Forms of Teeth

There are mainly two forms of gear teeth:

1. Cycloidal profile teeth
2. Involute profile teeth

Forms of Teeth

There are mainly two forms of gear teeth:

1. Cycloidal profile teeth
2. Involute profile teeth

Cycloidal Profile Teeth

A cycloid is the locus of points on the circumference of a circle that rolls without slipping on a fixed straight line. An epicycloid is the locus of points on the circumference of a circle that rolls without slipping outside the circumference of another circle. A hypocycloid is the locus of points on the circumference of a circle that rolls without slipping inside the circumference of another circle. The construction of cyloidal teeth is shown in Figure 15.16.

Figure 15.16 Cycloidal Profile of Gear Teeth

Advantages of Cycloidal Gears

• Due to wider flank, cycloidal gear is stronger than involute gear for the same pitch.
• Less wear occurs in cycloidal teeth.
• There is no phenomenon of interference.

Involute Profile Tooth

An involutes profile is a plane curve generated by the points on tangent on a circle which rolls without slipping or by points on a tight string which is unwrapped from a reel as shown in Figure 15.17.

Advantages of Involute Gears

• Centre distance can be varied within limit without change in pressure angle which is not possible in cycloidal gears.
• Pressure angle remains constant throughout the engagement but in the case of cycloidal gears, pressure angle is maximum at the beginning and end of engagement and minimum at the pitch point.
• The face and flank of involute teeth are generated by a single curve where in cycloidal gears, epicycloids and hypo-cycloid are required for face and flank, respectively. Thus, involute teeth are easy to manufacture than the cycloidal gear.

Figure 15.17 Involute Profile of Gear