Fabricating a full-size reproduction of a 20-inch Rodman cannon required the help of a 21st century 3-D computer modeling program. The artisans at LF Creative Group needed about two months to complete the job.
"It takes amazing technology to make this kind of copy," LF Creative partner Travis Gillum said.
"What is more amazing is that workers were able to make something this big in the 1860s."
The barrel of the Rodman reproduction is about 20 feet long and about 6 feet in diameter at its widest point. When mounted on its iron carriage, the artillery piece will stand about 20 feet tall.
The model will serve as the centerpiece of the 9,000-square-foot "Pennsylvania's Civil War" exhibit that opens June 22 at the Heinz History Center.
The original 20-inch Rodman cannon was cast in 1864 at the Fort Pitt Foundry, That manufacturing plant was located on the banks of the Allegheny River, just across Smallman Street from the history center.
The "20-inch" refers to the interior diameter of the weapon's bore.
The giant gun was built according to a design developed by U.S. Army ordnance officer Thomas Jackson Rodman, the one-time commander of the Allegheny Arsenal in Lawrenceville.
Rodman's cannons were made of cast iron and cooled from the inside out by water flowing through the center of the mold. The metal shrank inward as it cooled, producing a stronger barrel far less likely to blow up while being fired.
Rodman developed several other military innovations, according to Andrew Masich, president of the Heinz History Center.
"He perfected a bullet-making machine that used compression rather than casting," Mr. Masich said. "It allowed workers to crank out thousands of bullets per hour, each uniform in weight and size."
Rodman also designed new cartridges for use in breech-loading, rather than muzzle-loading, weapons.
Because they offered increased strength and safety, Rodman cannons could be made much larger. Charged with 200 pounds of gunpowder, the 20-inch Rodman could fire a half-ton ball 4 1/2 miles.
The barrel of the smooth-bore, cast-iron artillery piece weighed more than 58 tons and required a special railroad car to transport it to Fort Hamilton in Brooklyn. Its original role was to protect the Verrazano Narrows entrance to New York's upper bay. While it no longer keeps watch over the harbor, the cannon remains near its original location in a small park.
The only other cannon Rodman made this size is at Fort Hancock in Sandy Hook, N.J.
The model of the Rodman cannon is one of the largest single pieces that the Ohio-based LF Creative Group ever has produced, Mr. Gillum said. With a foot in several different worlds, LF Creative does work for both museums and theme parks, he said.
Previous projects for the history center have included life-sized figures of Fred Rogers, baseball star Josh Gibson and Rosie the Riveter. "Rosie" was a well-known symbol of women's home-front contributions during World War II.
The history center's version of the Rodman cannon is based on the original gun's dimensions. The model was carved from Styrofoam on a five-axis milling machine directed by a three-dimensional computer program.
The foam was reinforced with a steel frame and then covered with an outside shell made of fiberglass, Mr. Gillum said. The date and place of original cannon's manufacture have been reproduced on the end of the model's barrel: Fort Pitt, 1864.
The cannon model was made at LF Creative Group's workshop in Bowling Green, Ohio. The company, previously known as LifeFormations, now operates studios in Bowling Green and at a second location in Cincinnati.
The 20-inch Rodman was both a potent weapon and a symbol of mid-19th century technology, Mr. Masich said. Casting the barrel required a continuous pouring of 80 tons of molten iron, he said.
"Pittsburgh was the arsenal for the union, and factories here could do things that could not be done anywhere else in the world," he said. "Nothing epitomizes that better than a 20-inch Rodman cannon."
The giant cannon was moved from Fort Hamilton to Philadelphia to be displayed at the nation's Centennial Exposition in 1876. "Twelve years after it was made, it remained a wonder of the industrial world," Mr. Masich said.
Len Barcousky: email@example.com or 724-772-0184. First Published June 10, 2013 4:00 AM