A question was recently asked,” If Spiral-flute taps will work in both blind and through holes, why do I need a Spiral-point?” Sounds a bit like the lyrics to a sad Country song.
The answer to the question lies in the details of the application. Technically, all flute configurations will make threads in both “through” and “blind” holes. The decision on which is appropriate is based on producing desired chip flow. Chip evacuation is an issue that contributes heavily to the success, or failure of a tap. Also remember that flutes accommodate the volume of coolant or lubricant applied, not just the material chips created in the process. It can get crowded in there!
Straight-flute taps, frequently described as “Hand-taps”, provide room for the material chips in the flutes. But, they do not offer any directional assistance to chip evacuation. Chip flow is determined either by gravity, or direction and pressure of the coolant/lubricant flow. These taps are usually fine for general-purpose use. Their straight flutes also facilitate the alteration of the cutting edge geometry to suit the material being tapped.
Spiral-fluted taps “pull” chips out of the hole. This is especially useful when tapping a “blind” hole, but this flute geometry would have the same effect in a “through” hole. Spiral-flutes can actually cause chip flow in both directions, depending on the direction of tool rotation. Visualize the propeller on a boat motor. The pitch of the prop doesn’t change, while the direction of force changes with the direction of rotation. Forward and reverse are accomplished with the same prop.
Spiral-pointed taps move chips in one direction, forward. They are ideal for through holes. Spiral-point, also known as “gun” taps, are free cutting. They are not tasked with flutes that are filled with chips.
As the geometry of both spiral-fluted and spiral-pointed taps create a hooked cutting face, they are not appropriate for materials like Cast Iron, Brass, Bronze, and glass-filled or thermosetting Plastics.
All things considered, the straight-flute hand tap may be the most versatile. Cutting edge geometry can be modified in manufacturing to suit the application, and chip evacuation can be aided by directed coolant flow, or the addition of coolant-thru capabilities.
Each design has practical advantages. Let the conditions of the application influence your first choice, and adapt as necessary from there. Need more help? Feel free to contact our knowledgeable customer service department at 800-872-8277 for a second opinion.