Core Factors Affecting the Machining Precision of Granite (Jinan Blue) Equipment Bases

Divided into six major areas: raw material itself, stress and aging, machining process, grinding process, environmental conditions, and post-transportation/installation. For 00/000-grade precision bases, every factor directly affects flatness and parallelism.

I. Stone Raw Material Factors

1. Ore Material Grade
   Premium Jinan Blue (gabbro) has fine grains and a uniform structure; ordinary black granite has uneven grains, cracks, and mica inclusions. Even if ground, it will undergo slight deformation later, making it difficult to stably achieve 000-grade precision.
2. Internal Cracks, Pores, and Mineral Impurities
   Small dark cracks are hard to detect during machining. After grinding and cutting, stress is released, causing local warping; mica-rich areas are prone to local wear, resulting in failed flatness.
3. Block Extraction Direction
   The direction of rock layer texture is critical. The base surface should avoid the bedding direction as much as possible; otherwise, it is prone to warping and deformation due to temperature and stress.

II. Internal Stress (The most easily overlooked, the number one killer of precision bases)

Granite mining and large-saw cutting generate a large amount of residual stress.

1. Insufficient Natural Aging: If the raw blocks or semi-finished products are not allowed to rest long enough to release stress, they may pass fine grinding but warp on their own after a period of time, causing precision to drift.

000-grade bases typically require semi-finished products to rest for 30-45 days; high-requirement ones undergo secondary aging.

2. Surface Stress from Cutting Impact: The surface layer of large-saw cutting contains a stress layer. If fine grinding is performed directly, it will rebound and deform later.
3. Local Stress from Steel Inserts and Drilling: Drilling and pressing steel inserts create local compressive stress, causing the plate surface to bulge slightly.

III. Machining Equipment and Process

1. Cutting Equipment Precision: If the large saw or gantry saw has poor precision, the blank plate itself will be warped. Subsequent grinding will need to remove a large amount of material, increasing the risk of deformation.
2. Milling and Slotting: CNC gantry milling for T-slots and steps with unreasonable feed rates will generate local compressive stress.
3. Grinding and Polishing Process

• Rough grinding → Semi-fine grinding → Fine grinding → Ultra-fine grinding. Skipping steps and going directly to fine grinding cannot eliminate previous waviness;
• If the grinding disc is worn or not level, the workpiece will exhibit central convexity or concavity;
• Excessive grinding pressure: The plate undergoes elastic deformation under pressure. It may pass inspection, but will rebound out of tolerance once the pressure is released.

Point clé : Large-sized granite plates cannot be ground under heavy pressure, and 000-grade precision requires extremely high standards for grinding tooling.

IV. Machining / Inspection Environmental Temperature (Decisive factor for 000-grade)

Although granite has a low coefficient of thermal expansion, large-sized bases are still sensitive to temperature differences.

1. Non-constant temperature in the workshop: Temperature differences between day and night cause the plate to expand and contract, distorting grinding and inspection data.

000-grade verification standard environment: 20°C ± 2°C, constant temperature workshop, workpiece fully isothermal, placed for at least 4-8 hours before inspection.

2. Direct sunlight, proximity to doors/windows/vents: Local temperature unevenness causes the plate surface to warp.

V. Tooling, Clamping, and Handling

1. Unreasonable support during machining: Incorrect three-point support or uneven force distribution in multi-point support causes elastic bending of the plate; when the workpiece is removed after grinding, it rebounds, directly exceeding flatness tolerances.

Granite surface plate machining and inspection must strictly follow the three-point support principle.

2. Lifting and handling: Hard contact with wire ropes and single-point loading generate hidden micro-cracks, leading to gradual deformation over time; lifting large plates from a single point is strictly prohibited.
3. Stacking of semi-finished products: They must not be leaned against surfaces or stacked with local parts suspended, as this will cause plastic creep deformation.

VI. Post-use Environment (Passed factory inspection, but accuracy lost at the customer site)

1. Large temperature differences at the customer site, or direct sunlight hitting the equipment base;
2. Uneven foundation of the base, causing local suspension and bending of the base under gravity;
3. Forced hard adjustment or prying of the base leveling feet, causing deformation of the plate.