HISTORIC IRONWORK REPAIRS IN TIMBER-FRAMED BUILDINGS.

Chapter 6

Techniques used to form wrought iron components. 4/5.

6.5 Cold cutting: Material can be cold cut in a variety of ways: mechanically using hacksaws, guillotines, files, presses, punches and drills. Traditional blacksmithing uses only hot cutting.

6.6 Hot Cutting:

With a hardie. The hardie is a hardened sharpened wedge which is mounted blade up in the hardie hole on an anvil (Fig. 6.10). The metal to be cut is heated to red heat and struck over the hardie, quickly being turned to complete the cut. The hardie is usually employed to cut material to length.

Fig. 6.10. The hardie resembles a fuller except that it has a definite cutting edge. The red hot work is struck on the hardie until it parts. Large bars are hit with sledge hammers by a second smith called a striker.

With a chisel. The work is heated to a red heat and a chisel struck into the work over the anvil onto a piece of soft scrap metal to prevent blunting the chisel. Chisels are either the normal type or with the head set at right-angles to a wooden or metal wire shaft. These are known as hot sets (Fig. 6.11) and are designed to be hit by a striker wielding a sledge hammer while being held by the smith. Hot cutting can be used to split bars along their length, a technique which is employed in producing the shouldered iron ties where local upsets are required.

Fig. 6.11. A hot set resembles a hammer except that it has a chisel point. The smith holds the set while the striker hits it with a sledge.

6.7 Bending: Bending to shape can be done hot or cold depending on the section thickness and the intrinsic brittleness of the iron being wrought.

On the anvil. The iron can be hammered over the bick, table or step (Fig. 6.12). Bars can be bent cold by dropping them into the hardie or pritchel hole and using raw strength. Originally there were only two patterns of anvil, the London or Portsmouth. Nowadays there is a multitude of specialists anvils.

Fig. 6.12. A typical anvil of the London pattern. The curved bick (beak) can be used to form soft curves while right angles can be formed across the table.

With a scroll wrench. This is a forked implement designed to grasp the hot bar and twist it to shape. It can be set in the anvil (Fig. 6.13) and is useful in bending strips with their plane such that the iron tie can be laid perfectly flat. This is a later technique employed when the understanding of the strength of wrought iron became known in the 19th century. The curved iron can exhibit ripples.

Fig. 6.13. A scroll wrench set in the hardie hole of the anvil. This allows the smith to easily manipulate the bar to the right curvature.

In a vice. The vice grips the lower portion of the work which is then hammered, scrolled or pulled by hand. Vice marks may be evident and indicate a late date of manufacture (18th century onwards).

6.8 Punching, 6.9 Thread cutting.