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Aviation Boatswains Mate E - Aviation theories and other practices
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selection of the blades for the work to be done. Figure 1-14 will help you select the proper blade to use when sawing metal with a hacksaw. Coarse blades, with fewer teeth per inch, cut faster and are less likely to choke up with chips. However, finer blades, with more teeth per inch, are necessary when thin sections are being cut. The selection should be made so that, as each tooth starts its cut, the tooth ahead of it will still be cutting. To make the cut, first install the blade in the hacksaw frame (fig. 1-15) so the teeth point away from the handle of the hacksaw. (Hand hacksaws cut on the push stroke.) Tighten the wingnut until the blade is definitely under tension. This helps make straight cuts. Place the material to be cut in a vise. A minimum of overhang will reduce vibration, give a better cut, and lengthen the life of the blade. Have the layout line outside of the vise jaw so that the line is visible while you work. The   proper   method   of   holding   the   hacksaw   is depicted in figure 1-16. See how the index finger of the right hand, pointed forward, aids in guiding the frame. When cutting, let your body sway ahead and back with each stroke. Apply pressure on the forward stroke, which is the cutting stroke, but not on the return stroke. From  40  to  50  strokes  per  minute  is  the  usual  speed. Long, slow, steady strokes are preferred. For long cuts, rotate the blade in the frame so that the length of the cut is not limited by the depth of the frame. Hold the work with the layout line close to the vise  jaws,  raising  the  work  in  the  vise  as  the  sawing proceeds. To remove a frozen nut with a hacksaw, saw into the nut, as shown in figure 1-17, starting the blade close to the threads on the bolt or stud and parallel to one face of the  nut,  as  shown  in  view  A.  Saw  parallel  to  the  bolt until the teeth of the blade almost reach the lockwasher. Lockwashers are hard and will ruin hacksaw blades, so do  not  try  to  saw  them.  View  B  shows  when  to  stop sawing. Then, with a cold chisel and hammer, remove this one side of the nut completely by opening the saw 1-12 Figure 1-14.—Selecting the proper hacksaw blade. Figure 1-15.—Installing a hacksaw blade. Figure 1-16.—Proper way to hold a hacksaw. Figure 1-17.—Removing a frozen nut with a hacksaw.







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