Cutting ½” with the 1.4mm double has the same degree of difficulty as cutting ¾” or maybe even 1” steel (on the machine your working on). Its not easy. As Mr. Sandoval said, the beam quality has to be just right, the alignment, very good, nozzle and lens in great shape, and the focal point, almost perfect.
The way I try to explain it is, the cutting window is very small, not forgiving at all. What the previous post suggests, is breaking out a larger diameter nozzle and making the cutting window bigger, more lee-way on the other settings.
I agree the WACS set up is a pain. You don’t have to use this cutting head when you go with the bigger nozzle diameter. Use the WACS cutting condition just turn the water “off” and it should work out well.
To answer some of your other questions: new discharge tubes shouldn’t effect the laser one way or the other. If they are installed properly and the machine is aged and purged completely, you should not see a change in cutting.
The standard Amada and Fanuc procedure when changing out a turbo is to put the turbo in, purge and age the laser to get it back to where it was before the procedure then wait a few weeks or a month and then replace the internal optics. During this time its possible the cut quality to decrease. The best indicator that there is a change is to keep and eye on the Laser Calibration Coefficient, Parameter 15204
Please see attachment for cutting conditions