10 Must-Know Points Before You Start CNC Machining Process


The CNC machining process can be very complex sometimes and the high degree of complexity may reduce the processing accuracy. So, to ensure maximum processing accuracy, below are 10 important must-know points before you start the CNC machining process.

1: Learning the Principles of Processing Sequence

Processing sequence plays an important role in determining the accuracy of the whole process. The processing sequence should be determined very carefully. The processing sequence arrangement should be selected per the structure of the part, the condition of the blank, and the requirements of positioning and clamping of the workpiece. But during the whole process, the rigidity of the workpiece should not be ruined.

While determining the processing sequence, generally the following principles must be followed.

  • The positioning and clamping of the next process should not be affected by the processing of the previous process. The general machine tool processing processes should also be contemplated.
  • First, the inner cavity processing procedure should be executed and then the contour processing procedure should be started.
  • It is most appropriate and advisable, to execute all the processes in the same positioning, clamping mode, or with the same tool.
  • If multiple processes are required to execute in the same installation, then such a process should be selected first that could cause minimum rigid damage to the blank.

2: Determing the Processing Procedure Method

After we carefully think about the processing sequence, the next step is, how to determine the most suitable processing method.

1: Tool Centralized Ordering Method

In this processing method, we divide all the processes per the tools used. First, execute those processes that require the same tool to process all the parts. Then use a second knife and a third knife to complete the remaining parts.

2: Sequential Method of Processing Parts

The sequential parts processing method is used where there are a lot of processing points on the workpiece. Based on part’s structural characteristics, the processing workpiece is divided into many sub-parts to successfully execute the process. Part’s structural characteristics may include inner shape, curved surface, or plane.

3: Sequential Method of Roughing and Finishing

If there is a slight chance of workpiece deformation after roughing a part then a correction is required here to avoid it. It is most suited that all the roughing and finishing processes must be executed separately to avoid deformation.

3: Learning Important Aspects While Determining the Workpiece Clamping Method

Workpiece positioning and clamping are very crucial in machining process accuracy. If not selected properly then the degree of deformation might be too high to scrap the workpiece.

So, before starting the positioning reference and clamping plan, the following aspects should be kept in mind.

  • Try to integrate the design, technology, and programming calculation benchmarks.
  • Try to keep the clamping points as minimum as possible and strive to process all the surfaces after one positioning.
  • Avoid using the manual adjustment scheme of the occupied machine.
  • The fixture should be opened smoothly. Its positioning and clamping mechanism should not disturb the cutting during processing (such as collision). Whenever facing this sort of situation, use a vise or add a bottom plate to draw a screw.

    4: Selecting Tool Setting Point

    The tool setting point can be set on the workpiece that we are going to process. But the tool setting point must be according to the reference position or the part that has been finished. Carefully select such a place that offers a relatively fixed size relationship with the positioning reference When setting the tool in the first process.

    Preferably select a relative tool setting position. This is because, when you are required to relocate the original tool setting point then it can be done easily from the relative position relationship between them. The relative tool setting position is generally set on the machine table or fixture.

    While selecting a tool setting point, the following principles should be followed

    • It should be easy to find.
    • It should be easy to program.
    • The tool setting error should be small.
    • It should be checked easily during processing.

    5: Choosing Adequate Processing Tools

    It is again very important to choose an adequate tool when programming to manufacture a fine quality product. The general requirements to be fulfilled while selecting a CNC tool are

    • It should be easy to install.
    • It should be easily adjustable.
    • It must offer good rigidity.
    • It must offer high precision.
    • It should be durable.

    Other than these, comprehensive consideration of the cutting performance of the workpiece material, the amount of cutting, the processing capacity of the machine tool, the type of CNC machining process, and several other factors are also considered.

