TREATMENT OF MANUFACTURED IRON AND STEEL. 279 
plate of the boiler shell, closely against the outer surface of the 
adjacent shell plate, with the effect of temporarily stopping leaks, | 
but permanently separating the two plates between the rivets and 
edges. To provide against this defect, deep flat ended or deep 
convex ended tools are used, which, when driven against the planed 
edges of the plates, force the bottom surface of the outer plates to 
bear, within some little distance from the edge, against the adjacent 
ones, instead of tending to force them apart as is the case when 
the old fashioned caulking tool is used. 
Rivet Holes. | 
For cheap bridge work and ordinary builders’ girders built up 
of wrought iron plates, and wrought iron joists, or wrought iron 
plates and angles, the rivet holes are usually made by punching, 
and if carefully done the material is little injured ; but if the holes 
are carelessly made, then very rough treatment is required to 
enable the rivets to be passed through them. In such cases of care- 
less workmanship, the workmen have to use drifts having a long 
and acute taper, and the author has seen such drifts used; with 
satisfaction to the workmen; when they have been just able to see 
daylight through the holes in two or three thicknesses of plates. 
Punched holes should in all cases be marked off from carefully 
prepared templates, clamped over the plates or bars to be dealt 
with, and a centre punch used, the body having nearly the diameter 
of the hole in the template. Accurately punched holes are made by 
nipple punches, care being taken that the plates &c. are adjusted 
so that the projection or nipple, enters the centre punched holes in 
the plates. This system is adopted in the best works in England 
and on the Continent of Europe, where the work is treated with 
so much care, that the author has seen girders having as many as 
four thicknesses of five-eight inch plate and an angle iron, so truly 
punched that at first sight they appeared to have been drilled. 
The dies at the works referred to are carefully made and attended 
to, and have such little taper in them that the punchings are almost 
parallel, the taper being hardly noticeable with the callipers. 
