Increment borer is a very useful tool for dendrochronology. It is intended for fresh wood, but works also in constructions like timber walls.
Sampling in dry wood
Dry coniferous wood is much more fragile than fresh wood. The borer needs to be well sharpened, and the inside clean. After coring living pines or oaks and before coring dry wood again, the inside needs to be cleaned carefully. Lubricant oil (e.g CRC 5-56) and a piece of rag in the end of a string works fine.
The greatest problem is that the core usually falls into pieces. So be careful and see that all pieces are collected in their right order. Put them for instance in a plastic straw.
When boring in hewed blocks or block walls which are a bit mouldered you have to bore at an angle from below to get the wane from the block or to get as much sapwood as possible. Then there are two problems: one is that after a while the drill handle collides with the wall. Then it is fine to have a wrench with you... the other problem is that when the borer goes through a crack in the wood, then the outer part of the core drops out... So it is fine to anticipate that and put some sort of stopper into the pipe before starting to bore.
It is usually the best not to use the extractor, but rather push the core backwards out of the borer with a wooden or bamboo stick (Never use something that may damage the edge. No metal stick!).
Boring in dry oak wood usually gives more solid cores than in coniferous wood, though of course there may be some cracks. But it is recommended to use a two-treaded borer, and oil the tip before each new core. Otherwise there is a risk to crash the borer.
Before sanding the cores they have to be glued to a piece of wood, for instance a 6-10 mm thick "cut off" from a 45-65 mm beam. To get them straight and as vertical as possible, a matrix could be used. Such a matrix could be made with a milling machine and a 5 mm cutting tool. Cut 3 mm deep and 5 mm wide traces in such a "cut off" piece of wood, leaving about 2 mm wood between each trace. In this matrix you will be able to mount the cores dry. When satisfied just put glue on a plain piece of wood ("cut off") and press the matrix with cores towards it. When the glue is dry, just take apart, and the cores are fixed and the matrix is ready for a new set of cores! You can now sand the cores with a belt sander (fine paper) and then grind to required high finish before scanning.
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