The objective in tube bending is to obtain a smooth bend without flattening the tube. Tube bending is usually done with either a hand tube bender or a mechanically operated bender.

slide bar is moved around until the mark on the slide bar reaches the desired degree of bend on the radius block. See figure 5-6 for the six procedural steps in tube bending with the hand-operated tube bender.

MECHANICAL TUBE BENDER. The tube bender shown in figure 5-7 is issued as a kit. The kit contains the equipment necessary for bending tubing from 1/4 inch to 3/4 inch in diameter.

This tube bender is designed for use with aircraft grade, high-strengths stainless-steel tubing, as well as all other metal tubing. It is designed to be fastened to a bench or tripod. The base is formed to provide a secure grip in a vise. This type of tube bender uses a hand crank and gears. The forming die is keyed to the drive gear and is secured by a screw.

The forming die on the mechanical tube bender is calibrated in degrees, similarly to the radius block of the hand bender. A length of replacement tubing may be bent to a specified number of degrees or it may be bent to duplicate a bend either in a damaged tube or in a pattern. Duplicating a bend of a damaged tube or of a pattern is done by laying the sample or pattern on top of the tube being bent and slowly bending the new tube to the required bend.

Tube flaring is a method of forming the end of a tube into a funnel shape so it can be held by a threaded fitting. When a flared tube is prepared, a flare nut is slipped onto the tube and the end of the tube is flared. During tube installation, the flare is seated to a fitting with the inside of the flare against the cone-shaped end of the fitting, and the flare nut is screwed onto the fitting, pulling the inside of the flare against the seating surface of the fitting.

Either of two flaring tools (fig. 5-8) may be used. One gives a single flare and the other gives a double flare. The flaring tool consists of a split die block that has holes for various sizes of tubing,

a clamp to lock the end of the tubing inside the die block, and a yoke with a compressor screw and cone that slips over the die block and forms the 45-degree flare on the end of the tube. The screw has a T-handle. A double flaring tube has adaptors that turn in the edge of the tube before a regular 45-degree double flare is made. To use the single flaring tool, first check to see that the end of the tubing has been cut off squarely and has had the burrs removed from both inside and outside. Slip the flare nut onto the tube before you make the flare. Then, open the die block. Insert the end of the tubing into the hole corresponding to the OD of the tubing so that the end protrudes slightly above the top face of the die blocks. The amount by which the tubing extends above the blocks determines the finished diameter of the flare. The flare must be large enough to seat properly against the fitting, but small enough that the threads of the flare nut will slide over it. Close the die block and secure the tool with the wing nut. Use the handle of the yoke to tighten the wing nut. Then place the yoke over the end of the tubing and tighten the handle to force the cone into the end of the tubing. The completed flare should be slightly visible above the face of the die blocks.