Hi Guys,

I've gone through various alignment video's etc to see if I could improve the quality of our recently upgraded "Chinese Laser" engraver.
The problem began with a 'relatively functional" CO2 laser at our maker space which was "Upgraded" with a 50W 990cm Piri Laser tube.
The original was a 40w tube. We didn't change the power supply. The tube seems to reliably lase between 3ma and 10ma and beyond.

New mirrors and tube in place, we aligned the beam using thermal paper as targets. The first two mirrors were relatively easy but the 3rd mirror, on the head really doesn't have any adjustment capabilities in that the diagonal mirror is simply fixed in place with a piece of spring metal. The lens, a planoconcave mirror with a 65mm focal length is also new (previous was a 50mm mirror). The lens is ZnSe. The mirrors are Si.

The beam out of the head appears to not be perpendicular to the cutting surface. I say this because the cuts are not at right angles to the surface being cut. It's almost as if the beam (as a cone), is striking the surface at an angle of say 88 deg or so. One side of the cut is ~90deg while the other side is a more exaggerated bevel. It isn't as simple as "cuts along the X axis are square but along the Y axis, they are beveled". Not sure why, but I suspect the head alignment isn't right in both plains.

We do have air assist on but the pressure is relatively low and the cooling effect at the cut face doesn't seem to be a problem.

In trying to sort this out, we did a few things. First was to ensure we weren't out of the Fl of the beam. To this end, I made a wedge of wood, removed the honey comb deck and ran the beam "up" the inclined plain of the wooden wedge. As expected, the beam is a gradually narrowing dot that reaches a point, after which it begins to expand again. Using this method, the depth of focus appears to be a few millimeters, at least. This is pretty coarse measures of the beam, but it is a start.

The other thing I did to try and sort this out was to fire a test point on a piece of wood, then place the edge of a piece of 1/4" PMMA onto that point. Firing the laser at 3ma gave a pretty convincing image of the actual beam. That was how we came to the conclusion that the beam was striking the surface at other than right angles. Under a 10x stereo microscope, the image was pretty telling.

So, at this point, we have really pretty poor cuts on 1/4" plexiglass.
I know that this chinese laser is less than adequate, but since we've changed the tube, we've had nothing but trouble. I'm open to consider this a beam quality issue, rather than alignment, but the focused beam appears to be tight.

Any help at this point would be greatly appreciated!
Thanks,

Doug