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I have very little space for my setup. The MMU however, retracts a lot of filament for the 4 unloaded filaments. This design incorporates a wallet (thanks to some inspiration from TheBall and Abraham.M on the Prusa forums) that sits in the gap between each spool. This keeps the filament from getting tangled on things.

I haven't finished building mine yet. I'm waiting on a bunch of parts and finishing my enclosure. However, I've build and tested a single support/panel.

Low priority (for me), but I plan to add:

\u2022 A brace that clips on to the front, just under the filament roller, so that people can mount them freely without worrying about hitting the end supports and knocking the bearings out. Mine are braced by the edge of the enclosure, so it's a low priority for me.

\u2022 A table stand - so people can easily mount them on shelves, lacks, etc.

\u2022 A small clamp to clamp the top corner to the enclosure/wall - just to make them really strong.

To build this, you will ideally need:

24 - 42 x m3 x 3mm brass inserts. These go in the 3mm perspex (or printed panels) (key spots marked in yellow).

24 - 42 x 10mm m3 countersunk screws.

5 x 10x5x4 bearings (easily available in hobby/printer shops).

10 x m6-PC4 bowden connectors.

12 x M5 nuts and bolts to mount to the wall/enclosure. Length = wall thickness + 10mm.

You need 42 fasteners total for 6 wallets. However, 3 of those fasteners are at the back of the rack behind the spools, so they don't have to be mounted flush. For these you can use standard 12mm m3 nuts and bolts. If you have heaps of space, and spools have lots of clearance down each side, then you can probably use 12mm bolts and normal nuts throughout.

Note: The 6th wallet will be at the end of the row and won't be used. However, I think it's worth having one as a spare. If you only want to make 5, then you'll need to splice the lower part of the panels to stop the main bearings falling out. The side panels hold the bearings in place.

To build this, you will need a well calibrated machine. This print makes heavy use of supports and the layers above the supports need to be neat. Fortunately, you are probably making this to work with an MMU, so you can always use dissolvable supports. :D

First, print the parts.

I'd recommend ABS+ for the main support. PLA will probably do as well, but a bit of flex is a good thing for that part. PETG may be ok so long as you have dissolvable supports, or some immaculately dialled in support settings. 3-4 walls and fair bit of infill. Mine weigh 50gm each in ABS and seem very strong. I'd suggest printing the main support on its side so that the layers run through it. Support material will be harder to remove, but it will be strong.

I'd print one, and check for fit. I found that with such large objects, ABS shrinkage became a bit of a problem. You may have to scale them up by 1-2% to offset the ABS shrinkage.

The filament roller can probably be printed in anything. I used PLA.

The main spool rollers I'd probably use ABS/PETG for strength, but I would also expect PLA to be fine.

The panel divider can be printed from anything. I noticed that ABS shrank quite a bit over that length, so PLA/PETG may be better. I used ABS+

Side panels can be printed, but a much better solution is to get them laser cut from 3mm acrylic. There's a DXF in the files with outlines for 2 sets of panels. If printing them, make them as transparent as possible so you can see what the filament in the wallet is doing.

Next: Clean out support material and make sure the roller hole and filament hole are very clean. If you decide to hit them with a file, keep in mind that there's a small raised bit around the bearing in the roller hole to stop the sides of the bearing rubbing. Don't file that away.

Bolt them together. Assemble the panels and panel divider. Use a countersink to clear some acrylic for the countersunk screws. Leave the screws at the bottom loose so that you can fit it over the support.

Slot the roller on the bearing and slide it into place. Use a plastic pin to hold it in place. There's two different pins with \u00d8 of 5 and 4.9mm. Use whichever one seems best. Should be a tight fit.

Screw the bowden connectors into place. Make sure there isn't any plastic dislodged by the connector into the holes. For the lower bowden connector, it is probably worthwhile using a countersink to give it a chamfer.

Attach the wallet to the support.

Test feed filament through and make sure it moves through smoothly.

To calculate your optimum roller length, use ((L - 60)/5) - 0.2. Where L is total length available for the rack in millimetres.

eg: 456mm room for rack:

456 - 60 = 396 (room not taken up by the supports)

396/5 = 79.2 mm (space for each spool)

79.2 - 0.2mm = 79mm (leaving a little bit of space for tolerances).

Update 31/10/18: Minor update of geometry for the main support to make it easier to remove support.

Update 2/12/18: Update of geometry in V2 to make it easier to load filament. The earlier design has issues with rigid filament digging into the side of the 'chute'. I'll merge it with the original festo design later.

Added a new design (Shark main support V2 - no festos.stl) that doesn't require festos (uses couplers and festo-less brackets). Instead it uses rivnuts to hold the ptfe tube. This means that your PTFE tube won't wear out over time as the festos chew into it.

Changed the cage to include a door that can fold down. Makes it easier to load filament.

A video showing how to load filament. \nhttps://www.youtube.com/watch?v=7BhELwnWRnw

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The Shark (Spool Holder and Retraction Keeper) for Prusa MMU

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