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Special
drill bits and tools are needed if you will extracting increment cores
from archaeological samples where the wood (usually hardwood) is very dry.
Regular increment borers are insufficient and often unable to extract
sound cores from such samples. Instead, dendroarchaeologists use a
specially designed hollow drill bit that extracts a 12-13 mm (0.5 in)
diameter wood core. The drill bit is driven by a heavy-duty
industrial-style drill.
Forest
Research Tools
Dry Wood Borers
Forest
Research Tools
(my own outlet company) offers these drill bits, which come as a three-piece kit that also
includes a polyethylene guide plate and a sharp, curved extractor to
dislodge the core from inside the wood beam. Unlike drill bits made
previously, the drill bit made by this company has the drive chuck
fastened unto the drill bit, so that a separate and expensive chuck is not
required. This web site also provides a valuable
tutorial
for properly and safely using the drill bits. The cost for the 3-piece dry
wood borer kit is $US 159.95, and the company accepts payments of all type,
including credit cards. Note: recently, my good friend and collaborator,
Dr. Frank Speckhart, died after a courageous battle against cancer. My
company is currently looking for new local collaborators to continue
manufacturing the dry wood borer.
The
drill I use is a DeWalt 18-volt cordless drill ($260.00 with 1 battery
& charger included, while an extra battery is about $95.00). This is a
great tool and will last all day on one charge. Be sure to check out the
prices for these on my
Forest Research Tools Supplies page.
Rinntech Dry Wood
Borers
Extracting good samples
from dry wood is a delicate job. A good tool is the prerequisite for
every researcher investigating construction timber. RINNTECH offers dry
wood borers with 8/16 mm diameter. They were developed by Thomas
Bartholin and slightly improved by RINNTECH. RINNTECH dry wood borers
can be run with commercial electric drills (600 W power). They are
available in lengths of 150 mm, 250 mm and 350 mm. Application is
possible in softwoods as well as in hardwoods. A maintenance set allows
cleaning and sharpening of the borers.
Berliner Dendro-Bohrer
The
borers were developed in cooperation with the dendro laboratory of the
Deutsches Archäologisches Institut Berlin (the German Archaeological
Institute,
Dr. Karl-Uwe Heußner DAI, Ref. Naturwiss, Im Dol 2-6, Haus IV,D-14195
Berlin)
to be able to carry out samplings with minimal side effects. They are
suitable for dendrochronological examinations especially at historical
construction timber and are conceived for the use in solid dry wood.
Fresh wood can be bored more or less well depending on its nature.
Boring into wet wood causes problems with the chip removal. Moreover,
the wood core can become wedged in the borer by the swollen condition.
More information
Rob
Wilson adds this information: "I used three dry archaeological corers
in Germany which cost me about $US 20-30. They were home made. One can buy
cutting bits (with teeth etc) at most home hardware stores. I used two
sizes, 14 mm and 21 mm. The length of these bits varied from 2 cm for the
wider to 3.5 cm for the thinner. Luckily I had a friend who worked in a
machine shop, who welded the bit onto a tube of same diameter and
thickness. This is the tricky bit, because the join must be flush and
smooth (inside and out).
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"The
opposite end...i.e. the end that goes into the drill is also problematic.
The Tucson system has a separate attachment that the corer twists into.
Mine was a one piece system. Again a thick walled hollow piece of metal
(but smaller diameter) was welded onto the end. The diameter of this can
vary, but this depends on what diameter bits your drill can take. This
piece must have a whole through it, because you will quite often want to
push the wood sample out of the corer.
"A
little refinement on the Tucson system was an idea that I picked up from
the archaeological lab in Sheffield. At periodic intervals down the bit,
holes should be drilled through the walls of the corer (ca. 5 mm). Mine
were drilled in a pseudo spiral pattern of about 7 cm distance apart.
Because one is coring dry wood, there is a lot of dust that can clog the
corer and sample when drilling. A lot of dust will come out of these
holes. Be sure to smooth the burr created when making theses holes.
"The
problem still remains on how to get the sample from the beam. Quite often
once you have drilled your 30 cm into the beam, the sample will still be
attached to the beam (though it can sometimes come out in the corer). You
need an extractor. Bicycle spokes are good for this. You want to bend one
into a L shape with the longest end being the same length of your corer.
At the end of this, with some sharp pliers, you want to 'pinch' a sharp
point at right angles. When taking the sample out, there will be a gap
around the sample and the beam. Enter the extractor along this gap as far
into the beam as possible. When you reach the end, twist the extractor so
the sharp point will attach itself to the bottom end of the sample and
pull. The sample should come right out in one piece."
Geoff
Downes adds: "CSIRO developed a corer for a powered drill bit which
should do the job. It extracts a 12 mm core and leaves a 22 mm hole. This
is a standard dowel size for plugging. It comes in two lengths, 300 mm and
500 mm. I have used the corer myself and it does a good job. The only
drawback is the need to return it to the suppliers for re-sharpening. They
are yet to supply a sharpening jig for others to do it." Contact
CSIRO at: CSIRO Forestry and Forest Products, GPO BOX 252-12, Hobart,
7001, Tasmania, AUSTRALIA.
Olafur
Eggertsson writes: "You should contact Thomas Bartholin in Copenhagen
- he has the best corers, with prices from c. 4000.- DKR." |
