The replacement mirrors and lens arrived this morning, and I got them installed and working this afternoon. The laser is functional again, maybe even a little better than before. Let the artmaking resume!

I replaced mirror 2 (which might have been OK), mirror 3 (which was trashed), and the focus lens (which was destroyed). Did a full alignment on the optics, and a rough spot-check on the table leveling.

People have noticed that the laser seems weaker on the lower right and works best in the upper left region of the work area. It’s normal for there to be some small differential, because of the longer beam path to reach the lower right, but it was much worse than normal. I think it’s improved now. A cut that worked at speed 17 in the upper left required a speed of 13 in the lower right.

The new lens has a slightly different focus point than the old lens, for whatever reason. I have adjusted the autofocus probe to what seems to be the best focus point for the new lens. If you prefer to measure, you’ll find the new focus point is several millimeters longer than before. That is, the table is a bit lower with respect to the cutting head.

People have had trouble cutting half-inch plywood. I was able to cut a small square out of half-inch plywood today, in a single pass at speed 17 (or 13 in the lower right corner) at 100% power. There was some charring on the edge of the wood, but nothing that wouldn’t sand off. The only trick I used was to focus a bit down into the material, instead of at the surface. The Z axis setting I used was about where the autofocus probe touches the material, but that was just an educated guess. You’ll still need to experiment with settings and focus heights to find a configuration that works with your specific plywood.

I still think we can get better cutting of thick plywood (half-inch and maybe thicker) by getting a stronger air-assist compressor. I’ll look into that soon.

I hope to see you and your laser-cut art at YOUtopia!

The laser is offline for repairs. Replacement parts are expected to arrive on Wednesday, October 8, and if all goes well I’ll get them installed on Thursday. Apologies to those of you planning to use the laser in the next few days for last-minute YOUtopia projects.

In the photo gallery below, you can see the damage. The zinc selenide lens has a hole blasted in it, and most of the surface of the final mirror (a few inches above the lens) has been ruined, with the worst damage in one localized area. These parts need to be replaced (about $300). Besides that, there’s a notch out of the aluminum mirror holder at the top of the cutting head. That won’t cause any problems, as far as I know. There was also a coating of reddish powder on the inside of the tube between the mirror and lens, which I presume to be oxides of the material blasted out of the lens.

I am not sure exactly what happened. Clearly, the laser beam itself did all this damage, but what went wrong first, and are all three types of damage the result of the same sequence of events? I don’t know. There are basically two things that can go wrong: gross misalignment, causing the laser to hit the holder instead of the mirror, or crud on the mirror and/or lens. I didn’t find any gross misalignment when I checked, so I suspect there was crud on the mirror and lens.

If there was crud on the optics, it was probably a build-up of smoke deposited by burning plywood. If there’s crud anywhere on the optics when the laser passes through, it gets hot, possibly burns, and damages or destroys the optical surface it’s on. Once the optics are damaged, the laser beam can bounce around unpredictably and cause additional damage. Once the surfaces are no longer pristine, the heat left behind by the laser beam causes the damage to accelerate quickly.

Put this down as a lesson learned about keeping the laser’s optics clean. I will try to do more preventative maintenance, but every laser user needs to be aware of the issue. At the beginning of your laser session, shine a flashlight at the mirror in the cutting head (look sideways at the left side of the top of the head) and see if there’s any visible crud on the mirror. If you see any, you can clean it (if you know how to clean it without causing damage!) or stop and report the issue.

If you end up making a lot of smoke during your laser session, please inspect the mirror again at the end. Make a note in the log. Post a note to warn the next users. Let me know if the mirror needs cleaning.

Unfortunately, the lens can’t be inspected without taking things apart, so I don’t recommend you do that routinely.

If you notice the laser isn’t behaving as expected, please let me know directly. Email is best (my address is on the wall). Make a note in the log book, too. Sometimes we can catch a problem and fix it before it causes permanent damage to the optics.