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Milling Prototype
PC Boards with
Roland’s EGX-350
Desktop Engraver
Review by Mauro Grassi
We take Roland’s EGX-350 CNC milling machine on a
test run making fast prototype PC boards. We found it
surprisingly good – it can route, drill and cut out a complete
PC board quickly, without using chemicals. It lets you move
from concept to working prototype in a matter of hours.
18 Silicon Chip
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When that high-speed bit starts attacking the blank PC board, bits of swarf fly everywhere. Not only for this reason, the
Roland has interlocks on the cover to make sure it stays closed – and you stay protected.
T
here are several options when it
comes to making prototype PC
boards, whether at professional
designer level or in a school, college –
or even an advanced hobbyist.
One is to send the artwork to a
specialist PC board prototyping house
and pay for it to be done. While
relatively expensive, for many that’s
a completely viable option (and one
we’ve used here at SILICON CHIP), even
though the turnaround will normally
be at least 3-5 days.
A big advantage of this method is
that the board will (usually) be returned to you with all holes drilled,
perhaps with a “conformal” protective
coating on the copper and solder mask;
sometimes even with a silk-screen
component overlay.
Another option is to etch your own
PC boards, using perhaps a photoresist pre-sensitised board and a UV
light exposure box.
The results can be good but you
have to use chemicals and drill the
holes manually, neither of which is
particularly pleasant. The chemicals
are somewhat hazardous and must
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be disposed of properly. However, the
quickest, most hassle free method, is
to use a CNC (Computer Numerically
Controlled) milling machine.
A CNC machine’s head can be controlled precisely using a computer. It
functions very much like a plotter but
has a spinning head containing either
a milling (or engraving) “bit” or a drill.
How does it do it?
Blank PC board consists of a nonconductive base layer, usually of
fibreglass or a resin-bonded paper,
onto which is laminated a very thin
sheet of copper.
In the normal “etched” board, the
pads and tracks are protected by “resist” while the areas between them are
chemically dissolved away, leaving
the tracks electrically isolated from
each other.
Milling a PC board achieves a similar result but instead of etching, the
areas between the tracks are mechanically milled or engraved away, down
to the base layer, under the control
of a computer. In fact, the software
used to create the PC board pattern is
usually able to produce the file which
can control the CNC milling machine.
The CNC milling machine can
also drill the holes and cut out the
board, even in arbitrary patterns: nonrectangular boards with shaped edges
and cut-outs can be made in this way.
In this case, it is simply a matter of
instructing the bit to cut deeper, right
through both the copper and the base
layers.
The Roland EGX-350
Although normally marketed as a
general engraving CNC machine for
making signs, panels and the like
(which it does well), the Roland EGX350 is adept at making fast prototype
PC boards. It is also one of the most
affordable CNC milling machines on
the market.
However, to produce PC boards
you will need special software, as the
supplied Roland “Engrave Studio” is
geared towards general engraving tasks
and not PC board manufacture.
Although there are cheaper CNC machines on the market, few are suitable
for milling PC boards. To be suitable,
November 2009 19
Specifications at a glance:
Table (work) size:.................. 305(W) x 230(D) mm
XYZ-axes travels:................. 305(X) x 230(Y) x 40(Z) mm
XYZ-axes drive system:........ Stepping motor – 3-axis simultaneous control
Operating speed:
X and Y axes: ............... 0.1 to 60mm/second
Z axis: .......................... 0.1 to 30mm/second
Software resolution:.............. 0.01mm/step or 0.025 mm/step
Mechanical resolution:
X and Y axes: ............... 0.0025 mm/step
Z axis: .......................... 0.00125 mm/step
Spindle motor:...................... Brushless DC motor - maximum 50W
Spindle speed:...................... 5000 to 20000 RPM
Dimensions:.......................... 616(W) x 591(D) x 393(H) mm
Weight:................................. 34kg
a milling machine with good Z-depth
control, mechanical resolution and
repeatability is required. Repeatability
refers to how accurate the positioning
is over many movements.
To some extent, contactless laser
cutters overcome the problem of
having to have good Z-depth regulation – though these are prohibitively
expensive.
Z-depth control is critical if the milling bit does not have a square section
head – if it is conical, for example, a
thin track may be cut too much and
disappear altogether.
Resolution and Backlash
The resolution of a CNC machine
refers to smallest step the head can
move in each of its axes.
Good resolutions – of a fraction of a
millimetre – can be obtained by using
stepper motors, mechanical gears and
linear screws (the screw assemblies
that convert the rotational motion from
a motor into linear motion, such as
lead screws or ball screws).
As you can see in the specifications
panel, the Roland EGX-350 has impressive resolution figures for its price.
The repeatability can be adversely
affected by backlash. Backlash refers to
the unwanted movement in response
to a reversal in direction along an axis
– it leads to inaccuracies in the head
position and can be a problem where
high precision is required, as when
milling PC boards. This machine uses a
proprietary anti-backlash mechanism
developed by Roland.
