How to inspect your used cylindrical grinder?
1. Static Inspection (Power-Off)
This is a basic inspection, designed to identify macroscopic issues and potential wear on a used cylindrical grinder.
Appearance and Structural Inspection:
Bed and Guideways: Carefully inspect the bed for cracks and signs of weld repairs. Focus on inspecting the guideways (especially the table guideways) for wear. Feel the guideway surface for visible pitting or burrs. Minor wear is normal, but severe wear will directly lead to a loss of precision.
Rust and Maintenance: Observe exposed metal surfaces, especially the guideways and lead screws, to see if there is only light rust or severe corrosion. The overall maintenance condition reflects the previous owner's handling.
Key Component Inspection:
Headstock and Tailstock: Manually rotate the headstock spindle to check for smooth movement, unusual noises, or axial or radial play. Check the tailstock quill for flexible movement and secure locking.
Grinding Wheel: Manually rotate the grinding wheel spindle to check for stability. Any binding or unusual noise may indicate spindle bearing damage, which can be extremely costly to repair.
Screw and Handwheel: Turn the feed handwheel in each direction to check for uniformity and play (backlash). Excessive play can affect feed accuracy.
II. Dynamic Inspection (Powered on, Dry Run)
This step verifies the equipment's condition during operation.
Dry Run Test:
Spindle System: Start the grinding wheel spindle and headstock spindle and run them from low to high speed. Use a stinger or screwdriver to listen for a steady, low-pitched sound against the bearings, avoiding any harsh, creaking or periodic banging.
Hydraulic and Lubrication System: Start the hydraulic system and observe the worktable's smooth, uniform reciprocating motion, including any "creeping" behavior. Check all lubrication points for proper oil flow and check for leaks in the hydraulic lines.
Feed System: Test the automatic feed mechanism; it should operate smoothly and accurately.
III. Accuracy Testing (Core Step)
This is the ultimate criterion for verifying the value of a machine tool, and an on-site test grind is strongly recommended.
Preparing for the Test Grind: Prepare a pre-measured, qualified steel test bar (60-100mm diameter, length depends on the machine tool).
Performing the Test Grind:
Perform external cylindrical grinding on multiple sections of the test bar at regular intervals.
Test Items:
Roundness: Use a roundness tester or a scale to measure the same section multiple times. Half the difference between the maximum and minimum values provides an approximate measure of roundness. This reflects the accuracy of the spindle system and headstock.
Cylindricity: Use a scale to measure the diameter difference between the ends of the test bar. This reflects the straightness of the machine guideways and the alignment accuracy of the tailstock and headstock.
Surface Finish: Use a surface roughness tester or compare with a standard sample.
Reference: Request the machine tool's "Factory Accuracy Inspection Sheet" and compare your actual measurement results with the factory standard to gain a direct understanding of the degree of accuracy degradation.
