K40 Laser Worklog: Let's Be Realistic




Introduction: K40 Laser Worklog: Let's Be Realistic

About: Nothing special about me. Just voiding warranties. Admin of www.maker-forum.net and www.kodinerds.net

If you are at the point of deciding whether to buy a K40 laser or not, I would like to give you some advice.

How good is it? Wouldn't an expensive one be better? Do I still need accessories? What makes sense? How much time do I need until it works as it should?

I started with a K40 about a year ago.

And that was an odyssey with cursing and joy (and fire!).

So everything that goes with it :)

In this isntructable I want to show the limits, what you really need, what has to be done at least, what is total nonsense, how much money you really have to put down in the end and why this or that just doesn't work.


K40 Laser :)

And some tools

Step 1: It's Cheap, But...

It's cheap, but...

It's a CO2 laser for about $300. What can you expect?

The biggest problem with the K40 is that it's already assembled. You could think of the whole unit as a DIY that arrives at home pre-assembled.

If you invest enough time and patience, you can produce quite respectable results, repeatable.

If you value your health, you won't be able to avoid spending a bit more money on various protective measures.

But everything can be retrofitted somehow.

But is it still the cheapest and/or most sensible choice?

Well, if the space and the money are available: no.

Then I would directly advise a larger one around 1000$ (currently rather 1500$).

The next size is much better built.

Starting with the safety switches up to the linear guides.

And what about these diode lasers? Orthur and Co?

Yes, they are also interesting. But just diode. In cheap.

If you mainly want to engrave, then they are interesting (and also better than the K40).

But as soon as you want to cut something thicker than 80gramm paper: only more power helps.

And there the K40 has clearly won.

And when it comes to safety, a diode laser is even somewhere behind the K40.

And the expensive diode lasers? Mr. Beam etc.?

Oh yes. They are really good. And very expensive.

I can't say anything against the systems. Unpack them and go for it.

If you have the money for it and don't want to cut through to maximum thickness: go for it.

Still interested in a K40? 

Then let's go through what I consider to be absolutely necessary next.

Step 2: Barely Minimum Protection

You will certainly have watched a few YouTube videos about the K40.

What is the very first thing you should do?

Check the electrical safety! 

With all these tips, it's your responsibility what you do.

Use your common sense. Power cord out? You know what I mean.

Is the case grounded?

Just check the small screws at the back right side, if they are just lying on the paint of the case with the washer, or if they are in contact.

The simplest method is a continuity tester or a resistance measurement.

Where and how?

A blank spot on the cover and connect the screw with the cables of the test device.

This also directly checks whether the lid is also grounded.

If you don't have a tester, you should buy one.

No patience until it is delivered?

Then at least remove the paint under the grounding screw on the housing so that they have contact.

Extraction and respiratory protection

The laser does not cut - it vaporizes the material.

And it is this vapor that is in the air you breathe.

Think about what you are breathing when you cut (or engrave) acrylic.

I have a fan connected, which sucks about 300L/h out of the room.

And I also use a proper paint mask from 3M for almost everything.

I have contacted 3M and asked them which filters are suitable for acrylic.

6055 (the brown ones).

These things are absolute minimum. Electricity and breathing air pollution.

If we take a weighting here (10 is highest, 0 is lowest),

then these two items are a clear 10.

In the next part, we'll talk about other investments that I think should be made if you want to have long and constant enjoyment of the machine.

Step 3: You Should Buy This Stuff, Too

Electrical safety part 2:

Yes, it makes sense to screw a circuit breaker to your lid. This will switch off the current to the tube when the lid is opened.

Since I, and I alone, operate the laser, I did without it.

I consider myself reasonable enough.

In the previous part, I already mentioned "air" as a topic. 

During the laser process, the material is vaporized. However, part of it is also inevitably carbonized. And this mixture of vapor and dust is very clearly reflected in the cut quality.

The "double" combustion also makes the edges unclean.


I recommend with a 9 out of 10 a quiet compressor with supply line, closing valve and nozzle. Then add to that a drag chain.

An air-assist system not only provides clean cuts, but also keeps the lens clean because the gases are blown away before they reach the lens.

There are many solutions on the market. Most users print a nozzle and connect the air via an airbrush hose and a coupling.

An airbrush compressor is not enough! They are not designed for continuous load.

I use a rather expensive SchneiderSilent. But the pond pump used in most videos will also do.

When designing the nozzle, you should put some thought into it.

But any is better than none.

The straighter the airflow blows into the cut later, the better.

But since it is an almost impossible task to direct the laser beam out of the center of the guide, nozzles with a centered (small) opening are often useless.

I bring the air in from the side. Now and then, this leads to smoke trails on the material. 

And an added small 5V PC-Cooler is no Air-assist! It can blow out a flame. Nothing more.

(still better then nothing)

Height adjustable table

Another 9 out of 10. To get the most perfect result, the distance between material and lens must be 58mm.

This applies to engraving. For the cut, you start from the center of the material.

So 58-(material / 2)=height

And that's where a height-adjustable table helps immensely.

