Taps and dies are tools used to create screw threads, which is called threading. Many are cutting tools; others are forming tools. A tap is used to cut or form the female portion of the mating pair (e.g., a nut). A die is used to cut or form the male portion of the mating pair (e.g., a bolt). The process of cutting or forming threads using a tap is called tapping, whereas the process using a die is called threading. Both tools can be used to clean up a thread, which is called chasing.
A tap cuts a thread on the inside surface of a hole, creating a female surface which functions like a nut.
Tapping may either be achieved by hand tapping by using a set of taps first tap, second tap & final (finish) tap or using a machine to do the tapping, such as a lathe, radial drilling machine, bench type drill machine, pillar type drill machine, vertical milling machines, HMCs, VMCs. Machine tapping is faster, and generally more accurate because human error is eliminated. Final tapping is achieved with single tap.
Although in general machine tapping is more accurate, tapping operations have traditionally been very tricky to execute due to frequent tap breakage and inconsistent quality of tapping.
Common reasons for tap breakage are:
Wearing of tap cannot be easily quantified (use of worn-out taps)
Use of tap with improper tap geometry for a particular application.
Use of non-standard or inferior quality taps.
Clogging with chips.
Misalignment between tap and hole.
Over- or under-feeding the tap, causing breakage in tension or compression.
Use of improper and/or insufficient cutting lubricant.
Absence of a torque limiting feature.
Improper or zero float for use with screw machines (recommended feed .1 slower to establish float for 40 tpi or higher and .15 slower for 40 tpi or finer)
Improper spindle speed.
In order to overcome these problems, special tool holders are required to minimize the chances of tap breakage during tapping. These are usually classified as conventional tool holders and CNC tool holders.
Threading is the process of creating a screw thread. More screw threads are produced each year than any other machine element. There are many methods of generating threads, including subtractive methods (many kinds of thread cutting and grinding, as detailed below); deformative or transformative methods (rolling and forming; molding and casting); additive methods (such as 3D printing); or combinations thereof.