I cut my own slate ellipses, often up to 3cm thick. In the process of
marking out the ellipse I will have drawn both the major and minor axes.
I make a small indentation with a metal scribe at both ends of both axes
as well as the centre point. These indentations are deep enough to be
noticeable but shallow enough to be erased easily on the cleaning-up
operation after the eventual painting/gilding of the finished
inscription. The indentations can be made more prominent by painting
them with a spot of light-coloured acrylic paint. After the ellipse has
been cut out (which I do with a series of short straight cuts from a
bench-mounted, water-fed circular saw, followed by a hand-held water-fed
cylindrical abrasive drum) the axes are easily drawn through the
still-visible marks.
If the job of drawing and cutting out has to be done by another person,
such as at the stonemason's yard, they could be asked to leave similar
marks to help you with the alignment of the inscription.
David Brown
Somerton, Somerset, UK
On 30/10/2016 21:29, Karl Billeter wrote:
On Mon, Oct 31, 2016 at 08:24:04AM +1100, Karl Billeter wrote:
On Sun, Oct 30, 2016 at 02:37:04PM +0000, Frank King wrote:
...
Almost the first task is to find
the centre and the axes. Clearly
you cannot fold a slate in half
and the traditional way to proceed
is to put a large sheet of paper
over the slate and crease it down
all round the rim.
You then cut round the crease and
attempt to follow your procedure!
Wrap the slate with a reflective strip (smooth, shiny plastic? thin polished
metal?). Playing around with a laser should find the focii.
You could also try balancing the slate on rod to find the centre but it's
probably too hard to get the required accuracy and it might be a little risky!
K
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