Jojo's Bizarre Adventure Steel Ball Fidget, no supports

The Steel Ball should be rotating in your palm! In this model, this is achieved with a single 608 bearing located at its center.

Note: if this seems like fun to you, you might also like the seasonal Easter Steel Egg.

Printing

The whole thing can be printed at once, as the attached bgcode and 3mf files demonstrate. I print the model in PLA, with variable layer height (the top of the ball is printed with lower layers to keep the surface smoother). I keep the default 15-% infill but you can increase it to get more heft.

I recommend printing on a smooth sheet. At least in my case I get a smoother rim, and when I press the halves together, the gap is much less visible than when printed on a textured plate. I print with no skirt and it works fine, never had a piece shift on the print bed.

Assembly

This model requires additional hardware:

• One 608 bearing

• Eight M10 nuts

The bearing is placed in the center of the ball, and provides smooth rotation between the center hub and the ball envelope. The nuts play two roles: they work as pegs for alignment, and they improve inertia.

I recommend assembling the ball this way:

1. Take one half-ball (the outer envelope) and press the bearing in. It will sink half-way, the other half fits the opposing part of the ball.

2. Press the M10 nuts into their slots in the same half-ball. You can skip this step or use any other filler, but then you'll probably have to glue the halves together.

3. Press the opposing half-ball onto the nuts and close the gap. Optionally you may glue the halves together. Take care to have the outer ridges on the ball match.

4. Press the hubs into the ball so that they meet in the center, inside the bearing. Again, optionally you may glue their tips together.

Glue

I have not glued any of my models, and they hold together pretty reliably. If you decide to glue it up, apply glue in steps 3 and 4 as indicated. Be careful not to glue your bearing.

Alternatives

There are some ways to customise the print or eliminate the need for specialised hardware.

Finger-Ring

There is an stl for an alternative hub (half-hub, anyway) with a ring attached. This allows you to hold the ball in the palm of your hand and still make it rotate. Even palm down.

Plastic Hardware

I have tested 3D-printed bearing and nuts to replace the actual metallic ones. If you're in a hurry to try the steel ball action, and have no parts lying around, try this:

• 608 Bearing by firstgizmo

• M10 Nut (ISO 4032 Style 1) by Books but I get better results with the min version.