I built a 3D printer making the parts normally 3d printed out of wood. I made my own arrangement (out of wood) for the extruder and cooling fan etc  This arrangement was good enough to then print the 3d printed parts and a few other things as well. However,  when I printed all the parts for the Reprap extruder and assembled it all ready to try I found that the filament could not get past the hole following the drive spline. It was 3mm out of alignment. So I realigned that and after 2 more prints with corrections,  my final 3rd print was 3mm higher than original and 3 mm wider to the left of the stepper motor mount (see pic) I also had to adjust the extruder idler because it was 3 mm too long and holes for the springs did not line up nicely(not part of my mod) 

I also turned a a new pin for the axle of the extruder idler  as the 3d printed axle was not good enough. Fitted much better anyway.

As printed it all now works as it should, but the top hole no longer lines up, but the lower pair is Ok. Because of the adjustments the unit is a little lower than original too, but operation is not affected. See pic showing original and new version. I had to adjust the height/size of the output hole too , as it was too close to the spline. I am surprised that nowhere have I seen anyone pointing this misalignment out. The videos I have watched don't mention it either. 

 With the new extruder system I have now successfully printed  the Iris with 4 leafs and it works!

Files attached include the new extruder version and extruder idler. All printed with 0.4 nozzle at 0.2 layer height.