Gear Technology Manual

Module 3 - BASIC GEAR GEOMETRY

Now avalaible on CD-ROM

SYNOPSIS

The dimensions of gears specified by chosen values of tooth number, size parameters, and tooth alignment (helix angle) are found, and the centre distance at which such gears mesh together in pairs is determined.

CONTENTS

Motion transmission
The Involute
Mathematical description of the involute - the 'inv a' function
Involute function calculations
The involute tooth form gear
Base pitch pb and base diameter d_b
Tooth thickness 's'
The infinitely large gear - the rack
The basic rack concept
Module
Diametral pitch
Rack flank angle

Rack generation of gear tooth forms
Simple spur gears
The spur gear reference circle Tip diameter
Root diameter
Addendum and dedendum

General spur gears
Rack displacement factor 'x' (addendum modification coefficient)
General spur gear dimensions for non-zero 'x'
Tip diameter
Root diameter
Permissible parameters of a gear
Graphical recommendations for x
Helical gears
The transverse pitch and the helical gear reference circle
Tip diameter
Root diameter
Permissible parameters of a helical gear (limits on x and x)
Lead and helix angles
Reference helix angle
Variation of helix angle with radius
Axial pitch
Base helix angle
Tooth thickness
Arc thickness on the reference circle
The relationships between st_ref s_tb and s_ty
Transverse and normal tooth thicknesses
Helical gears - the equivalent virtual spur gear
Involute spur and helical gear PAIRS
Working pressure angle _tw
Pitch circles (meshing or working circles)
Centre distance

Unmodified spur gears (x = 0)
Gears in general
Using the equations
A simple method for = 20°

Practical values of the addendum modification coefficient sum x = (x₁+ x₂)
Allocation of x between the gear pair
Conditions for good continuity of tooth action
Contact ratio
Active profile
Single pair and double pair contact
Formula collection

Index: - Gear Technology Manual
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