Granite Platform Flatness & Geometric Precision Comprehensive Testing Methods (Factory Practical Operations National Standard Verification)
In accordance with JJG117-2013 Plate Verification Regulations, common testing methods for precision granite platforms are divided into: Traditional Level Method, Autocollimator Method, Laser Interferometry Method, Grid Point Testing, Optical Flat Interference Method, and CMM Comprehensive Testing.
I. Electronic Level Testing Method (Most Common in Industry, National Standard Arbitration Method)
Testing Principle
Move the bridge along the platform’s diagonal, longitudinal, transverse, and cross directions, read values point by point, calculate the rise and fall difference, and fit the overall flatness.
Applicable Grades
All granite platforms of Grade 000, 00, and 0.
Преимущества
Precise, not obstructed by workpieces, on-site testing at any time, meets requirements for metrological verification certificates.
Testing Items
Flatness, Parallelism, Torsion.
II. Optical Autocollimator Testing Method (Specialized for Ultra-high Precision Long Surfaces)
Principle: Convert light reflection angles to height differences for high-precision long-distance measurement.
Applicable: Large-size granite platforms, gantry bases, ultra-long guide rail surfaces.
Precision: Up to 0.001mm/m.
Advantages: No cumulative error over long distances, suitable for large granite components over 1 meter.
III. Laser Interferometer Testing (Highest-level Testing for Semiconductor / CMM Benchmarks)
Directly collect three-dimensional coordinates of the entire surface, and software fits the real plane error.
Precision can reach nanometer level.
Measures in one go: Flatness, Straightness, Perpendicularity, Positional Tolerance, Hole Position Accuracy.
Mainly used for Grade 000 ultra-high precision benchmarks, air-bearing platforms, and equipment whole machine acceptance.
IV. Precision Right Angle Gauge Dial Indicator Testing (Perpendicularity, Side Perpendicularity)
The granite right angle gauge is made to fit the working surface.
The dial indicator moves to scan; the reading fluctuation is the perpendicularity error.
Tests platform side perpendicularity and adjacent surface right angle precision.
V. Polished Optical Flat Interference Method (Microscopic Surface Finish Local Flat Precision)
The optical flat is made to fit the platform, observing the number of interference fringes.
One fringe ≈ 0.3μm height difference.
Judges local concavity/convexity, scratches, high points, collapse, and poor mating.
Only detects local microscopic precision, does not perform overall full surface testing.
VI. Dial Indicator / Vernier Caliper Grid Multi-point Inspection (Simple and Quick Workshop Self-inspection)
Platform divided int a grid (5×5 / 7×7 point array)
Gauge holder fixed, record height difference point by point
Maximum value – Minimum value = Flatness error
Suitable for daily insns and quick judgment of whether precision exceeds limits
VII. CMM Full-size Comprehensive Inspection (Highest Standard for Factory Final Inspection)
Issues in one go:
Full plane grid flatn
Parallelism and perpendicularity of each surface
Positioning of T-slots and coordinate tolerance of mounting holes
Straightness and twist
Suitable for acceptance of non-standard granite componemachine tool beds, and base assemblies
VIII. Bridge Plate Span Comparison Method (Old Traditional Pitch Method)
Old-style coincidence level standard bridge plate, segmental measurement and cumulative culation
Now basically replaced by electronic levels
On-site quick self-inspection process (easy for workers to learn)
Clean the platform → constant temperature stabilization
Electronic level traverses twdiagonals
Traverses longitudinal and transverse cross lines
Software automatically calculates flatness grade
Right-angle gauge checks side perpendicularity
Detection methods corresponding to different accuracies
Orinary Grade 1 platform: Vernier caliper grid method
Grade 0 inspection platform: Electronic level
Grade 00 precision platform: Electronic level Optical fat
Grade 000 ultra-high precision reference: Autocollimator / Laser interferometer / CMM
