Scratching that itch

I’ve made the leap and decided to cut my laser teeth and a decidedly lower quality laser.

This week my K40 Chinese laser came in!

For the sake of clarity, this same (or similar) laser cutter has been mentioned:

[Here in 60W] (20"x28" 60w Chinese Laser Cutter)
[Here in 40W]
(The Chinese laser experiment)
Here as a comparison vs GF

and probably a couple more that i missed.

BUT now its MINE;)
It came with the legendary Fu Yu acrylic.
No instruction manual.
Dodgy software
Minimal hardware
and it has been a blast to fiddle with!

Ive now had it 3 days, and today got my first cut and engrave out of it. I will say i have already nearly lit my apt on fire. It is not for the faint of heart. haha

Its crisp, but took several hours of guessing. and the repeat-ability without a fixture is gonna be hard. I am VERY excited for the GF now. Those cameras are gonna be awesome.

I feel like ive never owned a car, just bought a broken corolla, and have a Tesla 3 on order. So stoked to drive but really excited for the upgrade.

So as a side note to all you laser Pros out there. My laser tube is making funny noises. Can i get your thoughts on whether its a problem? When the laser fires, it makes a squeaking noise, it doesnt last long, and is usually at lower Amps. But i have noticed when rapidly turning it on and off (like rastering) it will squeak at higher amps. Here is a video of it. Thanks for your help!


I suspect a loose electrical connection with that sound. While searching to find support for this suspicion (no direct experience with such an issue) I found this reddit thread.

They seem to think it is impurities in your cooling water. I still lean toward a loose ground connection, possibly in the tube.


The purity of the water seems like a strange conclusion to me. I will have to look through the wiring and see if anything looks fishy. unfortunately I’m an ME not a EE haha


Odd to me as well, unless there is an area where the water is all that stands between a charged conductor and a ground connection, and so impurities degrade the resistance value which is assumed.

That would roughly match the problem which I expect to be the case, but with a compromise of design instead of a flaw in construction (though I would call it a flaw of design, since you shouldn’t rely on insulation from a customer supplied component.

The loose connection I suspect the most is inside the glass, right where the beam leaves the tube. If you had something which was non-conductive, reasonably heat resistant, and a good sound muffler, you could attempt covering up various physical locations to see if you can diminish the sound. That narrows down a physical location to focus troubleshooting on.

But a sound this piercing… good luck dampening that in an isolated area…

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I don’t have a video of it to show you for comparison but if it is a higher pitch in person than on the video I about gurantee it’s electrical not water related. Sounds like the same Noise you get when you are hipot testing, it’s the ionization of air at high voltage in my case. I don’t make a strong termination point for hipot test because it is static voltage so no heat to worry about and the area between the clamp you use and the cable termination produces a high pitch whine. I have zero experience with hooking up a laser lol but judging from video I would check the connection and also the insulation of the connection. Could be loose and causing a small high voltage arc or insulation could have left an exposed area and ionization could be occurring.

Again it may not apply to lasers lol just trying to help from experiences I have had. Good luck


yah the water explination does not make any sense. That sounds like bad connection I have heard that with cold solder joints. Its typically a vibration that your hearing not arcing. When i last had that problem with a pcb I used a insulated clamp to apply pressure(very lite) to each component so I could find the on that needed to be remounted

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So between this group and the Google+ group. I have found the sound to originate in the PSU. I took the cover off it, and the sound is definitely coming from the main inductor coil. I am well over my head fiddling with that, and a couple people in google+ mention having the same noise and no loss in cut quality, just anyoying. So i think i will leave it for now.

@elsman18 I have no idea what hipot testing is. But your answer sounds the most correct. haha


Pretty sure hipot is high resistance potentiometer. Also known as a Rheostat, or adjustable resistor.

Good to know you isolated the source. Sucks it is something you aren’t comfortable fixing. Any way to put the PSU behind a wall to save yourself some headache?

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That’s a hipot for electronics, I was referring to high potential testing. You do it when installing high voltage cable. Voltage in a cable actually wants to run on the outermost set of wires. When you hipot you force 8x the rated voltage into the cable to provide maximum “force” onto the insulation. You put a ground onto the shield that is wrapped around the cable then read the milliamp leakage to ground. This tells you if any wires have been cut, if the termination of the cable was done correctly and also if there has been any stress in the cable when it was ran.

Grabbed this picture from Google, I have a piece
at work I use to explain to guys in the field what I am testing that is cut out into layers of the cable. The shield is the layer you see right before the outer jacket.


You probably don’t need to be told but take care operating with the PSU case open, given the very high output voltages

You can often ‘fix’ a noisy inductor by pouring resin or varnish into it. The changing electromagnetic fields around the inductor cause it to physically vibrate, resulting in noise, and if you can stop it vibrating then you can stop the noise.

The root cause is probably poor design, which you can’t do anything about, but you may be able to mask the problem quite easily :slight_smile:

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Would seem like you want to attach a heat sink before you coat a large inductor with resin. Those things can get incredibly warm.

Are there maybe resins which are strong heat conductors, so in the end you are just increasing surface area and it is all good?

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Epoxy resin is a much better conductor of heat than air, so filling gaps in an inductor with resin will improve its ability to dissipate heat

@nick07lee’s inductor will already be varnished - it’s standard practice to varnish windings to keep them quiet and safe - just not as well as it should have been

Edit: well, actually, @nick07lee’s inductor may not already be varnished - but it’s still standard practice to do so :slight_smile:


Mine makes the same noise. Haven’t figured it out yet. Glad to hear there are some answers.


Mine makes the same noise. I kinda like it. Sometimes it sounds like it’s beat boxing depending on the pattern


Its the sound of power, creativity and possibly destruction…lol. :wink:


I just got mine last Friday…got it opened and set in place but haven’t had the time to get the software going so I can make some test cuts. Did you have any problems aligning the mirrors?

No its not bad. It’s takes some thought to make sure you are adjusting the correct screw the correct direction. But it was pretty reasonable. Took me an hour or two to get a decent result.

My advice is to do all your adjustment with the top two screws. You can get all the directional adjustment you need with just 2. and the bottom one is a pain to reach and fiddle with.

WOW! I think I might just perform my first few practice run outside in my back yard, with an electronics compatible fire extinguisher handy, just in case! LOL

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Nah. The issues are overstated by non-K40ers or those that aren’t tinkerers and were looking for something more along the lines of an HP LaserJet. There’s still more potential DIY with these than the pro-commercial ones costing 5-20K.

On the other hand, they are not 10% of the machine that a pro-commercial one is despite being less than 10% the price. Probably more like 70%. Some rough edges around component quality, certainly around service (in terms of being able to reach out to someone local) and software integration. But it will cut the same designs the big boys can (on smaller stock) and no one seeing your K40 produced artifact will be able to distinguish it from the one an Epilog cut.

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No, I just mean that I am very likely to burn my house down until I learn what I am doing…