New K40, laser not firing at all

Hi all,

I recently set up my new K40 and got it connected to K40 Whisperer. I haven’t sent it anything to engrave/cut yet, but I’ve noticed that the laser doesn’t fire at all when pressing the laser test button.

I assume the laser is supposed to fire when this button is pressed?

Is there anything I need to do before the laser will fire? I’ve made sure all the packing and padding has been removed and nothing is blocking the laser path. I’ve even held a sheet of paper at multiple places in the laser path and there is no marks on it at all (set at 60% power) after the button is pressed.

Really hoping my unit isn’t DOA.

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Does the display panel light up, if not you do not have main power.

if so …

Did you depress the “laser switch” that enables the laser?

if so…

Down on the laser power supply push the Test button does the laser fire?

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Yes, the panel is lit up and the laser switch is on. Pushing the Test button lights up the small red indicator light beneath it, but the laser doesn’t fire.

The pump is running and water is circulating through the tube as expected.

Can you please post a picture of your LPS showing the connectors and the test button you are pushing.

You did not mention what power level you had set on the digital display. Those are not accurate at all and most will recommend you never set it to more than 40% unless you put an analog 30ma current meter on the machine so you know, accurately, what current if flowing through the tube. A stock K40 tube will often burn out quickly when driven over 18mA. Same goes for running the tube with water temps over 25C.

I would try setting the digital display to something like 30% and see if it fires. Do that AFTER you answer Don’s question about putting the little TEST button on the laser power supply(LPS). A quick test of that button tells us the LPS and tube are functional.

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Ah yes, I was definitely pushing the wrong test button. I was pushing the one on the control panel, not the one on the power supply.

I’ll also make sure my digital display is set to 30%.

I’m on holidays for a couple of days, so it’ll report in when I get back.


So the issue ended up being caused by a small safety switch under the lid of the laser cutting bed. It’s designed to only allow power to pass to the laser when the lid is closed. But it’s misaligned! So the lid wasn’t depressing the switch, and power wasn’t getting passed to the laser!

Pushing the lid down onto the switch and pushing the laser test button gets a “buzz” from the laser, and a bit of light in the laser tube, but not much. As far as I could tell nothing was being reflected into the cutting area.

I’m a bit concerned about cooling here at the moment (currently 30 Celcius ambient temp), so I’m putting a hold on any more tests until I’ve got a solution for my reservoir sorted out. I purchased a 20L (5 gallon) bucket and have filled it with 15L of demineralised water. Once I’ve got one of the 5L water jugs frozen, I’ll drop it in, chill the water to 18-20 C and try the laser test properly.

I’ll report back tomorrow.

P.S. The pump that comes with this thing sucks. I’d welcome any recommendations for a replacement.


I use a HF 200gph pump, which I do not think they make anymore.

I have seen these pumps recommended by others…

Expensive but supposedly better reliability:

Sad that it was misaligned, but glad that they are actually putting a lid interlock in. It’s an important safety feature often omitted. Were you able to get it aligned to function without having to push on the lid?

FWIW, folks often use a series of 0.5 - 1L bottles to keep the water within range, rather than a single larger bottle.


I haven’t re-aligned the switch yet. The panel it’s fixed to moves laterally, so the switch often becomes trapped/obscured by the next panel across. I think it’ll need a 3D printed block to position it correctly so that it’s depressed by the lid and doesn’t move.

And yes, good tip regarding using smaller bottles to fine-tune the temperature. More surface area = better heat transfer.

But also, less surface area (one small bottle at a time) = less heat transfer so you can avoid making the water too cold, as well as avoid allowing it to get too hot.

Ok, I’ve got my reservoir cooling working well enough for a test fire. I can confirm that the laser is indeed firing, but the beam isn’t making it into the cutting chamber. I placed a piece of timber under the laser head in the cutting area and it didn’t leave a mark at all.

Here’s a video:

It looks like the first mirror is just badly misaligned. The laser is entering the cutting chamber, but missing the second mirror by a wide margin. The beam is hitting the inside of the front of the lid, half way between the handle and the front air vents.


After an hour or so working on the alignment, it looks like I’m in action!

Thanks everyone for your time and assistance!


It turned out you had a few problems to solve, so I couldn’t mark the one thing that resolved as the solution, but glad you got through all the confounding problems to a working machine! :relaxed:

I lived in the Phoenix area and purchased a 5202 chiller. It didn’t work when it was received.

I had some copper 1/4" tubing and a beer cooler. Put the coil in the cooler with ice and water and it lasted a long time as I was in the 105 deg plus area.

The copper tubing isolated my distilled water from the cooler water.



The copper tubing loops in the laser tube distilled water will keep down algae too.

@NedMan as the resident chemist: Would you expect distilled or deionized water flowing through copper tubing to become contaminated with ions that make the water somewhat conductive?


I believe Jack is doing similar things I’m doing and that is using a coil in the copper tube in the laser reservoir circulating water through the coil via a 2nd circulation system with the cooler. ie the liquid flowing through the coils is not flowing through the laser tube.

But the question is valid only that it is more of a coil of copper tubing sitting in gallons of distilled water which probably dislodges copper ions much slowly.

As hinted in its description, it’s the deionized water that causes the most havoc.