How do I check the accuracy retention of a used Yoga NBP-1000A vertical machining center?

Author:           Date:2025-04-08

Checking the accuracy retention of a used Youjia NBP - 1000A vertical machining center involves checking the geometric accuracy, positioning accuracy, and repetitive positioning accuracy, as described below:
1. Geometric accuracy check
- **Flatness of the table surface**: Use a level to place on the table surface, measure in different directions and positions, record the reading of the level, and evaluate the flatness error of the table surface. Generally, the flatness of the working table surface is required to be no more than ±0.05mm over the whole length.
- ** the perpendicularity and parallelism of the axes **: the use of a ruler and a percentage table, the ruler is installed in the machine tool on one axis, the percentage table is fixed to the other axis of the moving parts, moving parts for the entire movement, measuring the perpendicularity error between the two axes. Parallelism is measured in a similar way and is assessed by measuring the parallelism between the coordinate axes and the table surface or other reference surface. For example, the parallelism error between the X-axis and the table surface should be within ±0.05mm/300mm.
2. Positioning accuracy check
- **Laser interferometer measurement**: Use the laser interferometer to measure each coordinate axis. The reflector of the laser interferometer is installed on the moving parts of the machine tool, such as the table or spindle head, and the host of the laser interferometer is fixed in the reference position of the machine tool. Through the control system to drive the moving parts in each coordinate axis for different distances, the laser interferometer will measure the error between the actual moving distance and the commanded distance, so as to get the positioning accuracy data. Generally, the positioning accuracy of X, Y and Z axes is required to be within ±0.05mm.
- **Ballbar Measurement**: The ballbar can measure the roundness accuracy of the machine tool, indirectly reflecting the positioning accuracy. Fix one end of the ballbar on the machine table, the other end is connected to the spindle head, drive the spindle head to move along the circumferential path through the control system, the ballbar will measure the radius change of the movement trajectory, so as to assess the roundness error and positioning accuracy of the machine tool.
3. Repeat positioning accuracy check
- **Percentage meter measurement**: install a percentage meter on the table or spindle head, then let the moving parts of the machine tool repeat positioning in the same position several times and record the changes in the reading of the percentage meter, so as to assess the repetitive positioning accuracy. Repeat positioning accuracy is usually required to be within ±0.03mm.
- **Statistical analysis of data**: Record the actual position data of multiple positioning through the control system, and then carry out statistical analysis to calculate the value of repetitive positioning accuracy. Generally, the repeat positioning accuracy is evaluated by calculating the standard deviation, and the smaller the standard deviation, the higher the repeat positioning accuracy.
4. Verification of machining accuracy
- **Trial cutting workpiece**: Use the machine tool to process some representative workpieces, such as square, cylinder, cone, etc., and then measure the dimensional accuracy, shape accuracy and surface roughness of the workpiece. For example, machining a square workpiece, measuring the dimensional error of its side lengths should be within ± 0.05mm, flatness within ± 0.03mm, perpendicularity and parallelism within ± 0.05mm.
- **Detection of processing contour**: Process some complex contour shapes, such as curves, surfaces, etc., and then use the CMM to measure the processing contour and compare it with the design drawings to assess the processing accuracy and accuracy retention.

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