What else do I need besides my K40? Requirements and Recommendations

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.

The most minimal cooling water reservoir is a simple 5 gallon (20L) plastic pail, a 5+ gallon insulated cooler, or something like that filled with distilled water. You may need ice made from distilled water or in a container submerged in the water to maintain the necessary temperature range of 15⁰C (59⁰F) and 20⁰C (68⁰F).

Active cooling devices:

  • If your temperatures are always in the 15⁰C-18⁰C (59⁰F-65⁰F) range, a passive radiator cooler like the CW-3000 or clones may be sufficient
  • In most climates, a high-capacity active cooler like the CW-5000, CW-5200, or similar may be needed to provide reasonable laser tube life.

It is highly advisable to add:

  • A remote-sensor thermometer (~ US$10, ebay, amazon, etc.) to be able to see the temperature of your cooling water. Running with cooling water over about 20C/68F will shorten the life of your US$100 laser tube.
  • Metal vent tube for the exhaust fan. The supplied tube is essentially useless. Home improvement stores, hardware stores, HVAC, and hot water tank suppliers generally carry a 100mm/4” flexible ribbed aluminum vent tube that is much better than the stock plastic tube.
  • An analog ammeter, for units with only digital display. The digital display is not accurate. An analog ammeter may not be essential before your first test, but is a strongly recommended add-on. @donkjr describes how to add an analog ammeter.
  • Switched power strip to control all devices together to avoid accidentally running the laser without pump or fan running.

Is the exhaust fan that comes with it OK? Do I need a different one?

The exhaust fan that ships with the K40 style lasers is somewhere between marginal and useless. It’s a bathroom exhaust fan that might, possibly be OK for a little while – but only if you’re willing to take chance on breathing foul smelling and possibly toxic burning fumes.

DO NOT turn it on without the ventilation hooked up. The vapors and particles the laser beam makes in burning most targets are toxic to you and in some cases the machine itself. Do not even try to run this thing in a room without specific ventilation. That exhaust fan and flexible tubing that came with the machine are minimal, but they may be enough to keep you from poisoning yourself and/or your family. Don’t run the machine without something sucking air out of the back of the machine. Ventilate to the outdoors: blow that stuff out a window. In most cases, it stinks even if it’s not immediately deadly.

Is the exhaust vent tube that comes with it OK? Do I need a different one?

You need a different one. You need an all-metal vent tube at least the same size as the vent fan you use, generally about 100mm/4” diameter. There are flexible aluminum vent hoses for household dryers at most home improvement stores. Get one and use it, at a minimum.

The supplied exhaust tube is plastic, and will either melt if temperatures get too high, or may burn in the event of a fire inside the enclosure. If it’s a fire, this lets flames out into your work area.

Is the water pump that comes with the K40 OK, or do I need a different/better one?

The supplied water pump is actually OK. The amount of water flow through the laser tube needs to be at least 0.5 to 1.0 liters per minute. The supplied pump can do this.

TEST your pump. It’s easy. Set up your cooling water reservoir and hook up the tubes and such. Then instead of running the return water tube back into the cooling water reservoir, drop its end into a 2-4 liter (½ to 1 gallon) bottle, jar, pan, or other receiver, and plug the pump into the wall all by itself. Run it for one minute, and see if you got your ½ to 1 liter/quart. If you did, you have enough water flow. If you didn’t get this much flow, you would be endangering your ($100!) laser tube by running it with poor water flow.

The stock pump passes this test.

What other things need added or changed?

Air assist

There is strong agreement among experienced K40 owners that the first addition you need (beyond the minimal requirements for safety) is air assist. This is a jet of air blown right at the focus point. Air assist does at least a couple of good things. One is to forcefully clear away smoke and globules of debris from the cutting/engraving spot and make better cuts. Another is to actually blow out tiny flames at the focus spot, reducing fire risk.

Air assist is usually done by buying a biggish-capability aquarium air pump ($30-$100) to supply the air, and then routing a tube along the X-Y framing to the moving head so it can blow through either an after-market focus cone on the moving head, or a metal tube aimed at the focus spot. The picture shows one of the common of this type pump. This particular one is on Amazon for US$39 at the time of writing. Even smaller US$10-US$20 pumps are thought to be an advantage. You can go deluxe with the Zeny airbrush compressor with the small air tank for about US$70, and get into airbrushing at the same time.


The air from the pump is conveyed to the laser cutting head through a plastic tube which needs to end at the cutting head, and there is some mechanical work involved in getting the air tube to follow the head without impeding its motion while cutting.

Generally, there is some kind of metal tube that conveys the stream of air right down to the focus/cutting spot. Many K40s use a length of small metal tubing (4mm copper tubing, small automotive brake tubing, both cheap and widely available) bent to point the air at the spot. The high-dollar Epilog CNC lasers use the bent-tube method.

Another way is to put a metal or plastic air assist head on the lens holder. The air assist head adapter can be 3-D printed or bought. The 3-D printed versions get comments like “after a while, my cone started to melt”, so your mileage may vary. There is a lot of forum commentary on how to do air assist. Go do your homework when you get to this.

It may be useful to put an aquarium air valve in the air tubing line so you can tune the amount of air to the material being cut, the cutting speed, power and so on. This can get complicated, but offers the possibility of really clean cutting.

Engraving/Cutting Bed

The K40 style lasers were originally designed to engrave patterns and pictures on thin sheets, or to make rubber stamps by engraving rubber sheets. That is – the bed was not designed to adapt to the kinds of materials most K40 owners want. The stock bed is set up with a spring arrangement to hold small sheets. Unless your work uses thin sheets like the original design, and doesn’t vary in thickness much, you’ll likely want a different bed. The deluxe beds have height adjustment so you can move the material up and down so the (fixed height) focus spot is right on the material. This is a big deal, as a poor focus is one of the most reported problems with bad engraving or cutting performance. Changeable height beds make moving the material to the correct focus height easy.

Added Power Supply

The K40’s stock power supply is adequate, just barely, for K40 operations. If you add stuff on (like LED strips for strips for viewing the lasing through the window while engraving, or for better visibility to set up stock to work on) it may cause issues because the power supply is just barely able to put out the power required without those additions.


@donkjr At http://donsthings.blogspot.com/2017/04/adding-analog-milliamp-meter-to-k40.html the link to https://amzn.to/2Jsi9oK for a suggested ammeter to buy links to a part no longer found. Want to find another part?

I fixed the link…

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