Laser Tube Problem

[Mike Mcdonald]

I have an 80 W CO2 laser tube that I recently purchased (along with a red/black Chinese laser).
I have a 5 gallon bucket circulating water. It has been fairly cool in my garage.
The tube doesn't have much time on it. I've cut a few projects ranging from 50% to 80% power.
Now if I set the power on the Ruida 6442 controller above 60%, the tube doesn't fire. Also,
the beam seems to swirl at the discharge end of the tube, creating a wider beam pattern.
I'm new to lasers so any help would be appreciated. Thanks.

[Gene Uselman]

Hi Mike- do you have a mA gauge on your machine? The % of power is different on every machine and often even with different components on the same machine- if you know the max current on your tube, that is what you should really use. If you don't know the brand of the tube [very common] there are table that will give a general max for a wattage of tube. I do not really understand what you mean by swirling of the tube output- do you mean the visible blueish light inside the tube? That will be erratic at low power before the beam really forms- the invisible light beam that does the work in a laser can be checked with a piece of acrylic or similar held between the tube and the 1st mirror [it will burn].
Not firing above 60%- it sounds like it was firing above that at one time? You can test fire it at [for instance] 55% or 57% to see where it stops firing- that may make it easier to trouble shoot. My first suspicion is the HiVoltage power supply or less likely the controller.

[Dave Vigness]

I'll second Gene's comments.

The power percentage shown on the display is a pure fantasy number, and good only as a reference to that particular combination of laser tube, laser PSU, and controller. I have changed controller and laser PSU, and have had to redo my power curve to display percentage measurements EVERY time. They have been within around 3% each time, but they DO change with component change.

Without an actual power measurement, you will never know at what percentage you hit your 80W. EXAMPLE: My tube is labeled at a work current of 24mA for 80W. Actual measurement puts the 80W threshold at 22.5mA. Bumping to the 'full 24mA' only gained me a hair over 1W. Guess what my new max working mA setting is?

[Mike Mcdonald]

Thanks for your response.
50% power - 14ma - works good
55% power - 16ma - works good
60% power - 18ma - works good
64% power - 19ma - when cutting a straight line, starts cutting for an inch or so, fades out to no cut, then fades back in cutting again.
65% power - 19ma - tube has the blue beam down the center, but no cutting or even etching
95% power - 30ma - same
100% power - 31ma - same