b'Scratching the Surface larger numbers represent smallertemperatures. Also, unlike the edge particles, so a 24-grit sanding belt isof an endmill, the cutting edge is rougher than a 120-grit belt. expected to fracture during use, used loose. Delivering the abrasiveLike endmills and turning tools,which helps keep the grain sharp.at high velocity with compressedabrasivesmustbeusedunderOperating abrasive products at air, otherwise known as blasting, isproper conditions, and correct cut- optimal parameters ensures safe, the most standard method of appli- ting parameters are critical. In mostefficient processes. When high-vol-cation. Loose abrasives are used ascases, abrasives are used at muchume grinding, obtaining cutting well in processes like vibratory fin- higher cutting speeds than toolsparameters for a bonded abrasive ishing and waterjet cutting. Looselike endmills. Typical machiningproduct, such as a grinding wheel, is abrasive grains are combined withspeeds for milling and turning areusually an iterative approach involv-fluids to form lapping compoundsless than 305 m/min. (1,000 sfm), yeting calculations and testing. How-or combined with waxes or greasesthe usual abrasive is used betweenever, cutting parameters for oper-to make buffing compounds. 1,372 m/min. (4,500 sfm) and 2,134ations that utilize coated or loose m/min. (7,000 sfm). Abrasive materi- abrasives are calculated less easily, Considerations als can function at these speeds be- so they rarely receive any consider-All abrasive materials are catego- cause they are not affected by highation unless something goes wrong. rized by grain, or grit, size. Grit size is determined by sifting an abrasive through calibrated screens, usingabout the author air-blown separation orin someChristopher Tate is engineering manager of advanced casesemploying water separa- manufacturing engineering and machining at the Savannah, tion, all of which segregate mate- Georgia, facility of Mitsubishi Hitachi Power Systems Ameri-rial by particle size. Smaller numberscas Inc., Lake Mary, Florida. Contact him at chris23tate@indicate larger particle sizes, andgmail.com.The sanding machine (left) at Mitsubishi Hitachi Power Systems Americas uses 914 mm1,829 mm (36"72") sanding belts (right) to polish parts made of sheet metal.C. Tate32DECEMBER 2020Abrasives.indd 32 11/13/20 4:19 PM'