Rotary punch

In a pipe perforating apparatus of the type comprising a spindle having an axis of rotation and a substantially cylindrical base surface concentric with the axis, a cutting tool mounted on the spindle and projecting from the base surface, and drive means for rotating the spindle about its axis of rotation and simultaneously revolving the spindle about the pipe whereby the cutting tool periodically engages and perforates the pipe, the improvement wherein:

• the cutting tool is a punch with a piercing end adapted to punch an aperture in the pipe, substantially radially thereof;
• the punch is mounted on the spindle with the piercing end facing radially away from the spindle axis and spaced from the base surface a distance only slightly greater than the thickness of a pipe to be perforated;
• the drive means is constructed to rotate the spindle about its axis and revolve the spindle about the pipe while maintaining the relationship;
• W1/W2=A/B
• where
• W1 is the angular speed of rotation of the spindle about its axis,
• W2 is the angular speed of revolution of the spindle about the pipe,
• A is the outside radius of the pipe where it contacts the base surface of the spindle and
• B is the radius of the base surface of the spindle;
• whereby each point on the base surface of the spindle travels about the pipe in an epicycloid and the punch is driven into and drawn out of the pipe substantially radially, substantially without tangential movement relative to the pipe.