Gunfounding in the Late XVIIIth Century

Copyright 1999 Samuel E. Kimpton All rights reserved

Description of the Blast Furnace:

Fig. 1 A TYPICAL BLAST FURNACE (after Coggins 1969)

Figure 1 represents a typical blast furnace as it would have appeared in the late XVIIIth century. It consisted primarily of a masonry structure enclosing a fire-brick lined crucible and chimney. The furnace was charged through an opening in the chimney with charcoal, iron-ore, and small amounts of limestone in alternating layers. Oxygen for combustion was supplied by a water blower which supplied air through an iron pipe leading to one, or in some cases more, tuyeres (B). This blower, as well as other machinery in the foundry, was powered by water or, in the more technologically developed nations such as England by Steam power.

The ore melted and was deposited at the bottom of the crucible when the fire reached sufficient temperature (white-hot). Impurities floated at the top of the pool. This was periodically tapped through a cinder hole (A) and poured into crude-sand molds. The resulting billets thus created were, with a little imagination, reminiscent of a sow feeding her litter. This "pig-iron" was valued only as a raw material for reworking and was recycled by putting it back into the crucible for recasting.

The Iron industry was heavily dependant on water power and charcoal (In England the latter was being supplanted by coal in the form of coke.) A large blast furnace could easily consume 800 bushels during a 24 hour period. Coggins (1969) gives the amount of wood required to yeild this quantity as "50 cords of timber, of at least 20-year growth--perhaps close to the yeild of an acre of forest". The charcoal was produced by charing this timber in large stacks. Foundries were usually located adjacent to waterways and timber due to this dependance.

the XVIIIth century should be viewed as a transitional period in the iron industry, During which one period of technological stagnation coupled with refinements in technique gave way to another characterized by technological inovation and a decreasing dependance on water as a scource of power and an increasing dependance on coal as well as refinements in metalurgy. It should be noted that this transition was dictated by economic and geo-political factors originating in Britain and carried over into the IXXth century in other nations.

Historical background:

Fig 2. TESTING THE BORE (XVIIth century)

Gunfounding had always been a rather expensive and time consuming process. It required specialized skills and materials. The principle differences between the methods employed in the manufacture of cannon in the XVIth and XVIIth centuries and those of the XVIIIth century (which will be outlined below) are three fold. Early methods can be distinguished by the following differences: 1. The tube was cast around a spindle representing the bore. This resulted in undesirable texture in the metal surounding it when cast and frequently would shift in position when the metal was poured. 2: the use of simple smelters in distinction from blast furnaces which not only was less efficient in terms of fuel expenditure and heating the raw materials but which also could produce weak regions within the casting. This increased the risk of the weapon bursting when it was fired. 3. The bore was finished by turning a cutting tool while the tube was held stationary and the exterior of the tube was finished by turning it.

Very Early Patterns for cannon were fashioned around a spindle made of rope representing the bore. Regardless of the material used for a spindle. The methodology required that the Bore be finished by hand. This in turn exacerbated problems in standardization of bore size. Shot made to fire from one piece could not neccesarily be fired from another piece of the same size. Guns of the early period were also less accurate, weaker, heavier (this meant that fewer could be carried on board a warship), more dangerous to operate, and more expensive and time consuming to produce. The concept of mass production, which was in its infancy in even the most developed nations of the XVIIIth century, was non-existant in this period. The improvements of the XVIIIth century included the increased employment of blast furnaces, advances in the quality of iron, the intoduction of solid casting and the boring the tube by turning it when cold by Johan Maritz in 1715, The introduction of bronze bore spindles for use in the older casting methods in 1730, The introduction of sand molds which decreased cost and improved the quality of the casting in 1850. And the introduction of mass production. It should be noted that many of these improvements were regional and there implimentation and use was coterminous with older technologies and practices in use in other regions for some time. Indeed some of these advances did not take hold in parts of Europe until well into the following century. Change takes time.

Materials for Gunfounding:

The inadequacies of early iron precipitated the use of bronze as a material for gun tubes during the XVIIth century. This material, erroneously called "brass", posessed greater tensile strength than iron and could withstand bore pressures more readily when the weapon was fired. I addition it was relatively corrosion resistant, could be re-cast and lent itself to decorative motifs. On the other hand it was much more expensive than Iron and, although less likely to burst, was prone to overheating and deformation under reapeated firing of the piece. With improvements in casting and and the quality of iron, bronze gradually fell out of favor. According to Gardiner (1992) by 1781 only The Royal George of Brittain had bronze armament. Parodoxically France began producing bronze 18-livre guns for a new class of figate in the same year. There were also bronze pieces produced during the French revolution for the army. The author believes, however, that the typical naval gun of this period was iron and would remain so until the introduction of steel in the latter part of the next century.

