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Processing Size Problem of CNC Milling Machine (2)

5. The arc processing effect is not ideal, and the size is not in place

cause of issue

1) The overlapping of vibration frequencies causes resonance.

2) Processing technology.

3) The parameter setting is unreasonable, and the feed rate is too large, which makes the arc processing out of step.

4) Looseness caused by large screw clearance or loss of step caused by too tight screw.

5) Timing belt wear.


1) Find out the parts that produce resonance and change their frequency to avoid resonance.

2) Consider the processing technology of the workpiece material, and formulate the program reasonably.

3) For stepper motors, the processing rate F cannot be set too large.

4) Whether the machine tool is firmly installed and placed smoothly, whether the carriage is too tight after wear, the gap increases or the tool rest is loose, etc.

5) Replace the timing belt.

6. In mass production, occasionally the workpiece is out of tolerance

1) Occasionally there is a change in the size of a piece in mass production, and then it is processed without modifying any parameters, but it returns to normal.

2) Occasionally, in mass production, a piece of size is inaccurate, and then the size is still unqualified after continuing to process, but it is accurate after re-setting the tool.


1) The tooling fixture must be carefully checked, and the operator’s operation method and the reliability of the clamping must be considered; due to the dimensional changes caused by the clamping, the tooling must be improved so that workers try to avoid misjudgment due to human negligence.

2) The numerical control system may automatically generate interference pulses after being fluctuated by external power supply or interfered, which will be transmitted to the driver, causing the driver to accept excess pulses to drive the motor to move more or less; understand the law and try to adopt some anti-interference measures. Such as: strong electric cables with strong electric field interference are isolated from signal lines of weak electric signals, adding anti-interference absorbing capacitors and using shielded lines to isolate. In addition, check whether the ground wire is firmly connected, the ground contact is as close as possible, and take all anti-interference measures to avoid system interference.

7. Each process of the workpiece has the phenomenon of increasing or decreasing

cause of issue

1) Programming error.

2) The system parameter setting is unreasonable.

3) Improper configuration settings.

4) The mechanical transmission components have regular and periodic changes and failures.


1) Check whether the instructions used in the program are executed according to the required trajectory specified in the manual. You can judge by typing the dial indicator. Position the dial indicator at the starting point of the program and let the carriage return to the starting position after the program ends, and repeat the execution a few times. Observe the results over and over and grasp the rules.

2) Check whether the system parameters are set reasonably or have been changed artificially.

3) Whether the calculation of the relevant machine tool configuration on the coupling parameters of the connection calculation meets the requirements, and whether the pulse equivalent is accurate.

4) Check whether the transmission part of the machine tool is damaged, whether the gear coupling is uniform, and whether there are periodic and regular failures. If so, check its critical parts and exclude them.

8. The size of the workpiece is only a few wires away from the actual size

cause of issue

1) The machine tool is rubbed and worn in the long-term use, and the clearance of the screw increases with the increase of the backlash of the screw of the machine tool, which makes the size of the machining process floating, so the error of the workpiece always changes within the range of this gap.

2) The tool used for machining the workpiece is not selected properly, is easily damaged, and the tool clamping is incorrect or not tight.

3) In terms of technology, select a reasonable spindle speed, cutting feed rate and cutting amount according to the workpiece material.

4) It is related to the balance and stability of the machine tool placement.

5) The CNC system is out of step or the power is not enough when the drive is selected, and the torque is small.

6) Whether the tool holder is locked after changing the tool.

7) Whether the main shaft has the phenomenon of beating and tandem and poor coaxiality of the tailstock.

8) In some special processing occasions, the backlash cannot be filled, resulting in deviations in processing.

Solution (contrast with above)

1) After the machine tool wears the lead screw gap becomes larger, reduce the gap by adjusting the lead screw nut and the line of the trimmed carriage, or obtain the gap value (generally the gap is within 0.15 mm) by printing the dial gauge, which can be added to the computer. The gap is replaced by the computer’s gap compensation function to make the workpiece size meet the requirements.

2) Since it is the material of the tool that changes the size of the workpiece to be processed, the tool should be selected reasonably according to the requirements, and the tool angle and fixture should be reasonably selected according to the process requirements of the workpiece if the tool is not properly clamped.

3) When it is suspected that it is a process problem in processing, according to the nature of the material, reasonably prepare the processing technology to select the appropriate spindle speed, cutting feed rate and cutting amount.

4) Due to the resonance of the machine tool, place the machine tool stably, adjust the level, lay down the foundation if necessary, and install it stably.

5) For the dimensional changes generated by the numerical control system, first determine whether the program is prepared according to the drawing size requirements, and then check whether the set parameters are reasonable according to the selected configuration (such as: G0 rapid positioning speed and acceleration and deceleration time constants during cutting, etc.). Whether someone has deliberately changed it, and secondly, consider whether the power of the selected driver is reasonable, and observe whether the pulse sent by the computer to the driver is out of step by judging the phase light.

6) Check whether the reversal time of the tool holder is enough after changing the tool, whether the tool holder has enough time to be locked, and check whether the positioning of the tool holder and the locking screw are loose.

7) Check the coaxiality of the main shaft and tailstock for jumping, stringing and other phenomena.

8) Use programming skills to eliminate gaps.

9. The dimensional changes caused by the system are unstable

cause of issue

1) The system parameter setting is unreasonable.

2) The working voltage is unstable.

3) The system suffers from external interference, which causes the system to lose synchronization.

4) Capacitors have been added, but the impedance between the system and the driver does not match, resulting in loss of useful signals.

5) The signal transmission between the system and the driver is incorrect.

6) System damage or internal failure.

Solution (contrast with above)

1) Whether the fast speed, the acceleration time is too large, the spindle speed and the cutting speed are reasonable, and whether the system performance changes due to the operator’s parameter modification.

2) Install voltage stabilizer equipment.

3) Make sure that the ground wire is connected reliably, and add anti-interference absorbing capacitors at the pulse output contacts of the driver; under normal circumstances, the interference of the inverter is relatively large, please judge it under load, because the larger the load, the The greater the load current of the inverter, the greater the interference.

4) Select the appropriate capacitor type.

5) Check whether the signal connection line between the system and the driver is shielded, whether the connection is reliable, and whether the system pulse signal is lost or increased.

6) Send it to the factory for repair or replacement of the motherboard.

10. The machining dimension is unstable due to mechanical aspects

cause of issue

1) Whether the damping sheet of the stepping motor is too tight or too loose.

2) Water entering the motor plug causes the insulation performance to decline and the motor to be damaged.

3) The size of the workpiece processed is improperly clamped.

4) The workpiece appears elliptical.

5) The reverse clearance of the screw is too large.

6) The mechanical screw is installed too tightly.

Solution (contrast with above)

1) Adjust the damping disc so that the motor is in a non-resonant state.

2) Replace the motor plug, protect it, or replace the motor.

3) Check whether the feed amount is too large or overload caused by too fast, and check that the workpiece clamping should not extend too long from the chuck to avoid letting the knife.

4) Check the runout of the main shaft, overhaul the main shaft, and replace the bearing.

5) Check the reverse clearance of the lead screw by playing the dial indicator, whether the clearance has been filled from the system, and whether the clearance is too large after filling.

6) Check whether the screw is crawling and whether there is a slow response.

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