Calibration on X/Y/Z will not improve your ovals, as the reason for ovals is slack in one of your belts.
You'll have to make sure that:
1. The short belts have enough tension by pushing the motors down. (This usually has to be done once again after a few hours of operation, but then never again)
2. The long belts have enough tension, by adding belt tensioners.
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joergen 2
You really have to get your mechanical parts in order before you can expect getting something like proper prints out of your UM. if everything wobbles and has slack, please have a look at the assembly instruction again: http://wiki.ultimaker.com/Ultimaker_rev.3_assembly:_Extrusion_head
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