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Special Report: Innovative Fabricating

The perfect chunk

By Nick Wright

In a quest to catapult pumpkins farthest, fabricators put their metalworking skills to the test

December 2013 - As the Department of Defense braces for major budget cuts next year, money for weapons contractors could abruptly dry up. However, the military need look no further than central Delaware for the latest and greatest, where each year a veritable artillery range of American, homemade launchers convenes for a three-day display to determine which contraption can outperform the rest. The metric: distance. The projectile: pumpkins.

Since 1986, the World Championship Punkin Chunkin contest (yes, you pronounced it correctly) has drawn an armada of catapults, slingshots, trebuchets and cannons to a field in this East Coast state with the goal of sending the orange ordnance as far as possible. The competition, as well as the crowd of thousands of spectators, grows every year.

Beyond the three-day spectacle of watching pumpkins get sent skyward, the complex launchers are ingenious examples of innovative fabrication. In recent years, teams of fabricators, made up of “doctors, lawyers, plumbers, FFJ-1213-punkin-image1teachers, pipe fitters, a congressman, the unemployed and Indian chiefs” have come together to test what are impressive feats of metalwork, says Frank Shade, spokesman for Punkin Chunkin.

“We have generations of families that come out,” Shade says. “One young man who started it met his wife and got married here. In the following years, they brought their baby and now the child competes.”

Not all of the catapults are made from metal, but upon our visit to this year’s competition, a walkthrough of the launch pit revealed the vast majority included extensive metalwork. The structures need to withstand the serious thrashing that unleashing thousands of pounds of torque does to a pumpkin, let alone the launchers themselves. As the teams reinforce their catapults after this year’s launch—adding bracing here, welding a stronger joint there—the competition gets tighter to see who will take home the title “Lord of the Gourd” next year.

Man on metal

In all, there are 16 categories of catapults at Punkin Chunkin, divvied up among adults, youths and an all-female category. Mechanically, they can be broken down by method of propulsion: air, catapult, trebuchet, torsion catapult, human-powered and centrifugal. Each team gets three shots (one each day of the weekend).

One team, Shooda Node Beter, named after its unabashedly tongue-in-cheek country bumpkin sensibility, stood out with its human-powered catapult. While other human-powered catapults relied on bicycle power or brute strength to crank back the launching arm, Shooda Node Beter’s catapult featured an 11 ft. diameter, 30 in. wide aluminum hamster wheel fastened to its side. With the launch arm and pumpkin locked and loaded, one of the team members, wearing a harness tied to a platform, climbed the wheel from the outside with all his might, turning a spindle that tightened a rubber bundle inside the catapult’s 23 ft. tower. When he could turn it no more, he climbed down, his chest heaving under a sweat-darkened shirt.

As the announcer pumped up the crowd, the catapult was released with a snap, sending the pumpkin to a world record of 2,048.52 ft. for a human-powered catapult.

Kenny Kite, captain of the seven-person team, says they tried to use the strongest materials where strength was required. All the shafting was made from 2.5 in. Nass 45 stainless, which allowed easy disassembly of the catapult’s bearings. For welding ease, 4130 steel makes up some components. For the catapult arm, the team used 7068 and 7075 aluminum for its light weight and strength. Sections of diamond plate aluminum adorn the body of the FFJ-1213-punkin-image2catapult’s orange tower.

Kite owns K&K Machining, a shop in Elkton, Va., from where the team hails, and where the fabrication, machining and welding took place. “The metalworking technique is the most important,” he says. “This is especially true when fabricating the arm that throws the pumpkin.” 

That launch arm is 20.5 ft. long, trailing a 25 ft. sling from which the pumpkin is launched. At the moment the pumpkin leaves earth, it’s at 68.5 ft. in the air. Next year, the team is hoping for a half-mile launch (2,640 ft.). 

“We already have a new arm designed, which is lighter and stronger,” Kite adds.

Talking torsion

Up close, the torsion catapults are impressive machines, but can be terrifying to the newbie “chunker” (a term that seems to refer to anyone associated with the Punkin Chunkin contest). Torsion catapult technology uses a bundle of twisted ropes to store energy, which, when relaxed, releases a staggering amount of force upon the launch arm embedded in it. When the torsion catapults wind up, they slowly creak and pop under the stresses of force. A poorly constructed catapult could collapse on itself in a burst of fury.

Since 2005, team Roman Revenge, based in Gastonia, N.C., has contended at Punkin Chunkin with a Roman-invented torsion catapult. It is the first catapult in its class to shoot more than 3,000 ft. It has never won first place, but is a perennial contender with top tier teams. Painted red and black, it’s a striking, muscular steel machine that you’d want on your side in a battle. Led by captain Kim Moore, a veterinarian by day and self-taught fabricator, Roman Revenge earned third place this year with a 1,542.30-ft. toss.

Built upon a 1950s utility trailer, Roman Revenge is articulated by welded 3 in. square tubing that’s 1⁄4 in. thick. In some places it’s braced up to 1.5 in. thick. The launching arm consists of a 13 ft. 6061 aluminum I-beam reinforced with hickory boards and 1⁄4 in. aluminum plates, with an ultralight carbon fiber tube bonded at the tip—totaling more than 20 ft. in length.

“We had a beam that snapped three weeks before Chunk, and the past three weeks of Kim’s life was doing all of the work to get the beam remade so we had something to launch pumpkins with,” says Jordan Moore, assistant captain and Kim’s son. “It’s the most complex part and the component most likely to fail. It has to be extremely light and move fast, yet withstand 100,000 ft.-lbs. of torque. That’s enough to move a Boeing 747. It must withstand enormous crushing forces because the rope wants to squeeze the arm into oblivion.”

