K40 Laser Cutter Rebuild-12x24in Cutting Area

Introduction: K40 Laser Cutter Rebuild-12x24in Cutting Area

If you are reading this, you most likely already know about the cheap 40 Watt CO2 Lasers available from China which are commonly referred to as K40s. There are several sub variants of the K40 but generally they are in a white and blue or red steel case and have a cutting area of 12 x 8 in (500 x 300mm). The stock machine is capable of basic laser operations at reasonable speeds. However, it is ham strung by the use of a proprietary controller board, called a Moshi Board. This board communicates with a computer running Corel Draw. Most of the time, when you purchase a K40, it will come with an illegal copy (Trial Copy maybe) of Corel draw. I personally don’t like this as a permanent solution, so I choose right out of the gate to replace the electronics with a more legit, and open hardware/software solution. After reworking the electronics, I quickly became tired of the “sub-par” mechanics. After some tinkering, I decided finally to just rip those out too. Since I was already gutting the cutter, I decided to see just how big of a cutting area I could get. Please take note that I have included the F3D (Fusion 360) file on Thingiverse, please use this for reference as this guide may miss a few smaller details.


There are numerous bolts, belts, wires and bearings that are going to be required. My build was done with only parts I had laying around. Where not specified, bolts are M5 of various lengths.

You can download the STL files for printing at:


I printed all of my parts on a Creality ENDER 3 3D printer but most any will do.

For my most up to date supply list for the remainder of the parts can be found at:


Step 1: The Tear Down

To start, we will need to empty the case of everything (Proceed at your own risk as we are dealing with high voltage, cutting and Lasers).

1. Start by FIRST taking a picture of your wiring. That way, you will have a reference of how things were before you broke it.

2. Make sure the Mains power is disconnected and let the power supply sit over night (Just to be safe)

3. I would recommend you unscrew all of the wires and remove all of the switches, gauges, and everything else from the right hand side of the machine first.

a. If your machine is like mine, you will have a RED wire going from the PSU (Blue power supply) through the case to the back of the laser. You can follow the instructions online for changing the laser tube to learn how to disconnect this wire, or you can be lazy like I was and just cut the wire half way between the PSU and the Laser Tube. This wire appears thick on the outside but is actually very thin on the inside. It appears to have a LOT of insulation. Keep that in mind when splicing it back together. I wrapped mine with ample electrical tape.

4. Next, the two lids (Doors) can be removed. Raise them up and you will find a spring loaded pin on one side of each lid, pull the pin back and the lids should just come right off.

5. Disassemble / remove the X-Y mechanism. The whole unit will come out as one piece.

6. The center divider as well as the front support “shelf” will need to be cut out. Use a grinder or rotary tool to cut the tac welds. I was able to cut several of the welds and those I couldn’t reach I was able to bend the metal back and forth until they snapped.

7. I used an orbital sander to knock the metal burs down and get the bottom of the case smooth.

Step 2: Preparation for the New Install

1. I masked everything off on the case that I didn’t want to be painted. Then, I gave the interior of the case a good coat of self-etching primer

2. The bottom of the case is not actually super flat, nor rigid. Not to mention the two large holes that the manufacture thought were a create idea to add to the bottom of a laser.

a. To solve this problem, I cut a piece of 1/2in MDF (Any 1/2in sheet good will do) to 29.75in x 18.5in.

b. I cut a thin piece of aluminum sheet (Purchased at local Home Improvement Store) to the same dimensions.

c. I then laminated the aluminum sheet to the piece of MDF and sanded the aluminum sheet to remove the shine

3. Taking both the primed case and the laminated board outside, I applied several layers of Rustoleum Flat White.

4. Before placing the laminated board into the case, I added the two horizontal pieces of 2020 V slot. Two pieces, both 29.75in long were attached to the board, one along the front edge and the other along the back. I attached these to the board by drilling and countersinking 4 holes along the front and 4 along the back from the bottom of the board. The V Slot was then attached using M5 screws and T nuts.

5. Place the Board inside the case, but do not secure it. We will do that later, once everything else is installed.

Step 3: Assemble the Left Y Axis

  1. Start by assembling the Left Y Axis. Cut two lengths of 2040 V slot to fit (Mine were 17.75in each). All of the screws used were M5. I used full size V bearings with eccentric bushings for the top two bearings and fixed spacers for the bottom two.

