Tapping 101: Spiral Flute vs. Spiral Pointed Taps

Let’s talk Spirals – not the ones quarterbacks throw for touchdowns or the swirling stream down your kitchen sink, but spirals when it comes to tapping. 

The most common use of the term “spiral” is either when describing the flute configuration or the point geometry of the tap.

It is important not to confuse the two.

Spiral flutes are commonly used in blind holes and when threads are required close to the bottom of the hole.  They are available in many different helix options, which are chosen depending on the type of material being tapped.

A basic rule of thumb is ‘the softer and stringier the material, the higher the helix angle.’  The high helix brings the stringy chip up and out of the hole for easy disposal.  Harder materials require slower (lower) angles because these materials tend to break or crumble if curled too tightly.  This could cause problems since crumbled chips will fall back into the hole and either tear threads on reversal or break the tap.  Using this same reasoning, you should rarely – if ever – use spiral flutes of any kind in materials with fine or powdery chips, i.e. free machining brass, cast iron, etc.

Spiral pointed taps, on the other hand, are not even closely related since they produce an effect quite the opposite from spiral flutes. 

Spiral point taps, also known as “gun taps” because they “shoot” chips forward (clever, huh?), are very effective at clearing chips ahead of the cutting edge of the tap and pushing them out the other end of the hole.  This is especially effective for deep hole tapping.  The hole being tapped should be a thru hole, or have plenty of clearance to allow for chip collection.  

Spiral point taps are also very popular because of their versatility.  They work well in many types of materials due to the shearing action of the spiral grind, and the fact that chips exiting through the bottom of the hole virtually eliminates the issue of backing out over broken chips on reversal.

So, next time you set up that tapping application, selecting the correct spiral will help assure that your job won’t “spiral” out of control!