Mechanism Design and Mechanism Dynamics > Mechanism Design > Creating Mechanism Models > Modeling Entities > Gears > To Create a Worm Gear Pair
  
To Create a Worm Gear Pair
1. Click Gears. The Gear Pair Definition dialog box opens.
2. Under Type, select Worm.
3. Enter the following information on the Worm tab:
Select a rotational motion axis. A magenta arrow appears on the joint, indicating the positive direction for the axis. Use the right-hand rule to determine the direction of rotation.
The names of the bodies connected by the joint appear in the Body area of the tab. By default, the first body in the connection is called the Gear, the second body the Carrier. To reverse the body order, click . You can view the body order associated with a given gear in the Mechanism Tree by clicking Gears in the Connections folder, and then clicking the arrow next to the name of the gear.
Under Pitch Circle, type a value for the diameter of the pitch circle in the Diameter box.
Next to Icon location, click and select a point, a vertex, a datum plane or a surface perpendicular to the axis for the location of the pitch circle icon. The default location is at the root of the Gear1 joint.
4. Enter the following information on the Wheel tab:
Select a rotational motion axis that is perpendicular to but does not intersect the Worm axis, that is, an axis that is on a different plane. A shaded arrow appears indicating the positive rotation direction. To reverse the direction, click .
The names of the bodies connected by the joint appear in the Body area of the tab. By default, the first body in the connection is the Gear, the second is the Carrier. To reverse the body order, click .
The pitch diameter of the wheel is automatically calculated to connect with the pitch circle diameter on the Worm. The pitch circle locations are automatically calculated (through the Worm axis and perpendicular to the Wheel axis).
When you press ENTER, a spiral, representing the diameter of the pitch circle and the screw angle, is displayed. On the wheel, two circles with the calculated diameter, centred on the pitch circle location of the wheel, are displayed. These two circles are connected by smaller segments representing the helix angle. The line from the center of one circle to its circumference shows the zero reference point of the motion axis .
5. On the Properties tab, choose a Gear Ratio type from the list. If you select Pitch circle diameter (default), you can still edit the value of the diameter of the worm pitch circle on the Worm tab. If you select User defined, enter values for the number of worm spirals and the number of wheel teeth under Gear Ratio. The net gear ratio is displayed and the screw angle is automatically calculated.
6. Enter values for the Pressure angle (default = 20°) and the Screw Angle of the worm gear pair. The screw angle is applied to the worm gear, and the corresponding helix angle on the wheel is automatically set to match the spiral angle on the worm. If you selected a User defined gear ratio, the screw angle is automatically calculated.
 
* A positive screw angle indicates that the spiral is right-handed.