K40 initial setup and regular maintenance

A K40 may require regular maintenance as part of initial setup because many are shipped with quality issues. Therefore, initial setup includes checking periodic regular maintenance items before you start using it.

Regular Maintenance

The K40 contains some parts that will break or wear out, and some that need regular care. I’ll just mention some obvious ones and add to them as I think of more.

Lens and mirror cleaning

Your lenses either pass or reflect the entire power of the laser beam. This is fine as long as very little of the power in the beam stays inside the lens or makes it past the shiny surface to the inside of the mirror. A layer of dirt, condensed oils and plastic vapor, smoke particles and such can absorb a lot of the power and transfer it to the lens or mirror.

This picture is a bad example. And that is after I cleaned it with acetone. I got my K40 used, and I suspect that the seller thought he was taking me for a sucker. It simply cannot have been working well for him. Don’t let this happen to your lens or mirrors.


Lenses can fracture or spall off a piece of the lens, which of course ruins its ability to focus laser light, and makes it fail even more. What happens to the mirrors depends on what they’re made of. Some mirrors are silicon crystal (semiconductor wafer stuff) coated with a whiff of condensed gold vapor and some kind of coating over the gold. These are the cheapest, and also the most likely to break if dirty and then overheated. Molybdenum metal mirrors are much more durable and only mildly more expensive. A good thing to do is to replace any unsatisfactory mirror with MO (molybdenum) mirrors.

The actual cleaning is tricky if done right. Most of the commercial laser sites I’ve read recommend cleaning the mirrors with acetone – not water, not alcohol – and lens papers, not cotton swabs. I first used alcohol and swabs on mine until I read better. The best thing is probably to do a web search for laser optics cleaning procedures that are (a) recommended by professionals and (b) something you can actually accomplish.

The worst cleaning is no cleaning at all.


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:

If you prefer written instruction, here are two guides:

Unfortunately, all three of these guides recommend using tape as burn targets in front of the mirror. This tends to spread burned adhesive across your mirror. A dirty mirror can substantially reduce the power of your machine, and the more you use it the harder it is to clean. It will heat up in use and the mirrors may be damaged or destroyed.

Instead, use tape away from the laser path to hold plain paper in front of the mirror, or protect the mirror by shielding it from splatter.

Or prepare to buy new mirrors.

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.

Focus setup

You have to adjust the bed of the machine to hold the material you’re cutting or engraving to nearly exactly the focus length of the lens. Here’s why.

Your laser beam emerges from the tube about 5-7mm diameter (¼ inch, more or less), is reflected by three mirrors, and then focused by the lens down to a small spot. In a perfect world, the beam would be perfectly round in shape and “Gaussian” as well as “single mode”. These are not perfect lasers, so the beams are not perfectly round nor “Gaussian” nor “single mode”, so they will not focus to a supremely tiny focus spot.

This is worth knowing because it means that your focused laser burning spot will only get so small, and no smaller. If you’re getting 30W of laser light out of the tube, you will lose a few percent in the mirrors before the lens. Even then, if you accidentally get your finger or other body part into the beam, the 30W of laser light will instantly give you second or third degree burns in the roughly quarter-inch size of the beam. The lens can focus all that ~30W onto a spot maybe 0.010”/0.25mm diameter. The power to burn things at any point in the beam is dependent on how much power is in the area of the beam that hits. Since the area of a circle is proportional to the square of the radius, the same power that hits a ¼ inch diameter in the unfocused beam is concentrated into a spot (0.01/0.125) squared smaller, so the power per unit area goes up by 156 times. The power at the beam focus from a 30W laser is ~3000W in that tiny spot if everything is just right.

The spot power is close to this much for a short distance above and below the true focal spot. Depending on the material, there may be enough “depth of focus” to cut through a material in one pass. How thick the laser can cut through depends on the power density (power per unit area) the material needs to burn/cut it.

If you install your lens curved-side-down, it will not focus correctly. Always make sure the curved side is up.

The “Okay Power” range is not very thick. If your material is higher or lower than the tight, small spot region, it will be scorched or partially cut, but won’t cut through. The spot size is bigger both higher and lower than the perfect focus spot, so resolution suffers from poor focus too. For the K40, the OK power zone is probably no more than 6-7mm thick.

