Beside learning how to operate machine tools, programming
in G code and studying the properties of materials,
professional milling machinists in training spend a year
learning machining techniques. Naturally, the average
Profiler user does not have this knowledge.
Thanks to the user-friendly interface of the Profiler and modern
CAD/CAM packages, relatively inexperienced users
can also produce very nice results with CNC machines.
However, this does not mean that there is no longer any
need for some knowledge of machining techniques. Although
the user can usually have the machine do what
he wants, the machine does not always do what it is supposed
to do. In fact, it often doesn’t. Poor milling results
are usually not the fault of the machine or the software, but
instead almost always a consequence of incorrect settings.
Nevertheless, hundreds of users have shown that splendid
results can be obtained with a bit of patience and experimenting.
If you do something wrong and the Profiler gets
stuck, there’s no need to panic. It may complain, but it won’t
break. The message here is: try to find the best settings for
each machining operation.
Milling 2D shapes and engraving text
The Profiler is primarily constructed for milling all sorts of
2D shapes. Many users draw the shapes in ColiLiner, generate
the milling paths, and leave the rest of the work to
ColiDrive. ColiLiner is not a real drawing package, but can
still do quite a lot. For instance, you can use all standard
text fonts, and most drawings work out nicely. However,
if you want to use your own drawing package, simply export
the drawing as an HPGL file and import it directly into
ColiDrive.
Milling 3D shapes
The Profiler is not actually designed for 3D work. Nevertheless,
it can be used to make very nice 3D shapes. This statement
on our part drew a certain amount of criticism from
users, and some explanation is in fact necessary. With a
real 3D machine, the three axes are interpolated simultaneously.
This is not the case with the Profiler. Only two axes
can be interpolated at the same time, so the third one al-
ways comes afterward. It is thus possible to mill 3D shapes,
but the end result not as nice and it takes much longer. For
this reason, may people who like to make 3D forms first mill
the shape and then finish the piece by hand (sanding). The
final result looks surprisingly good.
Additional CAM software is necessary for 3D milling; it is
not included with the Profiler. For example, Colinbus can
supply DeskProto as an affordable solution. This package is
not especially suitable for 2D milling, but it is a very powerful
tool for making 3D models.
Milling PCBs
The Profiler is supplied with ColiLiner Lite (especially for Elektor
readers who would like to mill the occasional PCB). The
software supports reading in a Gerber or Excellon file and
then milling channels around tracks and pads. This isn’t as
easy as it sounds. As far as we know, there are only a few
software packages on the global market that can handle
this, and they are either very expensive or are only supplied
together with expensive milling machines.
The fact that the Profiler is supplied with this software does
not really mean that the Profiler is a true PCB milling machine.
This was already clearly stated in the first article.
However, the many links and photos that users sent us clearly
show that it is possible to mill good PCBs with this machine.
As we have received a lot of questions on this subject,
we want to address it here in somewhat more detail.
Milling PCBs is becoming increasingly popular. This is not
because it is better than etching, but instead because it is
faster and more environmentally friendly for one-off boards.
With a true PCB milling machine, you can easily mill five
tracks between the pins of an IC, which is more than good
enough for modern circuitry. If you want to get acceptable
results with the Profiler, it’s only logical to have a look at
how the pros do it: what tools do they use, and how do
they achieve such amazing results?
Fitting the PCB is an important factor. The best way to do
this is to use two small pins, since this way you can also
make double-sided boards (even with the Profiler). ColiDrive
is certainly not an obstacle here, since it is specifically
made for this and shows an imaginary mirror line on the
screen.
In practice, you start by drilling a hole with a diameter of
2.95 mm, located approximately in the middle of the X
axis and at the start of the Y axis. Press the first reference
pin in this hole [4]. Use a 3-mm dowel pin and ensure that it
protrudes by approximately 4 mm. Now drive the machine
bridge straight backward and drill a second hole approximately
20 cm away from the first one. Press the second reference
pin in this hole. Store the location data in ColiDrive
so the software knows the position of the reference line.
If you use a T-slot table, you can drill the holes in small
plastic blocks. You can then use all different sizes of PCB
material by sliding these blocks to different positions. To
avoid any misunderstanding, note that the idea here is to
mount PCB material on the machine and then mill one or
more PCBs in the material.
As you also have to drill holes in the PCB, you have to use
underlay material. Use a small board with a thickness of
2 mm for this – preferably a material that stays nice and
flat, such as MDF. In this material, drill two 3-mm holes with
exactly the same spacing as the on the reference board,
and then place it over the two reference pins. Do the same
thing with the PCB material. Note: single-sided PCB material
may be slightly bowed, and if it is, it must be held flat
with clamps or tape.
Now you have the material on the machine, and you can
start making the PCB. Drill the holes first, as otherwise thin
drills may break or thick drills may chew up the pads.
There’s not much that can go wrong during this process,
since ColiDrive always asks you to fit the right drill in the
holder. After all the holes are drilled, you can use small
conical milling cutters to the tracks. End mills are too fragile
for this work because the insulating channels are very
thin, and they also wear much to quickly. To ensure that no
residual copper is left, it is necessary to mill a little way into
the tough epoxy material, and this dramatically reduces the
life of the cutters.
Using conical cutters also has some disadvantages. In particular,
the milling depth must be controlled precisely, as
otherwise the width of the milled channel will vary, which
creates problems with fine circuit board tracks. Most Profiler
users solve this problem by first milling the base plate perfectly
flat. If the PCB material is then fastened securely and
held flat, the milling depth remains constant.
A better alternative is to use a floating cutter head. With
this arrangement, the spindle motor is mounted in a holder
that can move freely along the Z axis. The bottom ring
slides over the surface of the PCB and ensures that the cutter
– which is always at a fixed distance from the ring – maintains
a constant cutting depth in the copper. If you use this
arrangement, it doesn’t matter whether the material is flat
or bowed (within certain limits, of course) – the milled channels
will always have a constant width. As floating cutter
heads are usually adapted to the spindle motor that is used,
they are difficult to find as commercial products. However,
it’s fairly easy to make one yourself once you understand
the principle..
After the PCB has been completed, it can be milled out of
the base material. This is usually done with a 2-mm roughing
cutter. Do this at a very low feed rate, such as 5 mm/s,
since otherwise too much heat will be generated and the
tool will break.
A manual for using the Profiler to make PCBs is available on
the Colinbus website at www.colinbus.com. For instance,
it describes how you can make double-sided PCBs, despite
the limitations of ColiLiner Lite. Be sure to download it – it’s
certainly worthwhile.
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