Flare Tube Fittings

by B. M. Green

The North American Live Steamer, Volume 1 Number 10, October 1956

Bill Van Brocklin gave us a fine set of standards for the ferrule type of tube unions (see Union Nuts & Fittings) and, as he says, L.B.S.C. has used this type for many years. However, the less expert person may have considerable difficulty in making and silver soldering neat ferrules for the smaller sizes. Solder must be kept off the cone face and also off the rear face of the ferrule if it is to seat steam tight. These troubles may be avoided by using a flared type such as is used in automotive work. L.B.S.C. says that this type will not last long but many of my friends are using it with success. I have found no standard for tubing smaller than 1/4 inch and, even in this size, fittings are large and clumsy for our purposes, so I have made up my own standard s and offer them for what they are worth. It is interesting to note how closely Van Brocklin's dimensions and mine agree.

For the flare fittings several tools are required but they are easily made from drill rod quenched in oil. The standard flare angle is 90 degrees and the cone points on the punch and reamers should all be turned at the same time by setting over the compound slide. The exact angle is not important as long as all are alike. Only one punch is needed, large enough to flare the largest tube used. Polish the cone after hardening. A reamer is needed for each size of tube to form the seat in the nut as the angle is different from that left by the tap drill. These are simply D-bits and the lfat can be filed in the lathe, "miking" the thickness to ensure that it is filed just half way. The body is turned to a good fit in the tap drill hole and, for the smaller sizes, it is well to use a larger piece of drill rod and turn down the distance K, or a little more, to dimension J.

The die block is used to grip the tube when flaring. It is made in two pieces dowelled together to ensure accuracy of the holes and shouldered to rest in the bench vice. When drilling for the tube holes, nominal size, slip a piece of 0.005 brass shim stock between the halves, so they will later clamp the tube, and form the countersinks with the reamers already made. The die block should really be made of hardened tool steel but mine, of 3/8 inch key stock, has served for quite a while. If the shim stock is too thick a slight ridge will be left on the outside of the flare and this must be carefully filed off. Don't forget to slip the nut on the tube before flaring and also to anneal the tube. Otherwise the tube is likely to split.