3D Printed Planetary Gearbox! Resin vs FDM Printing?

Is resin printing useful for gears??? Results from my experiments show that the parts printed from resin are much more brittle and prone to failures from repeated loading. In this experiment, the PLA I was using was Inland "Tough PLA" and the resin was "ABS-Like" clear resin. This gearbox will be used in some future projects of mine so stay tuned for more!

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[xanxanariac]

I'm just impressed how clean the PLA prints

[ericseidel]

Keep in mind that there is only 1 tooth in contact at any moment. The bigger the tooth, the stronger it is .The minimum for teeth interference is 13 teeth for small pignons. Depending on the needed gearbox size, you want to choose the biggest possible gear modulus that allow for at least 13 teeth. Bigger modulus = stronger teeth and bigger contact area. Also fit tolerances and surface finish induced by manufacturing process have less impact on bigger teeth. Your pignons look like they have about 20 teeth for 10mm in D, then I assume 0.5 modulus. SO you could choose a bigger modulus for the teeth. In this case 0.75modulus would be the best = 15 teeth would be WAY stronger of course outer ring will also have a reduced number of teeth, but you can keep you diameter and ratio.

[coctailrob]

Could the WD40 be having an effect on the resin parts? It can make certain plastics brittle. Perhaps try a silicone grease.

[stevencrawford]

So one reason your resin appears to be as brittle as it is, is that you are absolutely baking your parts with UV. At 4:22 in the video you had the UV timer set for 10:00.

That's about 7 to 9 minutes too long, i believe, depending on your resin and the individual part sizes.

I've been printing UV resin for about 3 years now, thousands of parts, and i can tell you that curing time has a BIG impact on brittleness. My initial tabletop game pieces i cooked at about 15 minutes each. During a game session the board was accidentally tipped onto the floor. Of 12 parts, all 12 shattered. Some into seemingly individual resin molecules.

My current go to resin for tabletop durability is Elegoo ABS (80%) mixed with Sirayatech Tenacious (20%). Parts are cured for 30 to 60 seconds per side. This results in an excellent mix of durability and flexibility for tabletop miniatures.

Obviously, for planetary gears, you probably don't want something with much flex. However, you definitely don't want something that will shatter with shear force either.

Recommend you experiment with your resins and curing times (A lot less than you showed) and see if you can dial in something better.

All that said, i think even basic PLA will better in this application than even the best resin, although some of the Sirayatech resins may give that a run. PETG might be even better!

[omoralopez]

Very nice video! From our experience, basic resins behave more like glass than plastic. The "ABS Like" and "Nylon Like" resins have shown us to have a little more mechanical resistance and flexibility. Although, as in all things, there are different qualities.

[BlackBirdFactories]

In Addition to the other suggestions: you UV cured the parts for 10min. My usual curing time lies around 5min. To much exposure will damage the integrity of the material and make it brittle

[guyb]

Probably already mentioned, but its common to mix flexible resin with standard resin to reduce the brittleness. It opens a whole can of worms though, and it really fair to only test and compare with over the counter products.

[ericvenneker]

I did not expect that. I would have thought that the resin gearbox would be more durable. Great test. Thanks 👍

[Torskel]

You need specific resins for industrial use like this, you could mix 2 resins as well to achieve strong but yet tough

[gabrielenitti]

to make the gears last longer, try swapping the WD40 for some grease meant for plastic and when threading screws directly into plastic, tighten them by hand and before tightening, turn the screw counterclockwise until you feel it dropping into the already existing thread, so you don't run the risk of chasing new threades every time you screw it back together.

[jayliu]

Finally someone who is using appropiate screws for plastic parts. There are way too many designs out there with machine screws and brass inserts or nuts

[DprintedLife]

Great video and thanks for the shoutout! I've been dealing with some of the weaknesses of resin prints lately in my own projects, it's great for a lot of things but for functional parts like gears, I definitely prefer FDM. Even if it's just PLA.

