HISTORIC IRONWORK REPAIRS IN TIMBER-FRAMED BUILDINGS.

Chapter 5

5. Types of iron ties. 6/6.

5.14 Threaded Bolts.
Salzman believes that threaded bolts were introduced at the beginning of the 1500's but it appears unlikely that they were available commonly for at least another hundred years. Screw threaded bolts were certainly being used in cathedral work of the later 17th century. (Hewett CA, 1980).

Early threaded bolts have very heavy heads, shanks and almost cuboid nuts (Fig 5.38) and this trend continued into the late 1700's. By 1800 machine tools were being developed that allowed the mass production of bolts and nuts. The forged bolts had square heads but with a slight dome (Fig. 5.39) and the nuts became very much slimmer (Fig. 5.40).

Fig. 5.38. Two bolts dated to 1714 by the accounts of Ashes Farm, Cressing, Essex. The heads are heavy and flat topped and the nut not far off being a cube of metal.

Fig. 5.39. A 19th century bolt head in the Horse Shelter at Cressing Temple. Built between 1842 and 1876 (from map evidence) all the hanging knees are bolted in place with these distinctively headed bolts.

Fig. 5.40. The other end of the bolt in Fig. 5.37 above. The nut is very much slimmer than those of a hundred years earlier and it sits on a machine made washer. The tip of the thread is blunt. Compare with Fig. 5.21.

Threaded bolts became routinely used in the fabrication of buildings in the early to mid 1800's where they were employed to bolt together trusses and secure hanging knees (Fig. 5.41). Bolts up to the first half of the 19th century have sharp pointed ends to receive the thread which has a swaged appearance. By the second half of the 19th century the ends become blunt and the threads much sharper in profile. (This is also a feature of tie-rods which are simply very long bolts). By the early 20th century hexagonal headed bolts were freely available for heavy engineering such as the building of steel framed buildings. It is very unlikely to find an earlier hexagonal headed bolt or nut in a timber-frame repair.

Fig. 5.41. The Horse Shelter at Cressing Temple is a typical mid-Victorian farm building. All the hanging knees are secured with wrought iron square-headed bolts. Repairs to the 18th century Wagon Lodge, close by on the site, mimic this design exactly.

5.15 Stirrups.
Stirrups are elongated U shaped straps whose terminals are specially forged to receive bolts or gibs and cotters. They became popular in the late 1600's as a way of reinforcing thin section trusses. Winchester cathedral has examples of stirrups secured with forelock bolts dating to 1699 while Lincoln Cathedral has stirrup, gibs and cotters dated to 1762. (Hewett CA, 1980). None were observed used as repairs during field work and this may be because of the difficulty of precisely cutting the housing for the gibs and cotters. They are also unnecessarily complicated for a simple repair.

5.16 Composite ties.
This is a term here employed to describe a tie that has more than one component to effect its use (Fig. 5.42). Tie rods or bars with special terminals may be considered as composite ties but their form is commonplace. Unusual forms need to have their characteristics closely examined to determine a period of use.

Fig. 5.42. A composite tie on the front of the Marlborough Head public house, Dedham, Suffolk. This resembles the pin tie found in the Wheat Barn at Cressing Temple (Fig. 5.27) but it has been passed through a face-plate to secure the joint.

5. A Note on Reworked and Re-used Iron.