HISTORIC IRONWORK REPAIRS IN TIMBER-FRAMED BUILDINGS.

Chapter 6

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

6.8 Punching: Holes in most wrought iron components are punched with a set (Fig. 6.14). They can be a variety of shapes but are most often rectangular or square. Round punched holes are uncommon and occur later when round clout nails appear in the late 19th century. Drilled holes are uncommon in historic repairs of more than one hundred years old.

Fig. 6.14. A set for hot punching holes. This would be placed on the hot work over the hardie or pritchel hole and struck with a lump or sledge hammer.

6.9 Thread cutting: Early threads were laboriously filed by hand by specialist workers known as girders. They were not constant in pitch or thread form and were made to be paired with only one nut. Until 1800 good quality taps and dies were not available and so the local smith would always form his own threads using his own bespoke tools. Threads of this period always have a soft appearance so it is likely that they were formed hot by swaging the thread rather than cutting it. Another reason to believe this is that the thread diameter is slightly greater than the parent rod where the metal has been deformed rather than removed. It may even be that a clever smith could twist the thread form with a twisting bar. (See Fig 6.17).

Since the early 1800's the design of die stocks for hand cutting external threads (Fig. 6.15) has barely changed and in the Victorian period bench cutters became available (Fig. 6.16). These threads have rounded crests and roots and are of the same diameter as the parent bar. The thread pitch is constant and after 1860 the British Standard Whitworth thread form became the standard in Britain. See Chapter 7 for further details on thread forms.

Fig. 6.15. A die stock for cutting external threads. This example from 1900 illustrates the unchanged form that persists today.

Fig. 6.16. A hand driven bench thread cutter used for cutting British Standard Whitworth threads. A standard universally accepted by the 1860's. On the bench in front is a small die stock with two adjustable dies.

The identification of some of these techniques could lead to the development of a local typology with which to date and identify iron ties. The smith of old had an enormous range of equipment at his disposal but its form has scarcely changed (Fig. 6.17).

Fig 6.17. A collection of wrought-iron smith's tools. Their form, although refined by time, remained constant. (Seymour Lindsay J, 1964).

7. The origins of nails, staples, screw fixings and bolts.