Unit 18 Gears, Splines, and Serrations

Learning Objectives Identify spur gears and their representations and specifications. Identify bevel gears and their representations and specifications. Creatas

Learning Objectives Identify worm gears and their representations and specifications. Identify splines and serrations and their representations and specifications. ra3rn/Shutterstock.com

Gears, Splines, and Serrations Gear: A wheel-like machine part with a number of equally spaced teeth –Teeth mesh with the teeth on another gear –Purpose is to transmit power in a mechanism Splines: A series of ridges on a shaft –Match to serrations on a mating part –Purpose is to maintain the position of the parts

Spur Gear Terminology

Diametral pitch (P d ): Number of teeth in a gear per inch of pitch diameter –Mating gears must have identical diametral pitches Pitch diameter (D): Diameter of an imaginary circle located approximately halfway between the roots and tops of gear teeth –Used to calculate the gear ratio

Spur Gear Terminology Circular pitch (P c ): Length of the arc along the pitch circle between one point on a tooth to the same point on the next tooth –Calculated by πD ÷ n Circular tooth thickness: Thickness of a gear tooth as measured along the arc –Calculated by P c ÷ 2

Spur Gear Terminology Addendum (a): Radial distance between the pitch circle and the top of the tooth –Calculated as 1 ÷ P d Dedendum (b): Radial distance between the pitch circle and the bottom of the tooth –Calculated as 1.25 ÷ P d

Spur Gear Terminology Clearance: Radial distance between the top of a tooth on one gear and the bottom of the tooth space on the mating gear –Calculated as b – a Working depth: Overlap of two mating spur gears –Represented by the sum of the addendums (a + a)

Spur Gear Terminology Whole depth: Total depth of a tooth space on one gear –Calculated as a + b Pressure angle: Angle between the tooth profile and a radial line at the intersection on the pitch circle –Pressure angles of mating gears must be the same –Standard angles include 14.5° (former), 20°, and 25°

Gear Ratios Using the Pitch Circle Pitch circles of mating gears are equivalent to theoretical friction roller diameters and used to calculate gear ratios

Measuring with a Gear-Tooth Caliper A gear-tooth caliper measures straight distances, as reflected in this diagram

Bevel Gear Terminology

Worm Gear Terminology

Splines and Serrations Photo: Daimler

What do you see? Print supplied by Gleason Works.