Auto-rewinder stand for Rubbermaid 16 cup container

prusaprinters

<p>This is an auto-rewinder stand designed for use with the Prusa MMU2S multi-material unit. I designed this rewinder stand to meet the following criteria:</p><ul><li>Must accommodate a spool 90mm wide by 200mm diameter, which is the size of a spool of Prusament as supplied with the MK3S kit. All other drybox rewinders I found cannot fit a spool that wide at full 200mm diameter.</li><li>Must work with low-friction PTFE feed tubes having 3mm inner diameter (not the too-tight 2mm inner diameter supplied with the MMU2S) without pulling the filament out of the MMU2S after a retraction.</li><li>Fits inside a Rubbermaid 16-cup (cloudy) food storage container.</li><li>Can stand alone without the drybox.</li></ul><p>Overall, I consider this an improvement over <a href="https://www.prusaprinters.org/prints/129092-auto-rewinder-stand-for-rubbermaid-21-cup-containe">my design for the 21 cup container</a>, because this design doesn't require the filament to be threaded through the cover, making it more convenient to load, unload, or remove the cover during a print. This convenience comes with disadvantages, however: this 16-cup design uses far more material, the size of the part makes it susceptible to warping away from the bed if printing with PLA, it requires a longer feed path (or mounted on a raised platform as shown in the picture) due to the feed tube being at the bottom, and I have to recharge the dessicant more often.</p><p>The Rubbermaid 16-cup container has the same rim profile as the 21-cup container, but because it's shorter, it must be raised to clear the height of a 200mm diameter spool -- and then raised even further for the rims of a wide spool to clear the sloped vertical corners of the container, which slope more from vertical than the 21-cup container. Of course, a 21-cup container can also be used with this rewinder stand.</p><p>For each drybox rewinder, you will need:</p><ul><li>A Rubbermaid 16-cup cloudy dry food container with lid -- if you buy too many, you can always use them to store food.</li><li>M6 PTFE tube fitting. The OpenSCAD model also can be set for an M10 fitting.</li><li>M6 nut to fasten the fitting.</li><li>Two 608 bearings -- you can use the ones that came with the MMU2S spool stands.</li></ul><h3>Printing the auto-rewinder hub</h3><p>The auto rewinder hub is based on the <a href="https://www.thingiverse.com/thing:3781815">Integrated Auto-Rewind Spool Holder</a> by VincentGroenhuis, modified specifically for the requirements above.</p><p>If printing the rewinder spring with PETG: Use the IntegratedRewinder STL file ending in "PETG". This prints 3 spring blades, each 1/11 the interior volume of the hub.</p><p>If printing the rewinder spring with PLA: Use the IntegratedRewinder STL file ending in "PLA". This prints 5 spring blades, each 1/9 the interior volume of the hub.</p><p>If printing the rewinder with ABS, use the STL file for PLA.</p><h3>Printing the stand</h3><p>Two STL files are included for the spool stand: one for PLA and one for PETG. The only difference is the recycle logo engraved on one end.</p><p>The axle can be printed with any material. The axle STL model includes two retainer ring slots (for the two spring configurations possible) and a snap-on spring retainer ring.</p><p>After printing the axle, the edge of the flat bottom surface may protrude slightly. Smooth these edges a bit with a flat file or sandpaper to prevent the edge from interfering with the spring coils. Then slip the retaining ring into the correct position (near one end for 3 sprint blades, near the middle for 5 spring blades) so you don't lose it later.</p><h3>Assembly</h3><p><strong>Spool stand:</strong> Fasten the PTFE fitting into the hole using a nut. My PTFE fitting had a sharp metal edge that shaved off a tiny thread of filament as the filament fed through it, so I used a countersink drill bit to chamfer the fitting. You may want to do that. Finally press the stand into the container lid. If you want, you can make this permanent by putting a small bead of silicone sealer or caulk inside the groove of the lid before pressing the stand into it.</p><p><strong>Rewinder spring:</strong> The spring blades snap together in an obvious way. The blade with the teeth goes on the bottom of the stack, and the blade with the flat-sided hole goes at the top of the stack.</p><p><strong>Axle:</strong> The flat surface of the axle has the word "SPRING" printed on it, to indicate the side that your spring goes. Slide the retaining ring (washer with a break in it) over the shaft until it snaps into the indentation. There are two retaining ring positions. The position nearest to the word "SPRING" is for a 3-blade spring (PETG), and the other position is for a 5-blade spring (PLA).