# Creation method of spur gear

Gear transmission is one of the most important mechanical transmission. Gear parts have the advantages of high transmission efficiency, stable transmission ratio and compact structure. Therefore, gear parts are widely used, and the structural forms of gear parts are also various. According to the different generation lines of tooth profiles, gears can be divided into involute gears and circular arc gears. According to the different structure of gears, gears can be divided into spur gears, helical gears and bevel gears. This chapter will introduce the design process of creating standard spur gear, helical gear, bevel gear, circular arc gear and worm gear with Pro / E in detail.

##### 1.geometric analysis of involute

Figure 1 Geometric Analysis of involute

Involute is a curve formed by the rotation of a line segment around the gear base circle. The geometric analysis of the involute is shown in Figure 3-1. When segment s rotates around the arc, one of the tracks marked by one end point a is the involute. The coordinates of the midpoint (x1, Y1) in the figure are: X1 = R * cos (ANG), Y1 = R * sin (ANG). (where R is the radius of the circle and ang is the angle shown in the figure)

For the Pro / E relation, there is a variable t in the system, which varies from 0 to 1. Therefore, the coordinates of (x, y) can be established by (x1, Y1), that is, the involute equation.

Ang=t*90

S= (PIrt) /2

x1=r*cos(ang)

y1=r*sin(ang)

x=x1+(s*sin(ang))

y=y1-(s*cos(ang))

Z=0

The above is the involute equation defined on the X Y plane. You can define the equation on other planes by modifying the coordinate relations of X, y, Z, which will not be repeated here. 