Table saw

Table saw

A table saw, equipped for cutting large pieces of sheet stock.
Other names Sawbench
Classification Power tool
Manufacturer Delta, SawStop, Bosch, Makita, Ryobi, Black & Decker/DeWalt, among others
The blade of a table saw cutting into wood

A table saw or sawbench is a woodworking tool consisting of a circular saw blade, mounted on an arbor, that is driven by an electric motor (either directly, by belt, or by gears). The blade protrudes through the surface of a table, which provides support for the material, usually wood, being cut.

In a modern table saw, the depth of the cut is varied by moving the blade up and down: the higher the blade protrudes above the table, the deeper the cut that is made in the material. In some early table saws, the blade and arbor were fixed, and the table was moved up and down to expose more or less of the blade. The angle of cut is controlled by adjusting the angle of blade. Some earlier saws angled the table to control the cut angle.

Types of table saws

A rudimentary table saw

There are four general classes of table saws: benchtop table saws, contractor table saws, cabinet table saws and hybrid table saws.

Benchtop table saws

Benchtop table saws, sometimes known as job-site saws,[1] are lightweight and are designed to be placed on a table or other support for operation. They commonly have direct drive (no v-belt or pulleys) from a universal motor. They can be lifted by one person and carried to the job location. These saws often have parts made of steel, aluminum and plastic and are designed to be compact and light.

Benchtop table saws are the least expensive and least capable of the three major types; however, they can offer adequate capacity and precision for many tasks. The universal motor is not as durable or as quiet as a brushless AC motor, but it offers more power relative to its size and weight. The top of a benchtop table saw is narrower than those of the contractors and cabinet saws, so the width of stock that can be ripped is reduced. Another restriction results from the top being smaller from the front of the tabletop to the rear. This results in a shorter rip fence, which makes it harder to make a clean, straight cut when ripping. Also, there is less distance from the front edge of the tabletop to the blade, which makes cross cutting stock using a mitre more difficult (the mitre and/or stock may not be fully supported by the table in front of the blade). Benchtop saws are the smallest type of table saw and have the least mass, potentially resulting in increased vibration during a cut.

Contractor table saws

Contractor table saws are heavier, larger and have an attached stand or base, often with wheels. The motor either is "direct drive" to the blade (drives the blade directly without a belt) or hinges off the rear of the saw and drives the blade via one, or occasionally two, belts using a 1 to 2 hp (750 to 1500 W) induction type motor. This is the type often used by hobbyists and homeowners because standard electrical circuits provide adequate power to run it, and due to its low cost. Because the motor sometimes hangs off the rear of the saw on a pivot, dust collection can be problematic in comparison with a cabinet saw.

Cabinet table saws

Cabinet table saws are heavy (using large amounts of cast iron and steel) to minimize vibration and increase accuracy. A cabinet saw is characterized by having a closed (cabinet) base. Cabinet saws usually have induction motors in the 3 to 5 hp (2 to 4 kW) range. For home use, this type of motor typically requires that a heavy-duty circuit be installed (in the US, this requires a 220V outlet). The motor is enclosed within the cabinet and drives the blade with three parallel v-belts. Cabinet saws are heavier and offer the following advantages over contractor saws: heavier construction for lower vibration and increased durability; a cabinet-mounted trunnion (the mechanism that incorporates the saw blade mount and allows for height and tilt adjustment); improved dust collection due to the totally enclosed cabinet and common incorporation of a dust collection port. In general, cabinet-mounted trunnions are easier to adjust than table-mounted trunnions.

The American-style cabinet saws generally follow the model of the Delta Unisaw, a design that has evolved since 1939. Saws of this general type are made in the USA, Canada, Taiwan, and China. These saws are characterized by a cast iron top on a full-length steel base, square in section, with radiussed corners. Two 3/8" deep by 3/4" wide miter slots are located parallel to the blade, one to the left of the blade and one to the right. The most common type of rip fence mounted to this type of saw is characterized by the standard model made by Biesemeyer. It has a sturdy, steel T-type fence mounted to a steel rail at the front of the saw. It has replaceable laminate faces. American cabinet saws are normally designed to accept a 13/16" wide stacked dado blade in addition to a standard saw blade. The most common size of blade capacity is 10" in diameter. The blade arbor has a diameter of 5/8". American saws normally include an anti-kickback device that incorporates a splitter, toothed anti-kickback pawls and a clear plastic blade cover. American style saws have an easily replaceable insert around the blade in the table top. This allows the use of zero-clearance inserts, which greatly reduce tear out on the bottom of the workpiece. It is common for this type of saw to be equipped with a table extension that increases ripping capacity for sheet goods. The saw blade can tilt to either the left side or right side of the saw, depending on the model of saw. The original Delta Unisaw and early cabinet saws based on it were all right-tilt units while newer Delta Unisaws and most other cabinet saws made after 2000 are left-tilt saws. The switch to left-tilt design is due to a lower propensity for the cut piece to become trapped between the rip fence and blade and kick back when the blade tilts away from the rip fence (left tilt saw) versus towards the rip fence (right tilt saw.) [2] While relatively simple in design, these saws are highly evolved and capable of efficient and precision work.

