Author: Terry Williams, Conservator
Drill – check. Bits and extenders – check. Cannon with concretion in the bore – check. On the QAR wreck site, two things you always find together are iron (or remnants of iron) and concretion. This holds true, even for the most inconvenient places, namely the interior of cannon, called the bore. Concretion develops down the bores of all our cannon, no matter how big (6-pounder) or how small (1/2-pounder), and every cannon must be cleaned out to remove this concretion. While a lot of tasks at the lab can be done independently, this one requires a team effort from start to finish. As this event only happens when a cannon has been de-concreted, an arduous task in itself, you can imagine cannon boring happens only rarely: a total of 13 times in the history of the project. As luck would have it, lab personnel bored two cannons in two weeks in May of this year!
As the cannon is being de-concreted, conservators are only able to clean just inside the muzzle area. There may be concretion or a tampion (a plug in the bore to keep the bore dry when prepped for firing). Once the muzzle is clean, conservators can determine the diameter of the bore. With this crucial information, drill bits are then ordered to size. Once all materials are on hand, boring the cannon can be scheduled.
Another important element of boring is the leveling the cannon, making sure it is perfectly aligned with the drill. The floor space selected for boring is one of the most level spots in the lab. Once upon a time, we used to spend hours leveling the gun – chocks, concrete blocks, level, a little here, a little there. In the hopes of streamlining the process, one of our conservators worked with students in ECU’s Engineering Department. Their clever design resulted in two tables created from modified trailer jacks which not only support the cannon but allows for even small changes with the twist of a lever.
We use a horizontal drill press and a water-fed drill with custom coring bits to remove the concretion. Slowly and carefully, the drill forces the bit down the bore, while the water reduces heat from friction. During drilling, extenders are added to the bit so that eventually the full length of the bore is cleaned. Inspections are done regularly to ensure an even result and to see if the front rope wad (part of the gun’s ammunition) is in place and unscathed from the drill bit. If there is no wad, then the gun is presumed to be unloaded and boring continues to the back of the bore. If there is evidence of a wad, then drilling is halted and plans for unloading the gun begin.
This all sounds pretty straight-forward doesn’t it, but it’s amazing the little details that must fall in line to have a successful boring: enough people to move a cannon weighing anything from 300 to 2000 pounds, uninterrupted time to do this, the right size bit, the right size adaptors… but if all this falls into place, what a feeling of accomplishment!
Images:
-Conservators Kim (left) and Terry (right) cleaning the exterior of cannon C15 - note the rope wrapped around the muzzle. Image by NC Department of Natural and Cultural Resources.
-Head conservator Kim preparing the drill and aligning it with the bore of cannon C16, which is sitting on top of the specially built cannon leveling table. Image by NC Department of Natural and Cultural Resources.