TABLE OF CONTENTS Tapping operation on conventional mills, lathes, and CNC machines has been one of the basic operations to machine holes. To this day, with all its disadvantages, one of the most common methods of tapping uses special tapping heads, known as the push-pull type in the shop, or tension-compression type more formally. Another term for this type of tool is a floating tap holder.
In a typical tension-compression tap holder, the tap is held firmly so it cannot fall out, but loose at the same time to provide axial flexibility upon entering a drilled hole. Thread in the hole is formed by the size and shape of the tap. Although still very popular, floating tap holders present one major problem they make it difficult to maintain precise thread depth, particularly in blind holes.
The main principle of standard tapping is the synchronization of spindle speed and tapping feedrate. That is achieved by multiplying the spindle speed (r/min) by the tap lead (pitch) resulting in a feedrate in inches or millimeters per minute. At the beginning of the cut, the tap has to accelerate from zero feedrate to a rather heavy feedrate. The time required to reach the programmed feedrate is called ac celeration. In order to reach the programmed feedrate before any contact with the material, the tap must start further away from the hole this is the R-level in fixed cycles. As the tap enters the hole, it encounters a resistence, and...
