I recently posted about my first experiments with using PVA to print a water soluble support. I almost immediately began imagining using this to print more complex moving parts. I’ve never printed a single part that contains multiple moving sub parts before, but a ball bearing is a pretty good example of this.

So here are two pictures of it right after printing:

In these pictures, you can see the white PVA packing the green PLA bearing for support during printing. (I went with the bright green to see the artifacts and defects more clearly. The black and the clear PLA really hide these things.)

After almost 24 hours of soaking in water, the PVA dissolved off enough so the bearing can start turning.

The print has some little imperfections that I will have to look into recalibrating my printer if I want to get rid of. But functionally, it turned out to be quite a success. Maybe not pretty, but still quite functional.

Conceptually, I find this a very exciting breakthrough. Combine the potential of 3D printing with the added flexibility of water soluble support and then use this to print complex moving parts that don’t require assembly, and at least in theory you have a whole new type of engineering design. Just consider: if you want to design a toy car with a wheel on a bearing on a shaft, how do you keep the wheel from sliding off the bearing, or the bearing from sliding off the shaft? These sorts of things require parts like C-clamps in grooves or lock screw in extra holes, and all this stuff increases the complexity and number of failure points dramatically. But with a printed part, the hub of the bearing can be printed as a part of the shaft, while the outer rim would be printed as part of the wheel itself. The balls are printed inside of the bearing at print time so you don’t have to worry about leaving slots for sliding the balls inside. And the bearing hub can’t slide off the shaft because it is the shaft. And the rim of the bearing can’t “pop off” the wheel, because it is the wheel. No C-clamps, no lock screws, no extra pieces that serve no purpose but to keep A from falling off of B. This is pretty cool stuff, don’t you think?

As a side note, this is actually my second attempt at printing a ball bearing that I did. The first was an interesting failure. I printed it with 0.25mm tolerance between the balls and the hub as well as between the cage and balls. This resulted in a print where the pieces were so close together that the water couldn’t get in the dissolve the PVA. So after 48 hours of soaking, it still won’t turn.

This second one uses a much looser tolerance between parts (0.4mm)  and no cage around the bearings, which allows the water to get in quite a bit easier. The result is a bit too loose in that the balls are able to shift inside and form gaps (see the picture), and the 0.4mm gap between the bearing and the rim/hub leaves a bit too much wiggle in the bearing itself. Nonetheless, this was a very successful proof of concept. It rolls about as smoothly as you might expect a plastic ball bearing to, and I haven’t even tried experimenting with any lubricant yet. I will try reducing the gap between the pieces to .25mm but this time without the cage, and maybe try packing in another ball to reduce the amount of free space for the balls to shift within.

One last idea I am considering is to change the balls to cylinders and try making a roller bearing. Based on how 3D printers print, the rollers should probably roll more smoothly than the balls do. (This is because rollers roll only along 1 axis, so if you print them the right way they don’t need to roll over the bumps that occur between layers the way a ball will if it turns inside the bearing… which it will inevitably do eventually.)

My next big milestone in this direction is to try and print a functioning gearbox in a single print. If I can find the time to do the CAD design.