I had noted that nophead and others were lubricating the filament to keep friction down on the filament during feeding, and for my design wanted to come up with a better way.
These rollers are skate bearings with an aluminum ring pressed around them. The rings only took a few minutes to make from a piece of aluminum tubing on the lathe.
The rollers are mounted on a small stud of drill rod with an eccentric hole, so that they are adjustable by twisting the mounting stud and tightening the screw.
I tried designs that had 3 rollers and that had only 1. Based on some basic calculations, i'd computed that i'd need about 6-8 threads to engage to make ensure that the filament would buckle coming out before the threads would strip the ABS, so I was unlikley that 1 roller would work. That turned out to be the case-- 1 roller does not force enough thread contact to feed under worst case conditions. 3 was overkill, so 2 is what i ended up with.
This version is just a lashup, the rollers are too far from the exit at this point, but still the concept works very well.
I believe that the adapter rings could be rep-rapped also, and perhaps a semi circular profile could be used in that case. I did a v-groove because I could use a 90 degree lathe tool i already had and didnt want to grind a semi-circular profile tool...