You can buy them ready-made on ebay, or build them yourself.

You will need pulleys with gear, toothed belt, screws, aluminum profiles and 3D printed parts (at least they make it much easier).

The table can be a project in itself. 


In short, I don't have a chiller. About 20 liters of distilled(!) water and the included pump are enough for me.

So depending on the intensity of use and local conditions, 0 out of 10.

Or even 10 out of 10.

Monitoring the temperature

A 9 out of 10.

Generally it is said that the tube runs ideally around 19°C.

Much colder is not good either. Therefore, some users put an aquarium heater in the cooling water.

For me this went too far. I prefer to buy a new tube and readjust everything, than to bring the water to ideal temperature every time - to cool it again afterwards.

Too high temperatures are also very harmful to the tube.

I stop cutting at 24° and then add cool packs.

Then I wait until the temperature is down to about 21°.

You'll have to estimate how much more you want to laser.

And to get a feeling for all of this "temperature-related-stuff", I monitor the temperature of the water at two points. 

In the water near to the pump and directly behind the tube.

To check if water is running at all, I installed a water wheel from the PC modding corner.

Step 4: Bling Bling


Yes, this is useful, but not necessary.

I simply used an LED strip powered by a 5Volt cell phone charger.

Again, do not take power from the laser's power supply.

Laser pointer / cross line laser

I thought I needed this one too.

It looks really cool, but you put the material relatively generously into the laser or build a system where you put the laser material.

There the laser pointer is a nice help, but the effort to focus it exactly and to position it in a 90° angle is not so easy.

And if you want to laser thick material in the housing, you go deeper with the focus. Then the cross line laser becomes blurred again.

Again, please do not take power from the laser's power supply, if that is still not clear.

Bottom line: I don't use it anymore.

Better mirror mount , other mirror, other lens.

It's definitely easier to align everything if you use better mounts.

But you have to remember: you only do it once.

After that, it doesn't matter which mounts are installed.

The mirror and lens in the K40 are absolutely fine. Changing them does not improve the quality.

But it doesn't hurt to have a set of mirrors and at least one lens as a spare.

Linear Rails

Well, it does make a difference in terms of quality.

The X-axis becomes absolutely straight. Also the engravings will be better.

The whole machine runs much smoother than with the roller guide.

It is available as a set - or you can build it yourself.

It is not necessary. But, apart from the Air-Assist, it is the only change that improves the result.

-> https://www.ebay-kleinanzeigen.de/s-anzeige/k40-laser-linearfuehrung-einbauset/1926216806-168-1266

Better mainboard (to run the laser with other software)

From my point of view unnecessary. 

I will go to the topic "software" in the next step.

Step 5: Software (and Everything Else)

Software (no, it's not the whisperer)

You have read in various videos and posts that you should not use the included software.

I would sign off on that.

But I can't recommend the whisperer today either.

Because there is meerk40t.

Cutting and engraving in one step? No problem.

You don't even have to change the amperage.

Grayscale when rasterizing? No problem at all.

Grayscale in the K40!

Repeating, mirroring, scaling, decomposing ... No problem.

Positioning by camera or a rotation addon? Included.

If you could now automatically rasterize photos? No problem at all.

Even if it is only a 1-man-project, it is very well maintained.

I really can't think of anything you would want more.

You will need a laptop or PC directly on the laser, as it can only be connected via USB.

But since you don't run the laser unobserved anyway, this circumstance arises anyway.


Fire Extinguisher. I have had 3x fire so far. All still easy to extinguish without fire extinguisher. Each time with acrylic.

It should be clear to everyone that you should never(!) let the laser out of your sight.


Laser, pump, laptop, light, compressor ... a lot comes together.

In total, it is not 1000 watts. But some sockets.

And you handle electricity and water. So the cabling also has to be laid with care.


Yes, air again. That has to be routed outside.

If you have too much money, you can also think about a filter system.

And the air must also be supplied. If the room where the laser is located is very small, then the (room)door must remain open.


You need unexpectedly much space, because you have to reach the machine from all sides. Then there is the exhaust air, etc. It is easy to underestimate this.

Also the material storage can become very large very quickly.

Step 6: First Steps

Geometry alignment

When you look into the housing from above, check that the axes and profiles are at 90° angles to each other.

If this is the case, everything is in order.

If not, do yourself a favor and remove the entire guide. Put it on the workbench and realign it.

In the end, it's just a matter of loosening the screws, aligning them with an angle, and tightening the screws again.

When everything is at the right angle, check to see if the head is "yawing".

The carriage, with which the head is moved, is only in contact by means of the four rollers. You can align these, but it is a very tricky job.

If you don't mind a slightly wobbly line in the cut, you don't have to do anything to the rollers. If it is still too annoying, then only a conversion to a linear guide will help.

Optimization of the guide carriage

With me, the toothed belt has jumped off again and again.

The cause is the mounting bracket under the profile with the idler pulley.

This is fastened floating. It helps if you put washers between angle and profile.

The attachment of the toothed belt to the carriage is also often somewhat crooked.

