simplifies this process.  Figure 4-17  illustrates one type of  hole duplicator. The peg on the bottom leg of the duplicator  fits into the existing rivet hole. To make the hole in the  replacement sheet or patch, drill through the bushing on the  top leg. If the duplicator is properly made, holes drilled in  this manner are in perfect alignment. A separate duplicator  must be used for each diameter of rivet.  Powered and nonpowered metal cutting tools available to the  aviation technician include various types of saws, nibblers,  shears, sanders, notchers, and grinders.  The circular-cutting saw cuts with a toothed, steel disk that  rotates at high speed. Handheld or table mounted and powered  by compressed air, this power saw cuts metal or wood. To  prevent the saw from grabbing the metal, keep a firm grip  on the saw handle at all times. Check the blade carefully for  cracks prior to installation because a cracked blade can fly  apart during use, possibly causing serious injury. The Kett saw is an electrically operated, portable circular  cutting saw that uses blades of various diameters.  [Figure 4-18] Since the head of this saw can be turned to any desired angle,  it is useful for removing damaged sections on a stringer. The  advantages of a Kett saw include: The pneumatic circular-cutting saw, useful for cutting out  damage, is similar to the Kett saw.  [Figure 4-19] The versatile reciprocating saw achieves cutting action  through a push and pull (reciprocating) motion of the blade.  This saw can be used right sideup or upside down, a feature  that makes it handier than the circular saw for working in tight  or awkward spots. A variety of blade types are available for  reciprocating saws; blades with finer teeth are used for cutting  through metal. The portable, air-powered reciprocating saw  uses a standard hacksaw blade and can cut a 360° circle or  a square or rectangular hole. Unsuited for fine precision  work, this saw is more difficult to control than the pneumatic  circular-cutting saw. A reciprocating saw should be used in  such a way that at least two teeth of the saw blade are cutting  at all times. Avoid applying too much downward pressure on  the saw handle because the blade may break.  [Figure 4-20] Figure 4-19.  Pneumatic circular saw. Figure 4-17.  Hole duplicator. Figure 4-18.  Kett saw. 4.  Can cut an inside or outside radius. 1.  Can cut metal up to  3 ⁄ 16-inch in thickness. 2.  No starting hole is required. 3.  A cut can be started anywhere on a sheet of metal. Cutting Tools Circular-Cutting Saws Kett Saw  Pneumatic Circular-Cutting Saw Reciprocating Saw 4-8 New skin Old skin Angle