BACKGROUND

Grit Sizes: Grit size (particle size) is determined by the approximate number of openings in the final screen used to size the grains. The larger the number, the smaller (finer) the particle size or grit size. The U.S. Department of Commerce defines a standard specification for abrasive grit "screened" (screen sieve with a specific mesh size holes throughout) sizes from No. 8 through No. 240 in its Commercial Standard CS271-65. The number reflects the number of holes per inch in the final sizing screen. Usually, the grit size offered by the manufacturers is a reflection of the average size within a narrow range, i.e., between the smallest particles aniline largest particle in the batch. In general, the grit size is the number of particles laid end to end that equal one inch. Refer to Newport Glass Works’s web site for a comparison chart at www.newportglass.com .

Micron Sizes: Micron size (particle size) is designated by the manufacturer who relies on microscopic comparisons, Sedimentometer, and other sizing methods. The numerical coding is opposite that for grit sizes, i.e., the smaller the micron number the smaller the particle size. The particles are usually separated into sizes by use of either hydraulic or air separation techniques. The manufacturer designates the size of its particles by comparing them to the standards .established by the particular association to which it belongs, i.e., the American National Standards Institute, the European Federation of Abrasive Producers, the Japanese Industrial Standards Organization or similar organizations. Once again, the micron size offered by the manufacturers is a reflection of the average size within a narrow range, i.e., between the smallest particles and the largest particle in the batch. For reference, a micron is equal to 1 millionth of a meter. A meter is equal to 39.37 inches. A chart is furnished at the end of this catalog to assist you in comparing grit sizes to microns and in relating these terms to your country's industrial standards.

All the materials offered here are of the highest quality and are produced by manufacturers who supply material to the optical industry in the United States.

The following is a suggested procedure in grinding a mirror. The I suggests the starting point if you have purchased a mirror and tool whose curves have been diamond generated. Please note that all blanks sold in this catalog will not have their curves diamond generated unless R has been specifically indicated or unless you requested the curves to be generated for an additional service charge.

The following is one possible approach to grinding and polishing an 8 inch mirror. The amount of abrasive and polishing material required really depends on the skill of the fabricator. If the fabricator is processing a large mirror then the grinding effort may have to start with silicon carbide powder have a grit size of 80 to increase the material removal rate.