</p><p><strong>Axle+spring:</strong> Slide the axle into the spring stack so that the flat-sided hole is against the retaining ring. The axle should stick out the other side enough for the locking slot to go about 1mm past the 608 bearing in the hub. If it doesn't, you have the spring stack on the wrong end of the axle.</p><p><strong>Rewinder hub:</strong> Push a 608 bearing into the end of the hub shell (cylinder with diamond holes), and into the threaded end cap. You can use the bearings you got with the MMU2S kit for the spool stands.</p><p><strong>Hub assembly</strong> If the hub of your spool doesn't fit over the end cap petals, you'll need to assemble the hub in the spool. Otherwise you can assemble the hub and slip the spool over it. To assemble in the hub, put the appropriate spacer on the hub shell, and insert the shell into the spool so that the arrows on the shell point in the direction of the filament winding. Put a spacer on the other end of the shell. Then insert the axle+spring into the shell so the teeth of the spring mesh with the teeth inside the bottom of the shell. Screw the end cap on. If you push the axle toward the bottom of the shell and it bounces back a bit, the spring teeth aren't meshed. Wiggle and shake it a bit to settle it in.</p><p><strong>Final assembly:</strong> Put 2 or 3 packets of dessicant in the stand. Grasping the ends of the axle with your fingers, drop the ends into the slots on the stand support arms. Thread the filament through the M6 fitting. Put a paper clip on it to keep it from retracting, until you load the filament into the printer. Place the container over the lid stand and press it down. Finally, feed your filament through the feed tube until it is loaded into your printer, and then insert the feed tube into the fitting.</p><h3>Auto Rewind Spool Holder modifications</h3><p>I significantly modified the Integrated Auto-Rewind Spool Holder by @VincentGroenhuis at <a href="https://www.thingiverse.com/thing:3781815">https://www.thingiverse.com/thing:3781815</a> -- it works well for narrow spools, but a hub that accommodates a 90mm wide spool has some problems as originally designed. With the 9 spring blades recommended for 90mm width, the spring allows the spool to unwind at least 7 turns before the spool starts slipping. Because a retraction is only about 1 turn of the spool, the spring still has most of its stored energy remaining, and often continues rewinding after retraction, pulling the filament right out of the MMU2S. This doesn't happen with the MMU2S default PTFE feed tubes having 2mm inner diameter due to the high friction, but I replaced all of my feed tubes (including the extruder feed tube) with 3mm inner diameter tubes to reduce friction along the entire filament path.</p><p>So I had to modify the spring so to use 3 out of 11 blades (for a PETG spring) or 5 out of 9 blades (for a PLA spring), and design an axle with a retaining ring to hold the spring in place. This design has the advantage of needing less plastic to print the spring, instead of filling up the entire volume of the hub with spring blades.</p><p>I also fixed a coplanar-surface bug in the OpenSCAD rewinder design, which was causing undesirable artifacts in the STL output. In the OpenSCAD source file, all of my changes are indicated by a comment starting with //am.</p><h3>Rubbermaid container rim profile</h3><p>After careful analysis, the lip of this container appears to be constructed of three arcs: a 32mm arc for the corners, a 300mm arc for the narrow sides, and a 2250mm arc for the long sides. This was determined by measurements, using the 'optimizer' feature in Microsoft Excel to determine the optimal arc angles and arc origins, printing to check the fit, and repeating until perfect. It took 3 iterations. I published the initial version of this profile at <a href="https://www.thingiverse.com/thing:4004086">https://www.thingiverse.com/thing:4004086</a></p><p>The OpenSCAD model includes a function to generate a polygon of points representing the outer rim profile of the lip of the container. This is used to construct the spool stand.</p><h3>Print Settings</h3><p><strong>Printer Brand: </strong>Prusa</p><p><strong>Printer: </strong>i3 MK3S MMU2S</p><p><strong>Supports: </strong>No</p><p><strong>Resolution: </strong>0.4mm nozzle, 0.3mm layers (draft mode)</p><p><strong>Infill: </strong>15% gyroid</p><p><strong>Filament:</strong> Prusa PLA or PETG for stand, PLA for axle</p><p><strong>Notes:</strong></p><p>Use a 4-5mm brim when printing the stand with PLA. Large parts printed with PLA can warp and pull off the build surface, so the brim helps prevent this. No brim is needed for PETG.</p><p>For the stand, in PrusaSlicer go to Print Settings &gt; Advanced and set "Elephant foot compensation" to zero, otherwise the brim may not stick to the part. The part is already designed with a slightly smaller first layer anyway, so elephant foot compensation isn't needed.</p><p>&nbsp;</p><p>Category: 3D Printer Accessories</p>