S O M T A P 1 2 C A T A L O G U E
185
THREADING
TOOLS
Tap Terminology
MAIN TYPES OF TAPS
HAND TAPS
(SHORT MACHINE)
This regular type is the basic tap designed as a general purpose tool for hand and machine operation.
As this basic tap will give acceptable performance in most materials and for short production runs, it is usually the most
economical tap to use. However, it performs best in materials where the cutting action results in chips which break up
readily and do not present problems of chip disposal.
The regular hand tap has four flutes in sizes larger than 1/4 inch diameter. These taps may not be suitable because of
inadequate chip space when deep or blind holes have to be tapped in soft stringy materials. This applies particularly to
the coarser pitch threads such as BSW and UNC.
If a gun tap or spiral fluted tap cannot be used, a three fluted tap which permits extra chip space, is recommended.
PIPE TAPS
Pipe taps are supplied with PARALLEL threads or with TAPER threads.
These taps are shorter than a similar size of regular hand tap, but the design features are the same. They are suitable
for hand or machine use.
GUN NOSE TAPS.
(SPIRAL POINT) FOR MACHINE USE ONLY
Gun nose taps have straight flutes supplemented by angular cutting faces at the point. These faces cut with a shearing
action which propels the chips ahead of the tap leaving the flutes clear for the free flow of coolant to the point.
Primarily designed for use in through holes, these taps can be used in blind holes providing that there is ample clearance
beyond the threaded section to accomodate the chips. The advantages of a gun nose tap are, the shearing action of the
angular cutting faces which produce a fine finish on the threads and, shallower flutes which permit a stronger cross
section throughout the tap.
SPIRAL FLUTE TAPS.
FOR MACHINE USE ONLY
These taps are designed primarliy for machine tapping of blind holes, are used to the best advantage in materials which
produce long stringy chips. The shearing action provided by the spiral flutes produces a better finish on difficult to
machine metals and causes the chips to be drawn back, eliminating clogging at the cutting chamfer.
SERIAL TAPS
Serial taps comprise of one or more undersized roughing taps which remove most of the material before final sizing with
a finishing tap.
Some reasons for using serial taps are:
(a)
The toughness of the material being tapped.
(b)
The amount of material to be removed could cause swarf choking with a single tap.
(c)
The very small tolerance on pitch diameter.
(d)
An extremely good finish required.
FLUTELESS (ROLL) TAPS
(Fluteless Chipless Tapping)
These taps are designed for machine tapping in ductile materials, “Fluteless” taps have no flutes or cutting faces, but
have special roll forming lobes with circular lands and have long or short taper leads for through or blind holes.
