Page 219 - Demo

217DEEP HOLE DRILLING%u2022 The distance between the support bushings should be no more than 30D.max. 30Dmax. 30D %u2022 The minimum depth of the pre hole, when drilling without support bushings, depends on the drill length:%u2022 for depth of hole up to 12D the pre hole should be 0.5D-1.0D%u2022 for depth of hole 20D-30D the pre hole should be 8D-12D%u2022 for depth of hole 40D-50D the pre hole should be 20D-25D%u2022 for depth of hole 60D-80D the pre hole should be 30D-40D%u2022 Oil coolant in deep drilling is preferable over emulsion.%u2022 To minimize drill runout, if possible it is preferable to drill on both sides of the workpiece.%u2022 The drill length should be longer than the requested hole to guarantee enough space for machine accessories (guide bushing, support bushing, etc.).%u2022 To increase drilling stability, it is advisable to use the shortest drill if possible.