Spur gears transmit motion across parallel shafts and they are known to be the simplest type of gear. Spur gears can run with other spur gears, gear rack or face gears.
Spur Gears: +1 (215) 703-0390
Spur Gear Materials
Like most any gear, spur gears can be made out of most any material… to name a few: steels, preheat treat steels, hardened steels, stainless steels, delrin, nylon, uhmw, other plastics, brass & bronzes, not metallics (phenolics), wood, etc.
Although there are formulas to calculate all dimensions for spur gears such as the outside diameter, pitch diameter & root diameter, these formulas do not always hold true because spurs gears, like many other types of gears, can have oversized or undersized pitch diameters.
One reason or example of why a spur gear may have an oversize pitch diameter can be seen in the case of a gear that has a very low number of teeth, such as 11 teeth or less. Due to this low number of teeth and because gears are generated, the tooth form in 11 teeth more or less will be “hour glass” shaped. Because of this “hour glass” shape, near the bottom of the tooth, the tooth is not very broad and therefore weak. It is said to be “undercut”. To alleviate this undercut, the pitch diameter can be increased. Since the pitch diameter is increased, if a standard center distance is desired with it’s mate, the pitch diameter in the mate would need to be decreased. Keep in mind that a gear with any number of teeth (not just 11 teeth or less) can also have an oversized or undersized pitch diameter.
Approx 50% of the gears that we make here at Gearmakers, Inc. have oversized or undersized pitch diameters. This is why you may be confused, if you have a gear sample that you are trying by using standard gear formulas to calculate dimensions such as outside diameter, pitch diameter & root diameter.