One final detail of construction of many on these pieces of armour is their screws and bolts.354 There has been comparatively little study of early screws, particularly those used on armour, and the methods used to create them are poorly understood. However, by close examination of the few medieval pieces from the Royal Armouries which do have screws, along with the scanty evidence available for medieval screw-making, some of these questions may be answered.
There are three ways a screw or bolt may be used on a piece of armour. It may be used with threads which are formed directly on the plate, it may be used in
conjunction with a threaded plate which has been riveted or brazed onto the armour, or it may pass all the way through the plate and be secured with a nut. The use of these bolts is to either rigidly affix elements such as a lance rest or auxiliary pieces for the joust, to hold pieces of armour together or close them, or to act as pivots, without doubt
352
See Figure 119. 353
See Figure 120. 354
Screws are any fastener which hold plates together directly by the use of their threads and threads on the plate. Bolts pass through the plates without engaging any threads and are secured by a separate nut.
the least common use. Due to the difficulty of manufacture, the time needed to repair them, and the difficulty of repairing them in the field when compared to straps and rivets, bolts are more commonly found on armours of higher quality meant for the tournament, though some field armour also made use of them.
All of the pieces using screws are from the late fifteenth and early sixteenth centuries, and armour may be one of the earliest widespread uses of screws and bolts in Europe.355 Their use is rather evenly distributed among helmets and breastplates in various roles, with one arm defence, AL.90, and of the ten objects with screws and bolts the full range of uses is well represented. Some objects, such as the great basinet from II.7 and a number of other great basinets and helms have holes through which bolts passed but were not included in this group since they only have simple holes with no threads.
The use of bolts as pivots is in a way unusual, since the action of raising and lowering the visor could work the nut loose and cause eventual loss. Three of the helmets have this arrangement, IV.12, IV.13, and IV.502. The last is a jousting helmet and so would not have seen extended use on campaign, but the other two are for field use and of low quality. It is possible, though only conjectural, that these are later working-life modifications, but the holes on the skull of IV.12 are square to accept the head of the bolt. This prevented the whole bolt from rotating with the visor, perhaps as a solution to the problem of the nut loosening. The holes on IV.13 are round, and the bolts are modern, so the arrangement is possibly not original.356
355
C. F. C. Beeson, English Church Clocks (London: Phillimore, 1971), p. 27, quoted in Randall C. Brooks, ‘Origins, Usage and Production of Screws: An Historical Perspective’, History and Technology, 8 (1990), 51-76 (p. 55).
356
RA inventory entry. The sallet had this arrangement in the nineteenth century, as shown in de Cosson’s Helmets and Mail, pp. 180-83.
Holding pieces together in a more rigid arrangement is much more common. In this case bolts may be used, but screws are also a possibility, either threading into an attached plate or into the actual armour plate. For both these methods there is ample evidence. IV.502 contains, in addition to its pivot bolts, four other screws which fasten the sides of the bevor to the skull and close the shoulders.357 At the sides the screws pass through the bevor and into lobes brazed onto the skull plate. These lobes are irregular in shape and may be repairs or additions, but are in any case thickened in order to provide more purchase for the threads. At the shoulders small pieces have been riveted to the interior on the skull plate to serve the same function, thickening that area where the screw passes.
Similarly on III.96, a heavy jousting breastplate, a number of holes are pierced for the attachment of several components, including the plackart, the shield, the helm, the lance rest, and the lance brace.358 As such the whole of the piece is heavily
perforated, although some of the holes were later filled. For the shield, lance brace, and most of the lance rest holes large thread plates have been riveted to the inside to
correspond with the external holes. In the centre for the helm and just above the lance rest plate there are holes which are threaded with no internal plate. Significantly, not all the central holes are actually threaded, though neither have they been closed. The untapped holes on the breastplate may represent where screws could be put in the future if the breastplate was used with a different helm requiring a different arrangement.
It is likely that in some cases the plates were pierced and then threaded as needed, as with III.96, though it would have been unusual for a piece of field armour where efficiency of design was more essential. Pieces with separate threaded plates or lugs which were riveted on would also have allowed threading to be carried out without
357
See Figures 121 and 122. 358
directly impacting the plate. This would possibly be more efficient and present less risk of damaging the armour as it is only a small piece that need be worked at a time. The holes on III.96 also have threading on the breastplate itself, which would have been done after the already tapped plate was attached.
This is related to the question of manufacture of screws in the Middle Ages, and on this point there has been very little scholarship. Heron of Alexandria created cutting tools for both the male and female components of screws, and Randall C. Brooks claims that this same process was in use throughout the Middle Ages, though there is little, if any, direct evidence.359 Aubrey Burstall claims that taps and dies were in use during the fourteenth century but unfortunately gives no supporting evidence.360 There is a screw- lathe illustrated as early as 1483 in Das Mittlealterliche Hausbuch, but this is not a tap and appears to be meant only for making wooden screw presses.361
An alternative method for making screws would be to file them by hand individually. The threads could have been marked in the same way given by Heron, with a guide tracing the path of the thread. The thread would then be cut by hand with files, gravers, or chisels.362 However, this also meant that while screws could be similar, they were never exactly the same due to variations in filing, and also that they were extremely labour-intensive compared to other fasteners.
