Creality CFS Roller Bumper / Pusher / Tensioner / Adapter for better spool stability

This add-on improves the filament retraction of the spool in Creality CFS, by eliminating the friction between the factory bumpers and the spool, which can become problematic as spools get lighter with less filament on them. Also no more fine dust falling on the filament. Additionally also enhances compatibility with smaller spool sized like Sunlu has.

It requires no permanent modification of the factory unit, all that needs to be done is removing the factory bumpers from the CFS cover, and place these pushers in place using the factory original screws.

The main difference between this remix and the original is that I use 20mm copper stand-offs in the arms instead of 15mm, this displaces the rollers wider by 2.5mm on both sides. I noticed that there exist particularly wide spools which ran at the very edge of the rollers, with this small improvement it's ensured that rollers are 100% always pushing down the spool. I also have a cardboard spool which was likely dropped during shipping, and has the edge bent a bit, the rollers cover that area too. To accomodate the longer stand-offs, I remixed roller_arm.stl accordingly. This the only modded part.

For the screws holding the arms to the base, I chose screws with half thread, to exclude the wear possibility of the arm rotating on a thread. With a 45mm half-thread screw, the arm only rotates on the smooth area of the screw.

Bill of materials:

• 32x 693ZZ bearings (8 for each pusher)
  https://www.aliexpress.com/item/1005006749191340.html
• 16x M3x30mm screw (4 for each pusher)
  https://www.aliexpress.com/item/1005008147178507.html
• 8x M3x45mm half thread screw (2 for each pusher)
  https://www.aliexpress.com/item/1005006867847280.html
• 4x 5x20mm springs (1 for each pusher)
  https://www.aliexpress.com/item/1005002559118977.html
• 8x M3x20 stand-off F-F (2 for each pusher)
  https://www.aliexpress.com/item/1005006976341051.html
• 8x M3x3 Hex insert screw (2 for each pusher)
  https://www.aliexpress.com/item/1005008575430678.html

Instructions:

• Print the plastic parts in PETG (3 wall loops, rectilinear infill 15%, enable supports on build plate only) and the roller surfaces in TPU.
• You need to ensure that the bearings fit inside the roller cylinder just a bit thightly. To calibrate for this just import the roller_cylinder.stl in your slicer and using the Cut function make a short test-cylinder of about 5-6mm tall. Print it and see how the bearing fits in this. If the bearing is loose, scale to 99% and try again. If it's too tight, scale to 101% and try again. It has to slide in just a bit tight, eg. you'd have to use a pencil or a screwdriver against the table to be able to push it in, not too hard, just impossible by bare hand.
• For each pusher, you need: 
  • 1x roller_base.stl
  • 2x roller_arm.stl
  • 4x roller_cylinder.stl
  • 4x roller_bearing_spacer.stl
  • 1x roller_surfaces_tpu.stl
• Enable supports. Only roller_arm.stl will need just a little bit, but it's easy to handle.
• When done with the PETG parts, assembly as follows:
  • In each roller_cylinder push a bearing down to the bottom (use a screwdriver or a pencil). 
  • On each M3x30mm screw place another bearing and a roller_bearing_spacer.
  • Insert the screws with the spacer and the bearing in each roller_cylinder so the spacer goes right down to the bearing at the bottom.
  • Insert the copper stand-offs in each roller_arm so they are centered.
  • Screw in the M3x3 Hex insert screw through the small hole on each roller_arm, to tighten the stand-off so it doesn't slide sideways (probably enough to use Super Glue instead, but wouldn't be too sure on the longevity)
  • Screw each assembled roller_cylinder in the two sides of the arm's copper stand-offs. If you have thread lock liquid at hands, you could add a drop here, so you don't have to tight too much.
  • Attach each two assembled arms to a roller_base, by pushing through the 45mm M3x3 half thread screw.
  • Slide the TPU roller surfaces on each cylinder end so they snap-on at the inner end.
  • Attach the springs to the arm's hooks so they get pulled against each other.
• Remove the bumpers from the CFS cover, first with a flat screw driver on the sides (watch for the springs popping out) and remove the bumper bases too - keep the screws.
• Attach the new roller bumpers with the screws saved in the earlier step.

The video of the original make shows the steps above pretty well: