Laser Cutting Better On X-Axis than Y-Axis?

[hube268]

We were cutting some 0.25" Delrin with our LightObject 80W laser. The laser cut the internal holes and X-axis cuts very well but the Y-Axis cuts were not cut through even after several (~8) passes. I checked to ensure there were not multiple lines with different cut settings. Only one line with a single cut setting. What could cause the difference between cuts of X-axis (horizontal lines) vs. Y-axis (vertical lines)? Laser alignment issues would affect both horizontal and vertical cuts right?

[Tech_Marco]

The laser beam may not be straight from the focus lens to the materials. It could be off. That's they only possibility of cutting one direction better than the other. Even the alignment is good from mirror#1, mirror#2, but the mirror#3 to the focus lens is most signicant.