Laser Basics

Beginners Guide To The K40 Laser Engraver


If you are considering buying, or have just purchased a K40 Chinese Laser Engraver this Knowledgebase Article is the perfect place for you to start (well, except for maybe the safety article). We have done hundreds of hours of research on every aspect of these units and, with great input from many great people, have navigated through the initial rough waters of getting a poorly made Chinese clone of a machine to run far beyond our expectations. The reason I reference this unit in that manner is that my first experience with a laser engraver was spent on my ULS-25E. An American made, precision, workhorse that was built in 1991. But, I LOVE my K40!

Let’s get a few items out of the way from the beginning. Please make note of these observations and suggestions:

1. Please, for the love of all that is holy, never refer to your K40 as the “blue and white one” or the “orange and white one”. Try to provide accurate descriptors and/or photos when referencing your machine.

2. These lasers vary greatly in build quality and require a good deal of “tinkering” to keep them going. If that sounds fun to you then you will love it!

3. If you don’t like to tinker, if you are not at all mechanically inclined, or if this is a mission-critical business appliance you may want to find a US laser.

4. The tube of “goo” (silicone sealant) is for insulating the high voltage connections on the laser tube and nothing else. Put it up for safe keeping.

5. Take the included exhaust fan and ductwork out of the machine and very carefully place it into the nearest trash receptacle. Then see the alternatives below.

6. Do not plug anything into the “electrical outlets” on the machine. They are poorly designed and poorly wired. Use a proper power source. More on that later.

7. You MUST install Air Assist. Let me say that a different way: You MUST install Air Assist. There are many options and we cover a cost-effective solution in this article.

Okay, now that that’s all taken care of we can dig into the necessary initial modifications for a K40 to greatly enhance its performance and reliability.



The quality control for the wiring harnesses in these units is about as varied as the rest of the machine so great care needs to be taken to go through the wiring and make sure there are no bad terminations, loose lugs & screws, grounding issues, etc… These machines can be hazardous as far as the AC power and the high voltage power supply (flyback) goes. The “outlets” provided to power the water pump and exhaust fan are not suitable for use. A well made, surge protected plug strip is highly recommended for the accessories, upgrades, and peripherals. The main power for the laser engraver needs to be a dedicated outlet with a rating of at least 15 Amps. Most household outlets will suffice.

We did, after checking the wiring to these outlets, decide to hardwire our air assist pump to the feed for one of the outlets since we mounted our pump inside the chassis. We are using a commercial aquarium pump that has a relatively low current draw. That mod will be in another KB Article. There will be more information on the electrical system coming soon.



We are using a 5-gallon bucket with a lid for our reservoir and have, for the time being, retained the water pump that was included with the engraver. It is not very robust so we are looking for a more suitable replacement.

Distilled water should always be used as it is less electrically conductive than tap water. You also need to be very careful of the additives you choose to address freezing and algae. Many additives will cause the laser to arc or “short down” and corrode the cooling system components.

We used a near 50/50 mix of RV Antifreeze to prevent freezing as well as inhibit the growth of algae and other organisms. 10 or 12 drops of dishwashing liquid will act as a surfactant and release the surface tension that causes the tiny bubbles that cling to the inside of the tube. There should be NO bubbles whatsoever in your cooling circuit! We leave our pump running 24/7 to prevent bubbles, freezing, and algae growth.

Often times there will be a large bubble at the top of the tube near the outlet. There have been many posts on this issue and the solutions range from letting the pump run 48 hours to disassembling the machine and “shaking it” out of the tube; and everything in between.

We found that simply and CAREFULLY tilting the unit around (with 2 people) until the bubble was evacuated solved the problem. This is my recommended method because believe it or not, our K40 was PERFECTLY aligned right out of the box so we did not have to spend one second on realigning the optics! I’m glad we didn’t tear it apart for a bubble.

To monitor the flow and temperature of the coolant we chose a cheap and simple flowmeter/thermocouple kit made for PC cooling. We plumbed it in series with the OUTlet tube feeding back to the reservoir so we have a more accurate measurement of the coolant temperature inside the laser tube and not the ambient temperature of the reservoir.



Any smoke, fumes, etc… generated by the lasing process is dangerous. Some materials will give off poisonous gasses and WILL kill you. These fumes can also corrode the metal and electrical connections of your machine. PVC and other types of vinyl are a BIG NO NO! They will kill you and your machine. There are more materials that should not be lased. This will be covered in greater detail in my article on General Safety.

