Document 13gb0pLmGJDBx5ejbp90vyZm

MACHINE TOOLS metal slivers and chips Brackets of various lengths can be used, depending upon the depth of the hole to be drilled (see Fig 24-6), Breakage of tools results most frequently from use of dull tools A drill smaller than 54-in diameter will often break and cause injury. A larger drill may "fire up" to the extent that it breezes in die hole and then breaks. Furthermore, a frozen tool may spin unclamped or insecurely clamped work, with possible injury to the operator. A frozen drill may likewise strip a gear Al though no injury is likely to result, the damage to equipment and the resulting down time are expensive Drills also sometimes catch in thin material and spin it When deep holes are being drilled beyond the flutes of the dnll, the drill should be removed frequently and the chips cleaned out If chips are allowed to pile up in such I' 13' Fig. 24-6. Spring safety guard compresses as drill cuts into metal in order to contoin metal slivers and chips. an operation, the tool may jam, with results similar to those of freezing. Counterweight chains should be main tained in good condition, and a shield should be installed around the counterweight Radial dnll accidents are frequently caused by incorrect manipulation of con trols If the dnll arm is raised or lowered before the bolts clamping the arm to the column have been loosened, the threads may be stopped, the elevating screw bent, or one or more of the dnvmg gears broken Gears of elevating screws should be out of mesh before the machine is started Also, the bolts through the column should be secure ly fastened and the dnll head clamped in place Boring mills Among common causes of injury m bor ing mill operations are* 1 Being struck by insecurely damped work or by tools left on or near revolving table 2 Catching dothlng, wiping rags, etc, in re volving parts. 3 Falling against revolving work 4 Calipenng or checking work while ma chine is in motion 5 Allowing turnings to build up on table 6 Removing turnings by hands The same acadent prevention measures are effective on both the table type and the floor type of horizontal bonng mills The operator should never attempt to make measurements near the tool, reach across the table, or adjust the machine or work while the machine is m motion. When the work is clamped on the table or the bed, the damps should be placed and blocked with a secure hold on the work so that they cannot spring out of shape The fork end of U-damps should be placed on the work The nuts should be tightened only with a wrench of the correct size, oth erwise the wrench may sbp off and injure the operator If a vise is used to hold the work, the op erator should never tighten it by stoking the handle with a hammer, because the vise may be sprung or the end of the screw which carries the handle, broken off. He should make sure that die bolts holding the vise are securely fastened. 24-6