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An overview of structural tube sawing options

Select the right saw, and follow key tips to do the job more productively

Figure 1
Band saws have emerged as suitable tools for high-production cutting of structural steel tube.

Structural steel tube—ASTM A500-specified cold-formed welded and seamless carbon steel structural tubing in round, square, and rectangular shapes, to be more specific—is used in a variety of applications because of its uniform and tight tolerances, high strength-to-weight ratio, and general ease of fabrication. Because of these qualities, this steel tube is widely used in transportation, agricultural, racks and storage, bleachers/seating, scaffolding, signs/posts, and exercise equipment. In virtually all of these possible applications the tube is bent, formed, punched, drilled, swaged, coated, or in some other way transformed to meet the requirements of the project.

However, before any of these operations are undertaken, a fabricator has to cut the tube to length. That’s why fast, cost-effective, and accurate cutting of the tubes is a critical component in the timely turnaround and ultimate quality of the fabricated parts or assemblies.

Sinking Teeth Into Sawing Options

Cutting of structural tubing generally is accomplished with either a band saw (see Figure 1) or circular cold saw. Both of these saw technologies have their advantages and disadvantages, and of course, they are based on the requirements of a particular project or operation, as well as available budgets.

Band Saws. Historically, band saws have had the stigma of generating poor tolerances, finishes, and tool life. Further, they were seen as an unsophisticated but necessary piece of equipment. An old saying once suggested that when a saw operator proved successful, he was then promoted to the broom.

Today band saws have made great strides in technology and performance. Simultaneously, improvements in saw blade technology also have led to significantly better overall sawing results.

Many of today’s top band saws use PC controls, ball-screw technology, self-sensing downfeed control, and advanced fluid and cooling technology to produce higher-quality cuts than previous generations of band saws. They also feature better bundle-cutting capabilities and design modifications that foster longer blade life.

For example, with the introduction of a ball-screw feeding gripper, a band saw can deliver very tight length tolerances and repeatability. Rigid saw construction design helps to ensure both proper blade tension and vibration elimination, which generate squarer cuts and longer blade life.

These advancements in band saws have greatly closed the gap in cut quality and production levels when compared to circular saws.

Circular Cold Saws. Similarly, technological advancements have been made in cold sawing as well. High-speed carbide saws, for example, have taken cutting speeds to entirely new levels when compared to high-strength steel (HSS) blade technology. High-speed carbide saws are cutting faster and with better finishes than ever before.

Meanwhile, cold saws that use HSS blades have made advancements in speed as well. In addition, many of these cold saw models also have an added mitering functionality.

Figure 2
Upcutting keeps chips from falling back into the cutting area, which helps to extend blade life.

As noted previously, structural tube often is modified in some way, shape, or form and includes miter angle cutting. Both band saws and circular saws have the ability to miter-cut, and with each this can be done manually or automatically. Many of today’s advanced saws use a PC control for job storage, programming, and miter angle setting. High-volume production models often include automatic feeding options, such as loading magazines.

When comparing a band saw to a circular cold saw, the discussion often revolves around speed. It is generally safe to say that part for part, a circular saw is faster than a band saw for cutting one tube at a time. However, for layer or bundle cutting, a band saw can meet or exceed circular saw production levels. Of course, miter cutting requirements eliminate the opportunity to cut in bundle-loading fashion.

Tips for Sawing Structural Tube

Here are some general points to consider when sawing structural tube:

  • Look for variable clamping pressure. This allows for the vise-clamping pressure to be reduced to prevent deformation of thin-wall tube. The pressure should be enough to hold the tube firmly to ensure it doesn’t move, but not enough to bend it.

  • Watch for the weld orientation. Although quality saws will cut a tube regardless of the weld orientation, a fabricator should position the weld at the top or side of the saw entrance, rather than at the bottom, to maximize tool life. (Note: In a bottom-up cutting configuration, the weld should be at the bottom or on the side.)
  • Be aware of blade bias. When cutting nonround tubing in a band saw, it is preferable to have a bias on the blade. This is valuable for both good cut quality and longer blade life. Having the blade penetrate the material at an angle allows the fabricator to use the most efficient tooth configuration and prevents overloading of the blade gullet. Even a 1- to 3-degree bias will do the trick; a very large bias, however, will add to the overall cut time. (Of course, on a circular saw, the natural curvature of the blade eliminates this concern.)
  • Keep up with the cooling/lubrication. Most sawing systems allow the option of flood cooling or spray mist lubrication. Flood coolant generally correlates to longer blade life, while a spray mist is a cleaner option when cutting tubes.
  • Don’t forget material handling. Having a very fast cut time is a real advantage for most tube cutting operations. However, cycle time is the true measurement of efficient production. If the saw cuts very fast but the next part has to be loaded manually, the fabricator is not using the saw to its highest capabilities. Understanding material flow is an important consideration in saw and material handling equipment selection.
  • Pay attention to tooth geometry. Using the correct tooth geometry for a particular application helps to ensure a quality cut, while also prolonging the blade life. Although it is possible to use one type of blade for most structural tube applications, fine-tuning it for longer production runs is worth the additional effort. As a general rule, a fabricator using a circular blade wants three to five teeth to be exposed to the widest part of the cut, and one using a band saw wants six to 12 teeth.
  • Think about upcutting. When considering a circular saw for tube cutting, a fabricator can enjoy a measurable advantage in tool life by choosing an upcutting design (see Figure 2). When the tube is cut from the bottom up, the chips fall back down to the bottom of the tube. When a tube is cut from the top down, the blade is regrinding these fallen chips at the bottom of the tube.

Finding the Right Saw

Ultimately, cutting structural tube can be efficient and cost-effective using either of the saw technologies, depending on particular needs. The key to selecting the appropriate saw is to determine the type of sawing generally done on the shop floor. Are production runs long, or is most sawing a job-by-job short run? Are cutoff lengths long or short? Is cutting mostly straight or miter? Are secondary operations involved or just cutting to length? How much automation or material handling assistance is required?

When the question is whether a circular saw or a band saw is the better choice for a particular tube application, the answer is always “It depends.” As a general rule, the fabricator will obtain faster speeds and a better finish using a circular saw, but will have more flexibility, more forgiveness, and larger capacity with a band saw.