b'Boring Bar NoneBoring bars made of cemented carbide provide min-imum deflection because their moduli of elasticity are higher than those of steel and tungsten heavy alloys.Moment of InertiaThe moment of inertia is a property of areas. Because boring bars are available in various diameters, it is im-portant to calculate the area of a bar cross section using appropriate formulas. A boring bar is usually round with a solid or tubular cross section. The moment of inertia of a solid cross section area is calculated by:I = D 4 64 (6)0Where D 0is a bar OD in in. or mm. Moment of inertia of a tubular cross section area is calculated by:I = (D 4- D 4 )64 (7)0 iWhere D iis a bar ID in in. or mm.Example of calculating the moment of inertia I (cus-tomary U.S. units of measure)Given: Outside diameter is 1". The moment of inertia is calculated using formula (6).I = 1 4 640.0491 in. 4Example of calculating the moment of inertia I (met-ric units of measure)Given: OD is 25.4mm. The moment of inertia is calcu-lated using formula (6).I = 25.4 4 64 = 416,231.464 = 6,503.6 = 20,432mm 4Theres nothing wrong with Deflection off-the-rack tools. But if you Example 1: Unsupported length of a boring bar (over- need that extra boost in cycle hang), L = 4". time and tool life, its time to Calculating deflection of the bar (customary U.S. units of measure) consider your custom-made y = FL 3 3EI = 207.84 3 33010 6 0.0491 =option: GWS Tool Group.12,652.84,419,0000.003"Example 2: Unsupported length of a boring bar (over-hang), L = 101.6mmCalculating deflection of the boring bar (metric units of measure)y = FL 3 3EI = 911.1101.6 3 320.610 4 20,432 = 955,536,25734,208,992,000 = 0.0757mmLets compare: Deflection of the boring bar in exam-ple 1 is 0.003", or 0.0762mm, and deflection of the bor-ing bar in example 2 is 0.0757mm, or 0.00298".To help ensure a successful boring operation, the overhang should be as short as possible to minimize boring bar deflection. In addition, the boring bar should be made of either tungsten heavy alloy or cemented carbide, and the bar diameter should be as large as pos- GWSTOOLGROUP.COMsible to achieve the maximum moment of inertia.CTEctemag.com/cteguide.com73Boring.indd 73 6/17/19 10:14 AM'