Many filament suppliers are starting to offer their filaments as refills.

At Prusa, this is quite simple: Simply store the old roll, remove the sides from the cardboard roll and place it on the refill roll.

But what about the other suppliers? You can buy reusable master spools from some or you have to print your own side parts. Now if everyone had the same cardboard roll diameter, the world would be relatively simple. But it isn't.

Here is my solution: I've created an OpenSCAD file that makes it fairly easy to create your own custom side panels. Enter the outer diameter of the spool, the wall thickness of the side panels, the height of the spool without side panels and the inner diameter of the cardboard roll. Determine the number of ridges and how far the ridges should reach into the cardboard. Finally, you can determine how well your spool rolls with the number of circular steps.

2 tips:
1. test your settings by printing only the last 10 milimeters of the spool. Move the object down in the slicer program.
2. bevel the sharp edges in another 3D program. OpenSCAD is known to have problems with beveling edges.

My thanks go to the inventors of OpenSCAD and Philipp Reichmuth for donating a few lines of code. This Master Spool will be continued under Philipp's license: CC-BY-SA 4.0.