The Production of Cannon:

Making the Pattern


Fig 3. depicts a top view of the principal steps in the fabrication of a pattern for a gun tube as practiced in the XVIIIth century. The work begins at the upper left hand side of the illustration with a tapered piece of wood around which the mold will be made and ends in the lower right hand corner with a finished mold. The material used for the pattern consisted of a mixture of clay and sand bound together with horse dung. This latter ingredient also gave the pattern a friable quality which would be useful in removing it from the mold later in the process. The pattern and mold for the breach and cascabel was made seperately.


The first step in the process after turning the wooden spindle was the application of a rope or straw-plait winding to aproximate the general shape of the tube (Fig 3. left hand side and Fig.4)


The next step was the application of the pattern material (Clay) in such a manner as to approximate the shape of the tube (Fig 3. right and fig 5.). This process is much more hap-hazzard looking in fig 5 than in the period illustration (fig 3.).


The final step in making the pattern, before drying it, was to shape either it with conventional lathe-type cutting tools or by turning it against a metal edged modeling board (Fig 6.). The latter method ensured a higher degree of uniformity in the finished product.

Fabricating the Mold


The first step in making the actual mold in which the tube would be cast was to attach cylindrical forms for the trunnions with an iron pin running longitudinally through the elevation axis of the gun and transversly though the its long axis. The pattern was then coated with a mold release consisting of wax. This facilitated ease in cleaning the mold of the pattern material when it was removed. Once the pattern was thus prepared the mold material, which was comprised of clay and sand bound together with an agent like animal hair, was applied in layers. The first layer was usually reinforced with a winding of rope or cord. Then subsequent layers were applied. After the actual material was applied the mold was reinforced with iron bars and bands (Fig 7.).


After banding the pattern was removed from the mold by first withdrawing the pin holding the trunnion pieces in place. The spindle was dislodged with a hammer and removed. The mold material, which was friable owing to the horse dung binder, was removed as were the trunnion pieces. The inside of the mold was then cleaned and the entire mold fired to harden it. This firing was done by burying it in hot coals and then covering with earth. This is not as depicted in Fig 8. This also served to remove all moisture from the mold material. This was important as the presence of moisture could result in an explosion during casting.

Casting the Tube


Once the mold was fired it was again cleaned and prepared for casting by plating or otherwise plugging the holes left by the pin which held the trunnion-forms in place. The mold was then assembled, breech downward, in a casting pit (Fig 1C) located near the gate of the furnace (Fig1D) in which the iron was smelted. First the mold for the breech and cascabel was placed in the bottom of the pit. The mold for the tube was then placed in position on top of this mold. A dam for extra casting material, called a deadhead, was placed at the mouth of the configuration and secured by wiring it to the main mold. The entire configuration was then bedded by tamping earth in the pit around it. finally a system of branching clay channels were formed leading from the gate of the furnace to the openings of the molds (customarily two molds were poured simultaneously).

The actual casting was accomplished by first driving a fire-clay plug in the gate of the furnace with an iron bar. the castings were then poured up to the level of the top of the deadheads to ensure that enough material is allocated to properly fill the mold. The gate is then closed with a fire-clay plug and the casting allowed to cool in situ.

After a few days the casting, still in the mold, was exhumed and the mold removed by removing the re-enforcing bands and breaking the clay away by hammering. The entire process up to this point was some what destructive. The pattern and mold were fashioned specifically for each casting and could not be used over. This was both expensive and time consuming. The differential cooling of the iron caused by the mold also contributed to its brittleness. The introduction of sand molds around 1750 alleviated these problems to some degree. It would take at least five decades for this inovation to become universal practice in Europe.

Boring and Finishing the Tube


The first step in boring and finishing the gun tube after cleaning was in cutting the excess material, contained and cooled in the deadhead during casting, from the tube. The trunnions were then turned to ensure their roundness by securing the tube to a paltform with the trunnions positioned vertically and then by placing a cutting tool over the upper most one (Fig 9). This tool was then turned by hand until the tolerances were met. The tube was then rotated 180 degrees on its longitudinal axis and the other trunnion was turned.


