@br7408 My main reason for using a second gantry was to keep the Bowden tubes as short as possible. They were about 150mm in length but if I'd mounted them on the frame (it's a largish printer), they would have been closer to a metre in length. My first attempt was to have the gantry passively driven by loosely strapping it to the hot end gantry but that wasn't very successful so I changed it to a driven gantry. AFAIK, that was the world's first CoreXYUV and the Duet guys made the firmware allowing both gantries to be homed individually. After homing, the UV motors were mapped to the XY axis so from a slicer point of view, it was just a CoreXY. Later on, I did some tricks with motion planning such that the UV gantry followed the XY gantry but within a tolerance of about +-30 mm. This meant that when printing circular features with radii less than 30mm, the extruders could be "parked" in the centre while the hot end printed the feature. But this is all digressing away from your OP