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".
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.
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.
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.