A very common form of stem brazing is shown by
sketch C. Here a hole is drilled through the body of the
valve, the stem is driven in, riveted slightly and then
brazed. This makes a very good joint but it is not quite
good enough for automobile work for there is a possibility
of the brazing becoming loose, allowing the stem to slip
in and out of the valve head.
The only form of brazing a joint which should be tol-
erated in automobile work is shown by sketch D. Here
a hole is drilled through the valve head as above but the
hole is made* much smaller and instead of having the stem
driven in the hole is tapped and a thread is cut upon the
stem, after which they are screwed together as tightly as
possible and the outer end of the stem riveted lightly
over the valve head, then after the brazing has been
effected a j6int is the result which is only weaker than
a solid stem to the extent of the difference in the diameter
between the valve stem and its diameter at the bottom
of the tapped thread.
Brazing Ferrules.
The beginner in brazing usually proceeds with a ferrule
for a chisel handle or for a knife handle. Usually the
ferrule consists of a bit of hoop iron cut to the right
length and rolled up until the edges butt together. Ferrules
are shown by Fig. 56 and it should be noted that in
sketch A the joint is a very poor one. Only one edge



158 SOLDERING AND BEAZINQ.
