I needed to cut 6.4mm oak with a 50w machine. Two passes doesn’t reliably cut thru. Below describes how to cut from both sides using mirror horizontal.
First laser cut a straight piece of thin wood or poster board that’s clamped or held with magnets to the table. Include a tick mark in the center of the new cut line. Jog the origin +Y slightly an reset origin. Reset Z focus for the cut piece.
Upload the first pattern with the origin set at the lower center
Put a notch in the cut wood and align it to the mark on the wood strip
So the notch in the wood strip should align with the notch in the cut piece which should be just below the current machine origin. You can check by test firing.
Cut the first patten then upload a horizontal mirror of the pattern. cut the second pattern after flipping the wood and aligning to the notch.
Don’t change origin between cuts.
Since everything is aligned you can take more passes by simply relocating the wood to the strip and above the notch.