How To Flare Tubing

Here’s what’s needed to make decent 45-degree double-lap flares on mild-steel or Bundy tubing: (A) a 45-degree double-flaring tool (Ridgid PN 345-DL); (B) an inner/outer reamer (Imperial PN 208-FSS); (C) tube cutters; (D) emery cloth; and (E) files.

Cut the tubing to the desired length using the tubing cutter. Smoothly rotate the cutter in one direction around the tube, gradually increasing the cutter pressure by turning the knurled feed-screw knob. This midget cutter (Ridgid PN 101) is designed for use in restricted spaces.

Extra time spent on preparing the tubing before inserting it into the flaring tool is the secret to turning out a durable flare. Deburr the tube end’s inner and outer edges with a suitable tool like this inner/outer reamer. Its inner hollow-ground tool-steel cutters take care of the inside. Flip the unit around and the opposite end will do the same to the outside of the tubing.

The tube end must be absolutely square and flat in relation to the tubing’s longitudinal axis—file as needed. Polish the tubing end with a piece of emery cloth. After the end is smooth to the touch with no sharp edges remaining, slip the flare-nuts onto the tubing. It is now ready to insert into the flaring tool.

Insert the tubing into the proper-size hole in the flaring bar. It must protrude above the top of the bar by a distance equal to the height of the step on the button-end of the adapter for the same tube size. Exception: Set the height of 3/16-inch tubing equal to the height of the first (large) step in the button.

Be sure the tubing end to be flared protrudes out the side of the flaring bar with the conical recess (the opposite side is flat with no recess). After setting the tubing height, swing the hinge-lever to the side to lightly hold the tube in position. Place the proper-size adapter over the end of the tubing, pin-end down.

Lightly oil the flaring-cone. Slip the yoke over the bar, positioning it with the flaring cone centered over the adapter. Screw the cone down until the cone and adapter engage. Make sure the adapter is centered in the tubing. Lock the tubing into position by tightening the clamp screw. Screw the cone down until the shoulder on the adapter touches the flaring bar.

Back off the flaring cone enough to remove the adapter. As shown here, this first step bell-mouths the tubing in preparation for the final double flare. Also note the visible seams (arrows) in this automotive-quality mild-steel tubing. A seam is a stress riser; a crack will eventually form at the seam edge unless it is double flared.

Screw the cone down again until it bottoms tightly against the tubing. This folds the tubing back on itself, forming an accurate and crack-resistant 45-degree double flare. That’s it—no runs, no drips, no errors.

Fluid-line tubing—aka “hard-line”—forms a critical link in most cars’ fuel and brake systems. Disc-brake conversions, carb and intake swaps, or damage caused by everyday wear and tear may require cutting and reflaring the tubing ends or replacing fittings. On its face, that doesn’t sound too difficult, but how many times have you heard a frustrated car crafter complain, “I don’t have much luck with tubing,” or “Hard-line sucks; my brake lines keep cracking and leaking”? Many will resort to cobbled messes of adapters and fittings rather than having to cut and reflare new or existing lines.

Tube-flare leaks can usually be traced to the wrong tooling or failure to properly prepare the tube ends for flaring. By procuring quality flaring tools—such as those made by Imperial or Ridgid (Ridge Tool)—that turn out the proper flare for the style of tubing and connections being used, and then taking a little extra time to thoroughly deburr the tubing after it is cut, there’s no reason why your flares shouldn’t last nearly forever. Let’s take a closer look at what’s involved in correctly forming the common 45-degree SAE inverted automotive double flare so that you too can form tubing with a flare.