European-style cabinet saws are often more complex and modern in design compared to American types. They often are equipped with a sliding table to make cross cuts easier and safer than by the use of an American style mitre gauge. Unless modified for the American market, European table saws are not equipped to allow the use of a stacked dado blade set (this is due to safety laws in European markets). Rip fences on European saws tend to be of lighter construction and less smooth in operation compared to American cabinet saws. European cabinet saws are often available in multi-purpose tool configurations that can offer jointer, planer, shaper or boring features. The blade arbor typically has a diameter of 30mm, though for the American market a 5/8" arbor is commonly available as an option. Note that American woodworkers are likely to use a stacked dado blade to cut dados (square sectioned grooves) where European woodworkers might use a shaper or other tool for this task. European cabinet saws often incorporate a riving knife to prevent kickback. Riving knives differ from American style splitters in that they rise and fall with the blade (splitters are fixed in place without regard for the height that the blade is adjusted to). Riving knives have since become commonplace on newer American-market tablesaws due to the Consumer Products Safety Commission and UL recommendation in the early to mid-2000s that American-market saws have riving knives (UL std. 987.)[3] European cabinet saws often offer as an option a scoring blade, which is a second, smaller diameter blade mounted in front of the regular saw blade. The scoring blade helps reduce splintering in certain types of stock, especially laminated stock. As of 2015, European-style sliding cabinet saws have a small following in the U.S. They are either imported from European manufacturers such as Felder, Hammer, and Robland or sold directly by U.S. based-companies such as Grizzly Industrial.

Hybrid table saws

Hybrid table saws are designed to compete in the market with high-end contractor table saws. They offer some of the advantages of cabinet saws at a lower price than traditional cabinet saws. Hybrid saws on the market today offer an enclosed cabinet to help improve dust collection. The cabinet can either be similar to a cabinet saw with a full enclosure from the table top to the floor or a shorter cabinet on legs. Some hybrid saws have cabinet-mounted trunnions and some have table-mounted trunnions. Hybrid saws tend to be heavier than contractor saws and lighter than cabinet saws. Some hybrid saws offer a sliding table as an option to improve cross cutting capability. Hybrid saw drive mechanisms vary more than contractor saws and cabinet saws. Drive mechanisms can be a single v-belt, a serpentine belt or multiple v-belts. Hybrid saws have a 1.5 or 2 hp motor and thus the ability to run on a standard 15 or 20 amp 120 volt American household circuit, while a cabinet saw's 3 hp or larger motor requires a 240 volt supply.

History

In the United States, perhaps the first recorded patent for the circular saw was issued in 1777 to an English man, Samuel Miller; it refers to a circular saw that was created in Holland in the 16th or 17th centuries.[4] The 1885 catalog of the W.F. & John Barnes Co., Rockford, Il. clearly shows a classic table saw and it is labeled as a "Hand [Powered] Circular Rip Saw".

Safety practices

The use of a push stick reduces the risk of injury.

Avoiding kickback

Kickback happens when the blade catches the workpiece and violently throws it back to the front of the saw, towards the operator. It can be thrown very hard and can injure the operator. It is not uncommon for the object to have high enough velocity to become embedded in a wall or to cause other damage or injury. For safety, the operator should never stand in a direct line between the blade and the fence when ripping narrow stock. A kickback can be fatal.

