Water leak, near catastrophe!

I was cutting acrylic the other day and, at first, all the cuts were fine. Gradually, the cuts started to fail. I looked at the temperature sensor for the laser tube and it read 44C! I took a look under the hood and saw water spraying on and around the laser tube and power supply. Before I could shut the machine down, the GFCI outlet the K40 is on tripped. Needless to say, I was pretty freaked-out about all this. I unplugged everything, opened the two top doors, put a fan on the whole mess and let it run for 24 hours. My first thought was the laser tube cracked. I gently removed the tube from its support brackets, removed the inlet and outlet hoses from this chiller:

and used a bicycle hand-push air pump to isolate the leak(s). Luckily, the glass tube wasn’t cracked. Instead, hose connections on the anode end were leaking. I replaced those with new tubing and used zip-ties to secure them. When I reconnected the water chiller, a new leak appeared on the cathode end of the tube. So…I replaced all the tubes on that end. That did the job and I replaced and re-aligned the laser to start cutting again. I’m sharing this experience with a recommendation that owners of K40 laser cutters, check their water hoses very carefully. For me, the original hoses were really easy to remove. When I trimmed the ends of the hoses, it was obvious they had stretched out quite a bit. Easy removal of the hoses could be a sign that they are about to fail.


You did not have water temperature and flow protection installed?
They cost way less than a new tube and LPS…

Depends on the type of flow switch and which side of the flow it is connected to.

One that works, is tied to interlocks and is on the output of the tube :)?

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Obviously not, right? Or I wouldn’t have had this experience. But, I understand what you’re getting at.

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After interlocks, we suggest that water flow and temp interlocks are the first upgrade.
With no safety interlocks your eyes are the next victim of a failure …

Perhaps you have the opportunity to install all this in the next cycle :slight_smile:

I certainly see the need for this kind of add-on for the K40. However, when I search “interlocks” and “temperature alarm” in the search box for this forum, it comes up empty. Any chance you could point to some examples of what you’re talking about or links to learn more??? Thanks!

Check this out and then if you need help come back.


My continuously-being-upgraded K40 has in the works a Raspberry Pi controller that will among other things read a temp sensor in the exit water, in case the pump quits, as well as watching pulses from a flow sensor.
There is another issue. Leaking water from this thing is an electrocution hazard, what with both AC mains voltages in there and with a 20,000Vdc power supply in operation. Not to mention what the water could do to the power supply.
I came up with a novel (as far as I can tell) water leak sensor. Ranch-kind-of-people will be familiar with electric fence tape. This is poly-mumble-ene web about 2" wide, with stainless steel wires spaced about 1/10 inch apart in the weave. You can cut a length, separate out every other thread and connect to a ground, and the other half of the wires to a uC sense line and sense water conductivity between the wires. It’s cheap, very effective, and could easily be laid under the laser tube and hose path to catch leaks as soon as the leak starts.

Thanks for this! I now realize I was only searching the page I was on, not the whole forum. Lesson learned (probably).

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If the water sensor detects the loss of flow the LPS interlock is broken and its shut down, there is no 20,000V???

… if the 20000v is connected to the water it will send a large audible warning not to touch it before it dies LOL

That same sensor could shut down the water pump if more protection is desired.

This website is spectacular! Being new to K40 laser cutting and only having basic knowledge of electronics, I will have to study much of what I see on that site for a while. I was familiar with switches to turn power off to the laser when the lid was opened, but hadn’t appreciated the term “interlock”. NOW, I get it and will see how much I can learn before burdening you and others with questions. THANKS! I appreciate the need for donations to keep sites like this one going and promise to “pay my way”.

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Thanks and we are here when you need us!

11 posts were split to a new topic: K40 Laser Beginner Insights draft document from FB K40 group

Here is my easy door lock solution:


So far :crossed_fingers: I’ve been able to remember to turn the laser power off before opening the door. But, this mod post has inspired me to do the same and make it fool and memory proof. Thanks!


You won’t regret it. It’s incredibly easy to forget that the laser is enabled when working around this machine. The beam being INVISIBLE makes you feel like it is safe when in reality you can be ms away from ruining you vision. This kind of damage to your retina cannot be corrected and at best you get permanently distorted vision and worst your blind.
Secondly getting into the 20,000 VDC high voltage accidentally can also be a lethal event (rear cover).

Unlike most tools the laser and the 20,000V are both invisible means of human injury. A user adjusting the machine can easily be exposed to an invisible beam reflecting from a random surface. So to the laser can be quietly firing and opening the cabinet and getting to close to the anode in the tube cabinet can result in electrocution. This voltage can easily jump > 2".

This protection is akin to using a push stick on your table saw vs exposing your fingers to the blade however the invisible ease at which this machine creates danger and the resulting damage from not being safe can be catastrophic. This is why machines that meet US standards of safety do NOT cost $400 they have well designed safety measures.

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