Practically Speaking
Hands-on techniques for turning ideas into projects – by Mike Hibbett
Introducing the K40 laser cutter and engraver
H
ard to believe, but it’s been
13 years since we first discussed
the beginning of affordable hobbyist 3D printers. This month, we explore
another tool that has moved from hightech industrial application to the hobbyist
space – the laser cutter.
Industrial laser cutters come in many
sizes, from relatively small, low-power
(100W and under) used for engraving,
up to large 1800mm-square machines
used for cutting clothing designs, and
much larger 15kW CNC machine tools
for cutting steel plate (https://youtu.be/
tbSfc_a1PQg). For our purposes, materials
such as wood and plastics of up to 12mm
thickness can be cut with relatively low
power and relatively inexpensive lasers,
in the 30W – 60W range, and it is this capability and pricing that has driven the
availability of hobbyist-level machines.
The K40 laser cutter
One such machine is called the ‘K40’. Unusually, it is a completely open design,
so there is no single manufacturer that
owns the copyright – yet the specification remains common (with minor
differences) across dozens of different
manufacturers. An example machine is
shown in Fig.1. It consists of just a few
modular components:
x-y mechanical bed, similar to a 3D
printer
Controller circuit, also similar to a 3Dprinter controller
22kV high-voltage power supply
The laser.
Fig.1. The popular, flexible and inexpensive K40 laser cutter and engraver.
see the tube in our machine in Fig.2 – it
is easily accessible from a hinged cover
at the rear.
Mirrors fitted to the enclosure and the
x-y bed direct the laser beam through a
small lens onto the work surface. The
controller controls the position for the focusing lens in the x and y coordinates, and
also turns the laser on and off, allowing
very precise and repeatable cutting. Etching – as opposed to cutting – is achieved
by manually reducing the power output
of the laser through a simple control.
There are two variations on the K40: one
with an analogue control and display of
the laser power, the other with a simple
digital display of the percentage of maximum power output.
The analogue display is considered
by the community at large to be the
better choice as it is more meaningful
– knowing the current flowing through
the laser tube allows you to get a better
picture of how hard you are driving it.
Minimising the power, thereby avoiding
over-driving the tube, can significantly
prolong its life. A laser tube is considered
a consumable, with an operational life of
approximately 1000 hours. Replacement
tubes cost around £70 – £100. You can
The laser is nothing more than a long
glass tube, much like a hugely oversized
valve (US tube) from the 1950s. You can
WARNING!
We highlight several safety issues
in this article:
• Eye protection
• Fume extraction
• Wiring/earthing
These are not nice-to-have optional
extras – you must follow all safety
guidelines to protect yourself and
those around you.
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Fig.2. The K40 laser tube – it’s delicate, so check it for damage as soon as it arrives.
Practical Electronics | October | 2020
What is supplied?
Fig.3. Analogue K40 control panel.
The machine arrived in a large cardboard
box, weighing in at 20kg and measuring approximately 900mm × 600mm ×
375mm. It took two people to move it
into the house and then to the workshop.
To our relief, there were no visible signs
of damage; it’s not unusual for these machines to be delivered with dents, or even
broken laser tubes. We were prepared
for some issues, but none were found.
Perhaps the seller, based in Germany
although clearly fronting a Chinese organisation, did some quality assurance
first… perhaps we got lucky.
Inside the box is the machine itself,
a water pump and flexible tubing (the
laser tube is water cooled) an air extraction fan, and a length of very cheap
100mm-diameter extendible ducting to
allow venting of the toxic fumes from the
device to, well, somewhere else.
A somewhat simplistic user-guide and
control software on a USB stick were the
final contents. Following the advice from
the Internet these were discarded; there are
far better and (frankly) more honest machine setup tutorials on YouTube, and far
better control software available for free.
Extras needed
Fig.4. Inside the K40 electronics area.
see an example of an analogue control
panel in Fig.3.
With many suppliers to choose from
and prices ranging from £300 – £600,
we went with a machine priced at £333
from an Amazon UK supplier based in
Germany. Slightly cheaper deals are
available through Far East suppliers, but
we wanted to avoid the risk of attracting
import duties. Also, our seller sold many
other etching and laser-cutting tools, so
seemed to be a specialist, and might be
knowledgeable in the appropriate handling and shipping of the technology.
The machine must be water cooled, and
for this you’ll need at least a bucket to hold
about a gallon of de-ionised water – available from DIY stores. Anti-freeze should
be added too if you live in a cold climate.
Two mains plugs are recommended
to replace the Chinese ones fitted to the
pump and extractor fan. To make life
simple, a switched mains socket strip
for all three is advised.
Unless you like to gamble with your
eyesight, a pair of 10600nm wavelength
protective goggles are a must. You can
expect to pay £40 for a reasonable pair.
Given that the laser beam is invisible,
and that misalignment of the mirrors
during shipment is not uncommon, this
is a safety precaution you must take. We
borrowed a pair from the local hacker
space while checking the alignment.