[natewebb]

I'm looking to print a gearbox for my extruder, and am trying to decide between ASA or Resin, and here this video shows up. Then switching to a cyclic test with a cleverly designed setup for testing to stall torque was the icing on the cake! I know ASA is lower modulus than PLAs, but the modified PLAs are usually a little lower modulus. Thanks for this video, this was perfect for what I'm working on!

[TAiiNE]

One thing to also take note it is it going to depend on the type of resin, or the type of FDM you use. Some are stronger than others. For example clear resin is known to be brittle. What you want is something like resione tough resin, siraya tech blu strong Resin, eSUN ABS-Like hard tough resin (a personal I use), then there's liqcreate tough-x that is designed for mechanical use. Theres also other brands but these I know and one I have used for more technical builds or things that may be taking a beating.

Also the cure time can have a BIG impact on resin, I saw you are doing them for 9 minutes? That is a bit much and over curing can cause any resin to become britle or form micro cracks. Even with the resin I use if I forget it in its curing box and over cure even the best resin will have issues. 2-5 minutes is normally the go to, though clear resin will cure faster and should be in half that. The fact your print shows yellowing means it cured WAY to long. The cure time also depends on the strenght of the UV light, stronger lights like in those cure stations don't need to be that long while weaker lights may need a few minutes more. For example my manual curing chamber uses a set up with a 405NM uv light and I only cure my prints for 2 minutes at the most. One minute for any clear resin or it starts to yellow and form cracks.

I don't know much about filiment printers as I've yet to get one, but I do know there's some that have metal mixed in that is really strong, and others like silk that are really brittle as well. So it really does depend on what you are using.

[PTReDaLeRtPT]

Wouldn't those gearboxes last longer if those gears were proper lubricated to reduce fiction, shearing and deformation under load?

[ethanjohnston]

You should try the resin gearbox with a resin that is 1:9 flexible to riding resin. I think it would help with the brittleness.

[flamewave]

If you could adjust your design a little, you could try using helical gears instead of spur gears. This would increase the surface area of the gear tooth interface and might distribute those forces more and reduce the risk of failure. They use helical gears in most automotive drive trains and are also supposed to reduce noise.

[JohnHansknecht]

So many resins on the market and new ones coming out all the time. I feel we will soon be looking at FDM as a dinosaur once the better resins are developed. I'm in a group that uses resin molds for DIY plastic injection molding, so this particular use is already something FDM cannot achieve because of the high temperature plastics being injected.

[lobsterbark]

I recently did a huge personal investigation into 3d printed gears and feel like this is a reasonable place to share my knowledge.

I found the smallest you can make an FDM 3d printed gear on an average printer with a normal sized nozzle and expect consistent smooth operation and accurately printed teeth is 1mm. That is, with a modulus of 1mm. You can go smaller, but there will be extra friction and noise and high speed operation will not work very well.

If you are generating the gears in a CAD package, check to make sure the program is actually generating accurate gears and not an approximation. Some programs will just generate an approximation because they expect you to order them off the shelf and only allow you to easily generate them for fancy renders. (SOLIDWORKS)

Herringbones are better to print than helical, and ideally you should be using double herringbone gears because I imagine you are using a 3d printed housing if you are printing gears and can choose your gear parameters, and that will reduce the strain on the housing. The self centering of herringbone gears also helps deal with any warping or tolerance issues.

If you're not using a sealed gearbox, use double helical gears instead because they deal with dirt getting between the teeth better.

Avoid the use of bevel gears if you can help it because they don't tolerate the flexibility of plastic as well, and you will have to take extra care to design everything very stiff.

Planetary gearboxes require way thicker housings than you will intuitively think you need when printed because of the flexibility of plastic.

Don't make the obvious mistake of printing double herringbone or helical planetary gearboxes, assembly is impossible on them. Yeah I made that mistake, felt dumb after.

Lubrication is super important, especially with PLA. "Just a quick test" can quickly warp your gears and you will have to print new ones if doing anything high speed.

[TheDainerss]

This test was like comparing a Microscope and a Telescope for looking at the moon, ofcourse one will be better as the other was never designed for this. The resin used in most home printers is for fine detail printing, hense the reason most model makers prefer resin. If you want something to withstand mechanical stresses, the FDM printer will always be the better choice here.