Machine Drawing

192 Machine Drawing

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d:\N-Design\Des13-1.pm5

13.10 Tooth Profiles

A number of curves may be used for the tooth profile. However, from a commercial stand point,

cycloidal and involute curves are used. Of these two, involute form is extensively used because

of its advantages from manufacturing and operational points of view.

13.10.1 Involute Tooth Profile

Involute is a curve traced by a point on a straight line when it rolls without slipping, on the

circumference of a circle. Figure 13.6 shows the stages in drawing the involute tooth of a gear.

The following are the steps involved in the construction.

Fillet

Face

width (B)

Root

Thickness

Circular pitch

Pitch circle

(a)

Dedendum

Whole depth Common tangent

Addendum

Centre distance

(b)

Pitch point

Line of

action

Clearance

Base circle dia (D )

b

Pressure

angle, ( )f

Addendum circle dia (D )

a

Pitch circle dia (D)

Dedendum circle

dia (D )

d

Face

Flank

Fig.13.5 Gear nomenclature