Tired of messing around with samples - and at the same time not interested in using the old big spools for one sample each, I created a separator, so you can have 2 or 3 samples on one spool. for 2, make sure to roll them up in opposite directions, so when printing, only one unrolls. - Or fix the filament you dont want to use really well while printing with the other.

No guarantees for any loops, knots and other mess ;-)

Gcode attached is for Tevo Tornado but might work with other marlin printers as well.

inner diameter 100mm - Fusion 360 file attached for adaptation