Check if the timing belt is stretched. If it is loose, it does not transmit the spin of the motor well. Check that guide roller is adjusted; tight at the spindle and all the rubber is moving during operation. Also, check that screws to fix timing pulley are not too tight. If they are too tight, timing pulley might not spin properly.
To see the precision, cut out a maximum size of square and circle, measure diagonal line, and adjust tilt of frame.