K40 laser tube replacement

Hi peeps, I’m new here and I thought I’ll introduce myself.

I’m a beginner, with lasers, having started with a diode and recently purchased a used K40, to try my hands at CO2.

The machine I bought was advertised to need a new tube and mirror adjustment.
Once I got the machine, I noticed that a bit on the tube came unglued, so obviously
I disconnect it, and I got my handy super glue out and glued it back on. Tried it and it turned on an made a mark on a piece of wood in from of the tube. Was very happy and thought I fix it.
That was until I got my distilled water, and tried to do a mirror alignment…
I noticed that the beam on the first mirror is not round, and on the second mirror is actually two dots, rather then one.
Can someone please confirm if I definitely need a new tube, and what is a best supplier to UK
I have been looking at Cloudray, on Aliexpress, with delivery to UK. They seems to do a lot of parts for the K40. Anybody used them? How is the support?

Also, on a different note, when aligning the 2nd mirror, is there a starting position I should set it to?
At the moment is all bent on one side, and missing the 3rd mirror completely.

Thanks in advance for any info

For selecting tubes, have you yet read Where can I find K40 replacement parts?

Have you read K40 initial setup and regular maintenance yet? It has several fairly comprehensive guides linked:

The path that the laser takes along three mirrors and the lens needs to be precisely aligned. Here are three resources that may help you understand how to do this.

If you prefer video instruction:

Ep6: Laser Beam Alignment. The DIY CO2 Laser Cutter / Engraver Build Series

If you prefer written instruction, here are two guides:

Note that if the third mirror does not align the beam with the middle of the lens, the beam will not be focused correctly and will not be aligned with the hole in the nozzle. You may wish to use a device that helps you align using a red visible laser. One kind uses a “beam combiner” that slightly reduces beam power, and the other is a tool used only while performing alignment .

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Hi Michael
Thanks for the info. I will check them out.

So the laser is out then. For a moment I though I saved it…

Do you have personal preference, and there’s any difference between the different brands of tubes, or are they all made in the same Chinese factory and re-branded?

At least SPT and Reci tubes have a good reputation.

In general, the whole Getting Started with CO2 Lasers category has lots of helpful information beyond those two posts. :smiling_face:

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When I got my K40 there was the same problem, during transport the front cooling ring for the tube mirror fell off. I was able to patch it with Patex and the tube worked fine for a long time. It could be that the mirror at the end of your tube has been damaged or has a blob of glue or similar…
Regarding new tubes, Cloudray is (for me) a trustworthy dealer/manufacturer.

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The mirror wasn’t broken, and i clean it. Maybe some glue got on it but the label on the tube says 2021, so more likely its just gone.

I was looking at Cloudray for the tube, and noticed that there is a version with a metal ring for $20 more… what’s the advantages of that? The wire connection is the same as the one with the glass ring, so not quicker to connect.

Measure your tube length before you order one to ensure it will fit in your machine.

The 35W tube is 720mm - 45W is 850mm…

I have one of the Cloudray 45W metal end tubes… I feel a lot better attaching a hose to metal than a glass nipple. There are probably other benefits…


Good point. Yes, I’ve measured the one inside atm and it’s 720mm.
As Michael suggested alternative brands, I have found an SPT supplier in UK.

Price for the 40W is a bit more than Cloudray from China, but cheaper than Cloudray on Amazon…

Main problem, the length of SPT it’s 800mm, which means that I will have to make a hole in the side of the machine to fit the tube, and will have to find a way to cover it as well…
Also SPT Rated power: 40w; Max power: 50w Will I be able to use the stock power supply? :thinking:

Cloudray has a metal extension box for the side.

There are designs available to 3D print, but I wouldn’t do that without lining it with aluminum tape on the inside at least, making sure that it’s electrically bounded to the case. (If the circuit fails open for any reason, you want a metal surround for safety.)

The laser power supply is, perhaps surprisingly, also a consumable.

You are likely to be able to use it.

But an alternative is to just buy a tube that has a lower rated power and fits in the case, without fixating on 40W as a magical number. Many people have reported that buying a new high-quality tube that fits in the original case still cuts substantially better than their original tube that shipped with the machine new.

That’s sounds even more work…

I’ve emailed the company that sell the SPT, to check on the power supply, as well as to see if the wires are pre-connected or not.

Considering what you mentioned about also having to lining the extension, and not fixating on the 40W I think I might go for the Cloudray delivered from China.
The k40 is my first CO2 laser, and I already see some limitations with the table size. Don’t really want to spend too much money on it, but it would be a good learning tool I think.


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I agree with @mcdanlj about not fixating on 40W. You can do well with these in the original state and I’ve heard many state the improvement in just a tube replacement.

I have a small extension on mine because of how it’s mounted internally, but it’s not lined and is really about physically protecting the tube from me, the stumbling operator.

There are limitations to 3d printing and adding a few hundred mm extension may not be feasible. I doubt I would have 3d printed it if I could have found a metal one I could purchase.

Do what you think is the safe option. You safety is worth more than all of this material stuff…

My replacement tube came with it’s wires already attached. It was easy on mine, I have hv connectors, so just used it from the original tube.

If you buy an OMTech/Cloudray labeled tube from an ebay or amazon type vendor, the main OMTech/Cloudray site will send you back to the vendor… If you have tube problems, you have to go through the vendor that sold it.

Good luck


Thanks everybody for the help so far. I have decided to try my luck and ordered a Cloudray from AliExpress. Hopefully will arrive in one piece & working :grin:

In the mean time I just received my new lens assembly with air assist nozzle, and a new 20mm lens, as the one that was in there 12mm has a chip on the side. Water pump, exhaust tube. I’m also looking at analogue Amp meter, as I have a digital % display, but not sure how will I connect it…

Could someone explain why different diameter lenses? I understand the focus length, but diameter? The only reason I can think of is maybe bigger tubes have a bigger beam diameter?

Sorry so many questions


In What else do I need besides my K40? Requirements and Recommendations (part of the Getting Started with CO2 Lasers category introduced in the K40 Intro at the top of the page) you will find a link to instructions for doing this. :smiling_face: