Cutting, Bending and Flaring Tubing  Page 3

Flares can be either single, one thickness of the tubing flared out to a specific angle or a double flare.  A double flare is two thicknesses of tubing created by folding the end of the tubing back onto itself, forming a double thickness flare.  The single flare is the most commonly used but the double flare is desirable in some applications where splitting of the tubing while flaring is a possibility.  Applications like thin-wall steel tubing are places where this would apply.

Preparing the Tubing:  End of the tubing should be cut off squarely and not out of round.  Any burrs in the end should be carefully removed with care taken not to create a thinner wall at the end of the tube.   Cutting with a hacksaw will leave a burr on the outside end of the tubing and this must be removed also before flaring.

Making the Flare: Standard bar and yoke type flaring tools are equipped with either a fixed or swivel cone.  Swivel cones remain stationary when the advance screw is turned; fixed cones rotate when the screw is advanced.  Either will create a smooth flare when the burrs have been properly removed.

A good, smooth, narrow-flared joint is much more desirable than a rough-looking, uneven, wide-flared joint.  A proper flare will have a uniform wall thickness from the base to the lip of the flare and will be unscored at the base.
Two types of flaring tool are commonly used.  The older style is the compression-type flaring tool.  It flares the cone spreading the tube end until its expanded outer diameter makes contact with the countersunk flare profile in the die.  Over tightening the flare cone can produce a thinning out of the flare and can cause score marks around the base.


Tubing is clamped in the flaring bar projecting above it equal to the depth of the recess in the bar


The compression type-flaring tool forces the cone into the tube creating the flare against the countersunk recess in the flaring bar

     The newer design is the generating-type flaring tool.  The flaring bar holds the tube end above the surface of the bar and the flare is formed in the air instead of against the countersunk form in the bar.  The base of the flare is above the die so there is no danger of thinning the flared tube wall by scoring or applying too much torque.

A generating-type flaring tool creates the flare above the die, leaving uniform thickness throughout the flare


     The most commonly used flaring tool by the home shop hot rod builder is the hinged bar design, a compression type flaring tool.  It has two bars that clamp the tubing between them in one of six standard size holes.  Two wing nuts at each end are used to tighten the serrations in the holes around the tube holding it in place.  The flaring yoke is then placed over the bar and the screw-fed cone fed into the end of the tubing creating the flare.  Care must be taken to assure that the tube doesn’t slip in the flaring bar.  If the wing nuts are not tight enough the tube will slip and create an unacceptable flare that will have a tendency to leak.  On tool bars with two wing nuts it is advisable to tighten the one nearest the tubing first, then tighten the other end.

Forming the Flare:  To form the flare place the end of the cone over the end of the tubing and turn it down until the cone is centered over the tube end.  On a compression-type tool advance the cone until the flared part of the tube is solidly against the countersunk recess in the flaring bar.  On a generating-type tool advance the cone the number of revolutions specified in the instructions furnished with the tool for the size of flare being formed.  Check for splits, scoring or imperfections in the flare to assure that a good connection can be made.

Burnishing the Flare:  Burnishing the flare can produce a tighter fitting joint.  Some flaring tools have an automatic burnishing feature that polishes the flare when the cone is withdrawn.  The cone is spring-loaded and polishes the flare without scoring the tube because there are no serrations in the die block.

Double Flaring:  In automotive applications SAE recommends double flares for hydraulic brake lines and AC and refrigeration systems on cars and trucks.  The double flaring tool is similar to the single flaring tool except for the two-step process utilized in the creation of the flare.  The tube is clamped in the flaring bar above the surface a distance equal to the thickness of the shoulder on the corresponding adapter and the adapter inserted in the tube.  The yoke is installed and the cone advanced against the adapter until it rests against the flaring bar forcing the end of the tube into a bell shape in the flaring bar recess.  The adapter is removed and the cone advanced into the bell in the end of the tubing creating the double thickness flare.


This double flaring tool kit includes a yoke, flaring bar and assortment of inserts that correspond with the sizes of tubing the kit will flare


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