Using a Dry Wood Borer
Using a dry wood borer with the archaeological drill bit is much different from using a regular increment borer. Learn the various steps below.
First, place the guide plate in the desired position, and fasten it to the log with two wood screws. I've found, however, that simply holding the guide plate up with one hand and firmly grasping the plate with your fingers works quite well (Figure 1) and prevents two additional holes from being drilled. Be extremely careful, however.
Figure 1. Holding the guide plate up to start the drill tip.
Next, slowly start your variable speed drill so that it is lightly cutting the wood (Figure 2). Slowly increase its speed until the drill has penetrated about 0.25-0.5 inches (8-12 mm). The guide plate should now be removed.
Figure 2. Using the dry wood borer with an electric drill.
To ensure you have the outermost ring when finished, place a black dot on the core surface with a Sharpie (Figure 3).
Figure 3. Notice the black dot that will help locate the surface.
Every 0.5 inches (12 mm), extract the drill bit partially several times after decreasing the speed of the drill bit to allow the sawdust to fall out of the hole (Figure 4). Alternatively, extract the drill bit and have an assistant use a can of compressed air to blow out the sawdust. Once the desired depth is reached, extract the drill bit and blow out any additional remaining sawdust. You should always extract the drill bit while it is still turning after decreasing its rotation speed. Do not try to extract the drill bit from the beam of wood when the drill bit is stopped completely. This will break the core.
Figure 4. Every so often,
extract the drill bit partially to allow
the sawdust to
fall out while drilling
Insert the extractor along one side of the core until it will go no further. Turn the extractor to cut the core. Repeat in several locations around the core if necessary. Depending on the wood, you may hear an audible break (as with oak, for example). Carefully pull the extractor from the hole and the core should follow (Figure 5).
Figure 5. Extracting the core
Once extracted, the core should be firmly glued to a wooden core mount. Because these cores often are already dry, they do not require additional drying time and can be mounted immediately after extraction with wood glue or Elmer's glue and fastened simply with masking tape (Figure 6). As with all cores, the core must be mounted with its cells vertically aligned (straight up and down). You can see this by inspecting the end of the core.
Figure 6. Note how the core
has been mounted on the
wooden core mount with Elmer's
glue and masking tape.
If required by the agency or person in charge of the structure, we can place a 5/8ths inch (14 mm) cork firmly in the hole, trim it if necessary, and then paint the hole with water-insoluble oil-based paint of the same color as the log to hide the hole and the cork (Figure 7). Note however that this is rarely necessary because the holes we leave usually are not visible.