Looking at Dave’s extruder, I noticed that the motor, belt & wheel setup he has are very similar to a set that I have here, salvaged from an old washing machine, except that what I have been wanting to do with this motor was to build a lathe, like this one.
So it just occurred to me, that with making this machine modular as one of the aims, we could possibly design one to be mounted in a lathe, so that when not extruding plastic, that bench and motor can have other uses (killing two birds with one stone, while saving workshop space and materials 
This may mean that the machine requires a stand to be clamped to the table, rather than bolted down, possibly with adjustable legs, unless the barrel can be positioned in a lathe tool-holder.