Granite slabs are precision measuring tools made from natural stone. They are ideal reference surfaces for inspecting instruments, precision tools, and mechanical components, especially for high-precision measurements. Their unique properties make cast iron slabs pale in comparison. Granite platforms are crafted from high-quality natural marble, machined and hand-polished. They feature a black gloss, precise structure, uniform texture, and excellent stability. They offer high strength and hardness. Granite slabs are machined from pebbled stone and manually ground in a constant temperature chamber to achieve high surface precision. The working surface of the granite platform should be uniform in color and free of cracks, grooves, or loose texture. It should also be free of wear marks, scratches, burns, or other defects that could affect the granite slab's accuracy. These defects are permitted on granite slabs in use as long as they do not affect accuracy. Repairs to dents or chipped corners on the working surface of the granite slab are not permitted. Even if a granite slab is struck by a heavy object during use, at most a few grains of stone will fall off. Granite slabs are superior to precision measurement reference components made of high-quality cast iron and steel, achieving high and stable accuracy.
The working surface of a granite slab must be free of defects such as sand holes, air holes, cracks, slag inclusions, shrinkage, scratches, dents, and rust that could seriously affect its appearance and performance. Repairs are permitted on dents or chipped corners on the non-working surface of a granite slab.
Granite slabs should be made from fine-grained, structurally consistent gabbro, diabase, or granite (biotite content should be less than 5%, elastic modulus should be greater than 0.6x10-4Ka/cm2, and water absorption should be less than 0.25%). The working surface hardness should be greater than 70HS. Carrying handles are not recommended for grade 000 and 00 slabs. If threaded holes (or grooves) are installed on Grade 0 and Grade 1 slabs, their location should not be higher than the working surface. The maximum allowable surface roughness Ra for the working surface of a granite slab is 0.32-0.63 μm, and 10 μm for the side surfaces. The perpendicularity tolerances for the sides of the granite slab facing the working surface and the adjacent sides of the slab are both in accordance with Grade 12 as specified in GBT 1184. The concentrated load area, applied rated load, and allowable deflection values for the central working surface of a granite slab are specified.