" objects: http://printrbot.com/shop/printrbot-simple/ (significant assembly required.)

Another option to try out 3D printing is to send your STL files off to shapeways.com. They can print in a variety of technologies for you, and you can do a fair amount of printing at their prices before you would have saved that money by buying your own printer. Especially if you go with high-end methods, like selective laser sintered metals.

Offline bdeuell

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #2 on: November 10, 2013, 06:37:27 PM »
Do you really need custom gears or could you use standard gears?

Fused deposition modeling (FDM) (which is what is most common in hobby level 3d printers) as mentioned before is limited by the size of the filament extruded. I assume that you are not considering any industrial as they are going to cost in the tens of thousands. Given the diameter of this filament is about .015" on the newest  hobby printers I wouldn't count on your accuracy being any better than that. Some very crude gears have been made on theses machines but they are no where near the quality of injection molded plastic gears.

Due to the poor tolerance capability the teeth will need to be designed with very large clearances, which will result in a large amount of backlash. this may or may not be an issue for your design. FDM will also leave a rough surface finish. gear design relies on sliding surfaces so a good surface finish is important for smooth, quiet and efficient operation. It will also lead to accelerated wear.

I would recommend finding some cheap injection molded plastic gears that are properly designed. you can buy them from a site like SDP-SI for a couple bucks apiece, depending on size. Or salvage them from old toys or equipment. cheap gearbox kits with small plastic gears are quite common and they can be configured for many different gear ratios. The challenging part may be finding them in the larger 2-3" range for a low cost. Is there a reason they need to be that large?

Given the limitations of FDM I personally would not use printed gears in any application that did not have very light loads and low speeds (i did not see any mention of the speeds you expect to see). Given the alternative of injection molded gears I would only print gears for applications where standard gears re not available such as the non circular gear mechanisms that can deliver varying gear rations through their cycle.

As for the press fit ... press fit tolerances are usually around .001" or less ... a far cry from the .015" of the printer. If you plan on using a press fit i would use a post machining operation and ream the hole to the desired size. The better design for plastic would be to use a knurled shaft that will allow the ridges to key into the plastic.


Offline jwatte

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #3 on: November 10, 2013, 08:50:22 PM »
Quote
gear design relies on sliding surfaces

The whole point of proper involute gear profiles is that they end up with a rolling, non-sliding contact.
However, you probably won't get to that point of precision with hobby plastic printed gears.

Offline bdeuell

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #4 on: November 10, 2013, 09:09:24 PM »
Jwatte - Thanks for the correction

I still support that the surface finish is key to having smooth, quiet, efficient, and low wear operation.

Offline jwatte

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #5 on: November 11, 2013, 10:30:46 AM »
Quote
I still support that the surface finish is key to having smooth, quiet, efficient, and low wear operation.

And I support you in supporting that :-)

Offline bdeuell

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #6 on: November 22, 2013, 08:40:37 PM »
Quote
gear design relies on sliding surfaces

The whole point of proper involute gear profiles is that they end up with a rolling, non-sliding contact.
However, you probably won't get to that point of precision with hobby plastic printed gears.


@jwatte - I was doing a little research on gear tooth profiles prompted by another one of your post on cycloidal drives ... anyways I found that there is actually some degree of sliding between the tooth faces on an involute profile. The sliding velocity is however zero at the pitch point.


Offline jwatte

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #7 on: November 22, 2013, 09:44:45 PM »
Right -- in the perfect case (zero backlash, infinite pitch, etc) we get zero sliding, but I've found that real mechanical systems aren't as close to that as I'd sometimes want :-)
Thanks for providing the additional detail!

Offline hobbes

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #8 on: November 23, 2013, 03:16:26 AM »
A CNC machine might do a better job making gears than a 3d printer.

Offline jwatte

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #9 on: November 23, 2013, 12:58:55 PM »
Funny you should say that, as I tried that, too :-) (I'm assuming you mean a CNC mill -- a CNC lathe isn't particularly useful for gears, for exaple.)

The main problem there is the radius of the end mill. If you want a reasonably small radius (1/64" or smaller) then you also get a very small cutting depth, so you can't really make gears strong enough to carry real load.
There's also an option to cut a gear crosswise with an end mill profile that matches the gear profile you want to cut; this requires a fairly expensive end mill, one per pressure angle / pitch / diameter combination!

Back when I did this, I ended up laser cutting the gears from plastic; that was the best compromise for my project. If making real gears is important, getting a small manual gear hobber is probably the best option. There are manual ones that aren't terribly expensive or complex, although Google currently fails me (all I get is $100k options from China...)



Offline waltr

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Re: Cheapest 3D printer Suitable for Gears?
« Reply #10 on: November 23, 2013, 01:42:12 PM »
Quote
laser cutting the gears from plastic

That would be a good option for low quantities.
Water jet cutting or EDM (Electro Discharge Machining) may be other options.

 


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