Reflections on a perfectly symmetric ellipse
Full-time sculptor, part-time fabricator overcomes bending challenge
Sculptor and fabricator Brett Richards of BR Sculpture, Chicago, got a contract to make a frame for an oval mirror—a length of square tubing bent to a perfect ellipse. Not knowing too much about the vagaries of bending tube, he figured he'd spend a few thousand dollars on a simple bender. After searching for months, he happened to see an elliptical shape made from square tubing in a vendor's booth at FABTECH.
A short tour of BR Sculpture, Chicago, is enough to show that it is anything but a typical fabrication shop. While fabricators usually cut, bend, and join carbon steel sheet and plate, BR usually uses metals such as silicon bronze or iron. While fabricators typically bend tubing, stamp sheet metal, or weld together subassemblies for automotive, machinery, or aerospace applications, BR Sculpture is likely to cast an artistic piece for a sculptor or make a vintage item for a movie set. Fabrication shops like to hire experienced fabricators with good mechanical aptitude; everyone at BR has either a master's or bachelor's degree in fine arts. And while fabricators look for the financial security of long-term contracts and high product volumes, BR rarely enjoys such a luxury. Most of its projects are one-off or low-volume runs that number in the dozens.
Despite the many differences, BR Sculpture does have quite a bit in common with a typical fabrication shop. Most of BR's work involves joining—many job applicants have to pass a welding test—and bending because much of the company's work is for unique furniture, appliance, and home decor applications. And like any fabricator, it relies on having the right equipment to get the job done. BR Sculpture is similar to fabrication shops in one other way: Occasionally it encounters a seemingly small fabricating problem that turns out to be a big fabricating problem.
From Fabricating to Casting to Fabricating
Brett Richards, BR Sculpture's founder, didn't start his career in an art studio. In fact, he started in manufacturing. After graduating from the Art Institute of Chicago with a bachelor's degree in fine art, he took a job as a fabricator in a production shop to earn a living. He craved more variety than the job offered, so he found some work moonlighting, doing some casting work and other projects.
Before long he quit his job, leased an 800-square-foot space, and started his own business doing foundry work and a little fabricating. It had just two employees, Richards and a welder. They cast items for other artists and fabricated architectural and structural projects such as handrails and mailbox stands. The work load grew quickly, and before long Richards moved to a 5,000-sq.-ft. location, and the company grew to 14 employees. Within two years it moved to its current location, a 20,000-sq.-ft. facility.
Because casting and fabricating are two completely different processes, BR has two modes of work. For castings, it uses an original piece to make the mold. When it comes to fabricating, the company relies on engineering prints. Of course, having a print isn't the end of it. In fact, that's just the beginning. Figuring out the best way to fabricate the part is the next step. And sometimes this is the start of a lengthy search for the right piece of equipment.
One such project involved a large, decorative mirror. BR's portion of the project involved fabricating the mirror's frame, which consists of three components: a piece of heavy, highly polished sheet metal that makes up the back of the frame; a small block of steel with a drilled hole, which serves as a hanger; and an elliptical border made from round barstock. Of the three components, the elliptical border was the biggest challenge.
Richards figured he'd spend a few thousand dollars on a simple manual bender.
Beyond the Ellipse
The frame is made from a length of 6063 T5 extruded aluminum. Material support and sufficient space were two issues that played into BR's bender choice. Although the material is strong, it is flexible and requires support to prevent sagging and twisting during the bending process. Also, long workpieces require substantial infeed and outfeed space. Many three-roll benders are built so that the rolls' central axes are horizontal and bending is done in the vertical plane. These work well for short pieces or long pieces with gentle bends. However, long items with complex bends can be difficult to handle. When feeding out upward, supporting them manually can be difficult; also, thin-walled sections tend to collapse under their own weight. When feeding out downward, they can run out of room and crash into the floor.
BR needed a bender with the rolls on top, with vertical central axes, so the bending would be in the horizontal plane. This arrangement would make it easy to support the workpiece manually or with stands.
