Spiral bevel gears (conical, helical), proof of conceptLook at : http://en.wikipedia.org/wiki/Spiral_bevel_gear for some theory. Actually my naming of these files is wrong, the gears ar not hypoid ! This means that the rotational axes of these two gears do cross through one point in space.Gcode generated with netfabb-Ultimaker edition, Martijn's build-style, 0.15mm layer height. Printed on my (standard) Ultimaker, speed 250%, fan on (great machine !)NB: the teeth were decreased in size somewhat to account for the fact that Ultimaker/netfabb produces parts that are almost exactly 0.3mm too big in x- and y-direction (z-direction is fine). Simply scaling the parts up or down (too much) would render the teeth too small or too big, respectively.NB 2: due to the nature of the ProE module I used the default Csys got rotated by the same angle that the teeth are pivoted, 45°. Rotate the STL (back) by the same angle and you should be fine.Print (0.15mm layer worked fine for me), consider re-drilling (straight) 2.8mm (~ core diameter of M3) holes into the knee, assemble with 3 M3 bolts, turn endlessly (hopefully).Printing them one after another eliminates almost all 'stringing' (using netfabb).