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The first step in selecting the proper bur to suit a particular operation is to establish which shape or style bur would best conform to the contour being machined. All catalog burs are supplied in standard, right-hand spiral or standard supercut fluting, each designed for a specific purpose. Fine and coarse cut burs are also available. Next is to decide on the type of cut to be used. The factors governing this selection are the material being cut, the finish required, and the bur shape itself. For general purpose deburring of steel, cast iron, or other ferrous material, the standard cut bur is considered and is the tool type most commonly used. The supercut design is recommended on these stock materials for faster stock removal and elimination of chatter. The medium right-hand spiral cut is recommended for light finishing cuts and profiling. Aluminum cut, or mill cut burs, are recommended for soft materials that have a tendency to cause loading and packing of the flutes. These materials are aluminum, magnesium, brass, lead, and most plastics. The supercut bur, because of its fluting pattern, has hundreds of chisel like teeth that result in rapid stock removal and better control when used in free hand operations. It is particularly suited to cutting stringy materials because it will produce a powder like chip as compared to the sharp slivers that constantly plague operators using conventionally fluted burs in these materials. When loading a bur in the grinder be sure to insert the shank as far into the collet as possible so that the overhang is kept to a minimum. This will help to prevent whipping or chatter, and because of the added rigidity the useful life of your spindle bearings will be greatly increased. When grinding, use just enough pressure to keep the bur cutting. Do not bear down because excessive pressure will only slow down the spindle and result in damage to the cutting edges. Let the bur do the work. The bur should be kept moving at all tines to prevent the tool from digging into the work. Do not run a carbide bur beyond the point of normal resharpening. This is false economy, because the resultant heat and pressure will cause excessive chipping of the cutting edges often times so badly that the resharpening life is greatly reduced or the tool may be damaged beyond repair. When carbide burs are used correctly they will outperform H.S.S. tools and mounted wheels as much as 30:1 and at the same time reducing machining time up to 65%. |