Two different systems are used to specify the number of teeth per inch. In the United States, the number of teeth in one inch is counted beginning at the bottom of a gullet. The count is either a whole number or, if the inch ends on a point rather than a gullet, a whole number plus ½. The result is called teeth per inch, abbreviated TPI.
In Europe, one begins the count at the point of a tooth, not a gullet, and counts the number of points within an inch. The result is called points per inch, abbreviated PPI.
For circular saw blades, tooth count is simply the total number of teeth on the blade.
Although tooth shape, set, and other factors are also important, TPI is associated with various uses.
|2-3||logger's saws, for cutting green wood across the grain|
|4½||rip saws, for cutting wood with the grain|
|9-20||crosscut saws, for cutting wood across the grain|
In the United States, circular saw blades for consumer use are made in inch diameters of 4, 4 3/8, 5½, 6½, 7, 7¼, 7½, 8, 8¼, 9, 10, and 12. All fit a 5/8 inch arbor, except 12 inch blades, which have a 1-inch center bore. The 7¼ inch size is the one most commonly used in portable saws, and the 10 inch in consumer table and radial saws.
An 8-inch blade with 48 teeth would be equivalent to a 10-inch blade with 60 teeth, or a 12-inch with 72 teeth. Such numbers would be typical of crosscut blades.
D. Plank and E. Stephenson.
Stobert & Son Ltd. of London, Priory House, Priory St. Heortford SG14 1RN, England, 1972.
There are two types of scroll saw blades: flat and pin-end. Many saws can accept either style. 130 millimeter (5 inches) long. Scroll saw blades are sold in sizes numbered from 0 to 12; the higher the number, the fewer the teeth. The smaller sizes are fragile and are used for veneer and other thin stock; the two largest sizes are typically used on stock ¾ inch or more thick. Between these extremes, the smaller the size number the smoother the cut.
The standard hacksaw blade is nominally 12 inches long (actually 12 3/8 inches). Ten-inch blades are also made, and the typical hacksaw frame is adjustable to take blades 8, 10 or 12 inches long. The blade is attached to the frame using small holes at each end of the blade, which fit over pins on the hacksaw frame. On a 12-inch blade, the centers of these holes are 11 7/8 inches apart. Power hacksaws take sizes as large as 30 inches.
There is also a midget, or junior hacksaw, which takes 6-inch blades. Unlike ordinary hacksaw blades, these blades have pins in the ends instead of holes, like a coping saw blade.
In the late 19th – early 20th century, hacksaw blades were also made in 9 and 11-inch lengths. Some manufacturers also supplied hacksaw blades in a continuous roll, as bandsaw blades are often supplied today. The hardware store would cut off whatever length the customer desired, and the customer was expected to punch the holes himself.
Blades are made with from 14 to 32 teeth per inch. As a rule of thumb, in cutting thin stock at least two teeth should be in contact with the work at all times.
These saws are made for cutting metal. The blades are 4 inches long.
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Last revised: 3 December 2002.