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(3) At the Royal Arsenal, heavy metal tampers on long rods were used to pack the fill, and the tampers were first heated so the dampened fill would not stick to them. Attention to every detail of this ancient art was the founder's only assurance of successful "pours"! Whether every such nicety as was observed at Woolwich was observed at Salisbury may be questioned, but equivalent strategems would have been required to keep down rejects. When the point of a knife could barely be stuck into the rammed fill, it was judged sufficient. It should be noted that several such molds could be, and were, set-up in the casting pit at the same time. Now, a long runner or gutter was cut into the dirt floor leading from the "breast" - a low clay or stone wall - which retained the puddle of molten iron collecting in the "bosch" or lower arched bottom of the furnace. Leaders were run off this gutter to the sprues of each mold. It can be seen that the sprues of molds farthest from the furnace had to be lower than those of molds which were closer to maintain gradient in the feeders. A rule in gunfounding was that the total area of the combined sprue openings must be less than the total area of the furnace tap hole. This assured that there was always more molten metal in the gutter than was going down the sprues, and prevented aspiration and bubbles entering the molds. Since dross and dirt float on top of molten metal, they were kept from the molds, too. It can now be appreciated why a "head" section was included beyond the cannon muzzle face. First, as just noted, it acted to prevent bubbles and dirt from going down into the mold. It was a reservoir which accomodated shrinkage as the molten metal cooled. And finally, and importantly, through hydrostatic weight it increased density of the metal in the cannon, particularly in the critical lower breech end. When all was ready for the "cast", the furnace was tapped by breaching the "breast" and with a rush, the liquid iron issued forth in the gloom under the cast-shed roof, tracing fiery rivulets down the runners toward the sprues and risers of the waiting cannon molds.
Residual ground dampness, even the slightest moisture - or any organic
material: a bit of straw or stray leaf - in the runners would be instantly
vaporized to superheated steam by these molten streams, causing showers of
sparks and tiny drops of hot metal to rain down democratically upon the
backs of the workers. It is probable that these foundrymen, as their more
recent counterparts known personally by the author, would now and then
have spat or even urinated in runners when no one was looking - in hopes
the resultant pyrotechnics would settle some grudge, or just liven up the
routine of "pour off"... Be that as it may, the buried molds would fill
rapidly as the iron drove out the air, hopefully not trapping bubbles
behind to form cavities in the castings and ruin them. The molds would be
filled to ground level or top of sprue and riser. "Shake-Out" When the casting had solidified and cooled, the earth in the pit was shoveled out, and the casting was "shaken out" and hoisted free of the pit. In brass gunfounding, this was within 24 hours, as it was desirable to have the still very-hot castings cool quickly to prevent crystalline growth in the metal. Whether this same factor obtained in iron casting, I have been unable to determine. Metal reinforcing straps and adhering mold fragments were removed from the casting. Flash and burrs were removed by hammer and chisel. Aaron Swetland, whom we have met twice previously, would be roused from his slumbers behind the woodshed to saw off the sprue and riser flush to the muzzle face. A large brass cannon at Woolwich necessitated ten hours of sawing by teams of sawyers, operating continuously. A 14-inch mortar poured there is recorded to have taken 30 hours of continuous team effort to saw free from the "head" section! After the castings were roughly cleaned, they were next conveyed to the Boring Mill.
Where cannon enthusiasts gather, talk often turns to whether and when drilling was resorted to as a first step when boring oldtime barrels. As far as activities at Salisbury are concerned, it seems this was done. As evidence is this excerpt from a letter of Gov. Trumbull to the foundry overseer, dated July 17, 1776: "Sir:...The nine-pounders being now wanted, you will proceed with all diligence to have them drilled and bored and deliver them when called for to Colo. Jonathan Pettibone, who will provide proper teams ... and transport them to Hartford as soon as may be..." In this same letter, reflecting the tension of the times, Trumbull further directs the foundry to get on with work on some 12-pounders to be dispatched "where the public service shall require them", but admonishing his overseer that "should requisition be made by General Washington, you will permit them to be transported to North River, without waiting further orders ...". At the time of the American Revolution, it was still the practice in some gun foundries - as those in Pennsylvania - to "found" barrels over cores. (Cores were expendable cylinders of sand temporarily "bound" with resins, oils, syrup, pitch, molasses, and combinations of these and other materials according to the art and artifice of the different founders). Placed in the mold and held suspended by chaplets, iron pins, and sometimes at the breech end by forged "crown irons", the cores occupied the space for the future bore. As the molten metal filled the mold, the cores retained their integrity just long enough for the metal to chill, whereupon they were supposed to disintegrate from the heat. (If they didn't, they could later be knocked out or poked apart with an iron rod). Cored bores were later finished and properly calibered by mill boring. At Salisbury, however, barrels were cast solid and bored direct. Boring mills of the time were substantial affairs of massive timbers and cross-braces (Fig. 14: original retained by publication). The cannon were bored muzzle-down