Step 4: Assemble the Right Y Axis

  1. Then assemble the right Y Axis

Step 5: Place the Y Axis Into the Case

  1. Place the Left and Right assemblies into the case, lining the brackets up with the front and rear 2020. Install the M5 bolts with T nuts into the brackets, but leave them loose in the V slot for now as you will want to be able to move the assembly in the next step.
  2. The left and right y carriages are driven by a single motor. They are connected in the back with a piece of 5/16 in threaded rod. Install the Motor to shaft coupler on the left side of the screw. Then Cut the screw to a length that is long enough to get through the bearing mount on the right carriage assembly, but not so long that you can’t get it installed with the amount of play you have available. Mine ended up just under 28in. You will want to also install the right pulley as well.
  3. Now is a good time to attach the belts on the left and right carriage. Reference the photo below for how I did it. I zip tied the belt to one of the M5 bolts on the carriage, then routed it around the pulley and then the idler before I zip tied the other end to the other bolt. (HINT: Loosen the pulley a little before routing the belt, then after the belt is secure, add tension by pulling the pulley back into position and securing.)

Step 6: Adding Lighting, Wait, Now?

  1. Okay, it is a little out of order, but I felt I needed more light while working. I picked up an RGB LED strip kit from a clearance isle but you can get them from Amazon Pretty Easily. I wrapped it along the top inner lip. It was super easy, super cheap and made a great addition. The one I got was USB powered.

Step 7:

  1. Cut a piece of 2040 V Slot to length (Mine was 29.3in)
  2. Assemble the X Carriage using 3 Large V Bearings with an eccentric spacer on the rear bearing. Slide it onto the rail.
  3. Attach the Motor Mount, with stepper motor and the pulley.
  4. Attach the mirror mount
  5. Attach the end stop (M3 screws)
  6. Attach the Mirror Holder (Stock from K40)
  7. Route and attach the belt in the same way as the y carriage assembly, loosening the pulley during routing and then tensioning the belt by pulling the pulley back into position.
  8. The astute observer may have now noticed that the X Carriage laser head is not stock. I picked this one up off amazon for cheap. It is solid aluminum with an adjustable height lenses and air assist assembly. This allows for adjustment up to 10 mm in height which will allow me to have a static cutting bed that does not need to adjust up and down. The build quality of this part is not the best, but the adjustability was worth the trouble.
  9. Take the X Axis assembly and place it into the case. Attach it to the Y carriages with M5 screws.

Step 8: The Bed Assembly

  1. I thought about how to build the cutting bed for a long time. The first iteration used a metal grate bought at the local hardware store. This worked fine, but left burn marks where ever the laser cut through and hit the grill. Professional machines use aluminum honeycomb, so I went looking for that. I found a reasonable price on Amazon and picked up a 12x24x1in piece. When I got it, I was surprised that although 1in thick, it was still a little bit flexible… I would have to support it on all sides…
  2. A little bit of time later, I came up with the configuration you see in the images above
  • Four Lengths of 1in Aluminum angle iron
    • 22.9in (QTY 2)
    • 18in (QTY 2) with one side cut to a 45 deg angle

3. I 3D printed the corner pieces, used them as a guide for drilling the mounting holes into the aluminum, then tapped the aluminum. I then used (Don’t be mad, its what I had) #4-40 x 0.25in screws to secure through the plastic and into the aluminum. You could just as well use M3 or M2.5 screws.

4. The whole assembly slides into the case and secures in the front with M5 bolts. The back is left floating, resting on the rear 2020 V slot.

Step 9: The LID

  1. I reinstalled the lids and bolted the two halves together, using an existing hole in the middle of the two halves.
  2. Then, I used some of the left over aluminum sheet from the bed and taped it in place with Aluminum Tape over the now exposed holes in the lid.

Step 10: Electronics

  1. I was putting this off. The first thing you may notice in the images above is that there is no longer any room for the electronics inside of the case. Luckily, I had a salvaged case that worked perfectly for my needs. I’m sorry I don’t have a source for this part, it literally was pulled from a trash bin. You can see it mounted to the right side of my machine immediately above.
  2. First, I made a new face plate for the case. This face plate had an Amp meter, a Main Power and a Laser Power Switch. I cut this from sheet plastic by hand:

Step 11: Electronics Cont...

  1. Then, in the upper right corner of the case I drilled a 1in hole into the Laser Tube area. This hole served to route the laser power wires. I also drilled a hole in the lower right corner to route the motor and end stop wires.
  2. I then secured the PSU (I removed the blue film from the PSU, so now it is silver) and the Arduino Uno with GRBL shield.

Step 12: Electronics Cont...

