What Is CNC Tapping?

Posted on Dec 25, 2020

CNC Tapping

CNC Tapping is normally performed on a CNC turning center. The CNC turning center is a powered and computerized controlled machining lathe. The feeding of workpieces in this process is mostly done by the automated line or it can also be done manually by the operator or mechanist. Regardless of the method, the tapping process is always conducted on the fully automated CNC turning center.

CNC Tapping is a machining process where a thread inside a hole in a workpiece is created in order for a screw or a bolt to be threaded into the hole. Tapping is also used to make the thread on nuts. CNC stands for computer numerical control. In a CNC tapping process, the operation to create a thread in workpieces is pre-programmed and controlled by the computerized control unit so that the precision and accuracy of the process can be maintained.

CNC Tapping is normally performed on a CNC turning center or a tapping center. The CNC turning center is a powered and computerized controlled machining lathe. The feeding of workpieces in this process is mostly done by the automated line or it can also be done manually by the operator or mechanist. Regardless of the method, the tapping process is always conducted on the fully automated CNC turning center. After the thread is created, finishing treatment such as chamfering is needed.
 

Tapping Preparation

The general outline of a complete CNC tapping process is as follows: tapping tool selection, tapping tool installation, workpiece feeding, tapping, and finishing. One thing to know is that tapping can only be done in a pre-created hole; a drilling process to create the hole in the workpiece is necessary. The workpieces are only ready to take the tapping operation after the holes are drilled.

The first thing to do before tapping is to select the drill bits, the taps. To create the thread as precisely as possible, the choosing of the taps is rather crucial. There are several properties to pay attention to when choosing the tap drills: the screw size, the diameter, the threads per inch, the material, and the fit. The tapping process would not be successful with a poor selection of tapping tools.

Besides the selection of tapping tools, it is also essential to make sure the quality of the pre-drilled holes is good enough for the following operation. That is, the surface of the holes should be smooth without any imperfection or rough edges. These imperfections will for sure compromise the precision of the process. Therefore, chamfering and countersinking of the holes are sometimes required before tapping.
 

:: Read More: Automatic Drilling Tapping Machine - An Overview

Subsequent Operation of CNC Tapping

Once the preparation is done, it is time to carry out the tapping process. In a CNC tapping operation, the feeding of the workpiece is usually done by an automated feeding system. Before the operation starts, the operator should set the CNC machining center to the proper speed and make sure the tapping tool is set with the required depth. When the values and settings of the machining center are all confirmed, the operation can begin.

During the operation, the workpieces may be rotated by the turning center. It is recommended to set a relatively slow spindle speed for the operation. The speed ranges from forty to sixty rpm is better. The whole process is controlled by the computer and the system will tell when the process is done. After tapping, the thread inside the holes is created. Chamfering is hence needed to remove the rough edges of the hole.
 

Tension Compression Tap Holder

Precision and accuracy are both required in CNC tapping; a tap holder is designed to make sure of it. The tension-compression tap holder is the tap head that holds and secures the tapping tools during the tapping process. A tap holder typically relies on precise synchronization with the spindle rotation. When it does, the two parts move as one. By achieving the synchronization, the precision can be preserved and the damage to the tap can be prevented. The tension-compression tap holders not only increase axial compensation but also improve thread quality and tool life.
 

Lubrication & Pecking

When drilling the hole and creating the thread in a workpiece, lubrication should always be involved. The oil keeps the workpieces from making sharp noises. It can also make the cuts smoother. During the process, tiny chips are removed from the workpieces and the oil helps clean out the chips as well. The oil also keeps the drill and stock from overheating.

Pecking also prevents the tapping tools from overheating or breaking during the operation. It is as important as lubrication to keep the working site cool. Pecking is usually involved in a manually operated drilling process. When the drill bits or tap is backed out, pecking can help remove the chips.
 

Rigid Tapping

Rigid tapping is one of the most common methods of tapping to date when it comes to CNC tapping. The rigid tapping refers to the tap remaining rigid throughout the tapping cycle. The tap can be held in a chuck on the lathe and the machine spindle locks in with the federate. With rigid tapping, there is no need for expensive tension and compression tapping heads, and the depth of the thread can be controlled very accurately. In addition, a re-tap is allowed if the thread needs to go deeper. In the modern CNC tapping operation, rigid tapping has increasingly become standard.

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