THE Laser engraver

In early 2015 I spent many hours googling laser cutters and engravers.

Most were over $3000 AUD, but had great reviews and seemed to be what I needed to engrave my own panels. I tried to justify the purchase to myself at the time, thinking that later on down the track (if my cockpit worked out) I may be able to make and sell a few to recoup my costs. This never happened.

My main goal at the time (it still is) was to make this cockpit for as little money as possible, so I decided to pull the trigger on the cheapest Laser cutter I could find, an eBay special direct from China.

They go by many names, but are commonly referred to as the 'K40,' and they are still on eBay today.

These are marketed as a 40 watt CO2 laser (hence the 'K40' designation), but they are usually running a poor quality laser tube that will struggle to output 20 watts.

The one I bought cost me a little under $500 AUD ($389 USD).

When I clicked 'buy it now' I had done copious amounts of research, so I knew what i was getting myself into.

The hardware, including the blue outer case, lid, the x and y axis with head and the stepper motors, are pretty good quality and quite solid, but the units have terrible electronics in them. They can even be down right dangerous, with many coming from the factories in China not wired correctly and using shoddy power supplies that were absolute fire hazards.

Lasers should not be treated like toys, they are very high voltage and can be very dangerous machines.

I don't say this to make people avoid them. As long as you do your research, understand what you are doing and always check that it is safe before firing it, you will have no issues at all.

I knew all this before i ordered it of course, so my immediate plan was to upgrade it.

After a lot of research, i found a website that sold high quality upgrades specifically for the K40, www.lightobject.com.

*I have no links to this company at all other than being a happy, full price paying customer.

I purchased a K40 upgrade kit, which included what they call a 'Digital Signal Processor', a better (and safer) 'Meanwell' brand power supply, and clear English instructions on how to perform the upgrade. It also comes with better software to run it, LaserCad.

When my K40 machine arrived, I turned it on once in stock form and tried to cut a panel. Nope. Nothing. It didn't fire.

Instead of fault finding, I immediately gutted it and binned all the stock electronics. Most importantly, all the earthing points were double checked. I unbolted them, sanded the casing to bare metal, and replaced most of the bolts (faulty earthing was a known issue at the time, and if the internet was to be believed- it had actually killed people).

The lightobject upgrade kit was installed, and after a huge learning curve I got it working well enough to cut and engrave plastic!

THE upgrades

The 'DSP'

What the manufacturer calls a 'Digital Signal Processer (DSP)' is basically the brain of the thing. It consists of a motherboard, that has all the connections for the stepper motors to run the axis, and the connections for the laser to fire it. The upgraded one also had lots of safety upgrades, including a water flow sensor that would shut it down it no coolant was flowing, and well as a fuse that would trip if anything shorted out.

It sounds crazy (by today's standards) but the stock K40 laser electronics could only control the position of the laser head... not the power output of the laser! For example, say I want to engrave some text onto, then cut a panel out. In its stock form, I'd have to manually set the laser power with a knob, then run the program to engrave the text. When that is done, i would have to stop it, manually set the power with the knob to higher so it will cut through the plastic this time, then run a separate file.

It was like having a printer that only prints in one colour, and if you want another colour you have to pause it and swap the cartridge out each time.

With the upgraded lightobject electronics and its PWM power supply, it can directly change the power of the laser tube based on what the LaserCad software tells it to on the fly.

Please note that the DSP I actually have is a 'AWC608,' a discontinued model nowadays.

The latest one (T9) seems even more capable, with more axis and better software!

The 'AWC608' control panel. I rarely change any settings on the fly using this, it's all dont in the LaserCad software on my PC. I only ever push test, start and reset, and the arrow keys to move the axis when removing something from the bed. The temperature sensor and display are PC water cooling parts.

Side cover opened. You can see the Meanwell High Voltage PWM power supply that runs the laser, the smaller power supply for the DSP itself, as well as the Three Stepper motor drivers on the right wall.

The 'AWC608' DSP mainboard. Eveything is clearly labeled and it was easy to install and maintain.

The three stepper motor drivers, for the X Y and Z axis. The Z axis table was removed so it is unplugged. I left the driver in there anyway, so if ever i want to use it again i can just plug it in.

The Laser Tube

I used the laser tube that came with it for about 6 months before I ordered a new tube from lightobject. The more powerful tube is longer, so I cut a hole in the side of the machine so it would fit and made a cover out of PVC pipe. This upgrade was not really necessary for just cutting and engraving 3mm plastic, and to be honest if i had my time again id probably sped my money elsewhere on the cockpit. The standard 40 watt (probably 20 watt) tube is more than capable of cutting acrylic and engraving the paint off it. I did it anyway, just because i like tinkering with things, and more power is always good. The machine can now cut through acrylic like a hot knife through butter. For example, a cut that would take 80-90% power at 10 mm/s, could now get done with 30-40% power at about 20mm/s. The tube as been running flawlessly for about 5 years, and I never need to go over 50% power so it should last a long time.

The Cooling System

CO2 lasers are a glass tube that requires active cooling. High voltage electricity goes in, which creates gas and heat. This make it very hot. There is a glass tube casing around it, that distilled water is pumped in one end, flows around the laser tube to remove heat, then out the other end. The cooling system it came with was basically a fish tank pump you can put in a bucket. The pump itself actually worked quite well, but I eventually changed to use a higher flowing D5 PC water pump I had spare. This is connected to an esky (a drink cooler thing, for all my US friends), that has a hole drilled and a hose fitting tapped into it. It holds 80 Litres of water, and I can add ice in the summer months if needed. I also added a PC Cooling temp sensor so I can monitor temperatures both at the laser tube and inside the esky. If it ever goes over 17 degrees celcius (62 degrees F), some ice goes in.

