Make sure your frame diagonals are spot on, as close as you can get them. Then before you start your cut make sure your rollers are equal distance from the corners on each axis. when you move the gantry around you can kind of twist it. I have been cutting the MP3DP frames that are 15.5″ squares and now they are coming out as perfect as I can measure with a tape, and a large square. The first time you do it it will make sense and only takes 30 seconds or so.