A while back, Norwich Hackspace (of which I am a member) invested in a second hand K40 Laser Cutter – the sort that are pretty darn cheap (for a laser cutter anyway) on eBay and other sites (search for ’40w laser cutter’). They are made for as little money as possible in China, and imported and sold from the UK/EU. Currently they go for about £350, I think ours was about £200 as it was ‘used’ (though as far as I can tell it never saw an electron in its life).

This all sounds great – and to be honest it pretty well is great: laser cutters are an awesome tool, and this is a quite-almost-fully-functional cutter out the box. But there are some issues we spent a day or so fixing – here’s what we did.

LAZORS! Observe the burn marks it’s made….

We started by testing the laser itself, and hooking it up to the awesome K40 Whisperer software. We propped a bit of plywood up on a block of wood, test fired it a bit and then cut away! It worked a dream.

After testing, the first thing to do was to set the cutter up with some water circulating, and extraction. The cutter came with an extractor, which isn’t very good but it does work a bit. This was attached with lots of parcel tape (we couldn’t find the actual duct tape), and a new pipe added to reach the window. The laser needs water cooling to prevent it overheating. We set up a water bath stackerbox filled with water, with the little fish tank pump that came with the laser in it. We’re going to swap this for a sealed container, as soon as we can find a decent one.

The main thing that’s wrong with the cutter is the total and complete lack of safety in any way shape or form. The thing has no emergency stop, no safety interlock on the lids, no key operation. Any two year old could quite happily come on in and shoot themselves with a 40W laser. Nice!

We added an interlock by simply sticking a pushbutton in the metal that the door rests on (we later replaced the one above with a thinner one salvaged from the control panel – more on that later). It works well – when the door is shut the switch is on, when it isn’t it’s off. It can be quite easily overridden, but there might be situations where you want to do that (IE testing the movement without the laser on whilst being able to move your material to get it to fit). We also added a cheap 2-position key switch (pics far below), so that you can turn it one way to move and not fire the laser, or the other way to activate movement and laser action. In hindsight this wasn’t really necessary as you can just put the laser cutter current to 0 but hey, it’s there now.

One of each of the key switch contacts (left and right) and the button contacts were hooked up to ground, and the other to pins on an Arduino Nano clone. With the internal pull-up resistors on the Arduino, this setup allows it to detect whether the button/switch is on or not. Then, we hooked the Arduino up to an 8-relay module. One of these is connected the laser safety switch on the power supply (if it’s not on the laser won’t fire) and two are connected to the live and neutral of the mains input (to power supply) respectively. The Arduino is connected to a cheapie 5V power supply, hooked directly to the mains (so it’s always on). The code on the Arduino continually checks what buttons are pressed and activates the right relay. We could’ve just used AND and OR gates but we’re a bit lazy so…


We also added a big red mushroom button to the mains input, that immediately cuts all power (though there’s a ~2 second delay ’cause residual current). The E-stop and key switch were added to a nice new control panel that was (somewhat ironically) laser cut on the other laser cutter (what do you mean, you don’t have 2 laser cutters?!). It looks pretty cool I think. The panel also includes a retro ammeter (because it was lying around and is cool), the original laser power knob (now with added arbitrary scale so we can experiment with it), and a cheap thermometer module from eBay. The plan is to put this in the water pump container so you can tell if it’s about to overheat, but the lead’s too short so we can’t do that at the moment!

Not so shiny

The old control panel also had the two buttons ‘laser switch’ and ‘test switch’ that can be seen in the image above. Now I don’t know if they were hooked up wrong or not, but both of them just seemed to fire the laser whenever they were pressed. One of them was latching – and a permanently turned on laser isn’t a good idea! We removed these from the cutter. The on/off switch also had to go – we have the E-stop for absolute power cutting, and the key switch to control the laser. Plus there wasn’t room on the new control panel due to the oversized ammeter.

Pew pew pew! And yes, I know that’s Comic Sans and it was a deliberate choice, aimed at the Hackspace’s resident graphics nerds :p

And it works! I’m really pleased with how the laser cutter ended up. There’s a few more bits left to do, namely….

  • Sort that water tank out
  • Add neopixels (as the Arduino is already there….)
  • Add a water flow sensor to the Arduino and water system so you can’t turn it on without the laser being properly cooled
  • Add a relay to the extractor so that it turns on automatically when you start lasing
  • Cut some inappropriate materials (bacon, biscuits, fabric, tin foil)
  • Check that the plastic in the lid is actually laser proof
  • Make a bigger and better extraction (another project entirely)
  • Make a proper, adjustable bed rather than a stack of beer mats – we’re planning to get a scissor lift platform and make a bed-of-nails (literally)
  • Put a lock on the lid to the electrics
  • Add an air assist to make it cut betterer


Would I reccomend a K40 Laser Cutter? If you want something that works well and safely out of the box, no. If you’re willing to put in a day’s work and spend another £20 making it safe (and perhaps another £100 and some more work to make it a decent cutter), absolutely. It’s a project before it’s a tool. But it’s a laser cutter for ~£400!

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