ATURAl - Arbortech

Sculpting the Hardest Woods. The tungsten
carbide discs that form the hollow ground cutting
edges last for ages. (VVe have yet to rotate ours!) We
decided that a rough finish suited this amazing burl.
the mighty
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Transforming burls into bowls with Arbortech.
Last year at the Maleny Wood
Expo, Kevin Inkster released his
latest carving innovation; the Arbortech Mini Turbo. We bought
one and have been using it with
great success in our workshop
ever since.
In Issue 102, we reviewed the
history of the Arbortech company
as it celebrated its 25th birthday.
The product that got the company
The Mini Turbo
Kit is designed
to fit both a
standard angle
grinder and the
Arbortech mini
grinder.
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off the ground was a woodcarving blade that fitted into a standard angle grinder. Kevin had a
commission to build a series of
Windsor chairs and decided that
there must be a quicker way to
carve the seat than with a gouge.
The Woodcarver blade was the
answer. From humble beginnings
Arbortech has grown into a company that continues to find new
uses for an angle grinder, and
along the way, has developed a
worldwide market for these clever innovahons.
BURL BOWLS. A visit to any woodworking expo will have a stall selling burls. A burl is an odd growth
found on a tree when a series of
dormant buds produces a protrusion on the trunk (also sometimes
underground). This protrusion,
for some reason, does not produce
a branch, but rather seems to just
grow into a bulbous mass. When
www.australianwoodsmith.com.au
harvested, green burls can be shced
into exotic veneers. Huon pine
and Bird's Eye Maple are prized
in cabinehnaking, while walnut
burls are veneered and used on the
dashboards of marques like Rolls
Royce and Jaguar.
Most burls are small affairs,
however, they can grow to enormous proportions. On Vancouver
Island in British Columbia, Canada, I have taken a photo of my
children dwarfed by a 15m-dia,
22-tonne Sitka Spruce burl near
Port McNeill. Closer to home,
Tamworth has Australia's largest
burl, standing 2 metres tall.
The burls that you will find at
a wood show are seasoned and
usually as hard as nails. These
quirks of nature are snapped up
by woodturners and sculptors
who then endeavour to showcase the grain in creative ways.
Sculptors will use whatever is at
No. lOB
hand, from a chainsaw to a chisel
to release the form from the burl
while woodturners w ill trim the
shape so that it can be mounted
on a lathe.
Turning a burl on a lathe is a
serious challenge indeed. It is not
uncommon for a scraping tool to
snap in half when it encounters
some cranky grain. This is a sobering experience for the woodturner
concerned. The end result will be
a symmetrical piece with wonderful grain full of movement and
life. But it will be symmetrical.
~ATURAl SHAPES. The bulbous shape
of a burl is often interesting in
its own right and can be spoiled
by turning it into a round shape.
What the Mini Turbo (and the
power chisel on page 18) can do
is to hollow out these fortuitously
beautiful shapes and create a bowl
that showcases both the delightful grain and organic shape of the
burl. The issue left for the artisan
is to find a way to stand the piece
up so that it can be used. What we
have done to solve this problem is
to add slender feet to our bowls,
creating a tripod effect with two
feet and a slightly flattened base
making the bowl stable.
SEmNG UP THE MINI TURBO. The Mini
Turbo is designed to fit most angle
No. lOS
Fixing feet. The stalactite-like growths on the outer face of the burl
suggested a similar design in rosewood for the two legs. The legs were
turned with spigots that seated into carefully bored holes The burl base
formed the third leg
grinders. All you need to do is lock
the arbor of the grinder (usually
a black button on the top of the
grinder does this) and then use
the spanner that comes with the
grinder to remove the old wheel.
The brass bush that comes in the
kit is then wound onto the angle
grinder arbor. Next step is to screw
the extension adapter onto the
brass bush. Seating the cutting
wheel onto the extension arm is
the next step. An Allen key is used
.to lock the wheel down firmly. Before you use the Mini Turbo for
the first time it is a good idea to
use the Torx key to loosen the cutters and spray the assembly with
a light mist of WD-40. Now you
can crank the screws home knowing that later in the year you will
be able to eksily release the Torx
screws and rotate the cutters.
COUNTERIORE WITH FORSTNIR IllS. The
first step is to remove the bulk of
the material by creating an overlapping terrace of holes on apedestal drill. Draw out your wall
thickness with a pencil and then
set the depth that you want to bore
on the pedestal drill. A mate with a
steady hand needs to hold the odd
shape of the burl on the table of a
pedestal drill while you bore to set
depths. This is the fastest way to
remove the bulk of the waste. It is
also the easiest. If you take a look
at the image on the packaging opposite you will notice that the Mini
Turbo is being showcased working
inside a counterbored hole. Although it is possible to just go for
it and dig your own hole with the
Mini Turbo we found that it suited
the design of the cutter to use the
rounded sides of the wheel as a
support to guide the blades.
