I've set up my ir probe today, got the latest duet firmware from here and duet web control 1.06 from the Ormerod section. Is that the right web interface version DC? The one you have linked to on your blog seems outdated and doesn't work. When I click the Auto bed compensation button the print head whizzes around and then gives me this: Error: Delta calibration error: 5 factors requested but onlby asbo - Delta Machines
Well the nozzle has to try and go lower than the bed, then if you've got your Z probe offset just right, it will detect the surface and stop the nozzle at the exact distance it needs to be from the bed to print. It can also then probe other locations on the bed to check it's level in relation to the nozzle and, if it's not, compensate(assuming the firmware supports it). So be very careful when yby asbo - Delta Machines
I think you need to increase your Z height by the distance of the gap between the nozzle and the print bed when its at 0. I don't use marlin so I'm not sure exactly what the setting would be called but it should be fairly easy to find. I've had a look now and I think its #define Z_MAX_POS in the configuration.h file.by asbo - Delta Machines