Metalworking
Practical Action
Hand lever shears bolt to a bench or a stand, and are of greater capacity than tin snips (e.g. 3
mm steel). Their use is generally, restricted to straight cuts, although it is possible to trim the
edges of a sheet to a convex curve by successively cutting thin strips from the corners. They
can be used to cut to a point on a sheet, rather than being restricted to cutting right across,
and so can be used, for example, to cut out squares from the corners of a sheet in preparation
for folding into a box. Having the shearing action of a pair of scissors, they tend to distort the
cut edges. However, this difficulty is overcome in one type of machine, in which the sheet lies
flat on the table, and a narrow strip is sheared out along the line of the cut.
How to Make Cutting Shears for Sheet Metal - Workshop Equipment 4
Rob Hitchings, Practical Action Publishing
Guillotines are arranged to cut across the entire width of a sheet, and can be treadle operated
(typically with a capacity of 1 m width and 1.5 mm thickness, or power operated. These
machines are quick and accurate in use, and leave clean-cut edges practically free of
distortion. They are used universally for the preparation of straight-sided shapes, except
where cuts into, but not right across, the sheet are needed.
Holepunch
How to Make a Hand-Operated Hole-Punch - Workshop Equipment manual 7
Ted Stone and Jim Tanburn, Practical Action Publishing
Drilling
How to Make a Foot-operated Workshop Drill - Workshop Equipment 2
Paul Smith, Practical Action Publishing
Lathes and milling machines
Machines such as lathes and milling machines are an expensive investment for a small
metalworking enterprise and so are not discussed in this technical brief. They can, however,
vastly improve the quality and versatility items that can be made providing the ability to make
screws and gears.
Jointing
The jointing processes used on sheet metal include:
Folding and seaming
Riveting
Soldering
Brazing
Welding
Folding and seaming,
The edges are folded over each other, is used particularly by tinsmiths, and in the volume
production of thin sheet metal parts. A jenny or folding machine is used to make the folds,
and then with either a seaming machine or a hammer the folds are closed together to make
the seam. The seam can be sealed if necessary with soft solder, or by hot dip galvanizing the
finished product.
Rivets are usually set by hand using a hammer and appropriate sets. The technique is low in
capital but takes time and skill. However, pop-riveting, in which a hand held tool is used to
set a hollow rivet, much quicker, as it requires access from only one side of the job. The cost
of the pop-rivets, which are made to suit the type of setting tool ("gun") are expensive. Except
for the jointing of aluminium and pre-coated steel, riveting has mainly given way to welding.
Soldering is used largely in tinplate and copper and brass, although it can be used on
galvanized and bare steel. It is not usually used for aluminium, as powerful fluxes are
necessary. The process consists of running molten solder into the joint, using either a flame
or a heated iron (made of copper) to heat the joint while the solder is applied. Cleaning and
the use of flux are necessary to enable the solder to take. Fluxes can be proprietary, or zinc
chloride can be used. This is made by dissolving zinc in hydrochloric acid (spirits of salts)
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