I’d be happy to share the design files if anyone is interested, but I doubt anyone has exactly the same setup as me. I also altered things as I went, so I don’t have any “final” versions.
One of the quickest ways to destroy a CO2 laser tube is to let it overheat. My laser has a very simple system – just a plastic breakfast cereal container of water with a small aquarium pump. It works well enough, but is easy to forget.
My first modification was to power the pump from the laser so that it’s running when the laser is switched on at the mains. That gets around the “oops, I forgot” problem, but doesn’t cover a pipe coming loose or the temperature creeping up. I really wanted to actually check cold(ish) water was flowing through the glass laser tube.To check the flow, I started with a LM35DZ temperature sensor and a cheap water flow sensor from eBay. For neatness I carefully milled the flow sensor to embed the temperature sensor in it. This was then attached to the output of the laser. I intend to check that enough water is coming out and that it’s below a temperature threshold.
I etched a board with a MSP430G2533 microcontroller that counted the pulses from the flow sensor over a fixed timer period and used the onboard ADC to read the temperature. I set the threshold at 40C and 75% of the normal flow.My initial attempt used a MOSFET to pull the last signal down to GND if things were awry. Unfortunately this fired rather than disabled the laser! This was replaced with a 74LSxxx AND gate so I could force it to 5V and disable the active low signal. Some connectors to match the controller board meant I could drop it in with no rewiring. So far it has been working well. (I actually finished this months ago but didn’t document it.) It’s not actually been needed to save my tube yet, but it’s nice to know it’s there. I might later and another sensor on the input and also flag if the difference between the two is too high. I could also add a cheap LCD display but that seems a little over the top. As it’s a single sided board with some through hole pin headers, when it’s in place you only see the “boring” side of it with not tracks or components. Oh well – there’s no need for it to look pretty. Here it is in place. It’s a drop-in addition on the 6 pin cable to the controller board. It’s powered from the existing 5V line and simply forces the signal to fire the laser high (as it’s active low) when it senses trouble. From teh top you can see:
- The connector to the sensor
- A debugging / programming header
- A currently unused connector for a screen
- The connectors to patch into existing power and signals
If anyone wants a copy of the PCB layout or code, just ask.
I’ve been making yet more improvements to my laser. Mainly because there are so many things that can be improved upon. This time it’s been mostly about safety. Probably wise after I managed to burn a hole in the back of my hand last week.
Operating the laser without the water pump running is a quick way to overheat the tube and kill it. As this is just plugged in separately it is hey easy to forget. And it uses up another valuable socket. I added two outlets to the back of the machine that are connected to the main power switch. If the laser is on then the water is on. Ditto the power for the exhaust fan – not as essential but might as well do that to. I was going to use a standard UK kettle style power outlet but as the supplied fan and pump have Chinese plugs and they’re the same as Us ones I just used US sockets from Maplin.
Whilst doing this I checked out the wiring and traced where the main be power was going. The colour scheme used was black for neutral (or sometimes live) and red for live (or sometimes neutral). Thin yellow wire for earth of course. The fan had these three wrong way round. And a connector strip mixed them up anyway. Astounding!
The final thing was a simple microswitch in series with the laser on switch the cuts the beam if the lid is open.
Next will be a water flow sensor in case the pump is unplugged or the tubing is blocked. Then a water temperature sensor. I could add an emergency stop and maybe even circuitry that kills the laser if the head isn’t moving. That should prevent it burning a hole if I forget to turn it off at the end of the gcode.
One obvious thing when looking at the Chinese laser is that the table to hold the workpiece is an unnecessary spring loaded contraption that limits what you can work on to 209 X 88mm. Why? Removing it reveals enough space to add a table measuring 350 X 230mm. It’s easy enough to trim the end stops so that the laser head can cover this area too. So on to making a more useful lasering area!
I started with some 10mm L shaped aluminium, cut some 90 degree notches in it so it could be folded into a rectangle. I made up some corner pieces to hold it in shape. These were initially 3D printed but I ended up CNC milling them from 5mm acrylic instead. The L shaped slot held the aluminium frame firmly and hex cutouts underneath held some M6 nuts. Some coach bolts provided simple height adjustment.
It was all finished off using some aluminium honeycomb (6.4mm cells and 10mm thick) from Easy Composites.
In the future this could be motorised, but for now this is all I need to cleanly cut sheet material up to A4 in size.
