Yet another simple extruder drive

SummaryI designed this to be machined out of aluminum. I printed it out of PLA and did a couple of test prints that way. Not sure how long it would last in PLA though. It uses a 1/4" spring (http://www.mcmaster.com/nav/enter.asp?partnum=9637K66) It comes in a set of 5 11" lengths that you have to cut to length but it's a pretty beefy spring. I'm sure there are some other 1/4" diameter springs that would work.