Gears are commonly specified according to AGMA Class Number, a code which denotes important quality characteristics. High pressure angle decreases the contact ratio (ratio of the number of teeth in contact) but provides a tooth of higher capacity and allows gears to have fewer teeth without undercutting.īacklash: Shortest distance between the noncontacting surfaces of the adjacent teeth. Pressure angle affects the force that tends to separate mating gears. Earlier standards included a 14° pressure angle that is still used. Pressure angle: Standard angles are 20 and 25°. This form is known as recess-action gearing. The addendum of the smaller gear (pinion) is increased while that of the larger gear is decreased, leaving the whole depth the same. Mating gears with long and short addendum have larger load-carrying capacity than standard gears. Undercutting reduces the active profile and weakens the tooth. Gears with small numbers of teeth may have an undercut so they do not interfere with one another during engagement. Full-depth teeth have a larger contact ratio than stub teeth. Stub teeth have a working depth usually 20% less than full-depth teeth. If the teeth have equal addenda (as in standard interchangeable gears), the addendum is 1/ P. Standard full-depth teeth have working depths of 2/ P. Fine-pitch gearing usually has teeth of diametral pitch 20 to 200.ĭepth:Standardized in terms of pitch. Coarse-pitch gearing has teeth larger than 20 diametral pitch - usually 0.5 to 19.99. Pitch: Standard pitches are usually whole numbers when measured as diametral pitch P, the ratio of the number of teeth to the pitch diameter in inches. The bit size is a very important consideration! Depending on your software, if the cutter is too large it will either over-cut the root and weaken the tooth, or leave a radius and not finish the involute profile or undercut.Gear tooth geometry is determined primarily by pitch, depth, and pressure angle. Pro-Tip! Notes for the wood shop or anyone using an endmill to make the cut:
For measuring and inspecting gears, using a Measurement Over Pins Calculator is one of the best methods to ensure your gears are perfectly in-spec. So we put the same attention to detail and mathematical skill to work for everyone. We also see low resolution involute shapes that could function better if they had the correct geometry with sufficient data points defining the involute.īeing members of the American Gear Manufacturers Association (AGMA) and having manufactured gears in most plastics and metals, the details count. This can make gears bind or function poorly. One of the more common mistakes we see in simplified gear software is the lack of undercut in small tooth count gears. Gear 1 and Gear 2 can have the same or different center hole diameters.Ĭenter Distance – This is the distance between the two shaft centers holding the gears. Another way to think about it is positive profile shift numbers will allow for more backlash between two gears en-mesh.Ĭenter Hole Diameter – Central bore hole in each gear, for standard size we’d recommend the Machinery's Handbook. A positive profile shift represents a theoretical cutter cutting deeper (leaving longer, thinner teeth), while a negative shift would cutter more shallow (leaving shorter, thicker teeth). Profile Shift – Default is 0 for most applications. To convert, use: Module = 25.4 / Diametral Pitch Module (Pitch) – this parameter sets the tooth size. The rack length defaults to the diameter of Gear 2.
Gear Type – External spur gears use a positive tooth count, while internal spur gears use a negative tooth count. Tooth Count – is set with the parameter "n" for Gear 1 and Gear 2