Learn basic knowledge about taps

2025-09-01 15:36:10

A tap is a tool used for machining internal threads in holes, widely applied in fields such as mechanical manufacturing, automotive, aerospace, and electronic equipment. By means of cutting or extrusion, taps form threads in pre-drilled holes, facilitating their use with external threaded parts like bolts and screws. There is a wide variety of taps, and different types can be selected according to varying processing needs, materials, and application scenarios. The following will provide a detailed introduction to taps, covering aspects such as structure, classification, usage methods, common issues, and maintenance.

1. Structure of tap

A tap is usually composed of the following parts:

Cutting portion: This is the front end of the tap, responsible for cutting material to form threads. The cutting portion is usually conical, facilitating the tap to smoothly enter the hole and commence cutting.

② Calibration section: Located after the cutting section, it is used to calibrate the size and shape of the thread, ensuring the accuracy and quality of the thread.

③ Shank: The tail end of a tap, typically cylindrical or square, used for clamping onto a tap wrench or the collet of a machine tool.

④ Chip flute: There is usually a longitudinal groove on the tap, known as the chip flute, which is used to discharge the chips generated during the cutting process and prevent chip jamming and thread damage.

II. Classification of taps

Based on different criteria, taps can be classified into various types:

① Classified by processing method:

Cutting tap: Forms threads by cutting material and is suitable for most metallic and non-metallic materials.

Extrusion tap: It forms threads by extruding material and is suitable for materials with good plasticity, such as aluminum and copper. Extrusion taps do not produce chips and produce threads of high quality.

② Classification by thread type:

Metric tap: used for machining metric threads, such as M6, M8, etc.

Inch tap: used for machining inch threads, such as 1/4-20, 3/8-16, etc.

Pipe Thread tap: used for machining pipe threads, such as NPT, BSP, etc.

③ Classified by structure:

Straight flute tap: The chip flute is straight, suitable for through-hole machining.

spiral flute tap: The chip flute is spiral-shaped, suitable for blind hole machining, and can effectively discharge chips.

Spiral point tap: It features a helical cutting edge at the front end, suitable for through-hole machining, capable of rapid cutting and chip evacuation.

④ Classification by accuracy level

General precision tap: suitable for thread machining with general precision.

High-precision tap: suitable for high-precision thread machining, such as in aerospace, precision instruments, and other fields.

III. Usage of tap

Select the appropriate tap: Choose the suitable tap based on the hardness of the processing material, thread type, hole type (through hole or blind hole), etc.

② Drilling: Before machining threads, a base hole needs to be drilled first. The diameter of the base hole should be determined based on the thread specification and the hardness of the material.

③ Holding the tap: Hold the tap on the tap wrench or the collet of the machine tool, ensuring that the tap is aligned with the center of the hole.

④ Thread cutting: Rotate the tap slowly to allow it to enter the hole and commence cutting. For manual operation, it is typically necessary to rotate clockwise by 1/2 turn, followed by a counterclockwise rotation of 1/4 turn, to break off chips and prevent the tap from seizing.

5. Lubrication: During the cutting process, using appropriate cutting fluid or lubricant can reduce friction, lower cutting temperature, and extend the service life of the tap.

6. Check the threads: After machining is completed, use a thread gauge or bolt to inspect the size and accuracy of the threads.

IV. Common problems and solutions

Tap breakage: It is usually caused by excessive cutting force, poor tap quality, or improper operation. The solutions are to choose the appropriate tap, control the cutting force, and use lubricant.

② Incomplete thread: This may be caused by an improper diameter of the base hole or worn tap. The solution is to check the diameter of the base hole and replace the worn tap.

③ Rough threads: This may be caused by too fast a cutting speed or insufficient lubrication. The solution is to reduce the cutting speed and increase lubrication.

④ Tap jamming: This is usually caused by chip blockage or misalignment between the tap and the hole. The solution is to regularly remove chips and ensure that the tap is aligned with the center of the hole.

V. Maintenance of tap

Cleaning: Clean the tap promptly after use to remove chips and dirt.

② Lubrication: Before storage, apply an appropriate amount of anti-rust oil to prevent the tap from rusting.

③ Inspection: Regularly inspect the wear condition of the tap and promptly replace any severely worn tap.

④ Storage: Store the tap in a dry and dust-free environment, avoiding collisions and squeezing.

As an important tool for thread machining, the selection and use of taps have a significant impact on thread quality and machining efficiency. Understanding the basic knowledge of taps, mastering the correct usage methods and maintenance techniques can not only improve machining efficiency but also extend the service life of taps and reduce production costs. In practical applications, appropriate tap types and machining parameters should be selected based on specific machining requirements and material characteristics to ensure the accuracy and quality of thread machining.