Plated-through holes
Although it is possible, given some
care with placement, to mill doublesided PC boards there is still the
20 Silicon Chip
problem of how to connect the two
layers together. Naturally, producing
plated-through-holes, or “vias”, cannot be achieved by a milling machine.
The simplest way around this is to
use small (conductive) pins soldered
on both sides. This is relatively easy
but labour intensive, because each
pin needs to be soldered individually.
It is therefore more suitable for PC
boards with relatively few inter-layer
connections.
Work area
At 393 x 616 x 591mm, the Roland
EGX-350 does not take up too much
space on a desk.
When it comes to making PC
boards with a milling machine, you
are restricted by the size of the area
over which the cutting head runs. In
this case, the work area is 305mm by
230mm, which represents quite a substantial PC board. In any case, you can
sometimes overcome this problem by
breaking up a big design into separate
PC board modules.
Connections
The connections to the Roland EGX350 are accessible at the back, on two
sides. Mains power connection is via
an IEC socket on the right hand side.
The serial, USB and hand controller
connections are on the left hand side.
The serial or USB connections can be
used to connect the Roland EGX-350
to your PC.
The hand controller
The Roland EGX-350 can be controlled manually using the supplied
hand controller.
This has a 16 x 2 line LCD display
that shows the X, Y and Z coordinates
in machine units, as well as a simple
menu system. You select a menu and
use the arrow keys to navigate through
different sub menus. There is also a
digital click wheel that can be used to
vary the spindle speed between 5000
and 20000 RPM.
Every detail seems to have been
well thought out in the design of this
machine – for example, the hand
controller contains no gaps between
buttons, so no dust can fall into it.
Safety features
The Roland EGX-350 has a number
of welcome safety features that make
it a particularly good choice.
The work area is completely enclosed by a durable transparent cover,
with microswitches which detect
when the cover opens and automatically cut power to the motors.
It is possible to manually override
the switches with the cover open; for
this reason, where required for certain
applications (eg schools), the machine
can be delivered with tamper-proof
micro-switches.
The machine also incorporates internal over-current protection which
activates if the motors lock up (for
example, if you drill into some hard
material and the bit becomes stuck).
In that case, the current through
the motor will rise steeply, which is
detected by the driving electronics and
the supply to the motor is stopped.
You will get a failure message on the
hand controller and the only way to
proceed is to then reset the machine
by turning the power off.
The other safety feature is the red
kill switch – pressing it immediately
cuts all mains power to the machine.
This can be used in an emergency to
stop the machine instantly. Apart from
those features, any running job can be
either paused or cancelled using the
hand controller.
Setting up a job
For general engraving work, the
machine comes with the Roland
Engraving Studio software but as we
mentioned earlier, for making PC
boards you will need additional PC
software – the one we tried is called
CopperCAM from Intellecta (see www.
galaad.net/coppercam).
This Windows software is normally
an option but Intellecta will be including it with any Roland EGX-350
purchased from them as a result of this
siliconchip.com.au
review (make sure you tell them you
saw it in SILICON CHIP!)
Producing Gerber plots
Gerber plots have been traditionally used to control plotters – they
are almost universally accepted by
PC-board-making houses. For that
reason, most PC board design software
such as Protel, Altium and Eagle have
the facility to produce these and other
CAM files. You will need Gerber plots
(for each layer) as well as the Excellon
drill file.
CopperCAM
Using CopperCAM, you can import
the Gerber plots and the Excellon drill
file. You select the layer and compute
the contour paths.
The drilling coordinates are aligned
to the copper tracks by selecting a
reference pad on both. You then select
‘adjust to reference pad’ to align the
two ‘layers’.
Tools
You can maintain a tool library
for the different tools under CopperCAM. As a minimum, you will need
an engraving bit and a drill bit. Each
tool will have its own plunge speed
and depth.
The top speed of the machine is
quite fast (see the specifications). But
the milling speed affects the quality
of the cut: too fast and there will be
noticeable burring of the edges along
the cut and you may also damage the
tool bit. Too slow a speed may well
mean a slowly-made board.
Different materials and tools have
natural milling speeds that are adequate for that application. For making
PC boards, Intellecta recommended
using paper phenolic PC boards,
as these are softer than the typical
fibreglass board, and therefore more
forgiving on the engraving bit.
The engraving bit is made from
tungsten carbide, which is a very
hard composite but is expensive. The
tools will wear out over time and they
should be reasonably sharp to obtain
a clean cut – especially if many thin
tracks, of the order of 15 thou, are on
the PC board.
It is also possible for the tool bit to
break in the middle of an engraving
job – the costs of tool replacement
can quickly accumulate but experience to some extent circumvents this.
The guaranteed life of the tool bit is
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Part of a PC board milled with the Roland EGX-350 CNC Desktop Engraver – one
of many boards we produced. It looks a little different to conventionally etched
PC boards because the cuts between tracks actually go a few thou into the base.
measured in metres, and therefore it
depends on the complexity of the PC
boards being milled as to how many
such boards can be made with the
same tool bit.