Australian Woodsmith
The two tungsten carbide cutting teeth are hollow ground to
maximise cutting in all woods.
A Torx head screw holds these
replaceable cutters in place.
Revolving them as they wear
maximises the life of the cutter.
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CARVING OUT THE BOWL Once you
have removed the bulk of the
waste on a pedestal drill the next
step is to find a way to support the
odd shape of the burl so that you
can cut away the waste and blend
the terraces. A vice or hold-downs
are just two solutions to this problem. The dilemma is to hold the
shape firmly but not to crush or
crack the burl at the same time. We
used some balsa blocks as soft jaws
in a wood vice to hold the delicate
edges of the burl.
When you have your burl securely pinned in place (and have
donned a face mask, ear muffs and
safety glasses) it is time to switch
the Mini Turbo on and go to work
The first thing that you will
need to do is rest the top edge of
the cutting wheel against a counterbored face. This top edge is designed to follow a template and
allows you a safe spot to tilt from
as you introduce the cutting disc
to the burl. You will quickly find
the sweet spot and will soon be
sweeping away the edges of the
terraced couterbores.
CROTCH SECTIONS. It is not only bur1s
that can be worked with a Mini
Turbo. Crotch and elbow sections
too can be carved out to form interesting fruit bowls. Arbortech has
several tools in their arsenal when
it comes to carving. The power
chisel is perfect (although a bit
noisy) if you are working with softer timbers. The chisels are notched
Brass Pins. The shape of this bowl suggested a
simple but elegant set of 6.4mm (1.4 ") brass pins
pressed into 6mm-dia holes to form a tripod stand.
Sanding. The Mini Turbo has four sanding pads as part of the kit.
Kevin Inkster suggests that you cut a length of 2" pipe, grind an edge
on it and use it to create a wad punch so you can make your own
replacement pads.
and lock into a pressure-activated
shaft. After you have secured the
crotch section in place all you do is
turn the power chisel on and press
the blade against the surface to be
worked. This pressure activates a
cam that hammers the chisel, making light work of an otherwise challenging exercise.
DAM CRACKS. The nature of burls
and crotch sections is that they are
under conflicting stresses as they
season and can easily crack. Filling the cracks with an epoxy resin
is the best solution to this problem.
The first step is to dam the base of
the crack with masking tape. Then
pour enough resin to fill half the
cracks onto a clean surface. Matching or contrasting stains can be
added to the resin and mixed until
the right colour is found. Folding
in the hardener and then filling the
gaps will create a resin check.
SANDING PADS. In nature a tree
will fill a wound with sap. These
sap-filled wounds are called resin
checks. Creating them with epoxy
resin is a neat solution to the problem presented by cracks. Next step
is to sand the resin smooth once it
has hardened. This is easily done
with a sanding pad from the Mini
Turbo klt. Once the surface is as
smooth as you want, it is time to
think about feet.
TRIPODS. We used 6.4mm-diameter brass legs for the crotch bowl
and turned two rosewood legs
for the burl bowl. The third leg of
each tripod was the burl or crotch
base itself. With the burl we turned
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Dam Cracks. Masking tape can
be used to create a dam base so
that epoxy resin can be used to
fill any cracks.
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6mm-deep spigots on the ends of
our slender rosewood feet and fitted them into carefully bored holes
on the base of the burl. It would
have been a crime to bore all the
way through so great care was
taken to flag the Forstner bit and
only bore to a depth of 6mm. The
same care was taken drilling the
6mm-diameter holes in the crotch
sections. Once stabilised it was
time to finish the bowls.
OIL FINISH. Food-grade finishes
need to be used when sealing
fruit bowls. We use Howards Orange Oil. Walnut oil or Butchers
Block Oil are other fine oils that
will penetrate deep and seal the
bowl. Tamping the oil with a foam
brush over a piece of cardboard
conserved the oil and protected
the bench from staining. The burl
bowl just burst into life as the finish was applied. The crotch bowl
too glowed as the Orange Oil
soaked in.
IMPRESSIVE. The bottom line for us,
after having carved bowls out of
burls, is that we think Kevin Inkster is a genius! One good idea is
understandable but to have created so many clever ways to use an
angle grinder really requires a very
special mind, and we are sure, a
tight team to bring each one off.
(See Sources on page 73.) 6!1
Walnut or orange oils
are
traditionally
used for bowls.
We used a foam
brush to tamp
the odd contours and protrusions of the burl
with orange oil. The
end result speaks for
itself.
I
' >
Organic Shapes. In the past I would not have
hesitated to cut this mterestmg section mto a disc
so that it could be turned Carving it produced a
unique sculptured bowl
Power Chisel. Crotch, knee and elbow sections in softer woods can be
made into bowls with a power chisel. This is yet another clever use of an
angle grinder by the boffins at Arbortech.
www.australianwoodsmith.com.au
No.l08
No.108
Australian Woodsmith
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