Fellow Shadow Watchers,
The following may not be new or of interest to long time
SML members but there are always new recruits who may find it useful.
I'm currently finishing a dial for a client in Colorado and have begun a plain
gnomon in 10mm thick PB 102 phosphor bronze. Years ago I would have cut out the
profile with a struggling mechanical fretsaw and hand hacksaws taking most of
an unpleasant day in the process. Phosphor bronze contains a lot of copper so
tools tend to dig in and stick in the kerf (cut) so there is little pleasure in
such a process and many broken blades. In comparison, the same task in
stainless steel would be so difficult as to be almost unthinkable by hand
methods.
Enter Waterjet Cutting. For those who are not familiar with this process it
involves a jet of water at 60,000lbs.sq/in exiting through a 1mm hole in a
diamond at three times the speed of sound. For materials like wood and rubber,
the jet alone will cut through 100mm thicknesses with ease but for materials
like hardened steel, marble, slate or even titanium a continuous pinch of
powdered granite is added to the waterjet. While watching 50mm thick titanium
being cut recently the jet was actually striking sparks!
Beneath the workpiece is a deep tank of water which immediately quenches the
energy of the jet. The jet is guided by a simple computer CAD drawing which in
my case is created in Adobe illustrator and saved as a DXF file. The cutting
software offsets the jet outwards by half its thickness so the resulting
component is the actual drawn size.
This is not always a quick process and my gnomon took about 30 minutes but only
because I had specified a smooth finish requiring a slow 'travel'. The profile
for a 'Rotary' gearwheel sundial plate 48" diameter and 10mm thick in stainless
steel took five costly hours. As a design tip for anyone using WJC for the
first time I would advise against any sharp 90° internal corners. These should
always have a small radius of about 3mm. For some reason when the jet turns
through 90° it cuts an unwanted notch in such corners. It also pays to
indicate which side of the line you wish to cut when a combination of outer
profile and inner piercings are involved. Guess how I learned that the hard
way!!
Next time you see the intricate cut out shapes in thick metal which abound in
public railings, grills and sculpture these days, or even elaborate armillary
spheres, don't imagine that these were necessarily produced laboriously by hand
as there is probably a CAD program and a jet of water lurking somewhere in the
background.
If this sounds like the deathknell of craftsmanship I'd refute that entirely.
It is simply a means of freeing the craftsperson from drudgery to pursue
excellence in other creative aspects. If Thomas Tompion were alive today you'd
meet him regularly at the local WJC plant I think ;-)
Two jpegs of the cut gnomon and its matrix on request for the curious.
Tony Moss
Lindisfarne Sundials
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