There are two definitions of a sawmill. One is a sawmill being the location where lumber milling takes place. It encompasses the entire area, including the log sort yard, the milling machines, the eventual sorting and storage area, and the administration and maintenance areas as well.
The other sawmill definition is the actual sawing or cutting machine that turns a round log into square timbers. In sawmill industry terms, that core machine is called a head rig. However, a head rig needs a support system of complicated machinery for it to function as a sawmill. Perhaps the best sawmill definition is it’s a complete system turning logs into lumber.
Whether you think of the entire operation or the individual machines, sawmills are busy places. Today, most sawmills are large commercial operations built in stationary locations. Some employ hundreds of workers who rotate on 24/7 shifts to keep lumber production at its premium efficiency.
The first known sawmill dates back 400,000 years to Nice, France, where archaeologists discovered a wooden hut built with processed logs. By 500 B.C., men used bronze axes, saws and chisels to mill rough lumber for wood homes and forts. And, in 375 A.D., the Romans built a waterwheel-powered sawmill that revolutionized the construction and furniture making industries.
The Romans used a reciprocating blade that cut wood in an inefficient back-and-forth motion, much like hand-sawing. A big breakthrough happened at the start of the Industrial Revolution with the circular saw blade invention. It’s unclear who invented it, though. Historians typically credit Samuel Miller, who was awarded British Patent #1152 in 1777. Others claim it was invented independently in America by Shaker Sister Tabitha Babbitt in 1810 when she attached a metal disc to her spinning wheel. But, before Sister Tabitha shared her idea, Englishman William Newberry patented the bandsaw in 1808. The band saw didn’t see widespread use until mid-century due to inferior quality blades. Today, industrial-sized band saws are the leading machines in a sawmill.
SAWMILL IN NORTH AMERICA
In North America, sawmills process two types of trees. One is softwood species such as pine, fir, hemlock, spruce, cedar and redwood. These are conifers or evergreens that have needles permanently attached. The second tree type is hardwood species like cherry, beech, oak, walnut, elm and maple. These are deciduous trees that shed leaves in the fall and grow new ones in the spring.
Most commercial sawmills specialize in processing either softwoods or hardwoods. A few sawmills tool up for both tree types, but that’s not common. The residential and light commercial construction industries primarily use softwood lumber for framing and rough carpentry. You’ll normally find hardwood materials used for furniture and finished products, including flooring, staircases and plywood veneer panels.
You’ll also get various finished product shapes and sizes at a sawmill. Three main lumber products come from a sawmill production line. First are large-cut materials called timbers. These are end-products measuring over 5 inches thick. Normally, timbers find their way to heavy structures like exposed beams and posts.
Dimensional lumber is the most common sawmill product. These cuts measure between 2 and 5 inches in thickness and range from 2 to 12 inches wide. You’ll commonly use dimensional lumber for plate, joist, stud, header and rafter applications. Sawmills usually plane dimensional lumber to specific sizes and smoothness standards. For instance, a rough-cut 2×4 coming from a head rig is exactly that nominal size — 2 inches thick by 4 inches wide. But, a 2×4 exiting a sawmill’s downstream planer actually measures 1-1/2 inches by 3-1/2 inches finished size.
The third lumber products you’ll get at a sawmill are called boards. These are thin cuts usually measuring 3/4 of an inch to 1-inch-thick. They range between 2 and 12 inches wide. Boards are popular for sheathing structures, planking floors and forming furniture frames. Rough boards are also common in pallet and crate making.
Something else you’ll get at a sawmill is specialized shapes. Sawmills produce interlocking tongue and groove profiles. They cut shiplap edges as well as rounding profiles for decoration. Some sawmills custom-cut orders to customer specifications. Select sawmills even source species for local and foreign markets.
The two main types of sawmills are stationary mills and mobile or portable mills. They range in size from large-scale fixed structures mounted on foundations down to small productions either trailered or truck-mounted. Both sawmill types have designs tailored to their intended production. They’re also designed for a designated number of operators or working employees.
You’ll often find stationary sawmill types near water sources. This is a historical practicality rather than a modern one. Decades ago, most sawmills used steam power, so they required a dependable and renewable water source. They also added value by using water as a log transportation tool and stored logs in rivers or lakes to prevent stored wood from drying out.
Today, steam power is gone, but land is in high demand. Age-old sawmill sites evolved in their established location, so you’ll still find sawmill sites around water. Portable sawmills don’t need a specific space or water supply. They move from site to site as and when required.
There’s another angle to sawmill types. This involves the saw blade types that mills use. Modern sawmills utilize a combination of blade types. Circular blades are excellent for cross-cutting or bucking logs into specific lengths. Bandsaws, on the other hand, are far more efficient for cutting logs laterally.
Circular sawmill blades tend to be thicker for strength. This creates more waste from the saw kerf, where thinner bandsaw blades have thinner kerfs and increase efficiency through less wood waste. For example, a 1/4-inch wide circular saw blade creates 20% more sawdust than a narrow-kerf bandsaw blade measuring 3/32 of an inch.