Roman Revenge has reached its yield point several times in the last few years, meaning most of the steel has bent after repeated throws, something not uncommon in these machines. For reinforcement, two 1⁄4-in. thick, 3 in. square steel tubes diagonally gird two 6 in. by 8 in. vertical steel beams that cradle the throwing arm at its pivot point. When the rope bundle is let loose, the horizontal compression is transferred instantly as vertical compression to the throwing arm and trailer. “Any junction where plate is touching metal, we reinforced it with gussets and welds in case they were to shear,” the younger Moore says. “The supports are reinforced with 1⁄2 in. plate, and some have I-beams sistered up with them, all of which we’ve bent to some extent.”

The team is wasting no time upgrading Roman Revenge. In the Moore’s backyard shop built for the machine, the team does almost all of its own grinding, cutting and fabricating. Its arc and MIG welders run off the house’s electricity, which “has been a problem on various occasions—my mom has been complaining to my dad about electrical connections back there,” Moore says. The engineering doesn’t begin and end at home, however. Roman Revenge outsources to a local machine shop for welding ultra high-strength parts and draws on the input of North Carolina State University professors and students, where Moore is earning a doctorate in materials science.

FFJ-1213-punkin-image3

Ground control

The production surrounding Punkin Chunkin is a spectacle on its own. It has grown from an ad-hoc Chunk of the early 1990s, where a handful of teams catapulted pumpkins only a few hundred feet. Now, a 38-page rulebook outlines safety, ASME requirements, and what size and variety of pumpkins—all 48 of them, with names like American Tonda, Cushaw Green, Iron Man and Queensland Blue—are acceptable mortar. This year, more than 100 teams competed. Some 20,000 fans turned out, many camping in RVs in a field next to the farm. Delaware Highway Patrol manages the influx of daily traffic miles away from the farm, which is in rural Bridgeville. Funnel cakes, live music and fireworks get under way at night. Media from all over the country cover the event, notably the Science Channel, which airs a special each Thanksgiving hosted by the “MythBusters.”

In the afternoon, in between the sound of Chunkers cracking open beer cans, the salvo of air cannons begins. Some groan that air cannons aren’t much more than big tubes with a bunch of compressed air behind them, lacking the sophisticated engineering involved in other categories. They do, however, require sound metalworking, plus quick adjustments of barrel angles to account for wind. One thing is for sure: Air cannons send pumpkins further than other categories—the longest overall shot was 4,694.68 ft. And they do draw the crowd.

One team, from Georgetown, Del., brought two air cannons, named Y Ask Y and Cuz We Can. Their barrels protrude from the rear of two modified school buses, a project that entailed more than simply attaching a compressed air tank to a tube.

Y Ask Y features a 1,000 gallon air tank modified with a tapered steel cone intended to direct more pressure into the barrel. Dwinton Morgan, a fabrication shop welder, says it took him two days and nearly 50 lbs. of MIG wire to weld the 1⁄4 in. thick cone to the tank. He used an old Panasonic welder, but says he prefers Lincoln Electric or Miller equipment. The 48-ft. long barrel is two sections: 9 in. ID schedule 40 irrigation pipe connected to an aluminum pipe. Bracing the barrel on the bottom side is what looks to be a steel crane boom. “It’s actually a recycled television tower,” Morgan says. “We didn’t even need to cut it. It has the same radius as the pipe, so we just ratcheted and bolted it on to stabilize the barrel.”

FFJ-1213-punkin-image4Assembly took place at Penuel Sign Co. in Georgetown, Del., owned by team member John Penuel. He enlisted some of the shop’s equipment that it uses to manufacture metal signage. “We’ve got the ability to weld, saw, frame and more,” Penuel says. “We’ve used the welder that’s on my bucket truck for the Punkin Chunker.”

To beef up the school bus, team Y Ask Y mated an old dump truck body to the frame. The truck’s five-stage hydraulic ram became the pivot point to adjust the barrel angle. Accommodating the hardware required cutting out the school bus’ roof. “We asked ourselves, ‘How are we going to do this?’ We just grabbed a big chop saw, climbed on top, and cut the bus open. It worked real well,” says Morgan.

As powerful as its cannon is, the pumpkin exited the barrel as an orange spray for Saturday’s launch. A pumpkin must land intact to qualify as a shot, so guys on ATVs can track down the impact site and mark it. When the pumpkin vaporizes, the occurrence is known as “pie,” a disappointing result given the hype preceding each shot. Ultimately, Y Ask Y landed a sixth place overall shot of 4,098.31 ft. on Friday. For next year, the team will improve its diminutive Cuz We Can and rename it to Y Ask Y (because at the end of the weekend, the team sold Y Ask Y to another Chunker).

For 2013, sunny weather and a steady tailwind on Saturday helped teams shatter several records, says Shade. He only expects the catapults to get better next year. “I’m always impressed with the centrifugal machines, they’re the biggest, baddest things on the planet,” he says. Although it’s a smaller field, the centrifugal machines spin with a devastating rage.

Not every team returns to Chunk. For those that do, the improved machines are as much a projection of the fabricators’ skill as the distance the pumpkins soar. “I’ll be going back,” says Jordan Moore. “Until I can’t or I’m not allowed to.” FFJ

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Camfil APC - Equipment Trilogy Machinery Inc. Metamation Inc. Admiral Steel
Camfil APC - Replacement Filters

LASER TECHNOLOGY

PLASMA TECHNOLOGY

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Burghardt + Schmidt Group Fehr Warehouse Solutions Inc. Rolleri USA Alliance Steel
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Flow International Corporation
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SAWING

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Behringer Saws Inc. American Weldquip
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HYDRAULIC PRESSES

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