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211DEEP HOLE DRILLING%u00bd%u0009Accuracy and Surface QualityDeep Drilling ToleranceDeep drilling configurations when used under recommended conditions can produce holes with tolerance of IT8-IT9 (Figure 6.1.1). When operating under optimal conditions, even better tolerance can be achieved.Figure 6.1.2N12 N11 N10 N9 N8 N7 N6 N5 N4 N3 N2 N1Indexable DrillsReamingHoningDeep DrillingDegree of Roughness (Ra Roughness Index)%u039cm 50 25 12.5 6.30 3.20 1.60 0.80 0.40 0.20 0.10 0.05 0.025%u039cin 2000 1000 500 250 125 63 32 16 8 4 2 1Tolerance range under normal conditions Tolerance range under optimal conditionsSurface QualitySurface quality that can be achieved in deep drilling is defined in Figure 6.1.2.Figure 6.1.1Nonferrous MaterialsMachinability of MetalsAluminumTool SteelCast IronHigh Alloy Steel>800N/mm2Hardened SteelLow Alloy Steel<800N/mm2Carbon SteelSintered SteelDrilling Quality IT 13 12 11 10 9 8 7 6 5Tolerance range under normal conditionsTolerance range under optimal conditions