Spool Rack for Printrbot Simple Metal for smaller diameter (25mm hole) filament spools - with mount-screw countersink to prevent spool rib snags
I ordered Sainsmart flexible TPU from Amazon and was pleased to find that it included a spool (earlier reviews of the product indicated it did not used to). The spool is small and the inside diameter is about 25mm. It would not fit on the rack that came from Printrbot.
I designed this replacement as a re-mix of their design with a smaller, rounded spool support arm and a thicker hanging base that keeps the mount screws recessed.
THIS IS A WORK IN PROGRESS - I WILL POST AN UPDATE WHEN THE LATEST STL HAS BEEN TESTED (see details in Post-Printing section)
25% infill (recommended min 20%)
This was created in DesignSpark Mechanical and printed with Cura. I chose supports with the standard (15%) support size so the spool retaining flange will print properly. I am working on a re-design in hopes of eliminating the need for print supports.
Post-Printing finishing and fitting
Note: This is a work in progress. Changes have been made to the current version of this part to eliminate some of the steps it took to make this fit. The original test piece had to be re-shaped at the spool retaining flange end allow the support arm to fit through the back side of the spool.
After removing the print support materials, I lightly sanded any major flashing left on the mount plate and filament spool rod.
Fitting: The fit of this piece was too tight when I first printed it. I drilled out the big holes at the bottom of the keyholes with a 7/64" drill bit so the cap screws would fit through as they should. I also had to do some minor filing to the keyhole slot sides so the part will slide down in place.
Measure once, cut twice (is the old saying in shop environments). I try to do my best to plan things out and not take pot-shots at designing. I did want to get this done in a hurry, so I set up a small test to help me refine this design in stages. As a budding maker, I'm finding that this approach works best for now. I hope skills with design and compensation for materials/printing tolerances will improve with practice.
I took caliper measurements on the Printrbot spool rack such as the base place size, the keyhole distance, the spool support arm, and the spool retaining flange. I checked the original base plate thickness and determined how much more I wanted to add in order to sink the cap screw heads. The filament spool support arm was re-designed as a half-round, taking into account the size needed for smaller center spools.
Initially, I designed the base place with the keyholes and a short (20mm) spool stem. I did a quick print of this test part and checked the placement of the keyholes. Ugh... off by 1 mm. After moving the keyhole mounts apart, I finished out the design by extending the spool support arm and added a retaining flange at the end. The the keyhole bottoms were enlarged to improve the install fit. At this stage, I modded the design with other finishing touches such as rounding edges, and the midpoint to back taper on the top edge.
One portion of the design that was not pre-tested was the spool retaining flange. It was too long to fit through the back side of the spool, so I tapered the support arm below the flange by sanding it. I have built this taper into the current design and will post an update when the final test is complete.