You’ll also need a PC to control the machine – we had an old laptop that found
a new lease of life. The control software
Fig.5. The K40 work area – it’s easy to upgrade this area’s size.
Practical Electronics | October | 2020
requirements do not require a powerful
machine – the K40 can even be operated
with a Raspberry Pi at a push. Control is
through a standard USB cable connection.
Installation
Once unpacked, the machine measures
84cm wide, 70cm deep and 27cm tall –
but you will need 67cm clearance above
any table it sits on to open the lid. You
will also need somewhere to place the
bucket of water.
Fume extraction posed a greater challenge; in the end, we moved our machine
closer to an outside wall, and drilled a
100mm-diameter hole, followed by installing standard air vent plates to the
outside wall. Adequate venting is essential, as the gasses given off during
cutting vary from unpleasant (if cutting
or etching wood) to highly toxic (if cutting unspecified plastic.)
We removed the two Chinese power
plugs and fitted UK mains plugs. Two
mains outlets are provided on the rear of
the machine, but we found them loose,
and preferred the mechanical stability
of the larger UK plugs.
The internals of the machine are easily
accessed and partitioned simply – the
laser tube area is at the rear, stretching
the entire width of the machine; and the
electronics area (with plenty of room
for additions) is front right, as shown
in Fig.4. The work area covers the rest
of the front, accessible via a hinged lid,
as seen in Fig.5. There you can see two
of the mirrors that direct the (invisible)
laser beam.
Submerging the no-name, mains-powered water pump into, well, water, was
a difficult challenge. We ended up putting it in a large sealed plastic container
and labelling it ‘Don’t touch when powered!’. There were no warnings from other
users about the use of this pump on the
Internet, but best to be safe. After eight
months of use, however, we have had no
trouble with it.
The air pump, on the other hand, was
another matter. We were pre-warned on
the Internet about the quality of wiring
on the pump and were not disappointed
– ours was wired exactly as discussed on
Fig.6. You must check the air pump wiring – see text!
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Fig.7. The upgraded K40 work area
Fig.8. Very nice! – a backlit front panel with etched scales.
forums, as shown in Fig.6. The mains wires from the input
supply are simply twisted to the motor wires! It’s unbelievable
that Amazon UK permit this equipment to be sold anywhere; the
device’s CE approval mark mean absolutely nothing in today’s
Internet-based consumer markets. Buyer beware! Thankfully,
we had done our research and were forewarned of these horrors, so we soldered the wires and fitted insulation.
Another point we were pre-warned about was the fitting of
the air extraction coupler. This (which is a combined coupler
and fan unit) is very loose when fitted to the machine, and
you would be well advised to fit at least duct-tape to hold it to
the laser cover, or use some better solution (again, the Internet
has many suggestions for improved air exhaust couplers, but
they do require access to a 3D printer.) We were happy with
the performance of this exhaust fan and so simply duct-taped
it to the enclosure.
area is straightforward using just common DIY tools and £20
worth of materials. This is considered a simple yet essential
upgrade. You can see our solution in Fig.7. This gives a much
nicer 30cm × 20cm work area.
Toxic plastic fumes
The controls
The machine controls are very simple amd consist of just the
following three items:
Potentiometer to adjust the power level, with an analogue
dial showing the value
Laser ON/OFF switch, which allows you to test control of
the machine without firing the laser
Momentary push button which allows you to manually
turn the laser on. This is useful for checking your power
level setting and confirming the exact position of the laser
head (handy when you are trying to minimise the amount
of waste material).
This is a good time to mention fumes: when cutting plastic,
perspex is safe, with appropriate venting. Plastics such as
PVC emit highly toxic gases when burnt that will injure both
you and the machine. You must research the material you are
thinking of using before cutting or etching. Wood, paper, cardboard and perspex are fine, with appropriate venting. Other
materials – assume they are deadly, until research says otherwise. All cutting operations give off bad-smelling smoke, so
even venting out of an open window can be a problem, both in
terms of back draught and sending the smoke into your home,
or to your neighbour. We have two friends who own laser cutters but accept they cannot use them during the summer due
to neighbour’s open windows. Fortunately, our vent is into
an unused alleyway.
The work surface comes with a simple spring-loaded
clamp which restricts the work area to 21cm × 9cm, as seen
in Fig.5. This is surprisingly small given the volume of the
work area. Thanks to the very simple design of these machines, modification to accommodate a much larger working
Software
Fig.9. Complex cut-and-fold enclosures are easy to build.
Fig.10. For chemists who cook! A nice example of wood etching.
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As mentioned, you can ignore any software or user guides supplied with the machine; the K40 laser is very well supported
on the Internet by a huge community of fellow makers. A free
program has been developed specifically designed to control
this printer, called ‘K40 Whisperer’. It has become the standard control software of choice for hobbyists.
Unlike 3D printers, which require design files to be created
in a 3D CAD program, laser-cutting profiles are two dimensional so they can be created with much-simpler 2D drawing
tools such as Inkscape. Images must be in SVG format, but if
you are looking to etch photos or drawings, Inkscape can convert them for you.