    6: Understanding the Function of Processing Procedure Sheet

    A processing procedure sheet is a map or a blueprint that tells the operator about the workpiece manufacturing process in CNC. It provides the precise route or sequence to successfully execute the processing procedure. A processing procedure sheet explains the series of actions to be performed to achieve a specific machining task to achieve maximum processing accuracy.

    The purpose of the processing procedure sheet is to elucidate the operator about the content of the process. It also clarifies the clamping and positioning method. It is very important to understand the function of the processing procedure sheet very well to achieve maximum processing efficiency.

    7: Understanding the Relationship Between Machine Tool Coordinate System and Workpiece Coordinate System

    The machine tool coordinate system is used to control the stroke of the machine tool. It is used to determine the coordinates of the machined parts for the machine tool, the position of the machine’s moving parts (tool change points, reference points, etc.), and range of motion (such as travel range, protection zone, etc.). The machine tool coordinates are the coordinates set by the machine tool itself.

    The origin of the machine tool coordinate system is called the machine origin or the machine zero points. It is a fixed point on the machine tool and also the reference point of the workpiece coordinate system and the machine tool reference point.

    A workpiece coordinate system is a coordinate system that is used by the programmer when they compiled part processing programs. It can be determined by the part drawing and used to determine geometric elements (such as points, straight lines, and arcs on the workpiece geometry).

    The origin of the workpiece coordinate system is called the workpiece origin or workpiece zero. It can be set and changed by program instructions. According to programming needs, the workpiece origin can be set or changed one or more times in the processing program of a part.

    To get the offset value of workpiece origin, after installing the workpiece on the machine with the fixture, just measure the distance between the origin of the workpiece and the origin of the machine. After calculating the workpiece origin offset value, just feed this value to the CNC system before starting the process. This value can automatically be added to the workpiece coordinate system during the processing. In this way, the CNC machine executes the processing according to the workpiece coordinate system value that is determined by the machine tool coordinate system.

    8: Learning the Important Factors While Determining the Knife Path

    A computer numerical control knife is a high-precision CNC digital cutting machine that is equipped with varied knife tools and blades such as an oscillating knife, tangential knife, drag knife, and router bits. This sturdy cutting tool is designed with greater adaptability and it offers high-precision cutting of heavier, flexible, and semi-rigid materials. It can be connected with other software well with the help of data converting software.

    Below are given some important factors that will help in knife path determination.

    • Fulfill the machining accuracy requirements of the parts.
    • Make easy and systematic numerical calculations and reduce programming workload.
    • Improve the processing efficiency by selecting the shortest processing route and reducing the empty tool time.
    • Minimize the number of blocks.
    • Make sure the roughness requirements of the workpiece contour surface after processing and the final contour should be processed continuously in the last phase.
    • To minimize the knife’s mark left when stopping the tool at the contour, the path of the tool’s advance and retreat (cut-in and cut-out) should also be carefully considered.

    9: Understanding Major Elements of Cutting Tool Usage

    There are mainly three elements to be considered while executing the tool cutting process i.e., depth of cut, spindle speed, and feed rate. The general rule while selecting these tool cutting parameters is that less cutting and fast feed. This means that the depth of cutting should be smaller and the feed rate should be faster.

    10: DNC Communication

    When we talk about the program delivery, it can be divided into CNC and DNC. CNC means Computer Numeric Control. In the CNC program delivery technique, the program is delivered to the memory of the machine tool through media for storage such as floppy disk, tape reader, communication line, etc. During the processing, the program is called from the memory.

    DNC stands for direct numerical control. In this method, the machine tool directly reads the program from the control computer during DNC processing.

    CNC program delivery technique has a huge drawback when passing a large program because the memory capacity is limited by the size.


    If you want to work well with CNC Machining, please read carefully above 10 points and leave us comment if anything not clear. and if anything ready to fabricate, please feel free to quote here. and we always reply within 12hours upon your email. thanks in advance!

      Cora Feng
      Cora Feng

      Project Manager working on CNC Machining since 2010

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