Lapmaster measuring machine

Lapmaster  measuring machine

Measuring Flatness with an Optical Flat and Monochromatic Light:

A) First, clean the surfaces of the component and optical flat with a lens tissue or soft lint-free cloth. Both faces must be absolutely clean.

B) Place the optical flat carefully on top of the component. Do not slide it across.

C) As the optical flat and component come together, lines will appear through the flat. Manipulate it to obtain a line pattern, as illustrated. The lines are interference fringes or bands and are an indication of the level the component's surface has risen or fallen in relation to the optical flat. The difference in elevation from one band to the next is 11 millionths of an inch (0.0002794 mm) using a helium light source. One light band being a complete light and dark area.

A flat surface will show different band patterns. Straight parallel bands show that the surface is perfectly flat to within one millionth of an inch (0.000001).

Convex & Concave Conditions:
The above patterns show a line running through the center of the optical flat, which is projected onto the flat by the line on the opaque screen of the monochromatic light. The line can be seen to bisect two of the black light bands indicating that the part is two light bands, i.e., 0.00058 mm (0.0000232 inches) out of flat over its diameter.