in a vertical position, according to Middlebrook, and he is probably right. Horizontal boring, however, was being used at some English sites at this time, and overcame many of the drawbacks of vertical boring. The apparent massiveness of the boring mill building at Salisbury, however, plus the request by the Committee of Safety to remove it to a more convenient place argue for a vertical setup. Horizontal boring lathes required less massive buildings. Modern engineering analysis reveals inherent flaws in such an approach, but it was "state of the art" in our forefathers' day. The cannon were secured to a wooden sledge which could be raised and lowered by block-and-falls, and rode in greased furrows of two massive vertical side beams. Centered beneath the suspended cannon was the boring spindle and its mount, turning in a heavy greased framework. Attached to the bottom of the spindle mount was a heavy iron base-ring. As shown in the contemporary French drawing, bolted to it was a horizontally projecting timber by means of which a horse might be harnessed to the entire engine, and turn the spindle by walking endlessly about the boring mill in a large circle. At Salisbury, however, it is most probable that the spindle was powered by water and not a horse. I am indebted to a student of Salisbury (Seymour, pers. comm.) for the information that on at least one occasion, one of the foundry operators bemoaned freezing of water in the mill raceway in winter with subsequent impairment of boring operations. The pressure of the workpiece (cannon) upon the boring tool was regulated by the weight of the cannon and the heavy sledge it rode in, which overall pressure could be adjusted by counterweights. We have already seen that these resourceful frontier mechanics made cutters for the boring mill from steel supplied by their sister Works at Colebrook. As the vertical spindle must have had some play in its position, and the cannon itself was not always fixed absolutely vertical in its sledge, the result was doubtlessly frequent off-axis bores. Gearing at the base-ring of the boring mill would have produced higher spindle speeds but whether this was done at Salisbury is unknown. It is also unclear as to whether there might have been batteries of two or more mills in the mill building, allowing work to progress on more than one barrel at a time. Lubrication of the cutter was important, and was apparently done by periodically stopping the mill, and packing grease into the hole or bore started in the gun. In horizontal boring, the bore is true to the casting axis. At Woolwich, clever cutterhead bearings controlled sideplay and wander. Also, barrel exteriors could be lathe-cut at the same time bores were being drilled. This was not cosmetic but was done as a check on porosity, granulation, and other defects in these brass cannons. Many guns of this period were seldom "true", even guns cast in the better equipped armories of Europe. Compounding this were loose-fitting and out-of-round balls which allowed "windage" or clearance between projectile and bore walls. (A different use of the word than by smallarms shooters). This meant balls sometimes skipped erratically down the barrels, picking up reverse spins like those of a pitcher's spitball or knuckleball. They might float slowly out through the air to their distant targets. Gunnery as practiced both at sea and in the field by formal forces of the day, included training and techniques to help gunners make allowances for these variances in their individual pieces. It is a tribute to the untrained Yankees who went against the professional gunners of the British Navy that they were able to compensate so well and fire their guns with such telling effect upon the enemy.
Upon completion of boring, the guns were ready for rudimentary inspection and testing, and then proof-firing. Proofing at Salisbury is said to have been done "near Barnet's old sawmill", and by most reports from the slope north of the furnace. (Some balls may have flown high over the present day roof of a Gulf gas station to land to the eastward. It is said the proofers sometimes practised ricochet firing - a cannoneering technique of the day. The methods used are educational, to say the least. It is recorded that on firing the gun, the muzzle and the touch-hole were stoppered, and resort made to visual inspection to see if smoke issued through any part of the metal! If not, the gun was pronounced sound. One authority believes fail rates in proofing at 18th Century American gun foundries was "very high" (Gordon, pers. comm.). For service, 4/5ths the powder charge for proofing, and 1/2 the weight of the iron proof shot were recommended. It is unclear to the author, in light of the latter statement, whether this means that a 4-pounder, say, would be proofed with 8 pounds - or two balls (whence why not say "double shotted"?). One half of such charge would, however, be 4 pounds or the service rating for the gun. Sunbeams were sometimes shone down the barrels with mirrors to aid inspection; sometimes lighted candles in long cleft sticks were inserted for the same effect. The iron was then struck with a hammer, and the discerning ear could detect "hoarse sounds" - taken as sure sign of "honey-combs" or porous spots in the metal. Powder charges for guns not true-bored were calculated after a number of fashions based on thickness of barrel wall at the thinnest part of the casting. Determining location of the thinnest section of the barrel, and its actual thickness, developed into a veritable art among the ancient ordnance makers. Numbers and other marks attesting to these individual determinations were then placed upon the barrels and trunnion ends. (See Straight Shooters and Crooked Barrels). One intriguing early method for determining whether a barrel was true-bored is here given verbatim. I assume the method worked, and will work, but must confess that I still do not fully understand the precise procedure. Readers must judge for themselves.
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