Machinery's Handbook, 31st Edition
Files and Burs 1055 The carbide bur may be used on hard or soft materials with equally good results. The principle difference in construction of the carbide bur is that its teeth or flutes are provided with a negative rather than a radial rake. Carbide burs are relatively brittle and must be treated more carefully than ordinary burs. They should be kept cutting freely, in order to prevent too much pressure, which might result in crumbling of the cutting epics. At the same speeds, both high-speed steel and carbide burs remove approximately the same amount of metal. However, when carbide burs are used at their most efficient speeds, the rate of stock removal may be as much as four times that of ordinary burs. In certain cases, speeds much higher than those shown in the table can be used. It has been demon strated that a carbide bur will last up to 100 times as long as a high-speed steel bur of corresponding size and shape. Approximate Speeds of Rotary Files and Burs
Medium Cut, High-Speed Steel Bur or File
Carbide Bur
Tool Diameter
Medium Cut
Fine Cut
Mild Steel Cast Iron Bronze Aluminum Magnesium
Any Material 45,000 30,000 30,000 20,000 24,000 16,000 20,000 13,350 18,000 12,000 16,000 10,650
inches mm
Speed, Revolutions per Minute
4600 3450 2750 2300 2000 1900 1700 1600 1500 1400
7000 5250
15,000 20,000 11,250 15,000
30,000 22,500 18,000 15,000 13,350 12,400 11,250 10,300 9750 9000
1 ⁄ 1 ⁄ 3 ⁄ 1 ⁄ 5 ⁄ 3 ⁄ 7 ⁄
3.2 6.4 9.5
8 4 8 2 8 4 8
4200 9000 3500 7500 3100 6650 2900 6200 2600 5600 2400 5150 2300 4850 2100 4500
12,000 10,000 8900 8300
12.7 15.9 19.1 22.2 25.4 28.6 31.8
7500 6850 6500 6000
14,500 13,000
9650 8650
1
… … … …
1 1 ⁄ 1 1 ⁄
8 4
As recommended by the Nicholson File Company. Steel Wool.— Steel wool is made by shaving thin layers of steel from wire. The wire is pulled, by special machinery built for the purpose, past cutting tools or through cutting dies that shave off chips from the outside. Steel wool consists of long, relatively strong, and resilient steel shavings having sharp edges. This characteristic renders it an excellent abrasive. The fact that the cutting characteristics of steel wool vary with the size of the fiber, which is readily controlled in manufacture, has adapted it to many applications. Metals other than steel have been made into wool by the same processes as steel, and when so manufactured have the same general characteristics. Thus wool has been made from copper, lead, aluminum, bronze, brass, monel metal, and nickel. The wire from which steel wool is made may be produced by either the Bessemer, or the basic or acid open-hearth processes. It should contain from 0.10 to 0.20 percent carbon; from 0.50 to 1.00 percent manganese; from 0.020 to 0.090 percent sulphur; from 0.050 to 0.120 percent phosphorus; and from 0.001 to 0.010 percent silicon. When drawn on a standard tensile- strength testing machine, a sample of the steel should show an ultimate strength of not less than 120,000 pounds per square inch (828 MPa). Steel Wool Grades
Fiber Thickness Inch Millimeter
Fiber Thickness Inch Millimeter 0.0025 0.06
Description Grade
Description Grade
Super Fine Extra Fine Very Fine
0000 0.001
0.025 Medium
1 2 3 4
000 00
0.0015 0.035 Medium Coarse
0.003 0.004
0.075
0.0018 0.04
Coarse
0.0035 0.09
Fine
0
0.002
0.05
Extra Coarse
0.10
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