  1. I then wired it as follows (A big thank you to http://donsthings.blogspot.com who has done a lot of research on these units and from which I based much of my work)
  2. In the above it is worth pointing out again the PWM signal. Using GRBL 1.1 the PWM signal was present on the End Stop -Z pin, not the Spindle Direction or Spindle Enable. I should also not that I tied the Laser Fire pin straight to ground to reduce the number of connections and complexity. I have not had an issue with this setup, but use at your own risk. I keep the laser switch off until just before I run a program. I also always turn the laser switch off before opening the lid. A recommended upgrade would be to place in series another switch to detect if the lid is open. I have opted to delay that upgrade
  3. The end stops and motors were then wired as the GRBL shield was marked.
  4. You will also need to install stepper motor drivers in the X and Y axis and tune them accordingly. I leave those details to other sources that have covered it much better than I will.

Step 13: Firmware

    1. GRBL (I don’t know what it stands for) is open source firmware for Arduinos to control a CNC via a serial port. Head over to: https://github.com/gnea/grbl to download the most recent version. On there site you will also find a wealth of information on how to configure it and get it up and running. Newer versions even have a dedicated Laser mode!!!

    2. GRBL will be installed on an Arduino Uno, then the GRBL Shield will be placed on top of the Arduino to make interfacing easier.

    3. Any G Code sender Software can be used to drive GRBL, but my two favorites are:

    a. Cncjs

    b. LaserWeb

    4. Coming from using MARLIN and other 3D printer firmware, configuring GRBL was a refreshing experience. Most configuration for Marlin requires you to edit the source files. GRBL doesn’t really require this step for most 3 axis setups. I downloaded GRBL 1.1 and uploaded the firmware via the Arduino editor and the instruction on the GRBL wiki. Then, using the Arduino Serial Monitor, I entered the following settings.

    Step 14: Firmware Settings

    I entered each one by typing the Setting number “$0=” followed by the desired value. You can then verify that the values have been entered by typing “$$”, which lists all of the configuration values. For more details, head over to the GRBL wiki. For my particular settings, please see the attached spreadsheet.

    For the most current GRBL settings, please visit: http://replicantfx.com/k40-laser-cutter-rebuild-12x24in-2/#FIRMWARE

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      8 weeks ago

      Great looking work and I may do something like this but not until I replace my k40 and considering she is only about a week old, it will be a while. But I wanted to say one thing. Why go though all that awesome work and not both just putting in a bigger window. I apologize if you mentioned it, honestly for now I just checked out a little text and all the pictures. Could have eliminated needing to cover the old control panel window. But again, great looking work.


      2 months ago


      I think it is OK but I would just like to make sure:
      Can I use the stock stepper motors that came with the machine?

      Thank you ,


      Question 5 months ago on Step 3

      I have started collecting the parts to do this conversion on my K40. I purchased the normal V-rollers you listed but I would to ask for clarity for the eccentric rollers. " I used full size V bearings with eccentric bushings for the top two bearings and fixed spacers for the bottom two"
      Can you please share a link or something to what is needed?


      1 year ago

      Awesome project! Do you think this would be doable for someone with minimal experience with projects of this type?


      Reply 1 year ago

      yes if you follow it slowly and carefully anyone can do it. If you have access to a 3d printer then its dead easy, if not then you can ask a friend who has or get them printed in a maker store or online, this is not the only version of a update to the bed, if you own a k40 then join some of the facebook groups to see whats out there, this is quite an easy fix to be honest. If you use a lightburn plug and play card then you will have a awesome laser setup, were working on converting 3 lasers to a bed double the depth but the same width. Its easy to do once you understand the basics and this is a very easy upgrade as you dont really do any work to the case, were welding in complete new sections to make the case larger, the only thing i would change on this setup is use a lightburn cards or 3d printer card that works with lightburn and make sure your electrics box is bolted to the side of the cabinet and not loose as shown in the photos.


      1 year ago

      This is a good build and a excellent diary for someone to follow , firstly you must remember this is a laser with a very powerful flyback transformer capable of creating 20,000 volts , it could kill you. None of this kit is CE approved and it would never pass a CE or PAT test anywhere.

      You do need to know what you are doing when you take this apart and rebuild it, firstly if you want to use decent and easy to use software like Lightburn you need to change the motion control card for either a proprietary plug and play one around 200 usd from Cohesion, VMS or slightly cheaper Super Mini Gerbil. Alternatively if you know anything at all about 3d printers you will understand that some 3d printer cards that are 32 bit will in fact work in place of a plug and play card. A good option is the Makerbase MKS 1.3 card, this can be purchased for about 23 GBP at time of writing and is more or less a drop in board, there is a little bit of wiring to do but not very much, you just need to rewire the stepper on the X axis with a new cable and put in two analog stop switches for homing.

      That and the firmware is all that is needed to make this laser into one that can run Lightburn software perfectly. Firmware is available from any decent K40 facebook group.

      On this build in particular there are a couple of things I dont like and that is the laminated wood thats placed in the bottom of the laser area, while the metal does protect the wood, if the laser is left on for a long enough time in one spot it can catch fiore through the aluminium. Even though the beam is not in Focus it generates a lot of heat.

