In addition to a loose filament attachment, the superb design also include printed wheels inside the spindle section, allowing it to 

rotate on the base smoothly - no more tangles on loose or reeled filament!

Printing it at a 20% infill throughout proved to be plenty strong enough even for a pair of full 1Kg spools I sat on it - it still 

dispensed the filament easily without binding or jamming.

The only part that I haven't used as yet is the (green) filament guide which can have a lubricated sponge fitted to clean filament as 

it passes, and also will accept a Bowden tube of either 3mm or 1.75mm. My reason for not using this is that I have the spool sitting 

behind the printer normally, and quite close - I found that feeding the filament through the guide caused it to be pulled up at a 

quite sharp angle which I was afraid would stress the extruder motor, so I just put a couple of simple loop guides on top of the 

Z rods instead. I do want to clean/lubricate the filament going forward, so may look at getting some PTFE tubing to act as a Bowden, 

even though the PrintrBot doesn't use it.

In total, all of the parts took around 20 hours to print over a two day period. I printed them quite slowly as I'm experimenting with speed vs quality currently and wanted a very strong print, which I'm really happy to say exceeded my expectations. The model is available on Thingiverse here.

General print settings were: PLA, 215c, non-heated bed with Kapton tape and a light coat of glue stick, layer height 0.2mm.