This is an adapter that allows you to convert an (empty) prusament plastic spool to a master spool.

Motivation
I love the concept of the master spool, but it's quite a heavy print (6+ hours for part B, 12+ hours for Part A). I saw that the prusament spools could dimensionally fit and be re-used as master spools with a simple adapter. I iterated over several designs and came up with this 3 part design, where the adapter core (big cylinder) is required and the screw and nut are optional (you can also use zip ties to fix the two parts of the spool together in the middle instead of the screw and nut provided here). This makes it a much faster and cheaper solution than printing the master spool, and it also helps reusing a plastic part that would otherwise (possible) go to waste.

Prusament spools have a cardboard core, and you can even re-use that to create something nice such as this.

Usability
Actually tested with prusament spools and dasfilament refill filament. Works fine, the core fit is a bit tight but do it slowly and you will end up with a good compact and sturdy spool. Plastic bag and silica gel that comes with the prusament are also to be re-used for storage later.

Assembly
First take the prusament spool apart, by gently pooling on the two plastic half parts. You should be left with two plastic sides (they are injection moulded and identical, apart from the laser edged label) and a cardboard core.

Option A: you printed just the core
Place the prusament spool half on the table, put the core, it should match the inner lines of the prusament spool. Now put your re-fill filament on (it should slide onto the core tightly, take care the 3 zip ties on the filament are aligned with the 3 slots on the adapter core). Now put the second half of the prusament spool on to the core on top, and use the hex holes bellow the core line to tie long zipties (two on each side should be enough) trough the spool to keep the two parts together. Happy printing with your new master filament spool!

Option B: you printed the core, screw and the nut
In this case put the screw down, slide one half of the prusament spool on it (screw goes in the middle), now slide the core on to the spool half, it should match the inner lines of the prusament spool. Now put your re-fill filament on (it should slide onto the core tightly, take care the 3 zip ties on the filament are aligned with the core 3 slots). Now put the second half of the prusament spool on to the core on top, and put the nut on the protruding screw, and start tightening. When the nut is flush with the screw, tight a bit more and you are done! Happy printing with your new master filament spool!

How to print this

Fastest way (actually tested):

• Adapter core: print with 2 perimeters, 3 top/bottom layers, 0% infill and 100% infill at the middle part (see picture with a cylinder modifier in slic3r pe) - around 3 hours of print time
• Screw and nut: print with 2 perimeters, 3 top/bottom layers, 20% rectalinear infill - around 3 hours of print time

If you want to print all together it fits the Mk* plate and takes around 6 hours with the above settings

Other way:

• Print with 2 to 3 perimeters, 2 to 5 bottom/top layer and up to 20% infill of your choice

No supports, brims etc. needed. Screw prints head down, core is printed upright (flat part down) and the nut the same as screw, horizontally. I used .2mm layers, it should work also for larger layers. PETG is recommended for strength and durability but it works also in PLA (I printed mine in PLA).