PART I: CHAPTER I
MATERIALS AND SIZES
Materials which can best be fabricated by cutting and welding are those
which need the least cutting and welding. This statement at first appears
a contradiction in terms, but will upon examination be found to he sound
economic sense. Steel plate and bar can often be formed more cheaply than
it can he welded.
For example, two sections of angle can obviously be welded into a box section with less preparation and welding time than four pieces of bar could be cut, set up at right angles to each other and four corner welds made to achieve the same result.
All fabrications should be reduced
to the smallest possible number of parts consistent with the requirements
of the finished part. This should always be borne in mind and the greatest
possible use made of the considerable range of rolled steel sections which
are available (Fig. 1)
Stock Sizes:
Rounds 3/16 in. - 12 in.
Squares 3/16 in. - 7 in.
Flats 1/2 in x 3/16in. - 24 in x 3/4in.
Angles (Equal) 2 in.x 1.1/2in. x 3/16in. - 8 in. x 8 in
x 3/4in.
Angles (Unequal) 2 in. x 1.1/2 in x 3/16in. - 10 in x 4
in. x 5/8in.
Tees (Equal) 5/8 in x 5/8in x 1/8in - 6 in x 6 in x 5/8in,
Tees (Unequal) 2 in x 1,1/2in x 1/4in - 6 in x 4 in x 5/8in.
R.S.J. 3 in x 1.1/2in - 24 in x 7.1/2 in.
Channel 1.1/2in x 3/4in - 17 in x 4 in.
Convex 1/2in x 3/16in. - 3 in. x 3/4in.
Plate 1/16in. - 1/2in. thick in sheets;
6 fl. x 2 ft. or 2 ft. 6 in. or 3 ft. or 4 ft.
9ft. x 2 ft. or 2 ft. 6 in. or 3 ft. or 4 ft.
Thicker and larger to special order.
Wide ranges of Pipe, Hexagon, Z section, bull head rails, etc.
Sometimes the most suitable section cannot always be obtained; or alternatively
is not obtainable in the strength required. Improvisation is then necessary
and a series of suggestions appear in Fig. 2.
These improvised sections obviously call for accurate setting up before welding. Distortion must be avoided and alignment maintained. The use of jigs to achieve this end should always be considered. A well-designed jig need not be complicated and can save the hours of work involved in temporarily propping in position the parts to he welded. Jobs are all too often set up with the odds and ends which clutter the welding bench; this causes much delay, collapse of the parts when the electrode is struck and frequent misalignment.
A Jig need only in many cases be a section of angle or channel iron to which
parts can he clamped to hold them at right angles during welding. The corners
of such sections must he chamfered away to prevent the arc picking them up
and the Jig becoming welded to the Job. Fig. 3 shows this.
Three other Jigs to preserve alignment or to allow a downhand welding position
are shown in Figs. 4, 5 and 6.
Fig
4
Fig
5
Fig
6
The three-point clamp (Fig. 4) enables fabrications of irregular section
to he firmly held. The three pivot points each permit 360 rotation, giving
virtually any position of the fabrication required.
The universal welding jig (Fig. 5) is constructed from flat, round and large
section angle iron. It can be fitted with a cross-shaped head to take four
such clamps to extend its versatility. Each clamp has two clamping screws
set at 90° to each other to minimise the need for moving the clamps for different
job,.
The shaft and stock welding jig (Fig. 6) is most useful for joining round
stock in perfect alignment. If stock of differing diameters is to he joined
packing pieces equal in thickness to half the difference in diameter between
the piece, to be joined should be used to pack up the smaller section
of round stock.
If a production run of a certain fabrication is to he undertaken it is always best to construct a special jig for this one purpose. The time saved in setting up each individual fabrication will far more than repay the cost of' making up the jig. There is usually no need to weld the jig fully. Strong well-placed tack welds will serve and can be cut out or broken after the jig has served its purpose so that the material of which it has been made can he used again.
The remainder of these pages describes the application of these principles.
