It is known that the parameter of an external cylindrical helical gear is Mn = 5, α n= 20 °， Z= 20， β = thirty °，χ N = 1.2, h * an = 1, c * n = 0.25. According to the formula: α t=22. 7959 °， mt= 5． 7735， χ t= 1． 0392，db= 106． 4507，hat= 0． 866、ct= 0． 2165。
Open CAXA program and click “gear” in “advanced drawing” box of “common” toolbar.
Input the tooth profile parameters in the dialog box of involute gear profile parameters. The basic parameters in the figure are the end face parameters of helical gear, and select parameter one to fill in the parameters.
In order to obtain the proper measuring ball diameter DP of helical gear by graphic method, the base circle dB and the cylindrical surface passing through the contact point between steel ball and involute surface of tooth profile are drawn in Fig. 1, and the diameter is DZ (see Fig. 2).
Click the “circle” command in the “basic drawing” toolbar to draw the base circle. The base circle diameter DB can be calculated from the formula. In example 1, the calculated value of DB is Φ 106． 4507; The diameter of the cylinder passing through the contact point between the steel ball and the involute surface of the tooth profile is DZ. Drawing method: click the gear center point o as the center of the circle, move the mouse pointer to any tooth profile involute, when the object capture point is marked as “Midpoint”, click to draw a circle, and mark the diameter DZ as “dimension” by “dimension” command Φ 127． 8505。