Setting the Z depth
Setting the reference Z depth is
particularly important for milling PC
boards. The reference Z depth will
affect how deep the cut is made into
the copper, because the depth set in
CopperCAM is relative to the reference
depth (which is the point of contact
between tool bit and board).
The uniformity of the Z depth is
especially important for those boards
with fine tracks of the order of 15 thou or
so (this was the smallest track we were
able to route consistently in our testing).
You can purchase accessories for
this machine including a vacuum
table and a T-slot table that may help
in achieving this uniformity. But we
found that we could get quite good
results simply by attaching the board
to the supplied base using doublesided tape.
Tool Changes
Unlike more expensive milling machines with automatic tool changers,
tool (bit) change is manual. While automatic changers are convenient, they
add substantial cost and are not strictly
necessary, especially for prototyping
PC boards.
CopperCAM allows you to mill each
layer separately, then the engraving bit
can be changed to a drill bit and the
holes drilled.
Drilling the Holes
Drilling is particularly easy, with
various options in CopperCAM. You
can select one drill bit for all holes – irrespective of the hole sizes embedded
in the drill file. This is a good option to
minimise the number of tool changes,
which is time consuming and delicate,
as the Z depth needs to be set every
time a tool is changed.
If you do not wish to use different
tool bits for differently sized holes,
CopperCAM also has an option to use
a single drill bit to make different hole
sizes by circular boring. This is where
the machine makes the hole by moving
the head around the centre of the hole.
However, this can lead to many
broken drill bits if not set up properly
and is obviously harsher on the drill
bits. In any case, for many PC boards,
the best way is to use a single drill
bit for all holes and enlarge the holes
manually as the need arises.
This is the method we preferred,
using a single 0.7mm drill bit. Most
standard components such as resistors, capacitors, transistors, diodes
and integrated circuits will usually
fit through this size hole. Larger hole
sizes, like those for TO-220 packages
can then be drilled manually using a
drill press.
Isolation Rub-outs
The quickest way to engrave the
PC board is if the software creates
a minimum isolation path around
tracks – in other words, it leaves as
much “dead copper” (copper which
is not connected to the circuit) on the
board as possible.
There may be legitimate reasons
for removing the ‘dead’ copper, however, such as electrical considerations,
ground planes, inter-track capacitance
or perhaps simply to make assembly
easier.
November 2009 21
This shot shows the large piece of MDF we used as a base (complete with drill holes from an earlier produced board). It’s
very important that the blank PC board is flat and level due to the tight tolerances used in milling and drilling.
It is not hard to get solder bridges
between a pad and an adjacent area
when the only isolation is a single thin
strip of missing copper.
Rub outs, although more time consuming and causing greater wear on
the tool bits, help reduce the chances
of solder bridges.
Conclusion
We tried this machine over a period
of days. In that time we were able to
manufacture a number of PC boards
with consistently good results.
We were able to go from the electronic concept conceived in the morning
to having a finished and working PC
board by late afternoon – this involved
not only designing the PC board on
computer but also writing firmware,
as the designs used a microcontroller.
Using a milling machine to manufacture PC boards, especially singlesided PC boards, is by far the most
convenient and quickest method of
production.
However, convenience costs: milling machines are not cheap.
This one, however, should certainly
be affordable for designers but also
fit within the budgets of educational
institutions and perhaps even for ad22 Silicon Chip
vanced hobby use – especially when
you consider that it can do much more
than produce PC boards.
Admittedly, the outlay involved in
purchasing a machine such as this
could buy you many PC boards from
your local board maker.
However, it is the convenience of a
very short turnaround, coupled with
the ability to test concepts on-the-go
that make a milling machine attractive
for situations that may require several
iterations of boards.
Of course, apart from the initial
capital outlay to purchase the machine, there is the ongoing cost of
consumables.
This includes the tungsten carbide
engraving tool bits, the collets, the
drilling bits and the blank copper
board. The bits wear out over time and
will need regular replacement. They
sometimes break too!
But if you chose the alternative
photo-etching route, you’d also be
up for the cost of pre-sensitised PC
board, the chemicals required, drills
and so on. And you’d certainly take a
lot longer coming up with a finished
board.
Simply put, we believe the Roland
EGX-350 is one of the best CNC ma-
chines for making PC boards in its
price range.
Price
The Roland EGX-350 costs $8795
(inc. GST) and can be purchased direct
from Intellecta Technologies.
Intellecta Technologies supply the
engraving tools for PC boards as well
as drill bits, collets and services of
interest to the education sector, specifically relating to PC board prototyping,
including the CopperCAM software.
Acknowledgement
Our thanks to Dr Tony Pugatschew
from Intellecta Technologies and Roland DG Australia for their technical
assistance in this review.
Contacts
Intellecta Technologies
51 George Street
Thebarton SA 5031
Phone: (08) 8351 8288.
Website: www.intellecta.net
Roland DG Australia
Unit 14, 25 Frenchs Forest Road
Frenchs Forest NSW 2086
Phone: (02) 9975 0000
Website: www.rolanddg.com.au SC
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