Miter saw
A miter saw or mitre saw is a saw used to make accurate crosscuts and miters in a workpiece by positioning a mounted blade onto a board. A miter saw in its earliest form was composed of a back saw in a miter box, but in modern implementation consists of a powered circular saw that can be positioned at a variety of angles and lowered onto a board positioned against a backstop called the fence. Powered miter saws also cut bevels into a work piece by adjusting the vertical tilt axis of upper portion of the machine while  the table lays flat horizontally. A miter saw for which the axis can be tilted in a single direction is known as a single compound miter saw. If the axis can tilt both left and right, it is known as a double bevel compound miter saw. Some are equipped with a sliding rail system or have a pivot arm to cut wider work pieces when laid flat on the table of the saw and flush against the fence. This is known as a sliding compound miter saw. Miter saws are primarily used for cutting wood trim and molding, but also  can be used to cut metal, masonry, and plastics, provided the appropriate type of blade is used for the material being cut. Miter saws come in a variety of sizes. The most common sizes are size blades, each of which has its own cutting capacity. Both corded and cordless versions of the saw are available from several different manufacturers. A common misnomer that is sometimes used to refer to a miter saw is the chop saw. Although somewhat similar in their cutting action, they are two entirely different types of saw. A chop saw is specifically meant to cut metal  and is typically operated while laid flat on the ground with the blade fixed at 90° vertical. A chop saw cannot make a miter cut unless manipulated by the operator as opposed to the function of the machine itself. Power miter saw. A power miter saw, also known as a "drop saw", is a power tool used to make a quick, accurate crosscut in a workpiece at a selected angle. It is commonly used for cutting of molding and trim. Most miter saws are relatively small and portable, with common blade sizes ranging from . The power miter saw  was invented by Ed Niehaus, the Chief Engineer in the Power Tool Division for Rockwell International, in 1964. The miter saw showcased several innovations still found today: radial arc spring action, blade braking and dust collection. Rockwell did not patent the design, leading to a large number of manufacturers and innovation improvements. The power miter saw makes cuts by pulling a spinning circular saw blade down onto a workpiece in a short, controlled motion. The workpiece is typically held against a "fence", which provides a precise cutting angle between the plane of the blade and the plane of the longest  workpiece edge. In standard position, this angle is fixed at 90°. A primary distinguishing feature of the miter saw is the "miter index" that allows the angle of the blade to be changed relative to the fence. While most miter saws enable precise one-degree incremental changes to the miter index, many also provide "stops" that allow the miter index to be quickly set to common angles (such as 15°, 22.5°, 30°, and 45°). Types. There are several types of miter saws: Features. Miter saws are dedicated cross cut saws; long rip cuts (in line  with the grain) are not possible. A "laser guide" provides a precise visual indication of where the cut will be positioned on the workpiece in the current configuration. Some models provide a single reference line for one side of the kerf, while others provide two lines to reflect the total kerf width. A "blade guard" is a cover for the teeth of the cutting blade. Most modern miter saws have self-retracting blade guards, which automatically retract when the saw is lowered onto a workpiece and re-cover the blade when the saw is raised. It is very dangerous to  use the saw if these guards are removed or damaged. A "dust bag" connects directly to the saw, and helps to collect sawdust away from the workpiece during cutting. Optionally, many manufacturers sell adapters to connect an industrial vacuum cleaner in lieu of a bag to capture more of the dust and simplify disposal. Dust removal with these saws is notoriously poor. A "safety clamp" helps to lock a workpiece into position prior to making a cut. This is an especially important feature when cutting smaller workpieces ( or smaller). The "miter table " is typically less than in diameter. Typically, the  work needs to be supported on the far end to stabilize the piece while cutting. Miter saws are inherently low-hazard as the work piece is held stationary against a fence while the saw head moves, making kick-back almost impossible, and normally allowing hands to be kept clear of the blade. Also the saw head is usually drawn back, then lowered and fed forward through the material so that binding is unlikely. Sliding compound miter saws are relatively portable, easy to set up, and robust enough to maintain accuracy even when moved around. Because they cut from above it  is not necessary to adjust blade depth for different thicknesses of work piece and, like any bench machine, repeat cuts are very easy. Most saws have an adjustable scale plate for table swiveling, with positive stops at commonly used angles. Also, there are usually adjustable stops at 90 and 45 degrees for tilting the head, allowing easy and very accurate adjustment of the saw. Table swiveling in both directions is universal but most saws allow head tilting only in one direction (counter-clockwise), although some saws allow head tilting in both directions. Normally the work piece is held flat on  the table and so table swiveling will produce a miter cut (blade vertical and angled across work piece), head rotation a bevel cut (blade angled from vertical and square across work piece), and in combination a compound cut. One of the main disadvantages is relatively poor wood chip and dust extraction, as so much of the blade is exposed when cutting, especially in bevel cuts; consequently there is a tendency for chips to fly about. Miter saw blades. Miter saws commonly come in blade size configurations and are commonly made of carbon steel and may come with a coating to  make the cut easier. While the blade sizes are interchangeable with table saws, a miter blade is optimized for short cuts across the grain of the wood with little pull, where as table saws are optimized for long rip cuts with the grain and pulling the material into the blade. Blades are marked with their number of teeth, kerf and hook angle. Tooth counts ranges vary from 24 to 100 teeth per inch (about 1 mm to 0.25 mm between each tooth). Blades with larger tooth counts results in finer but slower cuts. The kerf thickness denotes how much material  is removed when making the cut. The standard being a kerf with thinner options for working finer wood. The hook angle denotes how aggressively the blade will pull the material in. A low hook angle or even a negative hook angle is designed to cause little board movement during cutting of unclamped boards. Teeth design comes in many variations: ATB (alternating top bevel), FTG (flat top grind) and TCG (triple chip grind) are the most common. Each design is optimized for a specific material and edge treatment. An arbor bolt holds the blade to the saw rotor and its diameter  must match the blade hole size in order to properly secure the blade ( blades commonly use arbor holes and blades favor ). To prevent the saw from loosening the arbor bolt, the threads are reverse-threaded, the rotational spin of the saw blade exerts a tightening pressure on the blade. Development. Power miter saws have been available in various forms since the 1970s as specialized cross cut saws but with limited width of cut, especially compared to radial arm saws. Simple miter saws allowed the saw table to pivot allowing miters to be cut in one plane. Compound miter saws also  provided saw head tilting allowing compound miters to be cut. Miter saws with abrasive cutting wheels are often used in metal work where they are known as "drop saws" or more commonly "chop saws". Because the blade assembly could only pivot, not translate, these initial designs were limited by blade radius in how wide and deep a board they could cut. However, because their capacities were adequate for handling common sizes of dimensional lumber, and because they were more compact and portable than arm and table saws, chop saws quickly became ubiquitous in construction. Around 1982, the sliding compound miter  saw was introduced. This innovation combined all the best features of the compound miter saw with sliding tubes, allowing the cutter head to traverse for a much wider cut. Since then it has become the primary cross cut saw for woodworking, largely supplanting the radial arm saw. Manufacturers warn of possible electrocution when used near water, or other related saws in close proximity.