The Exhaust and Air Assist

Laser engraving plastics emits gas. Terrible smelling gas that depending on the material can be toxic. The stock exhaust fan was a terrible plastic thing that did almost nothing and went straight in the bin.

I bought a commercial exhaust fan, similar to this, which is what someone would normally purchase to grow 'hydroponic tomatoes'.

It is not attached to the machine, but on the end of a long duct that flows out of my workspace and onto the roof. You want it on the end of the duct, as far away from the machine as possible, so any leaks in the duct have negative pressure. The fan I have has plenty of power and does the job well.

The machine came with an air assist already fitted. This is a simple fish tank air pump, that is connected via a hose to the laser head. It pumps air down on the the material being cut, to remove dust and stop flames if the material is flammable. All the hosing is standard, all I did was add a larger fish tank pump with greater air flow.

View at the rear of machine. The aluminium ducting is connected with a flange where the stock exhaust fan would sit.

The exhaust fan. Cheap but powerful enough to get the job done. I normally have another duct attached to the exhaust side, which runs upwards and hooks on the edge of my roof guttering like a chimney, only to stop the smell from going into the windows of my house.

The larger air pump, with the one that came with it. Cost about $70 AUD from a local aquarium.

The air pump in place. Its connected with the soft silicon hosing that came with the laser. Positioned on the floor so vibrations are not transfered to the machine. You can also see the duct for the exhaust, and the D5 water pump for the cooling system.

The laser head, lens and the bed surface

Although the stock lens it came with worked quite well, I purchased a new, higher quality lens from lightobject.com. The lens I chose has a 50.8 mm focal point, which means the laser is at its finest point 50.8 mm from the surface of the lens. I measured out 50.8 mm with a set of calipers, then set the bed at a height so that distance is exactly in the centre of a 3mm piece of acrylic when it cuts, and just under the surface when it engraves. The result was a much finer, pin point size laser dot, which results in much more accurate engraving at smaller sizes.

I also purchased and installed a motorised Z axis bed, to make changing the heights to engrave different thicknesses of materials easier. If you are only doing aircraft panels, don't buy this.

This upgrade is unnecessary and I eventually removed it altogether, for two main reasons.

Firstly, I am only ever cutting or engraving 3mm or 2mm acrylic, so changes in height are not common. I only ever need two set heights, one for cutting so the laser focal point is dead centre of the acrylic, and one for engraving so the laser focal point is just under the surface.
Secondly, and the main reason I removed it, was the reduction in bed size. The bed of the K40 is small anyway, but with the mechanism needed to move it up and down with a stepper motor as well it was reduced even further. This meant I had to trim the size of the acrylic by hand before lasering them. Wasted time.

I also did not like the solid metal bed the motorised bed has. During cutting, residue from the acrylic has no way to escape against the solid metal so it would leave marks on it. The acrylic smell was also worse, as the exhaust fan could no longer suck air from underneath the piece being cut.

I ended up buying a aluminium honeycomb style bed that I found online. I cut it to size, then added legs I cut from aluminium L profile to get it at the right height so the 3mm material is exactly 50.8mm from the lens surface.

I marked the legs for the two height I needed, so to change between cutting and engraving materials I just pull the bed out, undo four bolts, move each leg to the right height, then put it back in.

Takes under a minute, is sturdy and maximises the usable bed.

The axis and the honeycomb bed. The head, mirror mounts and mirrors are all the standard ones that came with it. The only thing i have added in here is the lens itself, and a red laser pointer to make aligning material easier. You can see the simple method of mounting the bed, four L shape legs of equal size, bolted to the bed and sitting on the floor of the machine. It just lifts out.

Close up of the head. All standard, except for the laser pointer. The air assist is standard as well, I just upgraded to a more powerfull air pump.

TIP AND TRICKS

Using the laser to cut good panels efficiently took lots of trail and error. Balancing power and speed to engrave just enough of the panel so the text was was sharp can only be done this way.

I painted a few sheets of the white acrylic i had chose in the same black i intended to use, then cut the same line of text over and over again trying different speeds and power to get the best results.

A few things I picked up along the way:

You do not have to engrave text in one pass. Try lower power with two fast passes. On some occasions i did this with great results.
Ensure you take the time to get the height of the Z axis right. You want the exact focal point of the lens (50.8mm away from the surface of it in my case) to be in the exact centre of your panel thickness when cutting, but just under the surface when engraving. I took a long time to get this right, then when I was happy I marked the positions so it would be repeatable.
Once you have the alignment of your mirrors as good as you can get them, put a drop of superglue on the thread of the adjustment knobs so they will never vibrate loose. These machines vibrate a lot.
When you are designing your panel for engraving, used different layers for blocks of text rather that one large layer for all the engraving. This shortens travel time. The picture below tries to explain why.

The Laser settings that worked for me

This is very dependant on your setup. Again, I highly recommend you learn your machine through trial and error, as even if you have identical hardware to mine you will have likley have a laser tube that is manufactured differently, different acrylic material, paint, and ambient temperature.

But anyway, these are the settings I found worked best for me (with my 60 watt tube):

Cutting 3mm Acrylic or MDF: 50 mm/s, 12% Power, Single Pass
Cutting 2mm Acrylic: 50 mm/s, 12% Power, Single Pass
Engraving Text in 3mm or 2mm Acrylic: 250mm/s, 12% Power, Single Pass
Engraving Pockets for the LEDS in 3mm Acrylic: 150mm/s, 50% Power, Two Passes