Spur Gears – One Type of Cylindrical Gears

| December 22, 2016

Spur gears are cylindrical disks which have involute shaped teeth cut into their face. To meet your requirements, KHK’s spur gears are made in a variety of styles. Our spur gears are offered in many materials, configurations, modules and numbers of teeth. Many of the products that we offer allow for secondary operations such as opening the bore, adding of keyways, adding of tapped holes, or reduction of the hub diameter to be performed. Our offering also includes products which have already had some of these secondary operations completed. These products are identified by a “J” in their part number and they are available within 10 calendar days.

Among gears, there are two with parallel shafts and are called cylindrical gears.

Spur gears which are the simplest configuration and easily manufactured are one of these cylindrical gears in which the pitch surfaces are cylinders and tooth lines (the intersections of the pitch surfaces and the tooth surfaces) are straight lines.

Also, the efficiency of spur gears is about 95 – 98%.

The main materials used to make spur gears are, in terms of JIS Standard, structural carbon steel S45C, structural alloy steels SCM440 (medium carbon steel) and SCM415 (low carbon steel), gray cast iron FC200, stainless steels SUS303 and SUS304, nonferrous metal C3604 (free cutting brass), engineering plastics MC901 and MC602ST, etc.

Of course, in different countries other material standards are adopted, such as AISI, SAE, ASTM, AGMA, etc. in the US.

The production process of cylindrical gears, represented by spur gears, depends on consideration of tooth size expressed in module or DP (diametral pitch), configuration, material, heat treating, method of finishing tooth surface, precision of the gears and manufacturing quantity.

Also, production of spur gears, depending on the desired accuracy or strength, can be grouped into ones simply needing turning blanks and gear cutting and those requiring post gear cutting operation such as gear grinding or shaving.

Incidentally, representative teeth cutting methods of spur gears include hobbing, gear shaper cutting, milling, broaching, etc., and finish machining method can be listed as gear grinding, shaving, lapping and honing, etc.

To sketch spur gears, first determine module m, pressure angle α, number of teeth z and, if profile shifted gear, coefficient of profile shift x.

Also, outside diameter, tooth width, bore, etc. can be measured using vernier calipers or micrometers and pitch circle can be obtained by calculation.

In recent years, instead of using hobbing machines, a new method is being developed in which a 5-axis machining center is used in combination with a gear manufacturing software which generates the NC data from inputted number of teeth and module of desired gears (spur and bevel gears).

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