Helical, Spiral, Worm and Bevel Gears

Abstract

Cut a paper into the shape of a parallelogram and wrap it around a cylinder. The edge of the paper makes an angle ψb called the base helix angle.When you unwrap the paper, keeping it tight, so that it is tangential to the cylinder, see Figure 7.1, you are generating several involute profiles placed side by side starting from a line inclined at the base helix angle ψb to the cylinder axis. The surface thus generated is an involute helicoid and forms the shape of a tooth on a helical gear. If the helix angle is clockwise, then we have a right-hand helical tooth, otherwise it is a left hand helical tooth. The plan view of a left-handed helical gear is shown in Figure 7.2.