Proof of concept – printed ball bearings
Printed bearing, nearly 608 size
This weekend I tried printing Rayraywashere’s ball bearing with mixed success. The plastic spheres inside we pretty well fused to the sides of the bearing, which made for a difficult cleanup. Although it got better with time, it was a laborious process. Ultimately, printed bearings that rely on printed balls may not be the way to go for everyone. Even if you can print it without fusing the balls to the bearing, there’s no guarantee the balls would be sufficiently spherical to work properly.
That ball bearing design got me thinking – if I could find a reasonably ubiquitous and cheap alternative to small printed spheres, I could make the entire design much smaller and probably significantly more reliable. The photo above is rough draft/proof of concept for a printed bearing only slightly larger than a traditional 608 bearing. Rather than printed spheres, it uses plastic pellets of the sort typically used as stuffing in craft projects. I sorted through a lot of these and used only the most nearly spherical ones. However, there was still a lot of variation that lead to the bearing getting jammed.
Later I emptied the plastic pellets and tried out small spherical 3mm plastic beads. These have worked really well in this printed design. To improve upon this design I intend to move the “bead filling gap” to the interior ring or change the ring system so that two rings will snap together and cover the filling gap. Overall, I am very happy with this result. I’m looking forward to actually installing a slightly smaller version into my Cupcake 3D printer in place of a 608 bearing to see how well it works.
I spent $4.00 for 1700 identical plastic beads, silver in color, 3mm in diameter. It takes about a dozen of these beads to fill the bearing. The potential savings are pretty self-evident. The per-unit cost for each bearing is probably only about $0.05 or so in plastic and beads. That’s pretty good compared to $2+ for commercial bearings. The real test will be how smoothly they work, how well they work at high speed, how quickly they might wear out. However, I think I may be on the right track here.
Any suggestions?
| Tagged with | ball bearing, bearing, proof of concept | 16 comments |
16 Comments so far
Foxdewayne
How about using BB’s. the ones you shoot from a BB gun. They are small, cheap and very round.
MakerBlock
@Foxdewayne: I know Whosawhatsis had suggested those soft BB’s, but they’re 6mm in diameter which is too large for this particular design. I’ve seen metal BB’s as small as 4.5mm, but that’s still pretty large for my designs. A 608 bearing is 7mm tall, so if the top and bottom of the printed version are each 2mm thick, I’ve got 4mm for the small round sphere plus a little wiggle room. I’ve found the plastic beads to be spherical enough to work pretty well. However, I’m open to trying BB’s too.
MakerBlock
@Foxdewayne: It looks like the smallest metal BB’s I can find after a full 45 seconds of googling is 4.5mm. I could probably make this work with my design, but it would be tight.
TerryB
Could you use small steel rod cut into thin slices or rollers? I’m just starting to learn about mechanical systems and may be off base…. Like a needle bearing….
MakerBlock
@TerryB: That’s the theory behind jrombousky’s bearings http://www.thingiverse.com/thing:3256 . He uses slices of ABS filament instead of steel rod slices. However, his bearing is too tall to use as a drop-in replacement for a 608 bearing. As for cutting a steel rod – I was looking for a quicker easier fix with some cheap off the shelf parts.
Buzz
other options for small round objects:
* Junk Jewelery ( lots of glass and plastic beads , the small thread hold should not matter)
http://www.google.com.au/images?q=junk+jewelery+beads&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&source=og&sa=N&hl=en&tab=wi&biw=1112&bih=877
* the head off glass head sewing pins. ( remove from pin with piers and force)
http://www.google.com.au/images?um=1&hl=en&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&biw=1112&bih=877&tbs=isch%3A1&sa=1&q=glass+head+sewing+pins&aq=f&aqi=&aql=&oq=&gs_rfai=
tre3
The engineer’s thought process…
Why do we need ball bearings and for what function?
*Reduce rotational friction
*Carry a load (parameter P)
*Rotate at speed (parameter v)
*Carry a load AT speed (P*v)
*Hold accurate position
*Resist Thrust
What features meet these needs?
*Spherical balls
*Polished or ground Raceways
*Tight location between inner and outer race
McMaster part number 9292K33 – 100 precision 3mm ball bearings for $6.05. That’s 6 cents per ball at the high McMaster price (I’m sure there’s a vendor elsewhere that’s cheaper). Ask a local bike shop
$2+ for bearings seems pretty high… Even high cost vendors like VXB are cheaper… $4.95 for 10 608ZZ bearings (part number 608ZZ10) or 50 cents for one (608ZZ10-1). With shipping, if I only buy 10, they’re about a $1 each… If I buy 50, they’re $0.6588.
