Small bead ball bearing
There 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 “bead bearing.” My latest version uses super cheap mostly-spherical plastic beads from a local craft store in place of the normal metal ball bearings one sees in commercial bearings.
@tre3 pointed out printed bearings aren’t a good value proposition
VBX sells a RepRap’s worth (x53) of ball bearings for about $45.00, inclusive of their cheapest shipping option, exclusive of tax. The plastic beads I purchased were $4.00 for 1700 beads, or $0.04 for 17, which is a little higher than the number required for a single bearing. The design probably requires about 0.5 cc of plastic per bearing, at a cost of $0.04/cc of plastic. We’re looking at a materials cost of $3.18 for a full set of 53 bearings. I believe tre3′s main point is that for the quality you get for the commercially available without any of the printing hassle, the cost saving of printing your own just isn’t warranted.
To this, I would respond:
- This was a proof of concept to see if it was viable. I think it is for low load usages.
- For use in a RepRap or MakerBot replacement part it would only need to operate smoothly at speed, without much load.
- The price differential is significant. A $42 differential could actually be a deal breaker for some people.
- At 1/10th of the cost, the longevity of the parts probably isn’t as big a deal.
- Assuming the result of wear and tear turns the plastic bearings to plastic dust, the dust could be recycled into new parts!
- I believe the benefits of low weight, ease of assembly, and cost outweigh the potential problems with this design
@TerryB suggests slicing up a steel rod for circular rollers
This is the same essential theory behind jrombousky’s printed bearings – and it’s a good idea. 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. I think it would be really cool to design a printable drop-in replacement for the typical 606 and 608 bearings used in a MakerBot. As for cutting a steel rod – I was looking for a quicker easier fix with cheap off the shelf parts.
@Foxdewayne and @Whosawhatsis suggest soft BB pellets, @pandelume, @beak90, and @alansblue suggest metal ball bearings
Whosawhatsis had also suggested those soft BB’s, but they’re 6mm in diameter which is too large for this particular design. A 608 bearing is 7mm tall, so there’s just not enough room in the design of a 608 replacement. Others have pointed out I’ve found the plastic beads to be spherical enough to work pretty well.
However, I’m open to trying BB’s too. After a cursory search I found 3mm (1/8″) bearings, 100 for less than $3. However, this will bring the minimum cost to $0.51 per bearing assembly. At that price, you really might as well use a commercial bearing.
@Whosawhatsis says: “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”
Hey, who am I to argue with Adrian. 
@beak90 says: “Why not just make it one piece and add an operator stop to the gcode before it fills up the top layer to seal the balls in? That would make things pretty easy. The code is M01 (with the text to display in parenthesis). And as far as the balls for the bearing, why not use actual metal ball bearing balls? They aren’t too expensive and it would make a perfect bearing.”
The M01 operator stop is a great GCode trick for pausing a print while you do something. It’s a fantastic way to embed objects or materials within a printed object. I did not use that trick in my initial designs because I wanted to see if it would work with beads at all before investing the time in tweaking the GCode. With the small circles I’m printing to achieve this design, I’ve been printing from the SD card to allow for faster transmission and processing of the instructions by the MakerBot. However, a higher quality SD card print comes at a cost – it ignores M01 pause codes! By printing the two sections as separate pieces I have less concerns about strings, ooze, or other molten plastic issues. And, lastly, this way I don’t have to worry about the extruded plastic trying to fuse to the bead bearings themselves – which was the main reason for using non-printed bearings in the first place.
@Buzz suggests “Junk Jewelery” (lots of glass and plastic beads, the small thread hole should not matter) or the removing the heads off glass head sewing pins with pliers.
Both of those are excellent suggestions. Once we start to move away from thinking of bearings as only printed or commercial, I think the possibilities really open up. There should be TONS of possible replacement parts. If you operate your machine in sub-zero temperatures , you might even get away with using frozen peas!
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Thoughts:
If you haven’t checked out the Gada “RepRap” prize, it’s worth a look. Basically the goal is a mostly-autonomous printer that can make most of it’s own parts. Two of the most stringent goals are that (a) materials and parts cost under $200 and (b) it be 90% printed by volume. When you’ve got a total budget of $200.00, being able to have all of your bearings for under $4.00 is kind of a big deal. While the ideal winning printer is supposed to be able to generate all of the printed parts for a duplicate copy within 7, there are no explicit longevity or precision requirements. I suspect these parts might just be good enough for consideration in someone else’s designs. If these tests are successful, I hope that I would have contributed towards someone’s success in this prize.
And, as a side note, one of the benefits to having this particular bead bearing sized design is that you could always build a RepRap using these parts and “upgrade” to better commercial parts later one as time or money allow. They could also work as interim repairs.
Testing:
Overall, I have a feeling printed bead ball bearings can work as a possible replacement part in a Cupcake 3D printer or a RepRap. However, I intend to test out a newer, possibly more resilient version, this weekend. The new version has a two-part snap-together internal ring assembly for inserting the beads, is sized to the specifications of a 608 bearing , and is specifically designed for these 3mm beads rather than the larger plastic pellets. One test will whether the internal ring can snap together properly. One test will be how the part operates at high speeds. I’ll probably put it in an electric drill and see how it goes. If all goes well, I’ll try installing it into Bender‘s Z-axis and see how it goes. I will be monitoring it for smoothness of operation, sound, vibration, how well it holds up to speed.
Do you have any other suggestions on tests or criteria?
