Thanks a Bunch: General Industry Coverage

A bandsaw is a common sight in a machine shop. To get blanks on the floor faster, shops use bandsaws to cut several square, rectangular or round solid bars or tubes at a time. Knowing about the proper bandsaw, workholders and saw blades can make the bundle cutting process go much more smoothly.

Bandsaws have a fairly large work envelope that allows materials to be stacked and cut. But if a shop is going to be cutting a high volume of bundles for a specific job, it will need a dedicated bandsaw.

Courtesy of Simonds International

Cutting bundled tubing requires a bandsaw blade designed for interrupted cutting, such as the IC Enduro, which has a wide tooth set to help prevent blade pinching.

“It’s about efficiency and generating a high volume of parts in a short period of time,” said Michael Finklea, director of sales and marketing for bandsaw manufacturer Cosen Saws USA, Charlotte, N.C. “For example, we have a customer that makes keyways for holding gears in place. He cuts bundles of 1⁄16 ” square stainless steel, and every time he makes a cut he creates 900 parts. The only way he can do that [in a reasonable amount of time] is to have a dedicated bandsaw that can bundle cut. “

Bundle cutting is generally done with an automatic or semiautomatic vertical, horizontal or scissor-type bandsaw.

To cut tubing on single- or dual-column horizontal bandsaws—and some vertical ones—the machine needs a canted head, meaning it is mounted at a slight angle, producing the same effect as angling the workpiece. The bandsaw blade passes through the tube at an angle, improving the consistency of the cut and increasing blade life.

Courtesy of Cosen Saws USA

Cosen’s structural-steel horizontal bandsaw uses a bundle-cutting attachment, in addition to side vises, to hold tubes in place.

“With horizontal machines, the blade is offset anywhere from 3 to 5 percent,” said Ron Saxon, national accounts manager for bandsaw blade manufacturer Simonds International, Fitchburg, Mass. “The blade does not come in perfectly parallel with the material, and this helps eliminate tooth strippage. This is done more for tubing, where you have interrupted cuts.”

Scissor-type bandsaws do not encounter this problem with tubing because the blade comes into the workpiece at an angle.

Bundle Wrap

Vibration from poorly nested workpieces limits bundle cutting performance. Generally, workpieces are not perfectly straight and do not have perfectly identical dimensions, and therefore are prone to move within the stack. “If you have a bundle of 1 “-round workpieces five wide and five high, the chance that all 25 of those are the exact same size is pretty small,” Finklea said.

To minimize movement and vibration, workpieces must be tightly secured. In addition to the side vises already on the bandsaw, the most effective method to hold material in place is to use a top clamp, commonly referred to as a bundle cutting attachment, an option on most production bandsaws. The side vises maintain the position of the material and the top clamp applies down pressure, keeping an individual piece from popping up and out from the bundle.

Even with a top clamp, there is a chance for round workpieces to start spinning. “With round materials, if you have one in the middle that is on the smaller side, and the others around it are bigger, the middle piece is floating. Even though you have clamping on all sides, there is nothing holding that smaller piece and as soon as the blade hits it, the piece starts to spin,” Finklea said. “We tell customers the only way to guarantee that a piece won’t spin is to tack weld the ends of the pieces—put a dot of weld where the pieces are touching, just enough to keep them together so the one in the middle will not spin.”

Save the Blade

If vibration and spinning are not kept under control, they cause the blade teeth to chip or strip or even the blade to break.

For bundle cutting, the most effective cuts are those made in solid bars using bi-metal blades. When blades continuously cut solid material, stresses on the teeth after initial impact tend to be consistent. Bundle cutting solid materials is like cutting one big workpiece, noted Saxon.

Courtesy of L.S. Starrett

L.S. Starrett’s Intenss Pro bimetal blades are suited for tightly bundled solids, including tool steel, stainless steel and nickel-based and nonferrous alloys.

Conversely, cutting tubing typically abuses the blade because the teeth must enter and exit two walls. These sudden changes increase vibration and workpiece movement, stripping the teeth from the blade. When multiplied by the number of tubes in a bundle, it is easy to see how blade life would be reduced. According to Finklea, this reduction could be as much as 25 percent.

“That constant impact of leaving and entering a cut in interrupted sections does have an effect on the cutting edge of the tooth and you are going to see a little lower blade life no matter the material,” said Gene Ramsdell, manager of North America saw R&D for bandsaw blade manufacturer The L.S. Starrett Co., Athol, Mass.

Having an application-specific tooth design to address the problems inherent in interrupted cutting helps extend blade life.

Variable pitch is typically the norm for any bimetal blade. A variable-pitch blade has various tooth sizes to reduce vibration whether used for bundles or a single piece. Tooth pitch generally is based on workpiece size. It is recommended that the tooth pitch enable at least three teeth to be in contact with the workpiece at all times; having six to 12 teeth in the cut is optimal.