Calibration

If these are 2 runs of the same pattern, then a repeat-ability problem exists. I would check for loose belts, that is to say loose enough for the belt to slip over the pulley teeth. It is also possible for the belt to be too tight, but it is unlikely. Also, ensure that the head travels smoothly, if it binds at all during travel you will loose steps. If you have just received the machine, go over it looking for loose bolts, nuts, & screws. When we received our machine we found many that had come loose during shipping.

I am sure that some other can chime in with other suggestions.