A 3D Printed Filament Spool and a Discovery

I purchased a bunch of PLA filament for my Lulzbot TAZ4 a while back (from Ultimachine.com), and didn't realize until it arrived that I had bought the "Coil" version, instead of "on spool". For the first few months, I rigged up some crazy hanging jig which let the PLA feed out of the bag it came in - looking very much like a intravenous rig used to administer drugs or fluids (analogy un-intended). While this worked, it was wonky and suboptimal.

I decided to use this as an opportunity to design a 3D Printed spool to hold this PLA. I'm sure I could have gone out and bout one, or used the few (actually, just one) spools I have already depleted. But, as we say here at MkrClub, "Any excuse to design something new".

Design Goals

My main goal, of course, was to have something that worked. That meant it had to allow the PLA to be wrapped at a diameter which was loose enough not to snap it, and hold the PLA in place. The spool also had to have the right capacity to hold a full coil of PLA - about 1 Kg - and it should be adequate for both 3mm and 1.75mm PLA.

A close second goal was that the spool should print easily and quickly. I did not want to use tons of plastic printing a spool, and did not expect to just copy the dimensions and design of the standard spool. I expected - as I do so often - to have a multi-part design here.

Design Summary

The core of this design was, well, the core of the spool. I experimented in modeling a bit, and decided to design a hub and spoke model which had very simple and lightweight spokes coming out from the center (the hub). I did not think I needed any "rim" around the outside of the spokes, and that seemed to work just fine.

The spokes were designed as a pair of opposing spokes as a single object - which allowed me to vary the number of spokes used if I varied the size of the core/hob (for larger spools). I started with 4 pairs of spokes per hub, evenly spaced at 90 degree intervals.

Design Challenge

The connection of the spokes to the hub was a design challenge. I considered making each individual poke a separate object, but realized that as pairs they might be easier to connect in a strong way to the hub.

After some experimentation, I came up with a design that not only held very firmly, but used the slight flexibility in the PLA to allow the spokes to be "opened up" to grab onto the hub. Printing these parts flat also allowed for a slight "barb" on the connecting part, which helped created a strong connection until the spokes were physically squeezed to open the barbed ends back up again.

Testing Designs Efficiently

As with many designs, there are small parts that need to be tweaked before they are perfect. When the overall model is large, I like to use a novel approach to testing the most risky parts of the design without printing the whole model. I make a copy of the model and I slice it up into parts - isolating the part I want to test and printing ONLY that part.

For this spool design, it was the connection between the hub and spokes that was most risky and needed testing. Before printing the whole model, I cut off most of the spool, leaving only a small part of the circumference including the connecting part, and printed just that.

You can see in this picture what the TEST PRINT looked like, and this let me reduce the test print time and material by about 80% - giving me more patience to test until the connection was just right.

A Semi-Failure With A Discovery

Generally, the print did not work for me for a few reasons. First, the core was too small for 3mm filament - requiring too tight of a radius. I also need to add an angled hole in the hub to hold the end of the filament firmly. These are easy problems to fix.

So, while I was happy with the design overall, I'm pretty sure that using pre-used spools will suffice. This is likely another "unnecessary creation" which we 3D printing folk often produce ;)

The bright side of this design was the discovery of a new way to connect 3D Printed parts - a goal I've continually pursued. The flexibility of thin PLA prints created a locking mechanism that I'm sure will come in handy in other designs, as it gave me the best balance I've ever achieved between ease of connection and a firm hold.