A second challenge, and one that was more critical than the support and space issues, concerned the dimensions of the finished part. Accuracy and repeatability were paramount. While some bending applications can tolerate some latitude in the dimensions, especially if the part eventually will be hidden from view, ornamental or aesthetic applications such as this require tight tolerances.
Finally, BR wanted a bender that would be easy to program.
Richards looked at several benders, and sent several test pieces out for bends, but had difficulty finding a machine that would form the elliptical shape with the precision he needed. His search, which lasted quite a few months, ended at a tradeshow.
"I saw an ellipse [formed from tubing] in a vendor's booth at FABTECH," said Richards, referring to the annual FABTECH® Intl. & AWS Welding Show. That vendor was Profilbiegetechnik AG, and the machine was a PBT25®.
It looked like a good fit. With one glance, Richards could see that it met two of his criteria. First, it has vertical rolls and bends in the horizontal plane. Second, Richards knew it could handle an ellipse. That left just two questions: Could it make his ellipse accurately, and would it be easy to program? It turned out that these questions would be easier to answer than Richards thought. The vendor, Boschert Precision Machinery Inc., was located near Milwaukee, just 100 miles away from Richards' shop in Chicago.
Richards and crew made the trip to Milwaukee to evaluate the bender. They were pleased to learn that programming the bender wouldn't be too difficult when the trip to Milwaukee turned into a crash course in programming. Within a few hours they were programming ellipses. Richards soon determined the answer to the final question. The machine's X-axis accuracy is 1/100 mm, which turned out to be accurate enough to make the mirror's frame.
Bending and Blending
Although this particular ellipse is programmed as a series of nine distinct bends, the software has to turn this into something much more sophisticated: a smooth shape with no distinct bends. In other words, the finished product is a curve with a continuously changing radius. The semifinished product must have two legs, or drops, because it's physically impossible to roll a length of material all the way to the end of the workpiece.
To make this particular ellipse, an operator inserts the workpiece into the machine and initiates the bending sequence. The machine takes over and draws the part in, making the necessary adjustments to the roller location as the bend progresses. The bender doesn't attempt to form the shape in a single pass; rather, it runs the stock back and forth in a long series of small, incremental bends.
"It takes approximately 90 passes to make this part," said Richards. When the part is about 75 percent done, the bender pauses. The operator scribes a line on the part adjacent to the center axis of the center bending roll, removes the part from the machine, takes it to a band saw, and cuts off the first leg.
"Otherwise the two legs would collide as the bender finishes the part," Richards explained. The operator then returns the part to the bender, aligns the scribed mark with the center roll, and enters the command for the bender to resume bending.
When it's done, he unloads the machine and returns to the saw to cut off the second leg. After that, one of the welders joins the frame to the back and fastens the hanger in place. After some cleanup and polishing, the frame is packaged and shipped to the customer.
More Than Meets the Eye
While BR is happy with the bender's performance on the frame, the bender can do a few more things. For example, BR's staff has discovered that they can use the bender to make slight changes in a bent part. "We can always put a part back into the machine to tighten up the radius," Richards explained. "We can do this, if necessary, to reduce the gap where the two ends meet. This reduces the amount of welding needed to finish the part."
It's also suitable for bending square and rectangular tubing. For these shapes, the rolls generally must start fairly far apart to prevent crimping. The machine can be adjusted to a maximum of 40 in. between rolls. Also, because it bends in the horizontal plane, the machine's built-in workpiece supports come in handy. The operator can set the supports high or low to straighten twisted material, or to put a twist in straight material—that is, to bend a 3-D spiral. Although BR doesn't need to make spirals for any current projects, it has the capability, should the need arise. Finally, it is a convenient size. Because it is compact at 47 in. by 56 in., it doesn't take up much room. Moving it isn't any big problem—it weighs 525 lbs.
Searching for the right machine took quite a bit of time, and it was a bigger investment than Richards expected, but in the end it was worth it. The result, a perfectly symmetric frame, reflects well on both BR Sculpture and the mirror manufacturer.
The FABRICATOR is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971.