Enhanced Gear Bearing Fidget Script

I've had a small one of these floating around my desk as a fidget for years, which has led to lots of reprinting as they go missing. The more I mess with a model the more I tend to consider improvements, so here's Emmett's planetary gear bearing script with a bunch of configurable fidget-friendly additions.

STLs of my preferred customizations are included, but like Emmett's design the real point of posting this is the fully-parameterized OpenSCAD script that lets you tweak it yourself.

Features

Tweaks to the original design

• On execute the script now prints the usable diameter (inside the teeth) of the sun and planet gears to make custom sizing of their content easier.
• Number of faces on the center hole is now configurable (not limited to 6), and size can be configured either as a fraction of the size of the sun gear or in mm. Specifying in mm (center hole only) still calculates width based on distance between opposite faces to make sizing to an axle simple.
• Outer rim (single side) was 5% of the total width of the gear bearing, now this is configurable as a fraction (rim_width_fraction) or absolute value (rim_width_mm).

Additions to customize fidgets

• Adjustable beveling on the gears to reduce pinching of fingers if you're holding on the teeth when it rotates.
• Adjustable beveling on the outer edges as well as the edge of holes cut through the gears to reduce sharp edges.
• Adjustable knurling (straight or diamond) on the outer rim, as well as the inside of holes cut through the gears (when the holes are round) to improve grip.
• Holes can be cut through any gear (not just the middle) either round or with a configurable number of faces.
• Shapes can be cut into the gears for decoration (circle, arrow, polygon, star with 3-8 points) and can optionally have initial orientation set to point in, out, clockwise, or counterclockwise.

Files

The Script directory contains everything needed to use OpenSCAD to generate custom gear bearings. The presets used to generate the included STLs are included (gearBearingFidget.json.txt), but to get OpenSCAD to see the file you'll have to remove the .txt extension.

STL file naming is <width>-<height>-<tol>-<variation>, descriptions are as follows:

• 35-10-.15 (small): Miniature with slightly beveled outer edges and gears. Prints fairly quickly and easily fits in a pocket but is hard to hold if you don't have skinny/small fingers.
• 52-15-.15 (medium): Emmett's original size and tolerance with bevels on the gears, outer rim, and hole, as well as straight knurling for grip.
  • Hole: The original hexagonal hole to fit ¼ in hex drive bits.
  • Dimple: A round dimple for more comfortable grip.
  • Sparse: Reduced to 2 planet gears with teeth deep enough to keep them from falling out. Added diamond knurling and shapes to the planets.
• 79-15-.15 (large): Large enough to cover your palm with a grip hole through the middle with inner knurling. Outer edge has diamond knurling and the gears have arrows on the bottom (cycle though pointing in and out as the gear rotates) and stars on the top (all facing the same way as the gears turn).

If you have any other suggested/requested styles leave a comment and I'd be happy to add STLs.

OpenSCAD Tips

I've developed this using OpenSCAD version 2021.01, older versions may or may not support all language features in the script.

Parameters are all at the top of the file. If you're new to OpenSCAD I'd advise starting with just the Customizer window (if it's not visible go to Window menu > Customizer).

Start by tweaking the "Basic Parameters" section to set the dimensions, number of gears, etc settled before configuring the styling.

Planet vs sun gear size is constrained by the relative numbers of teeth: whichever has more teeth will be bigger. For bigger teeth reduce the number of teeth on both gears, for smaller do the opposite.

The "helix angle" is printed by the script when it runs. Keeping this under 45 degrees should make the gear more printable. To reduce the angle either reduce nTwist, increase the number of gears, or increase the thickness.

Shapes (in the sun or planets) are designed to be surface decorations, so they slant in at a 45 degree angle to the specified depth. If you set the depth deeper than where the 45 degree sides converge it will stretch down. To turn the shapes into holes you can set the depth to anything greater than half the thickness so the opposite sides intersect.

Printing Tips

Ideally these will print with no gears touching each other so it spins freely straight from the printer. More realistically there will be a little bit of binding but not so much that rocking the gears back and forth with your fingers can't pop it free. Things that can help loosen the initial binding include:

• Dialing in your extrusion multiplier
• Painting seams into grooves that don't come close to opposing teeth
• Reducing your layer height
• Adjusting the 'tol' value in the script and re-exporting it

Increasing 'tol' too much can result in the gears not engaging closely enough to hold the bearing together, so that should be a last resort.

If you're getting loose prints you can reduce 'tol' in the script to have tighter-fitting gears. This matters more on the smaller size, I've had very good results down to 0.13 or 0.12 'tol' depending on my layer height.

If you print a gear that sticks too hard to break free easily the best way I've found is to put something through the center hole that will give me more torque for twisting it (a hex bit driver, or a whole screwdriver handle for the large one), but that depends on having a model printed that has a center hole. If that's not the case I've used pliers (with rubber spacers to grip just the gears and not the rim) to twist individual planet gears: rocking them in and out independently of the rim/sun can pop them free.

If you have to go to extreme measures you should inspect the grooves/teeth to make sure they separated cleanly: if chunks of the teeth break off in the grooves it won't turn smoothly, but you may be able to file off the bits if you have small files.