The wandering can be caused by many factors:
- Sled tilting off working surface, Incorrectly balanced sled or add support scrap wood beyound working surface.
- Cutting too fast/too deep. Dull bit.
- Cutting at extremities of 8x4’ board which causes excessive chain slack. If you need accurate cuts then work in stages and keep cuts within center 6x3’ area. Can be fixed by extending top bar further past cutting area and adding longer chains.
The rounded/wonky corners on the rectangles can be improved by decelerating the cutting speed when changing cutting direction. This is done in you gcode creation software e.g. Fusion 360 see: