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HobbyParts Pitch - Glossary - Technical Information
Glossary - Pitch
The pitch circle is an imaginary circle on a gear, pulley or similar mechanical device that divides the teeth at the optimal contact point. The optimal contact point is where two gears or a belt and pully contact each other when in correct mesh. The pitch is the distance from center to center of any two adjacent teeth of a gear, toothed belt, sprocket, toothed pulley or similar mechanical device as measured along the pitch circle. Pitch diameter is the diameter of the pitch circle.
Pitch is also used to describe the distance between threads of a screw, ballscrew or acme thread. It can also describe the centre distance between holes in a predrilled item such as shafting, rails or gear racks.
Timing belt and pulley pitches are usually specified as the distance between the teeth in mm.
For gears, metric pitch uses the module designation. If you divide the pitch circle diameter of a metric spur gear by the number of teeth you arrive at the module. A spur gear of module 1.0 will have a pitch circle diameter (PD) equivalent to the number of teeth eg, module 1 with 25 teeth = 25mm pitch circle diameter. A Spur gear with a module of 0.8 will have a pitch circle diameter equivalent to 0.8 times the number of teeth eg; module 0.8 with 25 teeth = 20mm pitch circle diameter.
Imperial sized spur gears use the American Standard DP (Diametrical Pitch) numbering system eg 16DP, 24DP, 32DP. To arrive at the DP for imperial sized spur gears you divide the number of teeth by the pitch diameter in inches. A 16DP gear with 16 teeth will have a 1” (25.4mm) pitch diameter and a 32DP gear with 16 teeth will have 1/2" (12.7mm) pitch diameter.
The pitch diameter is the diameter across the gear from half way between the top and the base of the tooth. So for a module 1 metric spur gear with 50 teeth, the pitch diameter will be 50mm, but the overall diameter of the gear across the teeth will be 51mm (pitch diameter + the module) and the diameter fron the base of the teeth on one side to the base on the opposite side will be 49mm.
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H.E. Supplies (Hobby Engineering Supplies) offers thousands of products including remote controlled cars, planes, boats, and helicopters. We stock spare parts for remote controlled models. Our range includes the popular Solarbotics solar model kits and spares. We also distribute the full range of miniature engineering products from Miniature Bearings Australia. This range includes small bearings, timing pulleys, timing belts, seals, o-rings, gears and more. Also available from our store in Mansfield Queensland are a full range of lubricants, adhesives, kites, balsa wood and plastic rod and sheet materials. See our Online Catalogue for more information. Our main business is handled from our sales counter and showroom at 186 Wecker Road Mansfield, Queensland, Australia, but we also sell by phone, fax, online and mail order. We offer all of our hobby parts through our online store and some of the more popular MBA items. If you would like to purchase other MBA items online, Small Parts and Bearings offer the full range in their online catalogue.Using the links at the top of this page you will find extensive information including catalogues (Products and Store link), technical data, and other product specific information.
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