Scroll saws are often used to cut intricate curves and joints, a task they can complete quickly and with great accuracy. They can also be used to cut dovetail joints and are a common tool for thicker intarsia projects. When a fine blade is used, the kerf of a scroll saw is almost invisible. Along with band saws, jigsaws, and now recently seen chainsaws, scroll saws are used with modern intarsia. Scroll saws are comparatively safe. In particular, inadvertent contact between the blade and the operator's fingers or limbs is unlikely to result in serious injury, due to a smaller blade and relatively slower speed compared to tools such as a table saw. Mode of operation There are several types of scroll saws. The most common design is the parallel arm, in which a motor is attached near the back of the arms and the two arms always remain parallel to each other. The C-arm variant uses a solid "C" shaped arm, with the blade being mounted between the two ends of the "C". The parallel link type, used by Hawk, Excalibur, and DeWalt, has rods in the upper and lower arms that are "pushed" by the motor to move short (about 4 inches, or 100 millimetres) articulated arms which hold the blade. The rigid arm scroll saw was popular until the 1970s but is no longer made. It has a single-piece cast iron frame. The blade is attached to a pitman arm on the bottom, which pulls the blade down. A spring in the upper arm pulls the blade back up again. This design has a significant weakness in that the tension on the blade changes with every stroke; modern scroll saws are all "constant tension" designs. Blades With the exception of blades made for very light duty saws, typical scroll saw blades are long. The major types are: Skip tooth (or single skip tooth) which have a tooth, a gap, and then another tooth; Double skip tooth (two teeth, a gap, then two teeth); Crown or two-way, which have teeth facing both up and down so that the blade cuts on both the down-stroke (as with all other blades) and the up-stroke; Spiral blades, which are essentially regular flat blades with a twist, so that teeth project on all sides; Metal cutting blades made of hardened steel; Diamond blades (wires coated with diamond fragments), for cutting glass. Pin