http://www.getwoodworking.com October 2019 The Woodworker & Good Woodworking 71
6 ‘Magica’ clock 8 End-grain problem with plywood
5 ‘Aurora’ mechanism components7 Screen view while cutting components4 10 done and 10 more to goD’. True three-dimensionally curved objects
are a different ballgame but there are packages
which allow you to do this, such as Cut3D and
V Carve, made by the same company. All Vectric
software allows you to preview what the final
object will look like from all angles and warns
against cutting right through the material being
machined and potentially damaging the bed
of the machine. If this is the case, you can fix
a sacrificial board underneath.
The third stage in CNC is to take the output
from a CAM package and use it to drive the
machine. Again, there are both free and paid
for packages available. One of the most well
known professional packages is Mach3, which
many hobbyists also use. You pay for what you
get and this software can be used to control
industrial-sized machines cutting a wide range
of materials and the huge range of features
include things like automatic tool change and
allowing for backlash when the machine
changes direction, and even tool wear.
My machine came with software, which is
designed to work specifically with the machine’s
control unit but it still has more features than
I will ever need. The software has to be calibrated
to the machine during setup – e.g. you tell the
machine to move 200mm then measure carefully
how far it has actually moved and input this
figure. Further checks refine this and the final
figures are saved in a ‘setup’ file, which is
automatically loaded on start-up. Occasionally
this file gets corrupted, so I have learned to save
a backup copy if I ever make any changes to the
settings. Photo 7 shows the screen view while
cutting out an arm for ‘Aurora’. On the top left
is the current position of the tip of the cutting bit.
‘X’ is the left/right position, ‘Y’ is the backwards/
forwards position, and ‘Z’ is the vertical up/down
position. On the bottom left of the screen are
some controls that allow you to move the bit into
position before running the cutting programme.
The starting point (X=0, Y=0, Z=0) can be chosen
when creating the programme and is most
commonly in the dead centre or bottom left
of the workpiece and on its surface.So what can this machine do?
The usable size is approximately 290mm wide
and 390mm long but as the machine is open at
each end, longer lengths can be accommodated
and cut in two sessions. Vectric software allows
large items to be created by ‘tiling’. Maximum
depth of cut, which is dictated largely by the bit
size and shape, is about 25mm. Three ‘stepper’
motors control the horizontal and vertical
movement of the cutting head and each motor
drives a screw thread with a 3mm pitch. These
motors move in steps – in this case 1.8°, giving
200 steps for a full 360° rotation. So one step
advances by 0.015mm – a level of accuracy
probably swamped by the day-to-day movement
of the wood being cut!
The spindle motor is only 200W with a collet
chuck of 3.175mm. A range of cutting bits is
available such as ‘V’ bits, spiral two-flute upcut
or downcut, and straight-sided two-flute, indiameters from 3.175mm down to fractions
of a millimetre. Even with the largest of these
bits the depth and speed of cut has to be chosen
carefully to avoid overloading (and breakage)
of the bit. Typically with hardwood, a maximum
cutting depth of 1-1.5mm works well with about
2mm for softwood and plywood. Bits cost
between £8-12 for a pack of 10 so are not
a big factor in running costs.
As well as wood, I cut plastics. Perspex cuts
very well and I have cut templates for a friend
who is a professional box maker and uses a
router-follower for cutting recesses for inlay.
I was also able to produce very accurate angle
templates for cutting segments in veneers. High
Density Polyethylene (HDPE) cuts very cleanly
and I have made 25mm thick spacer blocks and
6mm thick zero clearance inserts. Acetal was used
to make a slender sprung ratchet for a clock as
wood turned out to be too fragile. Cutting thin
aluminium is also within the capability of the
machine, but so far I have not had the need or
the inclination to do this. MDF can also be cut
but isn’t very suitable for small components and
is useless for gears. It also wears the bit out faster
than other wood.Cutting gears
Ideal materials are good quality birch plywood,
plastics such as clear or coloured Perspex, or
well-seasoned hardwood. While plywood works
well it lacks the visual appeal of solid wood. The