The exhaust system provided is not adequate and needs to be modified. My ULS service manual recommends that the exhaust fan be placed OUTSIDE the wall where the machine is being vented. Most people don’t do this because it is not practical.

The logic behind this method is simple. Even if there is a leak in the ductwork there is negative pressure (vacuum) all the way outside so the fumes and smoke will be evacuated. If the fan is inside and the exhaust side duct leaks it will pump the smoke and fumes back into your work area. If you have the option to mount the fan outside I would do so.

We used an adapter made for woodworking dust collection systems that fits almost perfectly in the factory slot. You may wish to screw it in place or add some self-stick weatherstripping around the perimeter of the mating surfaces for maximum performance (we just slid ours in and the vacuum pulls it up tight). We added a 190 CFM 4″ inline duct fan and connected it all with semi-rigid metallic dryer hose.

I see a lot of posts about using a higher CFM fan and that is great in theory but the little rectangular exhaust duct included with the K40 can only move so much air. If you add a fan that is way too big it will be pointless and the drag on the motor will shorten its life. We cut our exhaust shroud back to allow a bigger z axis (table or bed) but that didn’t increase the airflow.



Okay, now to the air assist. I may have mentioned it but… you MUST install air assist! It will save you hours of cleaning, lots of money on replacement lenses, and give you superior results on a wider variety of materials. The air assist is basically a nozzle surrounding the head that does 2 very important things: Keep the lens clean & blow a jet of air onto the area being lased.

There are other versions of air assist. Many are adjustable tubes with tiny nozzles at the end that are on a mount and do not encase the head. We prefer this type because the air creates positive pressure inside the nozzle and prevents any smoke and debris from coming in contact with the lens. If smoke bakes onto your lens you will NOT be happy. Trust me, install air assist before you do ANYTHING.

We just happen to have a 3D Printer so we printed our nozzle from a Thingverse file and it works just fine. We do plan to increase our tubing size in the future but the 3/16″ standard airline tubing works fine for now.

You can also get this head instead of making one. it is well made but requires a 15mm or 18mm diameter lens (per mfg.) rather than the stock K40 lens which is 12mm. HERE is the link for the LightObject Laser Head with Air Assist on Amazon. You can see our KB Article about Lenses & Optics to find out more.

The air pump we utilized can be found on Amazon. It is an aquarium pump. THIS is the one we use.

Standard aquarium Airline Tubing is what we are using now but we have plans to go with a 10mm inside diameter tube direct from the barb on the pump to our modified and reprinted nozzle so eliminate the restriction of the 3/16″ tubing and get more volume to the nozzle.

UPDATE: I got the LightObject Air Assist and ditched my printed one (It started melting slowly over time and became ineffective). And I am using a shop compresor and remote requlator now. We also upgraded to this soft and pliable 1/4″ tubing:

UPDATE: There has been some research on air assist and smoke assist. It seems that “nozzle type” can acually pull smoke in (the venturi effect). Hakan has a very comprehensive website dedicated to K40’s ( and his article about air assist can be found here:


Most of the K40’s I have seen come with an M2 NANO board or similar controller. They are packaged with LaserDRW and come with a USB Dongle. I never even tried it so I cannot say if it is any good or not but, from all of the posts i have read it is troublesome, must have password authentication (which seems to give people huge headaches) and is very limited in what it can do.

The go-to replacement for this software is called K40 Whisperer and it seems do be the “bomb diggity”. And it is FREE! The companion to it is Inkscape. That is a vector design program and it is FREE also! My recommendation is to start with K40 Whisperer and Inkscape and never look back. Both of these applications are very well documented and have outstanding community support.

You can find K40 Whisperer HERE and Inkscape HERE.

To get the most out of your laser you need a more advanced control system. There are some pretty reasonable DSP controllers out there but we opted for the Cohesion3D Mini which is based on Smoothieboard. This replaces the control electronics (in about 20 minutes) and makes UNBELIEVABLE improvements to your system and its output. Find out more HERE.

And if you opt for the Cohesion3D (or even a traditional DSP (at over 3 times the cost of the C3D)) you need to try LightBurn! It is spectacular. Try it FREE for 30 days and if you want it its only $40 (for the G-code (C3D)) version! Check it out HERE.

UPDATE: I installed the Cohesion3D Mini Laser Kit in around 20 minutes and am using LightBurn Now! All I can say is WOW!!!!!!!!!!!!!!!!!!!



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