Prusa i3 MK2/MK3 Spool Holder - 100% Printed with Herringbone Planetary Gear Bearings

This model is a combination of two fantastic 3D models: Emmet's Herringbone Planetary Gear bearings and Martin Majewski's Spool Holder. The motivation behind this project was simply to remove the need for store bought 608 bearings. These printed ones are extremely smooth and more than sufficient for this use. They are also they are less likely than 608s to over-spin when the filament is pulled quickly. Plus they look cool and it's a great way to show what your 3D printer can do.

Features

• Fully 3D printed
• Herringbone gear bearings
• Holds any size spool
• No need for metal 608 skateboard bearings!
• Custom threaded nut and bolts
• Optional stabilizing bar
• Multiple arm lengths
• Multiple stabilizer bar widths

Printing Instructions

You will need to print:

• 4x Gear Bearings (in your chosen tolerance)
• 4x Nuts
• 4x Bolts (use .3mf file)
• 4x Bushings
• 1x Left Arm
• 1x Right Arm
• 1x Stabilizer Bar (optional)

Note: If you already have Martin's spool holder you can reuse the arms. The rest of the parts are not compatible.

Print Settings

• Resolution: 0.15-0.25mm
• Supports: None
• Material:
  • PETG or PLA. Bearings work better in PETG.
• Infill:
  • Arms: 25% honeycomb
  • Bolts: 100% for the stem. 25-40% honeycomb pattern for base.
  • Everything else: 15% is fine
• Perimeters: 2-3

To expose the honeycomb pattern on the arms and the bolts set the number of top and bottom layers to 0 and adjust the infill pattern.

Bearings x4

These are obviously the trickiest part to print. You should print a single bearing first to determine what tolerance and material works best for your printer. On my MK3S+ I found that 0.2mm was ideal. PETG seems to spin better than PLA. 

• 0.1mm (tight)
• 0.2mm (mid, start here)
• 0.3mm (loose)

They only need to be tight enough to prevent the gears from falling out. Start with 0.2mm. If the gears are fused and won't turn then try a larger tolerance. The OpenSCAD file is attached so if you want to tweak it more you can do so there. Credit to amasraff for the original SCAD file with the groove added.

Right off the printer these probably won't spin smoothly. Play with them for a bit to loosen them up! Spin them and wiggle the gears around and pretty soon they should roll well.

TL;DR: Print 1x “gear-bearing-v1-regular-0.2mm-tolerance.stl”. If it spins well print 3 more.

Bolts x4

Use the attached 3mf file. It has a modifier to print the shaft at 100% infill while leaving the honeycomb pattern visible on the ends. Honeycomb infill should be no less than 25%.

Arms x2 (one left, one right)

I like the spools sitting a little lower on the rollers, so I've included an extended version of the arms. Your choice.

• Normal (same length as Martin's spool holder)
• Extended (25mm longer)

Bushings x4

If these are too snug you can scale them up a bit (try 105%).

Nuts x4

No notes, these are easy to print

Stabilizer Bar (Optional)

I found the source model too wobbly, so I created a simple bar to run through the arms. It helps keep the holder steady while changing spools. If you find it too loose/tight you can scale the model up/down a little bit. This part is not required and could probably use some improvement.

If you use very wide spools you might want to print the extra long version. The normal one is fine for all 1kg spools I have tested.

Roll Tests