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Flatness and the measurement of bands to determine flatness


Flatness measurements are made using an optical flat gage block. The procedure is to put the optical flat on top of the surface to be measured, which results in interference fringes. Careful measurement of the fringes can yield flatness information.

Most flat surface:

Straight, parallel and equally spaced bands show that the surface is perfectly flat within 0.000001" (25 nm).

Slightly out of flat:

Bands do not curve enough for tangent line to intersect one full band. Curvature of bands is equal to one half the distance from one band to the next at 0.0000058" (145 nm) out of flat. Curvature away from the line of contact indicates part of convex.

Considerably out of flat:

Tangent line intersects one full band showing part one full band, or 0000116" (290 nm) out of flat. Again, curvature away from line of contact indicates part is convex.



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Monday October 13, 2008
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