TECHNICAL Small-scale CNC
70 The Woodworker & Good Woodworking October 2019 http://www.getwoodworking.comAN INTRODUCTION TO
SMALL-SCALE CNC
Geoff Ryan shares some useful tips for working with
various types of small-scale CNC machine as well as
providing examples of the pieces he’s made over the yearsA
s a hobby woodworker for much of
my life I have had three main problems:
first is time (or lack of it); second is
the cost of decent tools and machinery;
and third is the ever tempting array of ideas for
new projects generated by magazines such as
this one. I have largely solved the first problem
by retiring, the second problem by spending
wisely, and, where possible, careful second-hand
purchases. The third problem I hope will never
be resolved as I enjoy new challenges.
The right ‘gear’
It was a magazine that first exposed me to the
idea of building clocks with wooden gears, and
further research online provided free printable
plans for cutting gears using a scrollsaw. Now I am
sure there are plenty of people out there who can
make a very respectable job of using a scrollsaw,
but unfortunately this does not include me and
after many failed attempts at making something
that looked like a gearwheel and would actually
work, I came close to giving up the idea altogether.
Then, by chance, I came across a YouTube video
of gear cutting using a small CNC machine.
After much research and reading reviews, I
decided to order a small screw-driven (as opposed
to timing belt driven) Chinese CNC machine from
eBay (photo 1). These are a lot cheaper (currently
around £430) than UK produced machines, 2 ‘Aurora’ kinetic sculpture 3 Cutting one arm for ‘Aurora’
1 Overview of the CNC machinebut there is a price to be paid in that there is
no effective support from the seller and not
a single word of instructions. However, there
are plenty of user support groups and spare
parts are readily available if needed. After some
initial frustrations in setting up the software,
the machine has proven to be quite robust
and after two years’ use has not let me down.Repeatable accuracy
Accuracy and repeatability are two benefits of
CNC. I have just built a large (3ft diameter) spring-
driven kinetic sculpture called ‘Aurora’ (photo 2),
which required 20 identical arms with mountingholes to be cut from birch plywood (photo 3).
While this could be done using a scrollsaw,
bandsaw, or even fretsaw, it would require
a huge effort (and skill) to keep them exactly
the same (photo 4). In photo 3 you can also
see a sacrificial board is positioned under the
component being cut out. To stop the component
moving and being ruined, small ‘tabs’ are left
to hold it steady and these need to be cut and
sanded off later. Another benefit of a sacrificial
board is that material can be screwed down to it.
Photo 5 shows the components involved
in the ‘Aurora’ mechanism: on the ruler are the
tiny magnets that actuate the pawls controlling
the release of the spring energy. The holes for
the magnets in the pawls require very accurate
alignment and CNC excels at this. ‘Aurora’ is
just one of many designs available online from
Christopher Blasius, who is based in Germany,
and you can see his designs in action at http://www.
Holzmechanik.de or on YouTube by searching
for ‘Holzmechanik’. I have also built several
versions of his ‘Magica’ clock (photo 6).Software
CNC stands for Computer Numeric Control
and refers to any software-controlled machine.
There are three stages to CNC: first a computer
generated drawing of the object is needed and
this is done using a CAD (Computer Aided Design)
package. There are many free and paid for CAD
programmes – you can even use things like
Windows ‘Paint’ to produce simple drawings.
Secondly this drawing needs to be converted
into a format that a machine can understand and
this requires a CAM (Computer Aided Machining)
package. There are both free and paid-for
packages available and I chose to use a paid-for
combined CAD/CAM software package called
Cut2D, produced by British company Vectric.
The user support is beyond excellent with lots
of video tutorials, free projects to download,
and regular updates. I had a minor problem with
an item I was designing and contacted the help
desk. Within the hour I had a full solution in the
form of a short screen video taking me through
what was in fact my own error – the voiceover
used my name so it was a very personal response.
Cut2D, like the name suggests, is aimed at
producing two-dimensional objects, but as it
controls the depth of cut as well as the horizontal
dimensions, it is often referred to as ‘2 and a half