NC machining apparatus

A machining apparatus for making the scroll parts which comprises a headstock means including a spindle for supporting a workpiece for rotation;

• a tool holding means for supporting a machining tool;
• a first carriage means supported for movement of the tool holding means in a direction perpendicular to the spindle (an X-axis);
• a second carriage means supported for movement of the tool holding means in a direction parallel to the spindle;
• and
• a control device for controlling the movement of the first carriage means and the rotation of the spindle;
• said control device being programmed so as to calculate the distance x between the center of the base circle generating a desired involute curve depicted by the scroll parts and the center of the machining tool according to the following equation (I) and also to calculate the angle of rotation C of the spindle relative to the distance x according to the following equation (II):
• ##EQU4## wherein a represents the radius of the base circle generating the involute curve, .theta. represents the involute angle, .PSI. represents the angle as measured between the X-axis and the starting point of the involute curve, and D represents the diameter of the machining tool.