Choosing the correct Tap
There are several types of taps in general use. It’s important to use the style of tap that is
appropriate to the job at hand.
Straight Flute “Hand” Taps
Straight flute taps are generally called hand taps because, well, that is the way they are
generally used. The straight flutes, while providing room for chips, do not move the chips one way or the other. In materials that produce stringy chips, such as steel, aluminum, and brass, they must be frequently reversed to break the chips, so they do not jam the tap and cause it to break. Straight flute taps may be appropriate when cutting short chipping material such as cast iron. A straight flute tap can be used in through or blind holes. Straight flute taps are not generally used for machine tapping.
Spiral Point Taps
Spiral point taps are generally used for through holes. They have a very short spiral on the
cutting face of the first few threads. This “shoots” the chips out the bottom of the hole, thus they are sometimes called “gun taps.” Because spiral point taps do not have to be reversed, and because the shallower flute passages provide a greater cross section to the tap, they are favored for machine tapping of through holes with all materials.
Spiral Flute Taps
The flutes on spiral flute taps are, as you might surmise, formed in a spiral around the tap.
The spiral flutes evacuate the chips up and out of the hole. Because they are best for blind
holes, they are usually found in “bottom” configuration. Spiral flute taps are used for
machine tapping of blind holes. Spiral flute taps are not appropriate for materials with fine or powdery chips, such as free machining brass and cast iron.
