REPREWIND - AUTO-REWIND SPOOL HOLDER FOR THE REPBOX
This is a remix of the Universal Auto-Rewind spool holder. This remix is designed to be used with the Repbox Filament Management System and can hold 5 spools with rewinders inside the Repbox.
This was a unique undertaking. We had to thin down the entire assembly, while maintaining operability. Twelve some revisions later, we have a working unit thin enough to fit five of in the box, but strong enough to rewind a FULL kilo spool.
Here's the catch (for now): Each Rewind unit can only accommodate a spool up to 67mm in width (Fillamentum, ColorFabb, Amazon, Inland, Protopasta, Polyalchemy, Matterhackers Build, CHEP, AIO Robotics, Hatchbox, Polymaker, Nylforce, Nylon-X/G)
We are currently working on a system for spools over 67mm in width (Prusament, Atomic, IC3D, MH Pro, PS Daily, etc). It's just going to take some extra voodoo magic to make it work since space in the box is limited. Stay tuned for that.
To purchase a Repbox or find out what a Repbox is, goto here: https://www.repkord.com/repbox
This system not only allows easy use of the Repbox system with the Prusa MMU2, but also a 98% closed filament path from box to nozzle (only exposed filament is inside of MMU2 unit over hobbed gears)
You will need to print the following for a single rewinder (multiply all by five for a complete box)
All parts can be printed out of PLA, although PETG is recommended (Except for the Spring). Parts are printed without supports EXCEPT the side brackets. You'll need support on from the build plate. Three perimeters and 15% rectilinear infill minimum recommended on all parts. Spring should be >50% infill.
1 x Axle
1 x Spool
1 x Spring (PLA for added stiffness. Won't work with PETG spring! Also, print a few extras)
1 x Dial
1 x Clutch
2 x Side Brackets (Use Supports!)
2 x Crossbeams
Additional parts needed:
Four, 3x6mm PANHEAD/Button head bolts (DO NOT USE SOCKET HEAD BOLTS!. Space is tight!)
If you need some, Amazon has an assortment pack that is handy to have on hand: http://ln.jmt-3d.com/M3ButtonBoltPack
2 x 608ZZ Skateboard bearings (IMPORTANT: Remove grease guards and soak in 91% Alcohol for at least 48 hours to remove grease.)
You can use the bearings that came with the Spool rollers provided by Prusa with the MMU2.
If you need to purchase some, Amazon is your friend: http://ln.jmt-3d.com/602Bearings (These bearings have the easy to remove grease guards)
2 x Side Brackets
2 x Crossbeams
4 x 3x6mm Panhead/button head bolts
First, make sure your are using panhead (or button head) bolts and NOT socket bolts. Below is a picture of the difference.
Place the bolts through the holes of the Side brackets so they fit into the recesses
Attach the crossbeams using the bolts. The 'feet' of the bracket should be facing inward.
1 x Spool Holder
1 x Clutch
1 x Dial
1 x Spring
1 x Axle
2 x 608 Bearings
Insert a bearing into each side of the Spool Holder
Clip the Spool holder into the clutch.
Set the spring into the center of the clutch. Make sure the extruded middle of the spring is facing up.
Line up the arrow on the edge of the Dial with the 0 on the clutch and press the tabs of the dial into the internal grooves of the clutch.
Once pressed in, you should be able to twist the dial between 0 and 15 to adjust clutch tension.
Insert the axle through the assembly.
MOUNTING SPOOL ONTO BRACKET
Insert the assembly into spool and secure with nut.
Slide the ends of the Axle into notches at the top of each bracket. If you have difficulty you man need to carefully trim either the brackets or the axle notches.
IMPORTANT! Unwind some of the spool and check the way the spring is compressing. It should compress INWARDS like in the picture. If it does not, then you will need to unmount the spool, remove the assembly and flip the spring to the other side of the spool.
Once everything looks good with the spring, insert the entire thing into the Repbox (it should fit in the roller tracks). Make sure to PRE-TENSION the spring by spinning the spool a few times in the direction of filament flow prior to feeding it to the MMU2 or Printer.
Community improvements are not only welcome, but encouraged!
Not rewinding due to friction:
If you experience an issue where there is a lot of friction between the dial and the side bracket, you may have the nut on to tightly. If you over tighten the nut it will try to pull the threaded spool holder through the spool and causing the back of the rewind housing to deform. This opens up a little bit of space behind the spring and you lose the little bit of play needed to keep the dial from rubbing the bracket. Loosen the nut just enough that the spool stays in place, bit is not completely locked.
Another cause for friction is simply that the spool you're trying to use is too wide. This current version will only accept a 67mm wide spool MAX. Anything larger and you'll get friction. We are working on a separate design to handle the larger spools.
Not rewinding due to low spring tension:
Make sure the spring is printed from PLA! Also, make sure it's a good quality print. Too many print artifacts (blobbing, zits, over extrusion) can cause the spring to not coil properly or lock up once coiled from resistance. Make sure you have the clutch set high enough the the spring becomes COMPLETELY coiled before it gives. Finally, make sure to pre-tension the spool on the rewinder BEFORE feeding it to the MMU unit.
Spool coming loose off of rewinder:
Some thinner spools (half kilos, etc) may come work the nut loose during long prints. DO NOT OVER TIGHTEN THE NUT TO FIX THIS! You will cause more headaches. Instead, print out a second nut and thread it on backward BEFORE putting the spool and locking nut in place. Then use the two nuts to lock the spool in place. Do not rest the inner nut against the rewind mechanism for best results. Leave about 1 cm gap at least.
Spool failed to rewind and now there is filament everywhere:
No system is perfect and from time to time you may have a retraction that doesn't wind back on to the spool correctly. If this happens follow these steps:
1 - Ensure the MMU2 unit is not currently feeding from the spool in question.
2 - Pause the print.
3 - Remove the spool and rewinder from the box. Pull out ALL of the filament from the spool that is currently going to the MMU2.
4 - Remove the spool from the rewinder.
5 - Unspool the filament up to the point where the winds are tight again.
6 - Respool the filament back on to the spool tightly.
7 - Reinstall the spool back on to the rewinder.
8 - Ensure that it operates correctly by spinning it in the direction of filament draw and letting it spin back. If it doesn't spin back, troubleshoot the possible reasons.
9 - Reinstall the spool into the box, pre tension the rewinder, and begin feeding filament back down to the MMU2, but NOT all the way.
10 - The next time the MMU2 goes to print with that filament and the idler engages the gear, start feeding the filament into the MMU2 unit.
Good as new.
The best practice to avoid this is to ALWAYS check the rewinders from time to time to ensure proper operation. Reprint springs (having some spares handy is also a good idea) when you feel the current spring has reached end of life.