Laser cutter Maintenance - March 23rd @ 7pm

We will be doing some maintenance on the laser cutter at 7pm onwards tonight.

We will be installing a current panel meter onto the tube to give us a spot check about the amount of current being used to drive the laser cutter. We will also be looking at and cleaning the filtration system since the exhaust has been less effective at clearing smoke from the bed of the machine.

I will make an effort to announce earlier next time.

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@KevMacD and I had a pretty successful evening with the laser cutter maintenance.

Thanks to @JohnC and Science World, we were able to borrow a laser power meter. This was invaluable. We measured the optical power output before and after the optical components of the system. The measurement was performed on a Mahoney power meter calibrated to be accurate with a 35 second ‘heat up’ time. We found the following:

PlacementMeasured Power (W)Duty Cycle
Before Optics8570
After Optics7370

This means that we are losing about 15% of our power through the optics of the system. This seems high given that Si mirrors should have a reflectivity >99% and will be something that we will be addressing ASAP. We already have components to replace the entire optical system. I suspect the mirrors are getting fairly hot.

The other interesting thing we can learn from this is that the measured power of 85W actually exceeds the tube’s specification of 80W. This is a red flag since it suggests that we are over-driving the tube at 70% power. Over-driving the tube can quickly diminish the laser tube’s life.

The second thing @KevMacD and I did was install a new current panel meter onto the common leg of the tube. This meter allows us to see how much current is being driven into the tube at a given time. As we suspected, the current through the tube was registering 30mA at 70% power - we are expecting 27mA. I did check the panel meter with a known current before hooking it up to the laser cutter, so I am fairly confident in it’s reading. Frankly I am surprised the tube still works, it is certainly not good for it or the power supply. We found 60% is right at 27mA. Therefore, please use a maximum of 60% power for your cuts until further notice.

The laser current is not yet logged onto our stats collection server with this panel meter - we will be looking on how to do this in the future.

Lastly, @KevMacD gave the laser a good clean. It is shiny now and looks gorgeous!

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As a qualitative benchmark, we also found that we could cut through 6mm of plywood with speed 15, power 60. We are hoping that with replaced optics, we will be able to push this up a bit.

How many mirrors are there, dissipating the 12W load?

3 mirrors. We took off the collimating lens when doing measurements. You need to use an unfocused beam on the meter.

Therefore, we are probably dropping a bit more through that optical component.

That being said, I presume some of the energy is actually being reflected away and absorbed by the laser cutter’s housing. This is based on the observation that the mirrors look pretty scratched up.

Measuring the temperature of the mirrors during operation is another metric that might be useful.

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It’s worth noting that higher wattage CO2 laser cutters (>300W) tend to use water-cooled mirrors, so yes, some heating of the optics is normal, especially if dirty or damaged. A typical brand new gold-plated silicon mirror is about 99% efficient at reflecting the laser beam.