The great thing about the 40W Chinese lasers you can get on eBay is the price. For what you pay, the quality of the core components is surprisingly good. The laser tube and power supply are fine. The optics (mirrors and lens) are fine. It’s really only let down by the quality of the surrounding bits. Wires may be loose. Screws may be missing. Alignment may be off. The table to hold the workpiece is bizarrely small. The Moshidraw software is an abomination. However all this stuff can be change to turn your £500 laser into something you might have to pay 3-4 times the price for.
The first improvement to the laser had to be to ditch the Moshidraw controller board and software. I’d heard so many bad things about it that I decided to replace it straight away. I’m proud to say that I’ve never even installed Moshidraw.
I replace the board with one from ChrisCircuits. It’s basically a parallel port breakout with a couple of Pololu A4988 stepper drivers. However, Chris has done an excellent job sourcing the unusual connectors and making it a swift drop-in for the Moshiboard. There were a couple of tweak to be made to make his V1.1 board work in place of a V4.1 Moshiboard, but he documented these well and it was easy enough to do. Now I can conrol the laser using CamBam (for design) and Mach3 (for CNC control) and I’m right at home. This is the same toolchain I use with my CNC mill.
It wasn’t completely smooth. I was surprised to find a female connector on the board rather than the male on on my TB6560 mill controller. An annoying delay whlist I ordered a male-to-male DB25 cable. I also had to cut out a slot in the side of the machine that was big enough for the cable. The little USB opening wouldn’t cut it.
The X axis didn’t work at first but it turned out to be nothing more than a loose cable. I meticulously worked out how many steps per millimetre I needed by meausing the belt pitch, counting the teeth on the pulley and checking the microstep setting on the driver. I calculated it at ??. Way out. By measuring how much travel there was it turned out to be 79. Oh well. 79 it is. No idea why.
The only things that were missing from Chris’ installation instruction were on the homing settings. I had to tell it the the X axis homes in the negative direction and set the X and Y coordinates for the home position (0 and 220). I suspect I may have a different version of Mach3 to Chris. [To do – add details.]
Anyway, here’s the obligatory “first cuts” video.
OK. This bloody laser is trying to kill me.
Shortly after getting it I checked it over. It needs some water flowing through it to keep the glass laser tube cool and the tubing was kinked. So I decide to blow through it to ensure the thin flexible rubber tubing wasn’t blocked and the coolant would flow OK. I assume the tubes would be empty so I wasn’t expecting to blast a load of stagnant water out of the tube all over me. Yuck. Oh well. It seemed to work OK so I filled it up with clean water and some antifreeze and continued to test it out. I was pleased to find the tube and PSU in working order.
A week later I was struck down with a really dodgy stomach bug. My wife (a GP) checked me over for the usual things but the tests came up negative. I mentioned the stagnant Chinese pond water and she tested for a few more things you wouldn’t normally check for unless you’d been abroad. Bingo! It turns out my bloody laser had given me a nasty water-borne amoeba like gut parasite called giardia. Easily treated once I knew what it was but I felt shocking for a week.
Later on I was looking to fit a new Z table and wanted to measure how close the beam got to a bracket. I know! I’ll hold a piece of wood in place and quickly zap the laser to see where the burn mark is. What I forgot was the the beam doesn’t magically come out of the lens. It comes in from the left and bounces off a mirror. At least it would do if my hand wasn’t in the way. A few milliseconds of an unfocused beam was enough to make me think I’d got an electric shock. Until I smelt the burning flesh. Nothing too bad, but if that beam had been focused down to a point 0.1mm across it would be a different story.
This CNC stuff is addictive! A new toy has joined the CNC mill and the 3D printer – one of the cheap laser cutters you see all over eBay (of you’re looking for 40W infrared lasers of course). It was genuinely shipped from the UK as promised but it seems I’m now dealing directly with China to sort out some niggles.
These lasers are renowned for turning up with broken tubes, etc. so I feel I’ve got away with it in OK condition. Having said that it wasn’t anywhere near operable out of the box. The extractor fan had fallen to bits. A wire carrying 20,000V had come loose and was in contact with the casing. (Good job I didn’t test fire it!) The main problem I have is that the belt driving the X axis is not connected and either the belt is too short or more likely the belt tensioner is missing. I’m sure I’ll get it sorted but this is what’s preventing a test firing at the moment.
UPDATE: belt bodged, mirrors aligned and laser fired! Lots of bits of paper and masking tape have burst into flames.