@craigylad86 said in Loss use of z axis.:

The z axis started to play up by missing some steps and eventually juddering up down and in opposite directions as I was controling.

That's typically caused either by excessive friction of the axis; or binding (most common when there are multiple Z motors and they have got out of sync), or setting the Z acceleration (M201) or maximum speed (M203) too high.

It could also be caused by a bad connection between the stepper motor and the Duet, so that only one phase of the motor is being driven. If that's the case then you may get "phase may be disconnected" warnings from RRF.