Slitting is the process of cutting along the length of a sheet to divide it
into narrower pieces, or to trim the edge.
I do not really know what tools were used before the slitting mill and I am
not sure anyone else will.
The slitting mill was invented at the end of the 16th century as far as we
know and rolling came in at about the same time.
From "The Black country Iron Industry by WKV Gale.
"The slitting mill was simple but effective, and it continued to be used, in
spite of the fact that other methods of making rods had been introduced,
fight up to the time when hand-wrought nail making ceased to be of
consequence.~ It consisted of a pair of rolls, mounted horizontally, one
over the other and fitted with intersecting collars which acted as cutters,
together with a pair of plain rolls similarly mounted. The whole mill was
driven by water power. Iron bars were first drawn down to a suitable size
under the tilt hammer and were next rolled into strip in the plain rolls.
The strips were then passed through the slitting rolls, which slit them into
nail rods. Various sizes of rod could be produced by varying the thickness
of the strip and by adjusting the number and width of the slitting collars.
The slitting mill came to be an important part of many Black Country
ironworks."
Prior to the introduction of rolling the wrought iron sheet, presumably long
and narrow, would have been produced from a bloom under the hammer and must
have been cut with shears such as the ones in the illustration from Agricola
(1561) or with a chisel. I am attaching two pictures. The tinplate one was
difficult to scan in because of the moiré effect. Both show giant tinsnips,
They are clear in the original illustrations.
I will make some enquiries but I do not hold out much hope of a definitve
account. Very little process detail survives from medieval times. It was all
secret.
Peter
Peter Hutchison
Hon. Gen. Secretary
The Historical Metallurgy Society Ltd.
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