While the creation of the screw or bolt, no matter the method, is fairly straightforward it is the threaded hole in plate or nut which presents a particular problem. Without a tap there is no efficient way to create the threads; neither gravers nor files can reach into the hole. The holes on the armour plates which have no
359
Brooks, ‘Origin, Usage and Production of Screws’, pp. 52-53. 360
Aubrey F. Burstall, A History of Mechanical Engineering (London: Faber and Faber, 1963), p. 155.
361
Brooks, ‘Origin, Usage and Production of Screws’, p. 63. 362
Stephen V. Grancsay and Cyril Stanley Smith, Made of Iron (Houston: University of St Thomas Art Department, 1966), p. 134.
accompanying thread plates offer a solution that takes advantage of the plastic nature of ferrous metals.
The breastplate from II.1, a late fifteenth-century German piece, has a plackart which is attached by means of a screw, just as with III.96 although II.1 is a piece of field armour. There is a single hole in the centre of the plackart and two holes on the breastplate, allowing for a certain amount of adjustment. The two breastplate holes are threaded with no internal plate, and the interior of the holes is very ragged.363 In this case it is not a matter of the armourer not cleaning the interior but actually making use of them, formed when metal was displaced during punching. This created a slightly thicker area around the screw holes without resorting to leaving that area of the plate thick during forging. The thickness is especially important when considering the wide threads of the screw. Even on III.96, itself a very thick plate, there are burrs around the screw holes.
It was not only punching that caused this increase of thickness, and indeed it is this thickening which points most at the method of tapping; these holes were most likely tapped by the screws and bolts themselves. The screws were not self-tapping as we understand them today, but rather it was a combination of the helix of the screw, bevelled edges, and heat that allowed the holes to be threaded. There is precedence for this type of thread-making found in nineteenth-century screw threading plates. These plates consisted of a series of holes of graduating size which were threaded. The blank was inserted into the largest hole and the plate twisted around, and then each smaller hole in succession. ‘The forming action by a screw plate was to squeeze the metal blank into the threaded form...The addition of more rows of holes permitted a more gradual forcing of the shape into successively deeper threads’.364 The action of the
363
See Figure 125. 364
screw plate was thus more akin to a wire-drawing plate than a modern screw die. The same process would be done in reverse to create the plates, and so a set of taps and dies unique to the workshop would be created.
The 1611 and 1629 inventories of the Tower mention a ‘counter borer’, which was likely used for bevelling the edges of holes for flush rivets, but could also be used to prepare holes for tapping.365 The lance rest for III.69, a fifteenth-century German breastplate, has two threaded holes and three holes which are countersunk but not threaded, showing the preparatory step.366 The underside is clean on all the holes, since the rest’s base must fit the breastplate firmly and the plate it is made from is quite thick enough already.
This counter-sinking would have given the screw a starting point, making the tapping slightly easier, and also helping to align the screw. The last step of the tapping process would have benefitted from the plate being heated to make deforming the plate easier. The screw or bolt was put in the hole and turned, driving into the plate and creating the threads not by cutting away material, but by displacing it. That displaced material makes up part of the burr seen on III.96 and II.1. The threads of the hole would be an exact match to the screw or tap which created them, making replacements difficult if the originals were lost or unavailable.
4.7. Conclusion
Most studies of armour have focused on its outward appearance and changes in shape, but it should now be apparent that the interior of armour is just as varied and complex. These marks which were left by the tools are as much a part of the armour as the
365
Tower Inv., pp. 59 and 76. 366
decoration on the exterior, and one of the most important pieces of evidence for the manufacture of armour.
When discussing the marks on the converted kettle hat mentioned in the introduction, Hood describes some identifiable patterns:
...the thinning of the metal close to the apex corresponds with the process of deeply drawing out the metal in order to create the short comb. This same raising process is already evident on the inside of the skull where square- shaped hammer marks run in concentric circles. The hammer marks on the inside of the helmet are not matched on the relatively smooth exterior and this suggests that the outer surface was polished smooth...367
However, as has been demonstrated above the thinning of the metal was not from raising but from embossing, which pushed the comb out and thinned it, not raising which compresses. The concentric marks are not hammer marks but were made by a stake, from raising but made clearer through planishing which smoothed the exterior surface. Hood further states that 'The one-piece construction of the helmet and the deep drawing of the metal to create the short, crisp comb denote the hand of an armourer of considerable skill', but the techniques of raising and fluting were essential for all armourers to know.368 It was the skill with which the techniques were carried out that signifies the work of a master.
Although metallographic examination and related techniques may be used to determine some aspects of how an armour was made, each tool mark is the direct result of a single hammer blow by an armourer centuries ago. Those marks taken together may be analysed to read a piece of armour to better understand the actual working practice of the armourer for a greater amount of the process.
367
Hood, 'A Late Fourteenth-Century Transitional Kettle-Hat', p. 158. 368
Although the marks themselves are not immensely varied in shape, being largely either round or oblong, their precise shape paired with their size, pattern, and context within the armour may be used to accurately identify the exact technique used in making each piece. Overlap of marks from one feature to the next shows order of construction. Some of the assumptions about the ways in which armour was made have been found to be inaccurate.
The experimental plate work was especially helpful in this regard as it resulted in confirmation linking mark patterns and techniques. Greave mark patterns were demonstrated to come from internal curling rather than raising, planishing was differentiated from both raising and doming, and the marks from several different fluting methods were identified, providing a basis for further study and identification.
Chapter V: Case Studies