Kickback happens when ripping if:

  1. The wood pinches the blade because of internal stresses. This is difficult to predict and can be impossible to control when using fingers to hold the wood down. Many times the board pinches the blade and is thrown back before the wood reaches a splitter. This type of kickback never happens when a board is not cut all the way through (dado). By starting a cut with a dado and then raising the blade to leave a splitter tab of uncut wood, this type of kickback can be avoided, but raising the blade during a cut cannot be done unless anti-kickback hold downs are used, so it is safe to raise the blade with a free hand.
  2. The wood is allowed to raise up or moved sideways during a cut, then pushed back down, taking too big a bite at the top of the blade. This can be prevented by using feeder wheels very close to the start of the blade and hold downs after the blade to control the wood all the way through the cut. The right feeder wheels are very effective for both dados in plywood and for rip cuts on boards as narrow as 1/8". Feeder wheels can be powered or unpowered, clamped or held magnetically, and replace fingers near the blade so a hand can be free to turn off the saw during a cut.
  3. The board is pinched between the rear of the blade and the fence. The fence should be parallel with the blade, for the best cut on both sides of the blade. The fence can be set with the rear farther from the fence for safety, but at the expense of upcut marks on the "waste" piece. Never allow the fence to be closer to the rear of the blade than the front.

Kickback can also happen when crosscutting boards with internal stresses. A chop saw or circular saw is the best preference for cutting poor lumber.

The risk of kickback is reduced by certain practices:

Optional safety features

In recent years, new technology has been developed which can dramatically reduce the risk of serious injury caused by table saws. One way to prevent fingers from being severed is to use springs or feeder wheels to apply pressure on the side and top of the lumber when ripping. These featherboards and push sticks are substitutes for fingers. Traditionally they are clamped to a saw top.

A dust extractor should be fitted. If sawdust is prone to build up under the cutting blade, through friction the spinning blade will quickly ignite the accumulated dust, and the smoke can be mistaken for an overheated blade. The extractor also reduces the risk of a dust explosion and facilitates a healthier working environment.

Magnetic featherboard

The magnetic feather board was developed in 1990.[5] The patented Grip-Tite is held to a cast iron table top or steel sub fence by high strength permanent magnets. The advantage of a magnetic feather board is the fast setup time on any cast iron tool deck or steel faced fence. When used in conjunction with a steel faced rip fence, they are used to hold down ripped wood on any saw deck and prevent kickback. Feed wheels added to the Grip-Tite base pull ripped wood to the fence, allowing the operator to rip wood on any table saw with no hands near the blade.

Automatic braking

One new feature, commercially available in saws since 2005,[6] is an automatic braking system. The feature's inventor, after trying to license it to manufacturers without success, started SawStop, based in Tualatin, Oregon. SawStop's saws applies a small amount of electric current to the blade of the saw. This current is continuously monitored. If the saw detects a change in this current (as would occur if a hand or other body part came into contact with the blade) an automatic braking system is activated, forcing an aluminum brake block into the blade. The saw stops within five milliseconds, and angular momentum lowers the blade into the table. The operator suffers a small nick instead of an amputation or other more serious injury.[7]

There is a chance this may ruin the blade, however.[8] The feature must also be bypassed when cutting wet timber.

Blade height

Ideally the blade of the table saw should extend higher than the board being cut by about a quarter of an inch (7.5 mm); this lessens the risk of kickback and other injuries and enables smooth cutting.

There are two competing schools of thought when it comes to properly setting the height of the blade for sawing. The first is commonly expressed thus: "Only allow the blade to rise above the work by the amount of finger you wish to lose." That is, the blade should protrude above the piece as little as possible, to prevent the loss of a finger in case of a sawing accident.

Another competing view is that the saw functions at its best when the angle of the blade teeth arc relative to the top surface of the workpiece is as extreme as possible. This facilitates chip ejection, shortens the overall distance through which the teeth act on the part, reduces power consumption and heat generation, substantially reduces the peak pushing force required, thus improving control, and causes the blade's force on the wood to act mostly downward rather than largely horizontally.

Accessories

References

  1. ↑ "Mid-Priced Tablesaws". Wood Magazine 29 (4): 35. September 2012.
  2. ↑ http://www.ronin-group.org/shop_table_saw_tilt.html
  3. ↑ http://www.cpsc.gov/en/Regulations-Laws--Standards/Voluntary-Standards/Topics/Table-Saws/
  4. ↑ Manfred Powis Bale. Woodworking Machinery, Its Rise, Progress and Construction.
  5. ↑ US patent 5367933, J. F. Jaksha, "Power tool shield and guiding apparatus", issued 1994-11-29
  6. ↑ "SawStop — Company". SawStop. Retrieved 2011-06-18.
  7. ↑ "CPSC Chairman Awards Safety Commendation to SawStop, LLC". Washington, DC: Consumer Product Safety Commission. July 20, 2001. Retrieved 2011-06-18.
  8. ↑ "How It Works". SawStop. Retrieved 2011-06-18.
  9. ↑ See video at http://www.prowoodworkingtips.com/Table_Saw_Kick_Back.html

Further reading

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