Complete Process for Granite Stone Processing Equipment Bases (Jinan Green / Diabase, CMM and Lithography Machine Precision Bases)

Core Logic: Material Selection → Sawing Blank → Rough Machining → Stress Relief Aging → Functional Hole and Slot Machining → Embedded Threaded Inserts → Multi-stage Grinding → Manual Fitting and Grinding → Constant Temperature Resting → Final Inspection, high precision (00/000 grade) must be completed in a 20±1℃ constant temperature workshop, with continuous water cooling throughout, and dry cutting or dry grinding is strictly prohibited.

1. Raw Material Selection (Determines Long-term Stability)

Prioritize Jinan Green Diabase, which features fine grains, no cracks, no inclusions, no white spots, and no weathering; reject spliced materials, use whole-block blanks.

• Compressive strength ≥220MPa, high elastic modulus, low thermal expansion coefficient, and vibration resistance superior to cast iron bases.
• Machining allowance reserved on each side of the blank: 3-5mm, with a 0.4-0.6mm grinding allowance on each side of weight-reduction slots for large bases.
• All corners and slot corners must be rounded with R≥5mm; right angles are extremely prone to chipping and cracking.

2. Sawing and Rough Machining (Diamond Tools, Water-cooled)

1. Use diamond wire saws / bridge saws to cut the overall external dimensions.
2. Use gantry CNC grinders / stone processing centers to rough-grind the six faces: quickly remove excess material and correct overall parallelism and perpendicularity.
3. Post-rough machining state: leave a 0.3-0.5mm precision grinding allowance, and rough-machine all weight-reduction slots and clearance slots to position without reaching final dimensions.

⚠️ Sequence: Perform aging after rough machining, do not age after precision machining. Rough machining generates significant cutting internal stress; if not released, it will cause warping and precision drift later.

3. Stress Relief Aging (Essential for High-Precision Bases)

Option A: High-end 000 Grade (Natural Constant Temperature Aging)

Place the workpiece flat in a constant temperature and humidity workshop at 20±1℃, with 45-55% humidity; flip once every 7 days and let rest for 2-4 weeks to uniformly release stress.

Option B: Batch Expedited Artificial Composite Hot-Cold Cycle Aging

1. Insulate in an 80℃ drying room for 24h;
2. Insulate at -10℃ for 4h;
3. Slowly return to 20℃, rest at constant temperature for 72h;

The temperature rise and fall rates must be slow to prevent the formation of new micro-cracks.

The process for ordinary equipment bases can be simplified; CMM and semiconductor lithography machine bases must undergo aging, otherwise precision will drift after a period of use.

4. Functional Feature Machining: Drilling, Slotting, Counterboring, and Back-chamfer Bonding

Use diamond tools exclusively, with continuous water cooling and low-speed feed, and impact drilling is prohibited.

1. Drilling: Pre-drill with a small bit first, then enlarge the hole to prevent chipping at the hole entrance; edge distance ≥50mm, hole-to-hole spacing ≥100mm to reduce cracking risk.
2. Counterbore and stepped holes are milled in layers; weight-reduction slots and guide rail installation slots are rough-machined to position, leaving a grinding allowance.
3. Back-chamfer Bonding Process (for large base splicing)

• Grind the mating surfaces for a tight fit, then bond with a thin layer of epoxy structural adhesive;
• Cure at constant temperature for 24-48h after bonding, and perform overall grinding only after curing is complete;
• Avoid splicing for high-end metrology equipment bases as much as possible; spliced bases are not recommended for 000-grade precision.

5. Pre-embedded Stainless Steel Threaded Sleeve (The process most likely to compromise precision)

Process sequence: Rough grinding – Drilling – Pre-embedding threaded sleeve – Complete glue curing – Fine grinding, strictly prohibiting fine grinding before drilling and inserting the sleeve! This will cause stress rebound deformation of the base.

1. Select thickened 304/316 stainless steel sleeves with a wall thickness ≥2mm; thin copper sleeves are not allowed.
2. Clean the hole thoroughly, apply AB epoxy glue evenly to the outer wall of the sleeve, with a glue layer of about 0.5mm.
3. Press in vertically, ensuring the end face of the sleeve is slightly lower than the granite surface to avoid protrusion.
4. Cure at a constant temperature for over 24 hours until the glue is completely hardened before proceeding to the grinding process.

6. Multi-stage Grinding (Constant temperature workshop 20±1℃)

Use grinding wheels step by step, do not skip grits, all water-cooled:

1. Semi-fine grinding 200# – 400#: Remove tool marks, flatness ≤0.02 – 0.05 mm/m.
2. Fine grinding 800# – 1200#, then to 2000# resin diamond grinding wheels; leave a manual lapping allowance of 0.01 – 0.03 mm after grinding.

• Grade 0: Can be completed by mechanical grinding;
• Grade 00 / 000: Must be manually lapped (lapping), machines cannot achieve this alone.

7. Manual Precision Lapping (Core process for Grade 00/000)

1. Use a higher-grade 000 standard lapping plate, silicon carbide micro-powder, and cross-trajectory lapping with water lubrication.
2. Blue oil spot inspection: For a 25×25mm area, contact spots must be ≥20, spots must be uniform, and no large blank areas are allowed.
3. For defects such as the center of the base bulging or the ends sinking, lightly scrape the high points; this step takes a long time for large-sized granite bases.

Precision Reference (GB/T20424)

• Grade 00: Flatness 2 – 5 μm/m
• Grade 000: Flatness 1 – 2 μm/m; Ra ≤0.1μm or even mirror Ra ≤0.02μm.

8. Cleaning and Constant Temperature Resting

High-pressure wash and blow-dry all stone dust and grinding micro-powder; place the workpiece back in the constant temperature workshop to rest for 24 – 72 hours to eliminate surface thermal stress generated during grinding. Once dimensions are completely stable, perform the final inspection.

9. Final Inspection of the Entire Project

• Flatness: Laser interferometer / Precision level
• Parallelism, Perpendicularity: Electronic level, Autocollimator
• Hole position accuracy: Coordinate Measuring Machine (CMM)
• Roughness: White light interferometer
• Threaded sleeve: Go/No-go gauge, pull-out force spot check

10. Key Pitfall Avoidance Points

1. Maintain constant temperature throughout the entire finishing process, as temperature fluctuations directly cause micron-level deformation;
2. Drilling and inserting the sleeve must be done before fine grinding;
3. Aging cannot be skipped, perform it after rough processing;
4. Strictly prohibit dry grinding and dry drilling, as it easily generates internal micro-cracks, causing later precision failure;
5. Bonded bases can only reach Grade 00 at most; for Grade 000, try to use a single block of stone.

Simple Comparison: Granite Base vs. Cast Iron Base

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