Clam shell Prusament spool holder extension

Hey team,

I started this journey by purchasing a 2kg spool of Prusament filament and finding it didn't fit the standard Prusa spool holder inside the enclosure (woops). In an ideal world, being able to purchase an injected moulded spool holder directly when purchasing the spool would be ideal, but since that doesn't exist right now, and I wanted to hold the spool within the Prusa enclosure, I started investigating.

I began by downloading and printing this model (https://www.printables.com/model/295403-2kg-spool-adaptor), I liked the idea as it was a good use of space and leveraged the original spool holder which has been made of injected plastic rather than 3D printed. I suspect Prusa have done their research and found this to be a more reliable way to hold spools without failure. Printing this model however, the tolerances were a little tight, and although felt strong, I wasn't quite satisfied.

I then started experimenting with an alternative clam shell design held together with cable ties. The reason being, when printing in the vertical direction, the force applied to the spool holder in the mounted position will be along the weakest point of the print, between the layers, which could lead to a sudden and catastrophic failure, causing potentially 2kg of plastic heading straight for the printer bed (something that would probably keep me up at night).

My fist design didn't quite work out due to some sagging during printing from a lack of support material, as I felt I wouldn't have been able to remove the material effectively, but the concept I thought worked well.

In the second design, I made everything a little thicker and accommodated for larger cable ties, just to be on the safe side. Each of these cable ties has a 7.5 mm wide strap and 12.3 mm wide head. They are rated to a minimum of 55 kg sheer force each, completely overkill :-), so I can sleep soundly at night. 

This clam shell design means they can be printed in the horizontal direction, which means when mounted, the force will be applied along the print strands, rather than between the layers, which is the strongest orientation for a 3D printed part.

Finally with regards to this design, I decided to create the spool holder at the outer end of the original holder, rather than the inside, or recreate the entire holder as other designers have done, because this means the overall force applied to the part will be less. Effectively what we are dealing with here is a lever, and the force applied to that lever is determined by the weight of the spool and the relative position of that weight. The closer the 3D printed part is to the fulcrum of the lever, the greater the force applied to the part. This design is certainly less elegant, and is a little ugly to say the least, but I'll have greater faith in this design to hold up over the long term.

When I printed the part the fitment worked perfectly with the Prusament roller bearings I made earlier (https://www.printables.com/model/540483-prusament-roller-bearing), so well that I only needed one of the cable ties as the bearing held the extension together quite nicely. I did however notice once I mounted the spool, at the lower position it was a little close for comfort to the print bed, so with regret I moved it to the higher spool position which was a bit more risky for testing, given the additional height, but better than having a guaranteed collision.

Upon the print starting I saw a little bit of oscillation from the factory Prusa spool hanger so decided it would be best to give it a little more support by adding a magnetic hook and an additional cable tie just to take the pressure off a bit and to level out the spool (keep in mind this was a brand new 2kg spool at peak weight, so what I'm seeing here should be the worst it'll get.

With regards to printing, I have attached the gcode for your convenience but below is a summary;

Starting profile: PETG 0.30mm DRAFT (modifications below)
Material: PETG
Layer Perimiters: 6
Infill: 50%
Fill pattern: Gyroid
Generate support material: Yes
Support Style: Organic
Support on build plate only: Yes