Every sawmill type benefits from changing technology in saw blade construction. Superior products like tungsten carbide and Stellite™ tipped blades replace old-fashioned saw blade types like hot- or cold-rolled steel. These high-tech saw blade pieces last far longer and give greater efficiency to today’s sawmills, no matter what type they are.
Like so many industries, sawmills evolved in their power sources over many decades. The original waterwheels gave way to windmills, but each system suffered at the weather’s mercy. Water sources dried up, and winds died down. Water and wind-powered sawmills also used inefficient mechanization where cranks and rods sawed repetitively rather than continually.
In the early to mid-1800s, steam became the number one sawmill power source. Sawmills double-ended their resources by using wood waste to fire steam boilers. Steam-powered turbine shafts turned circular and bandsaw blades. Oil-fired burners never caught on due to the cost and overwhelming abundance of wood waste fuel.
By the mid-1900s, electricity phased steam power out at most stationary sawmills. Electric power wasn’t as practical with portable sawmills due to most remote mill sites being off the grid. Mobile mills turned to diesel and gasoline power sources. At present, there is no serious move towards solar power experiments for sawmills due to the massive energy consumption sawmills need.
Sawmills require power for other reasons besides turning blades and running conveyors. They need electrical power to operate advanced computerized systems that scan raw logs for optimum cutting efficiency and then relay digitized information to all sawmill components. These smart sawmills are so advanced that logs are laser-sighted for daily market demands.
Despite enormous technological advancements, sawmills operate much the same way they have for hundreds of years. They just do it much more efficiently today.
Sawmilling lumber is a throughput process where a raw or rough log starts a journey through mechanized steps and emerges as a smooth finished product. Modern sawmills operate as an on-demand, pull-through system with the mechanized mill parts sitting between the front end loggers and the tail end marketplace.
The sawmill process involves many intentional decisions during these steps. Although today’s sophisticated computerization maximizes efficient log use and removes a lot of guesswork, a modern sawmill operation still relies on the sharp eye and quick hands of experienced sawyers. Here are the process steps involved in making a sawmill work:
- Felling: Loggers cut or fell standing trees in various woodlots. Today, there are little original or old-growth forests left in America. Most raw log inventory comes from second or third growth woodlots. Gasoline-powered chainsaws are still the prime felling tool despite advancements in machines like feller-bunchers. Trees are limbed in the forest before getting loaded for transport to the sawmill site.
- Debarking: The first on-site sawmill step is debarking the whole logs. Most sawmills use debarking machines like mechanical ring cutters or cambio drums. Some mills employ water-jet blasters instead. Bark waste is an important by-product, adding value for the sawmill as landscaping mulch or fuel for the sawmill’s kilns. Logs are also bucked or crosscut with a circular saw into specific lengths at this stage.
- Metal detecting: Examining the log for metal contamination is a vital step in preventing ruined saw blades or sending shrapnel through the mill. Often, nails, sign attachments or fencing wire get embedded in standing trees and are covered over by years of growth. Any logs containing metal go for a secondary examination. If the metal can be removed, the whole log goes back into the production line. If not, it’s salvaged in small sections.
- Merchandising: This is a critical step in modern computerized sawmill operations. Laser scanning or camera viewing estimates the raw log for its maximum cut value. This information determines what sizes of timber, dimensional lumber and boards can come from a particular log. Merchandising takes in more than just the log’s length and girth. It assesses each log for market conditions and standing orders.
- Head rig sawing: You can say the head rig is the heart of a sawmill. Ready logs get clamped to a conveyor and fed to the head rig saw. In some sawmills, the conveyor is a stationary carriage, and the head rig moves its blades lengthwise through the log. Other sawmills have fixed head rigs. They move the log on a mobile conveyor. No matter which system, most modern sawmills use bandsaw blades in their head rigs. Some advanced head rigs can follow a log’s natural curve for maximum wood capture.
- Canting: The head rig cuts the log into sections called cants. The first or primary breakdown is called the best opening face (BOF). This sets a flat surface to square the work for secondary cants that turn into rough sizes for finished lumber products. Waste sections, or slabs, from cants are recycled into chips, pellets or mulch.
- Resawing: Large cut cants from the head rig enter a secondary process called resawing. Here, multiple bandsaw blades reduce the cants to smaller sizes according to the merchandising prescription. Resaws come in many profiles, including vertical and horizontal bands, twin or quad bands, circle gangs, double arbor gangs, band center splitters, band line bars and so on. Resaw steps also use the curve sawing technique.
- Edging and trimming: Moving along in the sawmill process, you’ll find the edging and trimming stages. Here timbers, boards and dimensional lumber get their sides cut to fit a rough grade size. Then, the products pass to a trimmer where they’re cut to specific lengths. For most of the lumber industry, those lengths start at 8 feet and progress in 2-foot increments going as far as 24 feet or more.
- Grading, drying and planing: All wood products emerging from a sawmill are graded in a quality control process. This ensures lumber pieces get separated into similar batches. All wood entering a sawmill is considered “green” or having a high natural moisture content. Once graded, products either air dry or get placed in kilns for forced drying. Planing is the last sawmill step before bundling and shipping. Planers give the products their final size and appearance. Once the lumber is planed, it’s marked with finished grade stamps and ready for market.
Guide from Yorksaw