The classic way to test focus, called a “ramp test,” is to set up some material purposely slanted so the laser hits it at different distances from the lens. If you do this right, you can lase multiple lines and pick the thinnest line. That’s very near the true focus length. Then you set up your bed so new sheets of material are close to this perfect distance.

The “perfect focus distance” is the lens focal distance. K40s typically ship with 50.8mm (2.0”) focus length lenses. You can get 38.5mm (~1.5”) lenses, which have a shorter focus length and so a narrower “Okay Power”range. Some people like to use this for engraving. You may need a different nozzle or head to accommodate the change in focal length.

Use a switched power strip

Here is one suggested way to plug in the K40, exhaust fan, and water pump. The grounding plug and two-wire outlets on the back of the machine are safety hazards unless you are an electrical expert. See Laser safety: Light and Electricity or better yet, use a multi-outlet power strip to turn on the laser, fan and water pump all at the same time. You could also plug your air assist pump into this as well.


Cooling water really ought to be distilled water. Water is actually an electrical insulator, but anything dissolved in the water makes it conductive. Conductive water in a K40 laser stresses the laser tube and power supply because of the 10kV to 20KV that the laser needs to operate. Distilled water is a reasonably good insulator, so use distilled. Most tap water contains from some to a lot of dissolved solids and other crud that make it more conductive; this stuff can also deposit out on the glass inside the laser tube or support algae growth inside the plumbing tubes or laser tube. Keep it clean, use distilled cooling water. (Be aware that some distilled water has some minerals added to improve taste; you want distilled water without the extra minerals added.)

Dunk the attached pump into the water, and connect the supplied tubing to the ports on the back of the laser. One tube connects to the output of the pump, the other tube returns water to the reservoir. Before you plug the laser proper in, set up the water tank, pump and tubing, and do a test run by plugging the pump into the wall power socket. Any water leaking out may have damaged your laser or electrocuted you if you haven’t already fixed the electrical safety grounding fixes above. Note that the pump supplied with the laser will not pump water any more than about 5-6 feet high, so the pump really ought to be no more than three feet or so below the laser tube.

Cooling your cooling water

Unless you have a big, already cold reservoir of cooling water – 50 gallons of water already between 15C to 20C – you will need to cool the cooling water somehow. The simplest way for getting started is to use a five gallon / 20 liter plastic bucket full of distilled water and drop into it rinsed and refilled plastic soda/juice bottles that you have frozen. A 1 quart / ½ liter bottle frozen will absorb the heat from a K40 operating for about 15 minutes before it’s all melted. Then remove that now-thawed bottle and drop in another frozen bottle.

[TODO: Add separate article just for cooling]

Good general K40 tech notes

I very much like DonKJr’s blog for no-nonsense tech info on the K40. It’s sometimes difficult to find things [use the tag cloud as an index], but reading it all will make you much more knowledgeable about your K40. Don has created kits of parts for useful hacks which are sold on Amazon of which he is an affiliate. I have not bought any of these, but I like the free tech information. Seriously, about 2/3 of the beginner’s mystification could be cleared up by just reading this blog.

Software Considerations

The earliest control cards with the K40 style machines was a “Moshi” and it came with only its own special “Moshi Draw software”. This software is generally agreed to be useless. The later lasers used a “M2 Nano” controller that was packaged with the Corel stuff above. There is a free, open source alternate program called K40 Whisperer that works with the M2Nano controller and frees you from the poor software shiped with the machine; ask about it on K40 Whisperer. There is also a newer free, open source alternative program called Meerk40t (prounounced “Meerkat”) that can control both the M2 Nano boards and the older Moshi boards, and which you can ask about on Meerk40t here. You can buy more expensive control cards (up to hundreds of dollars) and fancier control software that may enable you to do fancier burns. As you learn the machine, you can figure out how much you want to spend.

The CorelDraw supplied with the K40 is probably a hacked/cracked version of the commercial Corel Draw package. The Corel Laser supplied with the K40 is not a Corel product, it’s a separate add-on. Corel Laser requires the USB dongle supplied with the machine to operate. You can buy additional dongles, but they’re expensive, about US$30-$50 last time I looked. The dongle is an active USB processor/encryptor and cannot be copied or hacked in any simple way. So the K40 uses more advanced piracy protection for their add-on driver, and gives you a pirated Corel Draw package. Go figure.

[TODO: create and link to new document just for all the driver software options]

Next Steps

If you are bored with regular maintenance, you can move on to K40 enhancements and modifications