# Force analysis of helical gear

The figure shows a pair of helical cylindrical gears. If the friction between tooth surfaces is omitted, the normal force acting on the nodes can be divided into three components: circumferential force, radial force and axial force.

#### 1.Magnitude of each force

αn is the pressure angle of the normal indexing circle;

αt is the pressure angle of the end indexing circle;

β is the helix angle of graduation circle;

βb is the base circle helix angle.

#### 2.Direction of forces

Circumferential force: the driving wheel is opposite to the steering wheel, and the driven wheel is the same as the steering wheel;

Radial force: points to the wheel center respectively;

Axial force: the axial force of the driving wheel is judged by the “rule of left and right hands”: when the driving wheel rotates to the right, the bending direction of the four fingers of the right hand is used to indicate the rotation direction of the driving wheel, and the direction of the thumb is the direction of the axial force; when the driving wheel rotates to the left, the left hand is used to judge, the method is the same as above.

#### 3.Correspondence

The corresponding stresses on the main and driven wheels are equal in magnitude and opposite in direction. 