Laser Cutter Status

Current Status

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Josh brought in his Netgear Wifi Extender, set it to Makerspace_EXT, and plugged in its ethernet cable into the laser. The laser will now log on to our wifi network on boot up as long as the wifi extender is powered up and all three LEDs are green. So now you can run from the laser laptop no matter where it’s at. – Josh Pritt 4/12/2017

We had to replace the tube with the previous one and realign all the mirrors. Trevor, Arlo, Josh, Erin, and Rob all worked together over several different days over two weeks and got it working again! The laser cutter is back in service! – Josh Pritt 4/5/2017

After moving to the new space, mirrors need alignment. Trevor, Arlo, and Josh tried to align but the invisible beam comes out clipped (not a perfect circle/dot on thermal test paper) right in front of the laser tube aperture. This shows that it’s not getting clipped by the beam combiner. The plan is now to replace the laser tube and test / realign mirrors again. – Josh Pritt 3/30/2017

Eugene fixed the laser again by replacing the power supply with a brand new one. Feel free to use it for your projects again. – Josh Pritt 4/27/2015

The tube is not firing again. Either we’ve reached the life limit of total runtime hours on the tube and it’s time to replace it, or the power supply has gone out again. We will troubleshoot it some more on Monday April 13, 2015. – Josh Pritt 4/14/2015

The laser cutter was further aligned and now cuts the hobby plywood in one pass on both the top left and bottom right corners of the laser bed. Raster images are no longer “ghosted” as two slightly overlapping images and will etch properly and clear and focused. The mirror #2 had to be adjusted as so: loosen the top right screw 1.5 hex wrench faces. Note that the laser could probably be focused even more if we want to spend the extra 1 or 2 hours to really get it all dead center. – Josh Pritt 12/02/2014

The laser cutter has been aligned. It’s not quite perfect, but it’s pretty close and the beam is hitting the focusing lens over the whole range of motion. However, it’s evident that even though the tube is clearly firing, with a nice violet glow, it’s not developing anywhere near the rated power. It’s putting out enough to mark the thermal paper for aligning it, but that’s all, not nearly enough for cutting. I’m not sure what the problem is or, at this point, how to further diagnosis it. – SBB 11/06/2014

The laser cutter is awaiting re-alignment.

Thanks to Gene, the faulty power supply has been replaced and the laser tube is firing fine, but the mirrors are out of alignment and the laser beam is missing the focusing lens completely. It is normal that it should need re-aligning after replacing the laser tube. I was unable to do this Monday evening because I lacked the correct Allen wrench. We tried a number of alternatives, i.e. nearby sizes, non-ball end, or short ones, and only a long, ball-end 3/32" Allen wrench will do. –SBB 8/21/2014

Old status updates

Power supply testing

I built up two instruments to test the power supply. Both are 1000:1 voltage dividers, one with a total resistance of 10M ohms, the other 400M ohms. Using the 10M ohm load alone (no connection to the laser tube), this is the measured voltage from the power supply:

10M ohm dummy load

10M ohm dummy load

This was set up with the laser cutter set to raster scan a rectangular block, so you can see the initial spike as the power supply tries to turn tube on, then it falls back to constant current regulation once the gas in the tube has ionized. Once the horizontal raster line is finished, the laser turns off while the lens head retraces, then the pattern repeats for the next raster line.

So the pattern of the trace is pretty much what I was expecting. However, the voltage levels are not what I was expecting. The initial spike is only about 5kV where I was expecting 20kV or more. It’s possible that the spike was too short for my oscilloscope, but it’s a pretty fast scope (nominally 100MHz). The plateau of current regulation was also a much lower voltage than I was expecting (1kV vice 15kV). I think the 40W laser tubes should be drawing about 18mA at 15kV for full power operation. (The 10M ohm load was sized, approximately, to simulate a tube at the lowest power.)

The upshot is, I didn’t learn as much from this measurement as I’d hoped. The power supply seems to be trying to do the right thing, so it’s not definitively broken. Either it’s working and my dummy load isn’t simulating a laser tube well enough to get it to put out full voltage, or it’s failed in a way that prevents it from putting out enough voltage to fire the tube, but not totally busted.

The next test was to put a 400M ohm 1000:1 divider in parallel with the new laser tube:

Laser tube

Laser tube

This is not a pattern I expected. The power supply is trying to fire the tube, but apparently doesn’t succeed. The 400M ohm parallel path is would only draw about 50 micro-amps at 20kV, not enough to disturb the tube.

Possible diagnoses

  1. The new tube is defective.

  2. The power supply is broken, in a way that means it still puts out high voltage, but no high enough.

Options for next step

  1. Put a load on the power supply to simulate a laser tube at full power. I think this is about 800k ohms, rather than 10M ohms. I’ve ordered another batch of power resistors to build up another dummy load.

  2. Just assume the power supply is not working, and replace it. We have a spare supply in hand (I bought one at the same time I bought the resistors to build the first set of dummy loads.) This will be a somewhat tedious operation, but probably won’t take more than an afternoon.

  3. Neither the laser tube or the power supply can easily be tested ex situ. The tube requires a special power supply and water coolant supply. The power supply requires a number of control inputs. Both have the potential to do serious injury to a careless person.

The catch is, I will be out of town for most of the next two weeks, so the next opportunity I will have to work on the laser will be at two weeks from now. If anyone else has insight into laser operation, or wants to do some experimentation, that’s okay, but please be careful. –SBB 6/29/2014