K40 laser tube question

Hi ,first time posting here & I was trying to align the mirrors in my K-40 as it takes many cuts to do the same work as it use to (I’ve owned this thing for a few years now ) , but I noticed when i put a piece of paper next to the laser tube & between the first mirror & fire the laser i get 3 individual burns instead of one round hole . would this mean my laser tube needs to be replaced ? or any way to fix it ?

Hi and welcome to the forum. If you are getting a distorted or multiple spots that usually means the TEM mode of the tube has shifted to a higher mode. If that’s the case then you will need a new tube. If you can provide a picture of the test fire we can confirm.

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This a few test fires between the tube & the 1st mirror .

Looks like a bad tube… @NedMan what do you think?



@copperhead did you have any kind of overheat event??
What coolant are you using?
How old is tube and how hard do you run it?

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Yep, looks like you have shifted to TEM-01 like Don said. Common type of tube failure as your tube ages. I had to replace my stock tube after a couple of years because of this. Higher tube temps can lead to TEM failures.

This tube gets quite a bit of use ,I’ve ordered a replacement & I’ve been using a large container for my water for cooling & that may of been the down fall .as i didn’t realize the ideal temperature was lower than room temp . Has any one tried the CW-3000 water chiller ,is this refrigerator or just a fan blowing on a rad ?

A CW-3000 is just a radiator and a fan. It can dissipate about 50 W of heat per 1 °C difference between the ambient and coolant temperatures. E.g. if the ambient temperature is 24 °C and the coolant is 30 °C, it would manage to dissipate about 300 W of heat.

With a low-power CO2 laser, the math can work out if you’re living in a colder climate.

The CW-5000/5200/etc chillers use vapor-compression refrigeration. They are actual chillers.

If you need something cheaper, see if you can find a used aquarium chiller with compressor for around $150. The smaller ones are fine for low-power CO2 lasers.

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Here’s our article on the subject — we keep updating it as more information shows up, so please feel free to ask clarifying questions there.

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I think I will get a larger water reservoir & or run my pump outside in a large garbage can , with the hose running at a trickle .

It’s almost everywhere a bad idea to run tap water in your tube. It generally has impurities that conduct electricity. Distilled water is a much better choice, and frozen water bottles submerged in a bucket of distilled water are great for keeping the water cool enough.

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Yeah just get a 5 gal bucket with a pump and distilled water and use some frozen 1/2 litter water bottles. I like to use soft drink plastic 1/2 liter bottles because they are a bit more robust than the bottles water comes in. I’ve got about a dozen bottles in the freezer and I can basically run all day if I wanted to just by rotating them out in groups of 2.


and get a water temp device so you know what the temp is entering your tube and can adjust the reservoir as needed.

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I suggest a water temp controller that will stop your laser when the set temp is exceeded.
I use this one and wire it into the water flow sensor circuit.

while you are in there its easy to add cover interlocks :slight_smile:


Thanks for all the help ,I have my new Laser tube installed & it`s working well ,I am using distilled water & a couple of frozen pop bottles full of water keeps the water at 15 to 17 degress .