This reference illustrates the technical terms used to describe tap geometry, including blank designs, thread dimensions, flute and relief configurations, and cutting angles. The diagrams show three standard blank designs with labeled dimensions and detailed views of thread profiles, relief types, hook angles, and rake angles.
What are the three blank designs for taps?
Taps are manufactured in three standard blank configurations that differ in their shank and neck features.
Blank Design 1: A straight shank design with external centers, thread length (l), overall length (L), driving square length (l₂), and an optional truncated center.
Blank Design 2 (with optional neck): Features external centers, thread length (l), neck length (l₁), neck diameter (d₂), shank length (l₄), overall length (L), and driving square length (l₂).
Blank Design 2 (without optional neck): Similar to the necked version but without the reduced neck diameter section, showing thread length (l), shank length (l₄), overall length (L), and driving square length (l₂).
Blank Design 3: Features internal centers at both ends, point diameter (d₃), chamfer length (l₅), thread length (l), shank length (l₄), driving square length (l₂), shank diameter (d₁), size of square across flats, chamfer angle (90°), and thread lead angle.
What are the key dimensional terms for taps?
The following dimensions define the geometry of a tap:
- Land width: The width of the land between flutes at the tap’s outer diameter.
- Core diameter: The diameter of the tap body measured at the root of the flutes.
- Flute: The longitudinal channel that provides cutting edges and chip clearance.
- Overall length (L): The total length of the tap from end to end.
- Thread length (l): The length of the threaded portion, excluding the chamfer.
- Neck length (l₁): The length of the reduced diameter section between thread and shank (when present).
- Neck diameter (d₂): The diameter of the neck section (when present).
- Shank length (l₄): The length of the unthreaded shank portion.
- Shank diameter (d₁): The diameter of the shank.
- Driving square length (l₂): The length of the square drive section.
- Point diameter (d₃): The diameter at the tap point (Blank Design 3).
- Chamfer length (l₅): The length of the tapered lead-in section.
- Size of square across flats: The dimension across the flats of the square drive.
- Truncated center: An optional flat at the center of the tap end (Blank Design 1).
- External centers: Center holes at the tap ends for mounting during manufacture.
- Internal centers (both ends): Internal center holes at both ends (Blank Design 3).
What thread profile terms apply to taps?
The thread profile of a tap is defined by the following terms, illustrated in relation to the basic thread form:
- Pitch: The distance from a point on one thread to the corresponding point on the next thread.
- Tap crest: The top surface of the tap thread.
- Basic crest: The theoretical crest dimension of the basic thread form.
- Angle of thread: The included angle between the thread flanks.
- Flank: The side surface of the thread connecting crest and root.
- Basic height of thread: The radial distance from the basic minor diameter to the basic major diameter.
- Max tap major dia: The maximum allowable major diameter of the tap thread.
- Basic major dia: The theoretical major diameter of the basic thread form.
- Min tap major dia: The minimum allowable major diameter of the tap thread.
- Basic pitch dia (d): The theoretical pitch diameter where thread width equals space width.
- Base of thread: The bottom section of the thread profile.
- Basic root: The theoretical root dimension of the basic thread form.
- Basic minor dia: The theoretical minor diameter of the basic thread form.
What are the types of relief on tap threads?
Relief refers to the clearance ground behind the cutting edge to prevent rubbing. Three relief configurations are shown:
Concentric: The cutting face, cutting edge, and heel are all concentric with no relief ground behind the cutting edge.
Eccentric relief: The thread is relieved to the cutting edge, with the heel eccentric to provide clearance.
Con-eccentric relief: A combination design with a concentric margin behind the cutting edge and eccentric relief beyond the margin.
What is hook angle on a tap?
Hook angle describes the orientation of the cutting face relative to a radial line through the cutting edge. Three configurations are illustrated:
Negative hook: The cutting face is angled backward from the radial line, creating a stronger but less aggressive cutting edge.
0° hook: The cutting face is aligned radially, perpendicular to the direction of rotation.
Positive hook: The cutting face is angled forward from the radial line, creating a more aggressive cutting action.
The diagrams show tap major dia and basic minor dia as reference dimensions for hook angle measurement.
What is rake angle on a tap?
Rake angle describes the axial orientation of the cutting edge. Three configurations are illustrated:
Negative rake: The cutting edge is angled backward in the axial direction.
Radial rake: The cutting edge is oriented perpendicular to the tap axis (0° rake).
Positive rake: The cutting edge is angled forward in the axial direction, providing a shearing cut.
Source and updates
Source: taylortool.com engineering data.