To any that read my comment that I later deleted: I’m sorry for adding such nonsense. A closed belt loop is strictly necessary for continuous extruder operation. I had only seen timing belts being sold in very limited ranges of loop and open lengths. Thanks to @Tim_Rastall my eyes are now opened.
@Tim_Rastall Maybe. Your experiment on that one. I’m going to see about getting closed loops for my next bot… thanks for designing my concept! lol
@Matt_Kraemer that’s what open hardware is all about bro :). Go forth and develop.
This is back burner, unfortunately. I’m building a 1200x900 wood router for Chris Edwards over the next few months. (I get permanent access!)
Sweet!
What about combining Nicholas Seward CoreXZ with this CoreXE and just make it Dual CoreYZ and single or dual CoreXE on top. 
https://plus.google.com/104209901845806192943/posts/98dLQPwGHcx
So, it seems the E would need to be added to one or the other axis movements right? This would mean it needs to move very fast sometimes and super slow others to keep constant while riding on top of the carriage speed and direction, whichever way that is. I’m thinking that if one puts a 5:1 gear on the effector, there won’t be too much disruption to movement per se, but the E belt will need a pretty large speed capability.