July 2, 2010
The attempt to pour the light three last Wednesday did not succeed.
We started heating the furnace on Tuesday morning and buried the mold next to the furnace late Tuesday afternoon. We kept the heat low to bring up the temperature slowly until about midnight. At that point, we ramped up the heat until it was going strong on Wednesday morning.
Because the quantity of bronze was so much greater than in previous pours, we did not know exactly when to expect the charge to melt. By mid-afternoon, it was taking longer than anticipated, so we increased the airflow through the furnace using a fan.
To all appearances, it was burning well, and by about 4:30, the bronze appeared to be liquid. The crew then punched the plug out of the taphole. Aside from a few dribbles, nothing happened. Repeated tries were made from both the outside of the taphole and probing at the opening from inside, to no avail. A few minutes later, the skies opened up and it poured rain. We were all a pretty dejected and sad-looking crew.
We will not know what caused the failure until we partially disassemble the furnace. We need to do so to remove the 550+ pounds of bronze inside, and it will allow us to closely examine the masonry and metal.
In the meantime, our best guess is that, though undetected, there was a lump of unmelted bronze that was swept almost immediately into a blocking position. We are taking a few days to recuperate and grieve. We’ll post more when we have it.
May 28, 2010
The pour of the light three infantry cannon is scheduled for June 23, with the 24th as a rain date. Since we are melting a much larger quantity of bronze than in the past coehorn pours, we do not know how long the process will take, but we hope to pour late in the afternoon. That said, we’ll tap the furnace when the metal is ready, and that will be hard to predict.
Watch video from the first test pour.
Watch video from the second test pour.
The light-three will require us to melt approximately 650 pounds of bronze. The mold is in three parts: one for the barrel without its breech end (cascabel), one for the cascabel, and one for a large “dead head,” the mass of bronze above the barrel portion of the casting. The overall length of the assembled mold is 67 inches.
In the process of further machining the coehorn, the small mortar used to test the process, it became evident that the casting had a large area of porosity near the muzzle. It is large and deep enough to render the casting unusable. The flaw probably was due to the problems explained in the . Despite the lack of a definite explanation for the problem, we have decided to move ahead with pouring the light-three barrel. It will have its own casting characteristics, and there is little to be gained by additional smaller pourings.
If anyone is interested in coming to watch the pour, you are welcome to join us at the furnace adjacent to Great Hopes Plantation opposite the Colonial Williamsburg Visitor Center. We need all the crossed fingers we can get. Bring a chair and water, wear a hat, and remember that the nearest restrooms are at the Visitor Center, a few minutes’ walk from the furnace site.
Plan your visit to Colonial Williamsburg.
March 25, 2010
Check out a new gallery of images from the boring of the second coehorn casting. Tradesmen were pleased with the results, save for one obvious area of porosity/inclusion.
Learn more about the cannon project.
March 9, 2010
No, the cannon project hasn’t become a flash in the pan. We’ve just been on hold to get some other things done while we wait out this winter.
We have cleaned up the exterior surface of the second coehorn casting, and it is much improved over the first one. The porosity and shrinkage problems are much less, diminishing toward the lower part of the casting. So far, it does not appear they are serious enough to prevent the casting from being machined into a workable barrel.
The larger problem this time, somewhat to our disgust, is inclusion of what appears to be refractory mortar near the outside of the casting, especially around the moldings. This probably happened with the first casting as well, but there were so many inclusions that we didn’t focus on it as one of our primary concerns. We believe the mortar material was knocked loose when we rammed the crook into the tap hole.
We’re now looking at the construction of the tap hole, and more promisingly, a gentler and more controlled way to knock the plug loose. Despite these problems, we have decided to go for broke and proceed with casting the light three when weather permits this coming spring.
The toolmaker is about to return to boring the coehorn so that we have full information on its porosity. The founders are making the strickle for the light-three so that they can begin to make the pattern and mold when the weather allows them to set up outside again. The masons are checking the furnace after our recent snows to make sure it is ready to go. When we have set a pour date, we will post it.
In the meantime, the wheelwrights and blacksmiths are moving ahead on the limber construction, with the hope that it will be done within four or five months. We are tackling the limber before the cannon carriage because we need the exact dimensions of the finished barrel trunnions in order to forge the carriage ironwork which receives and secures the barrel. The carriage is best tackled only after we have a barrel in hand.
September 24, 2009
The pour on August 26 went smoothly. We followed several suggestions offered both by Colonial Williamsburg tradespeople and experienced founders from outside the Foundation. Before the pour, the mold was fired in a modern pottery kiln at the College of William and Mary (Brad, thank you!) to approximately 1500-1550 degrees Fahrenheit. This resulted in a much more “ceramic-like” material, with all the fiber and any remaining wax burnt out of it. That eliminated several variables. We eliminated two others by using a modern flux and degasser. When the furnace was tapped, the flow of bronze appeared to be less viscous than that of our first attempt, and the material itself was a bright, gold color. A bit of the initial flow was diverted from the mold cavity.
The mold filled nicely, and the observed shrinkage looked good. The next day, Thursday afternoon, we excavated the mold and broke it away to reveal a smooth-surface casting with nice detail. On Friday afternoon, we sawed off the deadhead. While the surface revealed was a vast improvement over the first casting, it still had a ring of small (pin-head size) holes just below the surface and some small shrinkage gaps. Slicing the deadhead a couple of inches above the first cut revealed more porosity.
Although we won’t know until we clean the surface of the mortar-portion of the casting, our hope is that the defects diminish toward the bottom of the casting. If so, we may have a mortar. We’ll find out over the next couple of weeks and let you know.
Once we are satisfied with these experimental castings, we will begin “reverse-engineering” the modern technologies we are using in an effort to complete the entire process using only period methods.
Watch The Second Pour.
August 17, 2009
We are in the process of completing the mold for a second coehorn pour, which is scheduled for August 26, weather permitting.
As a result of our own analyses, suggestions we’ve received via the blog, and discussions with several experienced and knowledgeable folks, we think we have discovered the source of at least some of our problems and are working to correct them.
The proof will be in the pour!
Listen to the podcast “The Joy of Discovery” to hear more about the upcoming pour.
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