The tube was placed in a water-powered machine designed specifically for boring cannon (Figs 10 and 11). The tube was secured in a horizontal position by means of a chuck and race. An iron boring bar tiped with a steel cutting tool was advanced into the bore of the piece through the agency of a rack and pinion or other arrangement as the gun blank was turned by the machinery. A series of cutting heads were used. The first would be small. subsequent heads would increase incrementally in size until the desired bore diameter was achieved. One option in this stage of the manufacture was the machining of the exterior of the gun. This was not always practiced but is depicted in Fig 10. Areas that could not be conveniently machined in this manner were finished by hand with chisels files and abrasives. It should also be noted that boring typically lasted for a period of days. In cases where the blank was cast around a central core, of brass or other material, Imperfections in the casting of the bore would be reamed in a method much like this. This would achieve a bore diameter within tolerances.

Fig 11. MACHINERY FOR BORING CANNON BY THE MARITZ METHOD (From an XVIIIth Century French Encyclopedia)

The Machinery and techniques of boring cannon heretofor described are based on the method developed by Johan Maritz of Switzerland in 1715. The method was introduced to France and Spain by his sons later in the century. Fig 11 illustrates the principal machinery used and is from a period-French scource. At the top of the illustration the method whereby the machinery is powered (water wheels) is shown. Also depicted are the drive gears for tuning the pieces, The boring bar, and three bits. It can be gathered from the illustration that four guns could be turned simulateously using this equipment. This is concrete evidence that the concept of mass production, albeit a new one, was known and practiced in France in the late XVIIIth century.

The Verbruggen family of Denmark further refined Maritz' Technique and established a gunfoundry in Woolwich, England. This foundry was reagarded as the the best in the world by 1780.

Final Touches

The next step in fabricating the tube was the creation of a vent through which the propellant charge for the piece would be ignited. The simplest method involved merely drilling a hole in the tube to serve as such a vent. More typically, a hole of about an inch diameter was bored into the tube. This whole was made to taper outwards towards the inside of the tube and a similarly tapered bushing, of a disimilar metal such as copper, was inserted into the hole from the inside. This bushing would be further pressed into place by the firing of the piece. The actual vent ran longitudinally through the bouching. This method was known as "bouching".

A still more involved and less common practice involved actually tapping the hole in the cannon and inserting a threaded bushing from the inside.

Inspecting and "Proofing" the finished Weapon


The Tube was inspected to determine the alignment of the bore with the geometry of guns exterior. This is depicted in Fig 2. and the actual geometry used is illustrated in Fig 12. After this geometry was deemed within acceptible limits the tube was "proofed" by firing it with a larger than normal propellant charge. Provided the gun survived this final test it was then deemed fit for service and the attention would shift to the next weapon to be completed.

The Production of Cannon in France During the Revolution


In the Early days of the revolution in France The proportion of servicable artillery pieces in France was very small. In 1793 Napoleon appointed his Friend, The eminent chemist, mathemetician, and physicist, Gaspard Monge to lead a special commision to oversee the production of, and meet the demands for, the production of artillery.

Monge issued edicts abandoning the use of clay forms in favor of sand casting for tubes, established gunfoundries in old churches and on farms throughout the French Countryside, and instituted training programs intended to familiarize workers with the techniques and skills needed to impliment the new methods to be used in making cannon. Establishments or specifications, for guns were defined. but these were seldom realized in the finished product. This is not unusual for any nation at this time. Just the same France produced 7,000 pieces for the army and navy under Monge in 1793-94.


In The XVIIIth century the industrial revolution was very much in its infancy. Technological advances often brought a whole range of problems related to there requirements in raw materials, skilled manpower, increasingly exact tollerances in machinery, and funding. As is the case throughout human history the progress of technology is inexorably linked with war, and the XVIIIth century was no exeption to this rule. War dictated the neccesity for such progress and gave rise to the political will to implement such change. Still the ability to carry out new inovations in industry was limited by geo-political and economic boundries. The technological and strategic rescources and wealth of certain nations might have created a disparity in military and/or naval developments with rival nations. Such disparity could also play a role in the outcome of conflicts be they potential or realized but most certainly not be the only factor. To ascribe political outcome to technology seems to easy. England did not fare as well as might be expected in her war with the United States given the comparitive status of industry in the beligerant nations. Gunfounding in particular was at a very primitive level in America as compared with Europe. Certainly other variables contributed to the outcome of the conflict. The exact nature of these factors is beyond the scope of this disertation.

One should bear in mind that the world in the XVIII century was, as it always has and will be, in a state of flux. Changes in one part of the world amy not be immediately felt in more politically and isolated regions, but they will have there effect as dictated buy time and circumstance. The truly interesting fact is that the less developed western nations were able do as well as they did.


DECEMBER 16, 1999