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When wanting
to make
a segmented object
one has first to work out the design. The simplest
way is just to use squared paper, or one can use
a spreadsheet finally one can use one of the many
CAD drawing programs on the market.
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Once the
number of
segments has been
fixed for your project you'll need a
suitable cutting sled to accurately cut the
angles. Here we see a framing square used
to obtain the correct angle. The long side
being set to 20" and the short side to N,
where N= 20 * Tan (180/n) and
n is the number of segments.
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Here we
transfer the
angle to a
bevel gauge.
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This shows
the
underside of the new sled.
There is a hardwood strip, machined to fit
the guide on my bandsaw, together with a
softwood strip which acts as an addition
guide and helps when setting
the cutting angle.
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This is the
top of
the sled and shows a
piece of temporary scrap cut on the same
line that the band cuts. The bevel gauge
then sets the "first guess" of the cutting arm,
which is then clamped to the sled.
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Here a stop
block,
together with
some strips of cardboard are fixed
behind the cutting arm. At this
point the piece of temporary
scrap can be removed.
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We now cut
enough
segments to form a quarter
circle.
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Once cut
they loose
fitted together and put
inside a carpenters square. Ideally we want
NO GAPS between either the segments or
the square, i.e. as shown at the top in the
next picture .
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Sadly most
of the
time you'll get
something like the bottom two of
the above. This is where the stop
block and the cardboard packing
come in.
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The above
shows
which way the cutting arm
must move depending on if you have "inner"
or "outer" gaps. So by adjusting the amount
of cardboard packing, usually replacing some
cardboard with pieces of paper, you keep
cutting segments until you get a "perfect"
fit in the square. Once at this point you then
cut a full ring of segments and cross your
fingers that you have NO gaps. You'll be
very lucky to get this first time so will have to
continue with arm adjustments until you do get
a perfect ring.
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Here I show
my
completed sled, not I've
found it a good idea to have some sort of
clamp to hold the wood whilst cutting as
the slightest movement will affect the fit
of the segments.
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When
assembling a
ring I usually
glue the ring in two halves. When
the glue has set I use a jig on my
beltsander to make sure the
two halves are a perfect fit.
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Currently I
use
either some sandpaper
stuck to some board to flatten my rings
prior to building ring stacks. Ideally if you
have space a drum sander would make
the task much easier.
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When I have
rings of
8" or above I
sometimes use my thicknesser to
flatten them. however if I use this
I take the SMALLEST cuts I can.
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The next tow
pictures show a jig I've built to
help with aligning the rings in a stack. The jig
consists of a board with concentric rings
marked at ¼" spacing.
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I've marked
the same
set of rings on some perspex and this is mounted above the
base board on dowels. It then becomes a
fairly easy task to align the rings in a stack.
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This
previously saw
life as a wine
press, but is now used with the
alignment jig just described
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