As an alternative to a machine that’s sole purpose is to make bearing parts cheaply (and is VERY good at doing so), it’s not a great value proposition to make your own. An additional 60 cents gets you precision ground races, precision ball bearings, a spec’d tolerance and shields (open bearings would, no doubt, be cheaper)
As a proof of concept, it’s great! Doing it cheaper is also great – but cheaper with poor design isn’t enticing (ABS, PLA, etc. will never be as durable as steel).
If you don’t need to operate at speed or carry a large load (or operate at speed with load) – you’ve already made the initial engineering decision of choosing a plane bearing
pandelume
You could try these:
http://www.mcmaster.com/#steel-balls/=9ksv5n
3mm Steel, $6.05/100, so each assembled bearing would still be pretty cheap.
However, I have to wonder whether printing a bearing of this type from ABS or PLA is really a great idea. Neither of those plastics have high hardness or abrasion resistance, and mass-produced bearings are pretty cheap – $9.43 for 608 ABEC-1 and $4.26 for ABEC-3:
http://www.mcmaster.com/#608-ball-bearings/=9kt5ev
http://www.mcmaster.com/#608-ball-bearings/=9kt5o7
And those aren’t even the cheapest you can find. Moreover, for most (hobby) purposes they’ll never wear out.
I have to admit that printing custom sizes might be useful, and the whole idea is pretty cool. I’m just not sure it’s all that practical. On the other hand, printing journal bearings from UHMW or something might actually be practical for 3D printing.
MakerBlock
@tre3: I started typing a long response, because you make some excellent points, but I think I’ll put it into a larger post.
Thank you for the inspiration!
Jack Poon
To reduce wear and maybe increase the smoothness of the bearing you might want to consider using some sort of lubrication. I’m not sure what kinda of lubrication you would use for plastic although for metal, a common one is grease to also prevent corrosion. The necessity of lubrication is also dependent on your needs. I’m learning about fluid resistances but haven’t covered bearings specifically but if i had to hypothesize, i would say grease would create some friction but definitely extend the lifetime of your bearings (the resistance comes from the fluid inertia and individual particles moving around one another). But I may have fallen asleep in class a bit so i’d say take what i say with a pinch of salt. But yea, definitely give lubrication a thought to smoothing out those bearings but also design a case to contain the lubrication.
Jack Poon
I forgot to include this website in my post. It explains the necessity of lubrication.
http://www.machinerylubrication.com/Read/751/lubrication-bearings-rolling
tre3
Coolio
I planted the seed of a post :p I hope it’s about standard parts (think of them as the leatherman tool of design). Hrmm, i wonder if anyone has compiled IKEA fasteners into a library – their fasteners are cheap and there’s some fun bits in there (cam locks, right angle brackets, etc.).
FYI – 6x15x5mm bearings (969ZZ), in china, in volumes of 500, cost less than 25 cents each for higher quality bearings (you can easily get lower quality for cheaper). Those are shielded too (as designated by “ZZ”). Given that’s arguably more obscure than a 608 size, it’s safe to assume 608′s are even cheaper.
A clever person willing to take a little risk could make such an order, pay $60 to have it shipped Fedex or DHL or UPS and have bearings for less than half of retail. YMMV for quality unless you have the luxury to test them before ordering (shipping costs still apply). You could ship from china VIA EMS for even cheaper (but no tracking number and the factory may not take you seriously).
Cheers!
whosawhatsis
On the lubrication issue, Adrian Bowyer mentioned a while ago that he would only trust silicone grease lubricant on ABS/PLA. This was in the discussion of printed gears, but the same should hold true for bearings.
itcamefrommars
I second the BB’s, or even slingshot shot for huge bearings!
I’m def going to try that when I get a chance.
Printed bearings would be phenomenal for many applications even if they are not SUPER smooth. Smoothness, I imagine, wouldn’t be too much a problem considering the direction of the layers.
Also this application, refined, would bring alot of attention to the cupcake from many different hobbies/interests/markets!
Brainstorming a printed bead bearing - MakerBot Industries
[...] has been a number of excellent points made in the comments to my last post about a printed ball bearing and the associated draft uploaded to Thingiverse. Oh, and I’ve decided to dub this the [...]
dee illuminati
ion-exchange resin or ion-exchange polymer[1]
Ideally you would get a aggregate shaker and start with removing the smallest, use a pan with small holes in it, then another pan with larger holes, repeat process to get desired size consistency.
There is also a means to roll between two plates in a short circular motion within a jig of a bead confined area to either reduce nominal or mark malformed product.
What would happen is that you would have a shrinking of the bearing, you should design the bearing to utilize a v-channel and allow for the nominal curf. Think a wheel inside of a wheel, inside of a wheel.
Cheap, +/- maybe .01 tolerance but as you pointed out inexpensive.