I. Basic Material Requirements (Ensure the stone itself first)
Stone: Jinan Green (G3701), Zhangqiu Black, or equivalent high-density fine-grain granite
Density: ≥3.0 g/cm³ (High-precision platform ≥3.2)
Water Absorption: ≤0.25% (Precision grade ≤0.05%)
Hardness: Mohs hardness ≥6, working surface ≥70HS
Structure: Crack-free, no sand holes, no slag inclusions, no weathering layer, biotite content <5%
II. Working Surface Processing (Most critical, applicable to CMMs / Micrometer bases)
- Processing Method
Must: Rough grinding → Fine grinding → Precision grinding → Polishing / Mirror grinding (High-precision platforms prohibit flame treatment, litchi surface) - Flatness (GB/T 4987 Accuracy Grade)
Common Grades (by working surface size):
Grade 000: ≤1.5 μm / 300mm (Ultra-high precision CMM)
Grade 00: ≤3 μm / 300mm (General high precision)
Grade 0: ≤6 μm / 300mm (Ordinary precision)
Flatness within any 250×250mm area shall not exceed half of the overall tolerance - Surface Roughness
Working surface: Ra ≤ 0.4 μm (0.2–0.4 μm optimal)
Non-working surface / Side: Ra ≤ 6.3–12.5 μm - Appearance Requirements
Working surface: No scratches, no impact marks, no rust, no pits, no discoloration
Gloss: Precision ground surface presents uniform matte / mirror finish, no local high/low gloss
III. Edge and Hole Processing (Essential for guides / platforms)
Corners: C0.5–C2 chamfer, no chipping, no burrs
Side perpendicularity: ≤0.02 mm/m (Grade 00)
Threaded holes / Mounting holes:
Hole spacing tolerance: ±0.1 mm
No chipping at hole openings, threads pass go/no-go gauges
IV. Non-working Surface Treatment
Back / Sides: Rough grinding or sandblasting, flat without large unevenness, minor repairs allowed
Bottom: Flatness of the mounting bottom ≤0.1 mm/m, ensuring contact with supports
V. Inspection Standards (Can be included in contract)
Flatness: Electronic level / Laser interferometer, grid method / diagonal method inspection
Roughness: Surface roughness tester
Appearance: Visual inspection under strong light tactile check for no unevenness
VI. Summary (For customers / Quotations)
Adopts Jinan Green high-density granite, with working surface processed by constant-temperature precision grinding. Flatness reaches Grade 00 (≤3μm/300mm), roughness Ra≤0.4μm. Crack-free and sand-hole-free, with smooth chamfered edges. Features stable precision, wear resistance, and deformation resistance.
