sawmill

 

installation or facility in which cut logs are sawed into standard-sized boards and timbers. The saws used in such an installation are generally of three types: the circular saw, which consists of a disk with teeth around its edge; the band saw, which consists of a hoop of flexible metal that runs over pulleys and has teeth along one edge; and the log gang saw, which consists of saw blades separated by desired distances in a frame that oscillates as a log is fed into it. Logs are fed to gang saws through pressure rollers that ensure straight cutting. With other saws the log rides on a conveyor or carriage. Provision is made for placement of the log in a new position for each cut, by the worker who rides the carriage or by the one who operates the saw. Recently it has been discovered that a jet of water at a pressure of several thousand pounds per square inch is capable of cutting a log at a rate comparable to that of sawing. Despite the fairly exotic hardware necessary for this method, it reduces the kerfs, or widths of cuts, thus wasting less material, and it does not produce the flammable dust created by sawing. In sawmills that use their waste as raw material for wood pulp, logs are passed through machines that remove their bark prior to sawing. A large sawmill may have a capacity of several hundred thousand board feet per day.

A sawmill is a facility where logs are cut into boards.

Sawmill Process

A sawmill's basic operation is much like those of 100 years ago; a log enters on one end and dimensional lumber exits on the other end.

• Logging fells and cuts trees to length.
• Logs are taken by truck, rail or river to the sawmill.
• Logs are scaled either on the way to the mill or upon arrival at the mill.
• Decking is the process for sorting the logs by species, size and end use (lumber, plywood, chips).
• Debarking removes bark from the logs.
• The head saw, head rig or primary saw, breaks the log into cants (unfinished planks) with a smooth edge.
• Edging will take the cant and trim off all irregular edges leaving four-sided lumber.
• Trimming squares the ends at typical lumber lengths.
• Drying removes naturally occurring moisture from the lumber. This can be done with kilns or air-dried.
• Planing smoothes the surface of the lumber leaving a uniform width and thickness.
• Shipping transports the finished lumber to market.^[1]

History

Sawmills seem to have existed in the medieval period, as one was sketched by Villard de Honnecourt in c.1250.^[2] They are claimed to have been introduced to Madeira following its discovery in c. 1420 and spread widely in Europe in the 16th century.^[3]

The sawmill was also invented by the Dutchman Cornelis Corneliszoon (1550-1607) by applying a pitman arm onto a wind mill, which converted a turning motion into an up-an-down motion. Corneliszoon patented the sawmill on December 15, 1593 and the pitman on December 6, 1597. He built the first sawmill there in 1594.

Prior to the invention of the sawmill, boards were rived and planed, or more often sawn by two men with a whipsaw, using saddleblocks to hold the log, and a pit for the pitman who worked below. Sawing was slow, and required strong and enduring men. The topsawer 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 topsawyer 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 (thus introducing a term used in many mechanical applications). A pitman is similar to a crankshaft, but in reverse; a crankshaft converts back-and-forth motion to circular motion.

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 steadily move the log through the saw blade.

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 sawmills was introduced soon after the colonisation of Virginia by recruiting skilled men from Hamburgh. Later the metal parts were obtained from the Netherlands,^[4] 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 were 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.

The next improvement was the use of circular saw blades, and soon thereafter, the use of gangsaws, 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 circular saw was a later introduction, perhaps invented in England in the late 18th century, but perhaps in 17th century Holland, Netherlands. Modern circular saw blades have replaceable teeth, but still need to be hammered.^[5]

The introduction of steam power in the 19th century created many new possibilities for mills. They could be built away from water and 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.

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.

A restoration project for Sturgeon's Mill in Northern California is underway, restoring one of the last steam-powered lumber mills still using its original equipment.

Current Trends

In the twentieth century the introduction of electricity and high technology furthered this process, and now most sawmills are massive and extremely expensive facilities in which almost every aspect of the work is computerized. Today a mill can make many hundreds of thousands of boards per day.

Small gasoline-powered sawmills run by local entrepreneurs served many communities in the early twentieth century, and specialty markets still today.

The latest trend is the small portable sawmill for personal or semi professional use. Many different models have emerged with different designs and functions. They are especially suitable for producing limited volumes of boards, or specialty milling such as oversized timber.

Technology has changed sawmill operations significantly in recent years, emphasizing increasing profits through waste minimization and increased energy efficiency as well as improving operator safety. The once-ubiquitous rusty, steel conical sawdust burners have for the most part vanished, as the sawdust and other mill waste is now processed into particleboard and related products, or used to heat wood-drying kilns. Everything is used. While the bark may be ground for landscapine barkdust, it may also be burned for heat. Sawdust may make particle board or be pressed into wood pellets for pellet stoves. The larger pieces of wood that won't make lumber are chipped into wood chips and provide a major source of supply for paper mills. Wood by products of the mills will also make Oriented strand board paneling for building construction, a cheaper alternative to plywood for paneling.

Sawmills in popular culture

A sawmill appears in a soap opera called Twin Peaks.

Additional Images

Inside a modern sawmill equipped with laser-guided technology

Wood traveling on sawmill machinery

Sawdust waste from the mill

Wood from Victorian mountain ash, Swifts Creek

See also

• Band saw
• Circular saw
• Saw
• Portable sawmill
• Sawfiler
• Log bucking
• Logging

References

External links

• Steam powered saw mills
• The basics of sawmill (German)

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