Just something I quickly hacked together to be able to feed my printer from a second Robox spool which is not in the printer.
I had some ~10mm plastic pipe laying around, so I used that to connect sides of the holder together and also as an axle that goes through the spool.
Version 2 of the middle path has teeth to grap the reel. This way the same setup can be used to spool different filaments on a Robox SmartReel using a drill.
Version 3 has a slot to accommodate for manually winching filament on the spool. Version 4 has a square hole through the whole adapter. A crank arm and related parts are only needed for this.
A round axle and robox adapter is recommended is crank arm will not be used.
I also added a taller version to accommodate for bigger 1kg spools. New spool adapters fit 3DPrima, Colorfabb and Taulman spools. These are not mandatory as the center of these spools is already a round hole (unlike Robox SmartReels which pretty much require an adapter for smooth use). Note that these reels are also wider than the robox reels, so make the holder and axle wide enough if you plan to use different reels.
I printed from PLA using ~15-20% infill. 4 top and bottom layers, 3 perimiters. No scaling for any parts except for the crank axle, where I used the scaled down version.
If printing from ABS (or other materials) scale up to keep the original size, so reels will still fit as expected.