Thanks for your comments on my extruder drive. I admit that by using printed parts and a belt drive it could be made lighter. This is my first printer so I couldn't print my own printer parts so used aluminium! I must stress that movement of the X axis DOES NOT affect the extruder in any way. As the X axis moves the chain unwraps from one sprocket and wraps onto the other and the net result is tby Douglater - Mechanics
I considered driving my extruder in a similar way to this thread but was worried by friction and finally went with a chain drive extruder and parallel bars - it works well and I'm very happy with the result. I don't think that this has been tried before. See video below:by Douglater - Mechanics