FORGEpiece slightly and then moving the carriage back out
from the workpiece to scribe a line. We then placed
the digital protractor on a jaw of the chuck, unlocked
the spindle, and hand-rotated the workpiece 36
degrees, locked the spindle, and repeated the process
until we had marked all ten lines (Figure 6). While we
had some doubts about how well this would work,
and we definitely could increase the quality of the
mark by grinding a purpose-made tool, we were very
surprised at how accurate this method was.
GETTING CREATIVE
With imagination, hackspace-type tools like laser
cutters, 3D printers, and CNC machines can be
used to create all kinds of tools that can help with
dividing tasks. Printing or cutting dividing plates that
can be attached to spindles can enable us to create
dividing heads, and we have seen many examples
of 3D-printed gears being used to index workpieces.
Taking things a little further, we created a tool that
helps us mark divisions around tubular workpieces,
which is a common task for those involved in the
building of model rockets who want to accurately
place fins around a tube. We based this tool around
a type of self-centring chuck called a Longworth
chuck which consists of two plates which, when
counter-rotated, can move four ‘jaws’ inwards and
outwards. This assembly allows a tube to be held in
position with the jaws either inside or outside of the
tube, (Figure 1). Instead of making the bottom plate
of the chuck assembly circular, we used Inkscape’s
‘gear generator’ plug-in to create a gear with 60 teeth.
We then numbered each gear tooth valley from 0 to
60, to allow us to rotate the assembly by a known
amount. We added a base, and created some sliding
gear locks which simply engage with the gear and can
lock it in place. The rest of the assembly of this tool
consists of a simple pair of stand-offs with a V-shape
cut into the top of them, which allows a pen or pencil
to be slid into position and mark a dot onto the held
tube Figure 7.If you have access to a laser cutter, you can easily create patterns that can assist in
drilling holes around a diameter. Often, software graphics packages have ways of
automatically cloning a circle ‘hole’ object around a circular path, or if not, using the x-y
co-ordinate calculation methods elsewhere in this article should enable you to draw the
required pattern. Laser-cut patterns cut in plywood or plastics can then be used to either
mark out on the real workpiece, or even can be clamped to a workpiece and used as a drill
guide. In the image, we have used the Inkscape drawing software to draw and cut a series
of seven 4 mm holes around a 30 mm pitch diameter that could be used as a drill guide.LASERS!
Figure 4
A rotary table can
be used to index
workpieces in various
ways – in this
instance to drill
a circle of
equidistant holes