If you are interested in designing front panels, The US
company Front Panel Express provide a free program, Front
Panel Designer, which make this task easy. Our back illuminated amplifier panel, shown in Fig.8, was designed in just a
few minutes, the file exported as an SVG image, then cut and
etched in just a few minutes.
Practical Electronics | October | 2020
K40 Whisperer permits three different
laser options specified in the image file
– cutting, vector engraving and raster
engraving. You specify which of these
operations to performing by assigning
different colours to your image – red for
cuts, blue for vector engraving and black
for raster engraving. Vector engraving
is useful for etching lines and thin text;
raster engraving is better for images or
thick lines.
In use
So, what can this machine cut? It works
with cardboard, 3mm perspex, 3mm plywood and MDF, and leather – we have
tested these with success. With multiple
passes it is possible to cut thicker materials, but with a reduction in accuracy
of the cut. One thing we have found,
especially with perspex, is that the cuts
are very clean, and the final parts look
very professional.
The cut width is approximately 0.2mm,
so you can cut very intricate shapes.
Unlike 3D printing it’s very fast – a 10
× 10 × 5 cm enclosure, consisting of six
flat pieces of perspex, took just three
minutes to cut.
With so many people using laser cutters
in the on-line hobbyist community, there
are thousands of free designs available
to download and cut or take inspiration
from. In Fig.9, for example, you can see
an enclosure design we downloaded that
uses multiple slits in the top piece to
make a curved lid. You are not limited
to enclosure and front panel designs; in
Fig.10 you can see an etching, that we
applied to a bread board for a unique
birthday gift. We also created a pair of
Christmas earrings – see Fig.11.
In the eight months since it arrived,
the K40 has been invaluable – even helping with fast prototyping of an enclosure
design for a commercial product: http://
bit.ly/pe-oct20-product
It’s been used to cut custom cardboard
packaging designs (including for the above
product,) as the power can be controlled
accurately enough to etch fold lines in
cardboard, not just cut around the edges.
Again, software is available for free on
the Internet to help create custom packaging designs.
Upgrading
As can been seen from the pictures, the
machine is incredibly hackable; indeed,
from the start, you have to hack it to
make it safe.
Increasing the bed size is the first
change, as it is so simple to do and gives
the device a massive boost in flexibility
to do large jobs. We followed one of a
dozen videos on YouTube to create the
bed shown in Fig.7 with material sourced
at a DIY store using simple tools.
Practical Electronics | October | 2020
Fig.11. Christmas ‘snowflake’ earrings.
www.poscope.com/epe
The next recommended upgrade is air
assist; this is an additional air pump that
blows air over the target spot on the work
piece. This not only reduces burn marks,
it makes the cut more accurate and powerful, as the laser beam passes through
less pollution before reaching the target.
A simple air pump and flexible tubing
costs around £20, via eBay.
Everything else can be replaced or upgraded from multiple vendors. It’s even
possible, with a little more skill, to upgrade the laser tube and power supply to
a higher power rating, making it simpler
to cut 12mm plastic or wood.
Conclusion – is it time to buy?
This is a great, affordable tool for the keen
hobbyist or maker, but where you live
may make its use inappropriate. Without
adequate ventilation away from humans
and animals, the fumes are too dangerous.
We are lucky, our lab is away from other
homes and at the end of a garden, with the
machine installed beside an exterior wall.
As supplied, the work area is 21cm ×
9cm, but easily expandable to 30cm ×
21cm, the size of a sheet of A4 paper. This
is a perfectly adequate work area for enclosures and instrumentation panels, as
well as art and craft cutting and etching.
This is a hugely popular machine around
the world, and there are thousands of
YouTube videos offering advice on setup,
modification and use.
Would we recommend you consider
buying one? Yes, but only if you have the
space to install it with safe fume venting. Does it replace a 3D printer? No, it
complements it.
3D printers have fallen in cost significantly over the years; our original £1000
3D printer was recently replaced with a
£140 Ender 3 machine, which performs
fantastically. Will we see a similar drop
in price for laser cutters? Unlikely in our
opinion. First, their use will remain restricted to people with well-ventilated
workspaces, limiting broad adoption;
second, these machines already benefit from the use of low-cost x-y stepper
motor control electronics and mechanical
solutions developed for the 3D printer
market. The main cost in these devices is
in the laser tube itself. So, while we will
see some reduction in cost over the next
decade, don’t expect it to be significant.
- USB
- Ethernet
- Web server
- Modbus
- CNC (Mach3/4)
- IO
- PWM
- Encoders
- LCD
- Analog inputs
- Compact PLC
- up to 256
- up to 32
microsteps
microsteps
- 50 V / 6 A
- 30 V / 2.5 A
- USB configuration
- Isolated
PoScope Mega1+
PoScope Mega50
- up to 50MS/s
- resolution up to 12bit
- Lowest power consumption
- Smallest and lightest
- 7 in 1: Oscilloscope, FFT, X/Y,
Recorder, Logic Analyzer, Protocol
decoder, Signal generator
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