For those of you using this laser, you'd note that the you tube alignment videos for the optics/ mirrors don't emphasize that centering the beam in the lens as important.

Well in vector cutting, it is important as noted here:

http://www.buildlog.net/blog/2013/05/why-are-my-laser-cut-edges-not-straight/

Although I had a perfect mirror alignment of the beam I still had this angled vector cutting problem....as the beam wasn't quite centered.

I had to

1) Adjust the nut and screw axle arrangement on the top roller pair to 'push' the z-axis top towards the front of the laser machine. this straightened up the sloped cutting parallel to the gantry.

2) Drill a NEW pair of 1/8" holes for the laser lens assy to attach to the Z-axis vertical adjustment, shifting the lens assy to the left by 1/4" relative to the mirror above it. This located the laser beam in the centre of the lens.

3) Drill and tap a pair of holes on the mirror above the lens to provide a 4 point mounting instead of a 3 point mounting for better mirror adjustment control. This proved to be not essential with the other mods in place.

4) Loosen the 3 silver hex screws holding the mirror block (above the lens) to the roller transport mechanism and 'twist' the whole z axis (incl mirror & lens) about 2 degrees clockwise, then retighten the 3 screws onto the roller transport. These screws are located under the top rollers facing the laser tube. The clockwise twist works if the slopes of the cuts perpendicular to the gantry go from left to right. Twist the other way if your slopes are right to left.

Items 2,3,4 straightened up the cuts perpendicular to the gantry.

The end result is near square cuts thru 1/4" thick acrylic on all 4 sides and better beam penetration for the same power setting.

They called it a "hobby" laser for a good reason it seems. You can improve it's precision & results with a bit of effort.