New to K40: Start Here

Is this you?

  • I’m about to buy a K40!
  • I just bought a K40!
    What should I look for/do/try/etc., etc.?

Start learning here.

What materials can a K40 engrave and/or cut? What materials should be avoided and why?

In general, materials that absorb the deep infra-red beam (10um) that the CO2 laser puts out are most affected. Materials that reflect it are not very affected, and the reflected beam can be dangerous to eyes and skin, as well as damaging the laser lens. Organics such as paper, wood, and organic fibers absorb strongly and can be cut and engraved. Glass absorbs, and can be etched easily. Stones generally absorb and can be etched. Bare metals generally reflect and can’t be cut. Marking bare metals needs special coatings. Plastic or paint coated metals can be marked, but this amounts to burning off the coating under the laser. Anodized and dyed aluminum can be marked fairly easily; this amounts to burning the dye out of the anodized layer. Plastics can in general be melted or burned by the K40, but the results depend heavily on the exact materials. Plastics and adhesives in composite materials may give off toxic or corrosive gasses. Acrylic cuts easily and nicely, some plastics only melt and discolor.

For more information: What can I cut with a laser cutter/engraver?

Where should I buy my K40?

“K40” is a class of various laser cutters, not a brand or model. There are many manufacturers and vendors, and there is no single best place to buy one. You are unlikely to get more than you pay for. You should expect to pay around $400 for one that works reasonably well, when you add the necessary other components.

Smaller (particularly, narrower) units have lower power. The power is a function of the length of the laser tube, which runs horizontally across the back of the unit. The “Mini-K40” is smaller and lower power. Even a typical “K40” is more like a 30W unit than a 40W unit; a typical Mini-K40 is 20-25W.

Do not buy a unit with a Moshi controller (unless you plan to replace the controller). There are three reasonable controller options:

For more information: Where should I buy a K40?

Is the K40 safe to use as it comes?

No. It’s not safe as it comes out of the shipping crate.

Electrical danger!

The electrical grounding is only one wiring failure away from putting deadly voltage onto the shell of the machine or into the cooling water.

Laser danger!

The K40 style machines come with labeling that they are “CE” and FDA approved / registered / compliant. This is at least an exaggeration, if not an outright lie. The grounding scheme would invalidate it from CE marking, for one thing. The FDA marking is intended to say that it’s safe for the laser classes recommended by the USA Food and Drug Administration. It is not.

The K40 style lasers all produce so much laser power that they’re in the most dangerous Class 4 category per the FDA’s rating scheme. Class 4 lasers require a complete enclosure that prevents even accidentally reflected laser light from escaping the enclosure, and also requires safety interlocks to stop the laser firing if the enclosure is opened. There is no hint of an enclosure interlock on most K40 units as shipped. The K40 is unsafe without an enclosure interlock on the opening panels to the bed, electronics, and laser tube sections of the box.

For more information: Laser safety: Light and Electricity

Fire danger!

There is a very real danger of starting fires with the K40 laser. Never operate it without a fire extinguisher nearby.

  • Stay present at your laser at all times while operating it. Do not leave it, even for 30 seconds. If you have any urgent need to leave, stop/pause the job first.
  • Keep a CO2 fire extinguisher immediately at hand, and use it if flames start. You must install interlocks, and you will depend on them to avoid eye damage when you need to use the fire extinguisher.
  • Add air assist and use it. This may “blow out” smaller flames at the focus point before they build into self-sustaining flames
  • Keep the inside of the machine clean. Condensed plastic fumes on the bed or scraps of work under the bed can ignite.

Is the K40 complete as shipped?

The K40 is incomplete as shipped. You need a source of cooling water before you ever connect power, and you will typically need to replace the exhaust duct when you vent the exhaust outside, which you must do. Water temperature sensing may save your $100+ tube. It is a good idea to add a switched power strip to control the K40, water pump, and exhaust fan from a single switch. There are several other recommended upgrades that you are likely to also want to do.

Start with cooling. It is potentially the biggest expense. Cooling the K40 laser tube

For more information: What else do I need besides my K40? Requirements and Recommendations

Is the K40 ready to start using as it comes?

It varies. If you buy the lowest price unit, you are at more risk of getting a unit with some dents and dings, bad alignment, incorrect focus. Some people report that they just did the minimal amount of setup and their unit turns out good engraving and cutting on thin materials.

You will probably have to do adjustments on the machine you get it to work right. Even if you got lucky and your machine’s supplier went the extra distance to send you a well-prepared and well-set up unit, you will eventually have to tinker with mirror adjustment and focus. This includes focusing the lens on the bed accurately, adjusting the mirrors to actually hit the middles of the three mirrors, or even adjusting the squareness of the X and Y axes, and will need to be done again after replacing worn parts or to compensate for wear.



  • Don’t ever fire the laser, even for a second, without water in the tube. You risk instant damage the tube to some degree – all the way up to instantly fatally – by blipping the laser on with no water in the tube. Set up a cooling water tank and circulating pump before ever turning on the laser, even for an instant.

  • Don’t ever fire the laser, even for a second, without cooling water flowing through the tube. It can overheat quickly if the water is not flowing.

  • Do not rely on the digital display as an indicator of laser power. The digital display values are not accurate. Most machines reach the maximum recommended tube current (15-18mA for a K40; 20,000V * 15-18mA = 30-36W) at a maximum 40-50% setting. If you use more power, the tube will degrade very quickly.

  • Don’t run the laser with the lid open, or with the laser compartment or controls compartment open. The laser and controls compartment are dangerous electrically. They contain either exposed AC mains voltage than can electrocute you, or 10,000 to 20,000 volts DC that can not only electrocute you, it can jump out of exposed wires you are not even touching.

    The laser compartment and main bed get watts of laser light. This can blind you instantly, even from a merely “shiny” reflection. This is the reason the FDA requires case interlocks to disable lasers when the case is opened. Some people are so fascinated by watching the laser burn things that they leave the lid open all the time. Mostly they get away with it. Do you want to take the chance that one day you’ll accidentally scar both corneas at the same time?

Go through all the regular maintenance items first

Read all of K40 initial setup and regular maintenance instructions before you turn anything on. Even a new K40 may need many of these tasks done.

Spare parts and replacements

It may surprise you how many parts of your new K40 will wear out and need replacement. Laser tube, power supply, lenses, mirror, and belts are all likely to need replacement sooner or later. Where can I find K40 replacement parts?