      Secondly and more concern is to mount the electrics in a case that is just left on the side of the machine and does not appear to be bolted to it.

      This is extremely dangerous, the PSU contains the electronics and flyback back transformer that creates the voltage required to energise the CO2 Tube, thats about 23,000 volts and while the current is not high its still enough to drop you on to you back and leave you there.

      The electronics package in my honest opinion should be bolted to the main case and a grommet protected hole drilled to allow the thick red laser flyback feed wire to pass through into the tube box and on to the laser for safety.

      I would much prefer to see it mounted bolted to the side of the laser case and then I would feel it would be safer.

      We are part of a group of 3 people actually rebuilding 3 of these lasers into a much larger bed than even this has but by welding in some panels we can use the existing cabinet for safety.

      The electrics are mounted in a box which is about 30cm above the laser on a twin pole arrangement and the wires come down the pole in a insulated tube inside and then into the laser tube compartment , no switches or meters etc are on the cabinet at all.

      If your heavy into safety then wire in interlock switches into the tube cabinet and electric box door, not the laser cabinet as you need to open this sometimes and it will drive you insane having a interlock on this as you will lose your work if you break the grbl stream.

      If you dont want switches there then use a tiny grub screw to hold it shut and also install a water sensor on the inlet side of the pump , there is a sensor wire available for it and it is the best safety you have to save your tube if the pump fails. While the optical sensors are useful they work on the basis that you must look at the sensor all the time to see that the wheel is turning

      Well in reality you dont do this and by the time you notice it the tube will probably overheat and thats the end of it. The thermo sensor is again useful as a indication of the water temperature but again does nothing to stop the machine, It requires you to watch all the time, this one can be replaced by a maximum/minimum thermo sensor off ebay that will shut the laser off if it goes outside a certain temperature range

      For instructions look at K40.se for a wiring diagram, even Amazon sells the sensor, cost about 10 gbp maximum for the water sensor and about 15 to 20 for the max min thermo sensor but whether you need that one is purely down to you. I always keep an eye on the incoming water temperature and if it creeps up I introduce a ice bottle into the tank.

      The pump sensor is in my opinion a must, It can save you up to 175 gbp on a new tube.

      Finally Wiring & Earthing, I have yet to come across a K40 with bad wiring or a failed earth, everything seems to be terminated ok and the sockets are always wired up correctly, the only thing that makes me feel it would no pass the appropriate tests is the thickness of the wiring, its only 1mm and I feel should be 1.5 or 2.5mm inside on the sockets and to the switch.

      The wiring is safe to a fashion, you are not going to get an electric shock off a bare wire but if you start putting your hands into the electrics box with the plug in the socket then you could get a shock off the back of the sockets. Its not to the safety standard of a uk 13amp socket so if something goes wrong the laser wiring would fail as it would act as a fuse rather than the fuse in the plug which is rated at 13 amp, if you are going to use this in the UK I would remove the 13amp fuse and replace it with a lower amp fuse for protection or possibly even wire in a low amp circuit breaker into the electrical cabinet.

      On earthing or grounding on the K40's I have worked on it appears to be ok although some people have noticed a slight tingling on the frame, if you get this then double check the grounding post on the back of the laser and make sure you remove any paint from the case so the wires on the terminals can touch the metal, if you still get tingling then run an external wire of 2.5mm thickness off this post onto a radiator pipe or failing that put the wire into a 13amp socket on the earth pole only !!!!! Plug it in to a socket and that will ensure your case is 100% earthed. Its not ideal but no qualified electrician would pass this machine safe in a PAT test although in reality it is ok to a point. If you are at all unsure of the safety of the wiring then get a qualified electrician to take a look for you.

      I always add this, the only wood inside the laser cabinet is the wood you cut and NEVER NEVER leave the laser unattended when in use . Always unplug at the end of use.

      I also recommend that you keep a Fire Extinguisher in the vicinity of the unit and also use a smoke alarm in the same room. Turn your back on these machines or laser the wrong material and you will have a fire. the use of a air assist greatly reduces the risk of a fire by not allowing flames to appear on the surface of the wood as you laser it.



      1 year ago

      Do you happen to have a "kit" available? It would be a good idea, if you don't - since I would likely buy one dependent on the cost. It's awesome and I really need to look into this. Thanks !


      2 years ago

      Parabens pelo projeto , ja estou a imprimir as peças e logo mas , estarei postando as fotos .
      Obrigado por dividir o conhecimento


      2 years ago

      Thanks for sharing. I appreciate how detailed you were!


      2 years ago

      These are some thoughtful upgrades! Thanks for sharing your process!