278 WILLIAM FIELD HOW. 
In high class bridge and boiler work, the plate edges are planed, 
and although this is not very necessary for wrought iron flange 
plates for bridges, yet it adds greatly to the appearance of a 
structure, and is usually specified when well finished work is. 
required. ; 
For bridges made of steel, it is of the greatest importance that. 
the plates and bars constituting the tension members should be: 
planed or have rolled edges; because such members, if left sheared, 
constitute a real weakness, and it would be far better to plane up 
any sheared edges that might otherwise exist and so slightly reduce 
the effective sectional area, than permit the sheared edges to 
remain, having starting points of rupture due to the slight initia] 
cracks caused by shearing, which are so serious to steel subject to 
tensional stresses. | 
It is usual to have all plate edges in a steel bridge planed, as. 
well as the butting surfaces ; but the planing of the longitudinal 
plates in the compression members is not of great importance. It 
is, however, invariably insisted upon for work of the best character 
on account of the improved appearance it gives. 
For built up iron girders used by architects, it is not necessary 
to have expense incurred in planing the plate edges, as such 
girders are seldom exposed to the sight; but if steel plates are 
used in their construction, it is of great importance to the strength 
of independent girders, that the edges of the bottom flanges should 
be planed, and if the girder be continuous, the edges of both top 
and bottom flange plates should be machined. 
For boilers, all plate edges are planed, whether the material be 
steel or iron; and when lap joints are employed, the edges have an 
angle of about seventy degrees, to enable the plates to be “fullered” 
both inside and outside, special attention being given to the inside. 
Caulking used to be adopted for completing joints in boilers, in 
which case a tool, somewhat similar in shape to a cold chisel, but 
instead of having a cutting edge, that end was made about one 
quarter inch deep and was driven into the edge of the overlapping 
