Friday, September 25, 2015
Sawmill History and Terminology
At one point in the poem he describes the shrieking sound of a watermill cutting marble.
Marble sawmills also seem to be indicated by the Christian saint Gregory of Nyssa from Anatolia around 370/390 AD, demonstrating a diversified use of water-power in many parts of the Roman Empire.
Sawmills became widespread in medieval Europe again, as one was sketched by Villard de Honnecourt in c. 1250. They are claimed to have been introduced to Madeira following its discovery in c. 1420 and spread widely in Europe in the 16th century.
By the 11th century, hydro-powered sawmills were in widespread use in the medieval Islamic world, from Islamic Spain and North Africa in the west to Central Asia in the east.
Prior to the invention of the sawmill, boards were rived (split) and planed, or more often sawn by two men with a whipsaw, using saddle-blocks to hold the log, and a saw pit for the pitman who worked below.
Sawing was slow, and required strong and hearty men. The top-sawer had to be the stronger of the two because the saw was pulled in turn by each man, and the lower had the advantage of gravity. The top-sawyer also had to guide the saw so that the board was of even thickness. This was often done by following a chalkline.
Early sawmills simply adapted the whipsaw to mechanical power, generally driven by a water wheel to speed up the process.
The circular motion of the wheel was changed to back-and-forth motion of the saw blade by a connecting rod known as a pitman arm (thus introducing a term used in many mechanical applications).
Generally, only the saw was powered, and the logs had to be loaded and moved by hand. An early improvement was the development of a movable carriage, also water powered, to move the log steadily through the saw blade.
A type of sawmill without a crank is known from Germany called "knock and drop" or simply "drop" -mills. In these drop sawmills, the frame carrying the saw blade is knocked upwards by cams as the shaft turns.
These cams are let into the shaft on which the waterwheel sits. When the frame carrying the saw blade is in the topmost position it drops by its own weight, making a loud knocking noise, and in so doing it cuts the trunk.”
A small mill such as this would be the center of many rural communities in wood-exporting regions such as the Baltic countries and Canada.
The output of such mills would be quite low, perhaps only 500 boards per day. They would also generally only operate during the winter, the peak logging season.
In the United States, the sawmill was introduced soon after the colorization of Virginia by recruiting skilled men from Hamburg.
Later the metal parts were obtained from the Netherlands, where the technology was far ahead of that in England, where the sawmill remained largely unknown until the late 18th century. The arrival of a sawmill was a large and stimulative step in the growth of a frontier community.
Early mills had been taken to the forest, where a temporary shelter was built, and the logs were skidded to the nearby mill by horse or ox teams, often when there was some snow to provide lubrication.
As mills grew larger, they were usually established in more permanent facilities on a river, and the logs were floated down to them by log drivers.
Sawmills built on navigable rivers, lakes, or estuaries were called cargo mills because of the availability of ships transporting cargoes of logs to the sawmill and cargoes of lumber from the sawmill.
The next improvement was the use of circular saw blades, perhaps invented in England in the late 18th century, but perhaps in 17'th century Holland, the Netherlands.
Soon thereafter, millers used gang-saws, which added additional blades so that a log would be reduced to boards in one quick step.
Circular saw blades were extremely expensive and highly subject to damage by overheating or dirty logs. A new kind of technician arose, the sawfiler. Sawfilers were highly skilled in metalworking.
Their main job was to set and sharpen teeth. The craft also involved learning how to hammer a saw, whereby a saw is deformed with a hammer and anvil to counteract the forces of heat and cutting. The Modern circular saw blades have replaceable teeth, but still need to be hammered.
The introduction of steam power in the 19th century created many new possibilities for mills. Availability of railroad transportation for logs and lumber encouraged building of rail mills away from navigable water.
Steam powered sawmills could be far more mechanized. Scrap lumber from the mill provided a ready fuel source for firing the boiler. Efficiency was increased, but the capital cost of a new mill increased dramatically as well.
In addition, the use of steam or gasoline-powered traction engines also allowed the entire sawmill to be mobile.
By 1900, the largest sawmill in the world was operated by the Atlantic Lumber Company in Georgetown, South Carolina, using logs floated down the Pee Dee River from as far as the edge of the Appalachian Mountains in North Carolina.