A hand tap is a device which is used to cut threads in material, normally hand taps are used for cutting threads in metal but frequently they are used to cut threads in nylon and other non-metallic materials used in industry. The objective of tapping a hole is so that a threaded fastener; a bolt for example can be threaded into the hole. There are two basic types of hand taps, they both perform the same job but they have different reasons to be used.
If the objective is to cut threads completely through the material, a tapered tap is usually used. This tap starts at a rather small diameter point and gradually increases in diameter until it reaches its specified diameter. As the tap turns, it slowly begins to cut a thread into the material. As the tap continues to progress, it eventually emerges out the other side of the pre-drilled hole, the entire hole is now threaded.
In the event the hole is to be tapped blind, the tap does not start at a point, it starts at the correct diameter and thread form. This type of tap will allow the operator to tap threads to the bottom of a blind hole. Using a tap in a blind hole takes more skill and caution as the cuttings fall into the hole and must be blown clean as the work is done.
Hand taps are held in a tool which is like the letter “T”. The tap is fixed into the jaws of the tool and then slowly turned to cut the thread. It does take considerable skill as the tap must enter the hole perfectly straight. To ensure that the tap does not break, the operation is done with cutting oil which aids in breaking the chip loose and maintaining a cool temperature.
The difficulty with a hand tap is the degree of accuracy that the machinist must be capable of. As the tap is withdrawn as the hole is threaded which expels the cuttings, the tap must go back exactly otherwise the thread form will be ruined. A hand tap is only used for one-off threading, for volume parts a machine is used to tap the predrilled holes.
For a complete range of hand taps in different diameters and thread forms you are invited to visit the online store of Drills n Supplies.