The purpose of this design is to create a moisture free storage container for spools of filaments that are loaded and available for selection by Prusa's MMU2 accessory.
This design incorporates and modifies two existing files:
- Parametric Auto-Rewind Spool Holder by VincentGroenhuis and
- Filament Spool Stand for Rubbermaid Container by MysteryDough
The containers sit on the top of an enclosure, such as the one referenced below, and feed filament into a PTFE tube that connects to one of the MMU2 input ports. The filament container or Dry Box contains packets of desiccant that absorb any humidity that does infiltrate the container. Except for a very short piece of filament that is within the MMU2 feeder, no part of the filament is exposed to the surrounding atmosphere.
Also incorporated in this design is the Auto Rewind mechanism that applies rotational pressure in opposite direction to unspooling motion. This re-spools the extra filament that is returned to the container upon Prusa i3 MMU2 filament Unload or Eject.
Included in the file section is an OpenSCAD file that can be used to generate rewinders of different sizes. As a matter of convenience a Hub and several Adapters are included in the file section that will support most spool sizes.
Typical Enclosure: https://www.thingiverse.com/thing:2396990
Spring is printed in PLA for stronger rewind characteristics. All else is printed in PTEG for strength and flexibility
This Prusa i3 MMU2 accessory consists of a spool rewind mechanism capable of rewinding the amount of filament returned from the Prusa MMU2 upon UNLOAD or EJECT and is enclosed in a transparent (translucent) box. This permits semi permanent mounting of filament that can be loaded upon command in a moisture free environment.
Each accessory houses one spool. The Prusa MMU2 filament loader supports loading up to five (5) filaments at one time. Therefore five (5) will be required to fully support the MMU2.
Dry Box Base
The Dry Box Base is a modified version of Filament Spool Stand for Rubbermaid Container by MysteryDough. The following modifications were Made:
- Deleted the horizontal M10 PTFE Connector boss,
- Added Boss and PTFE clamp to accept PTFE tube from beneath the Base,
- Added reinforcement between the vertical spool mount brackets,
- Modified the top of the Spool Mount Brackets to accept rewind Axle,
- Modified Spool Mount Brackets, filling in the space between each leg.
A Clamp is provided to secure the PTFE in position and keep it from falling out of the Dry Box. The clamping portion has a radius of 3.8mm and will slightly compress a 4mm PTFE tube but not sufficiently to cause filament binding.
The Base in this version fits the "Cloudy" Rubbermaid Dry Cereal Boxes but not the Clear versions:
The Auto Rewinder included in this design was developed from VincentGroenhuis's Parametric Auto-Rewind Spool Holder.
By design, the rewinder tightens the coil Spring as the filament is played out under normal operation. When the spring is tightened to near its physical limits, the Hub slips on the filament spool so as not to damage the Spring. The amount of slip is controlled by the friction between the Hub and the filament spool and/or Adapter. The Hub must be loose enough to allow slippage only when the Spring is near its limits but not so loose that the Spring completely unwinds.
The core part of the rewinder consists of the following:
The Spring is a coil spring printed in PLA for higher rigidity compared to other filaments. The Spring mounts to the Hub via interlocking tabs. No fasteners are required.
The Hub is printed as one piece and contains flanges that apply pressure to either the filament spool or to an optional Adapter. Adapters allow one Hub size to be used on spools of varying hub diameters and widths.
The included Hub is designed for spools measuring:
Inside Spool diameter 47.5mm
Spool width: 64.0mm
The Hub mounts to the Spring via interlocking tabs. No fasteners are required.
608ZZ Bearings may optionally be inserted into the Hub to reduce rotational friction, if needed. They can be purchased here:
The gripping flanges are printed with horizontal supports to improve their stability during extrusion. It is necessary to cutaway these supports before inserting the Hub into either a filament spool or a spool Adapter. Failure to do so will likely damage the flanges and therefore the Hub.
As the name implies, the Adapter adapts the Hub to the filament spool hub diameter and width. The included Hub supports spools or Adapters having inner diameters of 47.5mm and a width of 64mm. The Dry Box supports widths up to approximately 75mm.
The adapter is a simple 3D print that takes approximately 1 hour to print in low resolution (higher resolution is not required). Infills of 10-15% are acceptable.
Included with the Files is a .dfx sketch that can be imported and modified to accommodate various spool dimensions.
Also included are the PrusaSlicer .3mf files for the adapters where contrasting labels printed into the face of the adapter flange are desired.
The Axle goes through the Protector, Spring, Hub and optional 608ZZ Bearings. The Axle is 8mm in diameter with flat surface on 1/3 of the diameter. The Axle shape matches that of the Spring inner attachment portion and causes the spring to tighten as the filament is played out.
One end of the axle has a flange that prevents axle rotation when properly mounted in the Base.
The Axle is 3mm longer that the Base mount to mount naturally accommodates. This preloads the mount and prevents the Axle from falling out of position during use.
The Protector is positioned on the Axle in front of the spring. The purpose of the Protector is to prevent the spring from moving out if its normal position and keeps the Spring from dragging on the mount.
The Spacer is optionally positioned on the Axle on the opposite side of the Spring. In addition to keeping the Hub in position, the Spacer also insures no portion of the Hub or spool contact the mount.