Tube Cutting and Deburring

contraction. Bends are preferred to elbows, because bends cause less of a power loss. A few of the correct and incorrect methods of installing tubing are illustrated in figure 5-1. Bends are described by their radius measure- ments. The ideal bend radius is 2 1/2 to 3 times the ID, as shown in figure 5-2. For example, if the ID of a line is 2 inches, the radius of the bend should be between 5 and 6 inches. While friction increases markedly for sharper curves than this, it also tends to increase up to a certain point for gentler curves. The increases in friction in a bend with a radius of more than 3 pipe diameters result from increased turbulence near the outside edges of the flow. Particles of fluid must travel a longer distance in making the change in direction. When the radius of the bend is less than 2 1/2 pipe diameters, the increased pressure loss is due to the abrupt change in the direction of flow, especially for particles near the inside edge of the flow. During your career in the Navy, you may be required to fabricate new tubing to replace damaged or failed lines. Fabrication of tubing consists of four basic operations: cutting, deburring, bending, and joint preparation. Tube Cutting and Deburring The objective of cutting tubing is to produce a square end that is free from burrs. Tubing may be cut using a standard tube cutter (fig. 5-3), a chipless cutter (fig. 5-4), or a fine-toothed hacksaw if a tube cutter is not available. When you use the standard tube cutter, place the tube in the cutter with the cutting wheel at the point where the cut is to be made. Apply light pressure on the tube by tightening the adjusting Figure 5-2.—Ideal bend radius. knob. Too much pressure applied to the cutting wheel at onetime may deform the tubing or cause excessive burrs. Rotate the cutter toward its open side (fig. 5-3). As you rotate the cutter, adjust the tightening knob after each complete turn to maintain light pressure on the cutting wheel. When you use the chipless cutter, take the following steps: 1. Select the chipless cutter according to tubing size. 2. Rotate the cutter head to accept the tubing in the cutting position. Check that the cutter ratchet is operating freely and that the cutter wheel is clear of the cutter head opening (fig. 5-4). 3. Center the tubing on two rollers and the cutting blade. 4. Use the hex key provided with the turn the drive screw in until the cutter touches the tube. Figure 5-1.—Correct and incorrect methods of installing tubing. 5-4 kit to wheel