Fig. 2.7 Center distance
Gears can mesh as shown in the Figure 2.6, however, it is important to consider a proper backlash (play) so that the gears can work smoothly. Backlash is a play between tooth surfaces of paired gears in mesh.
Mating gears also have a clearance (play) vertical to tooth depth. This is called Tip and Root Clearance (c), the distance between tooth root and the tooth tip of mating gears.
Tip and Root Clearance (c)
c = 1.25 m - 1.00 m
= 0.25 m(2.12)
Fig. 2.8 Tip and Root Clearance
Fig. 2.8 Tip and Root Clearance
(Important Gear Terminology and Gear Nomenclature in Fig 2.8)
Addendum circle
Dedendum circle
Tip and Root Clearance
Calculation Examples
The following are calculations for Center distance (a) and Tip and root clearance (c), when Module m = 2, Pinion z1 = 20, Gear z2 = 40
Reference diameter of Pinion d1 = 20 × 2 = 40
Reference diameter of Gear d2 = 40 × 2 = 80
Center distance a = (40 + 80) / 2 = 60
c = 0.25 × 2 = 0.5
Calculation Examples
Practice calculating the dimensions of gears.
Terms Symbols Formula Pinion Gear
Module m - 2.5
Pressure Angle α 20°
No. of Teeth z 15 30
Reference diameter d z m 37.5 75
Addendum ha 1.00 m 2.5 2.5
Dedendum hf 1.25 m 3.125 3.125
Tooth Depth h 2.25 m 5.625 5.625
Tip diameter da d + 2 m 42.5 80
Root diameter df d - 2.5 m 31.25 68.75
Center distance a d1 + d2 / 2 56.25