Spool Bearing Hub: 54.3 hub diameter for Polymaker, Inland, and Hatchbox

This is a center spool hub made specifically for 54.3 cardboard spools, as it fits them exactly. It fits the Polymaker brand cardboard spools and one variation even has their logo on it.  It fits Inland cardboard spools (many of which I think are black label polymaker) and Hatchbox3D plastic spools perfectly. Use it with the Prusa 22mm MMU bearings on a 5/16 inch rod. The fit of the hub in the spool center hole is good and there is just the slightest amount of space with almost no wiggle at all.  But it is not an overly tight fit and doesn't need to be since the  metal 5/16 nuts hold the sides against the spool firmly. 

Here is the  MCS larger system that I use it with shown in the pictures. - https://www.printables.com/model/555238-mcs-multi-color-system-for-prusa-mmu

See the video here of it being printed and used:

Includes Different Versions for Multicolor and Single Color 3mfs

Bearinghub - plain version no logo

This is the same geometry just no logo on it.

PolymakerMMU - for printing the two polymaker curves in a second color

Includes an MMU version with a logo that has four tool changes so it could be printed without an MMU or with an MMU and will give you the Polymaker logo on the bottom.

Polymaker non MMU - the two polymaker curves are indents

Also included is a single color version without the logo lines and they are just indents so at least you can see the logo imprint there in a single color print. 

Uses Center Hub Bearings for Low Friction with Cardboard

A center rod design reduces friction and allows easy spin, especially for cardboard spools. However, the hub needs to fit the spool with only a little room to fit. 

What Else do I Need?

Use 5/16 inch 4 inch rods

5/16 nuts

Spacers are included in the print. Resize their length if needed. There is also included a plate of various sizes so you can see which work best.

I use this center hub exact fit spool setup with my MMU overall design shown here for five spools on a wood structure. - https://www.printables.com/model/555238-mcs-multi-color-system-for-prusa-mmu

The only thing you need here is a 5/16 inch 4 or 4.5 inch long bolt/rod coming from somewhere sturdy. I leave that up to you to decide how you do it. You only need to drill a hole in a ½ board really and anchor the board with a bracket to a base support.

How to Print

• Print two hubs and two or more spacers for each spool - try various sizes to see what fits
• Use 3 perimeters
• Use a .25 layer height and 25% infill
• PETG is preferred but PLA is fine  (the pics are all PLA)
• Print with snug supports with a .25 detach distance 

The assembly order along the 4 inch rod goes like this.

Assemble in this order along a 4 inch 5/16 bolt.  (You can also use a 4.5 inch bolt which makes it easier but you have the end of the bolt sticking out.) This assumes you are sticking it through  a half inch board.

You will need 1 bearing for each part. I am using the 22mm bearings that came with the Prusa MMU3/MMU2S.

The bearing holes face outward and are secured by the spacer and nuts against the spoolhubs. The spacers, rod and nuts do not rotate. Only the outer bearing spoolhubs and spool rotate. I have  marked the parts that actually rotate with a * so you can understand.

4 inch long 5/16 inch metal bolt goes into a 5/16 washer and then through a half inch thick wooden board (drill a 5/16 hole). On the other side of the board in this order use:

1. 5/16 metal nut
2. 6mm printed spacer (the ones on the sheet with the spoolhubs)
3. inner bearing (outer bearing*)
4. printed spoolhub*
5. spool*
6. printed spoolhub*
7. inner bearing (outer bearing*)
8. 2.5mm printed spacer (the .3mf with the 15 on one plate)
9. 5/16 metal nut

This arrangement has been tested and fits the Polymaker cardboard spool perfectly and lets them roll with little to no friction and allows the shortest rod, a four inch rod.

By the way I also recommend this insert for the Prusa Spool holder which works wonderfully with the Polymaker spools - https://www.printables.com/model/417333-polymaker-cardboard-spool-smooth-center-insert

Changes:

• Removed the outer ring
• Used a 54.3 hub diameter
• As one variation, added the Polymaker logo to the hub's outer face in .75 depth of two lines in multicolor
• Thickened the hub flange to 2.75mm for more strength and rigidity
• Included inner  spacer rings of various lengths for use with a metal 5/16 inch rod about 4 inches long so the this hub can rotate freely and not rub against the nuts at the ends of the rod