Is tapping with problem?


The tap is a tool for processing various medium and small internal threads. It is simple in structure and easy to use. It can be operated manually or on a machine tool. It is widely used in production. Can you tap the wire during the processing? Share some tips for you today and let you know more about tapping!


What is tapping?

Tapping is the use of taps to cut internal threads inside the bore of the workpiece.


(1) Factors determining the performance of the tap include:

  • Workpiece material
  • Cutting speed
  • Cutting edge material
  • Shank
  • Taper
  • Hole size
  • Tapping handle
  • Cutting fluid
  • Hole depth


(2) Pitch: The axial distance between two points on the middle diameter line of the two adjacent teeth on the thread.


(3) Lead: the axial distance of the corresponding points of two adjacent teeth on the same spiral line. Expressed by the code S.


(4) Nominal diameter of the thread: except for the pipe thread whose inner diameter (in units) of the pipe is the nominal diameter, the nominal diameter of the other threads is the nominal diameter of the thread (metric unit).


(5) Thread diameter: The medium diameter is the most important because it controls the fit and strength of all thread assemblies. The median diameter is on the pitch line, and the tooth width at this position is consistent with the adjacent cogging width.



Thread name


Inch thread: Inch thread is threaded in English and is developed by the United States, the United Kingdom and Canada according to a unified system.


Metric Thread: Developed according to the ISO (International Organization for Standardization) system, is the standard for global metric thread.


Design high performance tapping


(1) perfect application


The factors to be considered in the tapping process are: workpiece design, tap design, and application. The goal is to reduce the cutting force while maximizing the tap strength.


(2) Balance various options: Must consider all aspects of the application


(3) tap design points

1) For softer viscous materials that form long chips

  • Simple tap structure
  • Large front angle and hook angle
  • Back angle and avoidance
  • Free cutting
  • Easy to chip
  • The tap is generally weak
  • Large space


2) For hard materials

  • Tap has a heavy-duty structure
  • Front angle and hook angle are small
  • Small back and back angle
  • High cutting pressure
  • The blade design is thick and strong, reducing the chipping
  • Large cross section
  • Limited chip space


(4) Factors to be considered in tap design: tap groove type, tool material, surface strengthening treatment. These design features must be balanced to provide proper cutting, chip control, lubrication and torsional strength.


The hole must be stopped and reversed during the cutting, and the cutting remains in the groove. This poses the greatest challenge to the design of tapping and taps in metalworking.



Tap shape


(1) Type of tap cutting surface

1 correct choice of tap forward hook tap

2 Correct choice of taps or negative hook angle taps


(2) tap cutting cone

For each additional cutting bevel, the life of the tap is exponentially extended. Tests have shown that the tool life is doubled for every half of the cutting thread. Unlike other tools, the tap load can only change with the number of flutes and the length of the cutting cone.


(3) Inverted cone: Similar to all other tools, the tap also has a slight inverted cone.


(4) Thread back


The advantages of threaded shovel back are:

  • Light cutting and less heat accumulation
  • Winding on the tap, less bonding material (sticky, less built-up)
  • Higher tapping speed
  • Compensating the plastic deformation of the workpiece material


The disadvantages of threaded backs are:

  • The cutting edge becomes brittle and easy to chip
  • Insufficient rigidity of the spindle and the clamping (including the floating shank) will cause the thread to deteriorate.
  • Very fine chips may be embedded during the inversion to chip the cutting edge


(5) Tap tolerance

Each tap has a dedicated median size.

Taps marked with H or D tolerances (mainly American taps)

  • The H/D tolerance represents the thread size of the tap.
  • The letter indicates that the tap size is greater or higher than the basic median diameter ("H" = imperial, "D" = metric), or below the basic median diameter ("L" = imperial, "DU" = metric).
  • The actual tap size number is related to the basic mid-diameter, such as: H2, D3, L1, or DU2. Each tap has a dedicated medium diameter size!


Taps are often marked with thread grade

  • Universal HP Tap Series
  • Indicate that the tap is the correct size for the fit level of the part
  • Class 3B taps for Class 2B components
  • Tap grades marked with “X” indicate large tolerances for precision taps, plated or heat treated parts, or materials for proximity (elastic memory).


Electroplated tapping thread

  • For internal threads, you must select a tap with a larger tolerance class
  • Larger diameter will make the thread size slightly larger
  • The increase after plating will cause the thread size to return to the specified value.