I sawed elongated holes in my sled and then wrap the toothed belt around and fix it with cable ties. As you know it from the 3D printer.

Shortening the air connection piece

It may be that that it has to be shortened.

Simply try whether the sled passes it or not. 

Again, I recommend removing the part and then sawing it.

Who does not want to remove and would rather have all the saw dust in the housing: everyone as he likes :)

Aligning the laser beam (finally)

In almost every YouTube video you are told to hit the center in every mirror.

Well, that's a nice exercise, but not the goal.

The beam must be parallel to each axis. This means that the hit point must always be in the same place.

Set the energy to a value that just about creates a dot on the crepe paper.

Hitting the first mirror in the center is definitely a good start, since it's fixed anyway.

You have to hit the second mirror in 0-position and at the stop in the same place. To achieve this, the first mirror has to be corrected a bit.

Then move on to the opening of the laser tube.

Since you can bring it into position at 4 corners, this is exactly the goal.

In each processing position, the beam should hit the same point in the aperture.

If you are then too far to the left/right/up/down, then you can correct the tube a little. This is much easier with the rail linked under "Guide carriage".

If you still can't get out of the way, then the tube must be lifted at the back. It is almost always at the back. With the fewest, the front must be corrected.

But the principle is then the same again. Work through from axis to axis via the individual mirrors.

When you have finally achieved correct alignment and cleaned all the mirrors and the lens again, then laser a point in all four corners onto a piece of wood with more energy.

If you still have only one point, then everything is okay for now.

If you see two dots on the wood or a kind of crescent, then the laser beam is reflected somewhere in the tube. The only thing that can help is a correction at the last deflection mirror.

A very small amount of paper lining can help.

First real test

Take a piece of poplar plywood in 3mm.

Cut out a small rectangle in each corner.

This should cut through with about 4mA. If you need significantly more or the cutting only works in one corner, then it is still not aligned correctly.

If this works, then you are done. From now on there is only fun. Well, almost.

Step 7: Risks and "dont Do That"


You can put almost anything into the laser.

Only, and this is really really important: no PVC.

I didn't believe it myself and now it's rusting all over the place.

And I only lasered PVC once out of ignorance instead of acrylic.

Imitation leather is also often made of PVC. Self-adhesive foils too.


My small fires were all with acrylic. Cutting creates steam, which settles as an oily film under the acrylic. And this is easily flammable.

In the meantime I only cut acrylic very rarely. It stinks and is toxic and a fire hazard.

But it can be cut and engraved.

For example, if your timing belt comes off, it can also quickly catch fire. Especially when engraving, this would be an emense danger.

So never let it out of your sight.


All materials smell more or less strongly after cutting.

The air-assist helps a lot, but in the end, the only thing that helps is to let it outgas.

Temperature, e.g. on a radiator, accelerates the process.

Step 8: Final Thoughts

I cut poplar and birch plywood to 4mm in one pass. Paper, cardboard, acrylic, felt ... all no problem.

Apart from small deco stuff, the laser is used a lot for stencils.

I have engraved slate, anodized aluminum and painted surfaces.

A layout for the router is made much faster with it than with the 3D printer.

Small boxes, stamp rubber ... there is always something that goes faster or better with the laser than with other tools.

I can recommend the K40, as long as you are aware of the work and the risks.

If you burn down your house due to negligence, no insurance will probably pay.

Lung cancer due to inhaled gases can also not be ruled out if you do not wear a suitable mask. And what is really "suitable"?

To be honest: the whole "safety stuff" cost as much as the laser itself.

I hope you enjoyed my contribution.

If so, then vote for me in the laser contest.

Thanks for reading,


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    1 year ago

    Do you know where I can buy that linear rail kit?
    Looks like the one you posted is dead.



    Reply 1 year ago

    Thanks. It just seems for Germany (you need a German phone number to sign up).
    It's a good idea though.


    Reply 1 year ago

    you can contact me at boardz@gmx.de
    I'm the one who sells those kits.


    1 year ago on Step 8

    i started with the k40....many years ago....$200 craigslist....guy could understand it...brand new... laser fired....was on my way.....i'm using whisperer on a 16x24 unit i built using 2020 extrusion and linear rails....3 years now....works great and i do work for a few business making power specification labels when they need them....along with my own personel stuff....good retired part-time $$. i use an spt 45w laser for 3 years....has been incredible.....going to look into meerk40t.


    Reply 1 year ago

    OK......downloaded MEERK40T........Opened up a svg created in inkscape.....it was all outta wack.....did some positioning.....too much work......the template works perfectly in whisperer, but this stuff...........not for me......cant afford the time to redo templates i created for business....dont want to change font sizes to fit boxes.....soooooooo.....i guess not for all of us.


    Reply 1 year ago

    Maybe one day you'll need this extras.


    1 year ago

    Congratulations on being a finalist in the Laser Challenge Contest!
    Thanks for all the great info on the K40.


    Reply 1 year ago

    Thx :)


    1 year ago

    Lots of great info here - thanks for sharing your experience! :D