the surfaces to be joined have been properly prepared to receive the new
metal.

All spoiled, burned, corroded and rough particles must positively be
removed with chisel and hammer and with a free application of emery cloth
and wire brush. The metal exposed to the welding flame should be perfectly
clean and bright all over, or else the additional material will not unite,
but will only stick at best.

[Illustration: Figure 28.--Tapering the Opening Formed by a Break]

Following the cleaning it is always necessary to bevel, or champfer, the
edges except in the thinnest sheet metal. To make a weld that will hold,
the metal must be made into one piece, without holes or unfilled portions
at any point, and must be solid from inside to outside. This can only be
accomplished by starting the addition of metal at one point and gradually
building it up until the outside, or top, is reached. With comparatively
thin plates the molten metal may be started from the side farthest from the
operator and brought through, but with thicker sections the addition is
started in the middle and brought flush with one side and then with the
other.

It will readily be seen that the molten material cannot be depended upon to
flow between the tightly closed surfaces of a crack in a way that can be at
all sure to make a true weld. It will be necessary for the operator to
reach to the farthest side with the flame and welding rod, and to start the
new surfaces there. To allow this, the edges that are to be joined are
beveled from one side to the other (Figure 28), so that when placed
together in approximately the position they are to occupy they will leave a
grooved channel between them with its sides at an angle with each other