Smart Sawing: General Industry Coverage

Courtesy of Behringer

A Behringer 650/850A automatic bandsaw cuts a 25 “-dia. round titanium workpiece.

Whether using a bandsaw or a circular saw, mastery of the basics makes operators more productive.

Even the most complex machining operations start with a seemingly simple operation—sawing. Shops looking to optimize their processes shouldn’t ignore this step, because small improvements in sawing can pay big dividends down the part manufacturing line.

Metal suppliers use saws to process tubing, bar stock and solid materials for end users, and shops saw those materials into smaller workpieces. Band and circular saws are the two most common types found in shops. The bandsaw is a versatile machine that can be used for many different applications. For people who production-cut a variety of materials, a bandsaw is a good choice.

A circular saw has the ability to cut much faster than a bandsaw and provide a more accurate cut with a better finish. A circular saw performs a specific job more efficiently than a bandsaw, but is not nearly as flexible.

“A bandsaw is like a pickup truck—it can do almost anything,” said Dave McCorry, president of Structural Machinery Solutions, Columbus, Ind., a distributor of metal sawing and structural steel fabrication machinery. “The circular saw is more like a racecar. If it can be tuned to the application at hand, the circular saw can be more accurate and faster. So it is a question of flexibility vs. out-and-out production.”

Circular saws generally cut smaller workpieces. For example, most circular saws cut material from ½ ” to 8 ” in diameter, whereas a bandsaw can be made to cut material of pretty much any size.

A 4 “-dia. round solid bar of mild steel is the classic breakeven point between a bandsaw and a circular saw, McCorry noted. “They will both cut that material in approximately 1 minute,” he said. “Anything below that could be cut quicker with a circular, assuming reasonable materials, while anything above that would be quicker and cheaper with a bandsaw.

“But you get to a point where circular saw blades are just too big and heavy to go through really hard material,” he continued. “If you are cutting titanium or Inconel, for example, you can only take a very thin chip. When in the cut, the circular blade takes 3 or 4 times the width of that chip, so it takes much more power to produce the same effect as a bandsaw blade. That is why a bandsaw tends to be better on harder materials.”

Automatic or Not

Both saw types are available in manual, semi and fully automatic models. Manual is for users who are just cutting a few pieces periodically.

“Semiautomatic saws are for shops running different lengths of material and generally smaller quantities,” said Matthew Klipp, sales and marketing associate for saw manufacturer Behringer Saws Inc., Morgantown, Pa. “They can measure manually or utilize a material handling system that allows them to run material into a stop or feed it into a unit that will measure the length. They just have to input the length into a CNC, cut it and immediately change it by inputting a different length. So they can cut one piece at 2 ‘, one at 4 ‘ and so on.”

Courtesy of Structural Machinery Solutions

An RKL551AX circular saw cuts a large aluminum extrusion.

Automatic saws, according to Klipp, allow companies that have high quantities of the same size to run efficiently. “They can take long lengths of material, program the quantity into the CNC, and then it is automatically and continuously fed into the machine and cut to length.”

Even more sophisticated CNC versions of bandsaws and circular saws are available, right up to a fully programmable sawing cell. “You preprogram (the sawing cell) and it allows you to cut as many parts as you want at 12 ” long, 10 ” long, 6 ” long and so on,” McCorry said. “You can load different types of material into a magazine and program every single compartment. You can program as many parts as you want in each type of material, so you have full operational flexibility.” He noted that this type of system is only used by about 1 percent of his customers because of its high cost.

Cool Cutting

Coolant plays a major role in band and circular sawing. It keeps the saw blade cool and lubricates the face and gullets of the teeth so the chips will form easily in the gullet area and be carried out of the cut and drop off into a chip bin or be knocked off by a blade brush.

In both processes, users can apply flood coolant or spray mist, or cut dry, depending on what they want to accomplish, according to Klipp. “Some like to have clean material after they cut it so they have fewer secondary steps and therefore use mist instead of flood. The mist, in some cases, can lower blade life somewhat because it doesn’t keep the material and blade as cool as flood coolant. But in a lot of applications, it is still a good alternative as it will keep the shop floor and material cleaner.”

For shops cutting soft or thin-walled materials and aluminum, spray mist provides cut times and quality just as good as flood coolant. But Klipp recommends flood coolant for stainless steel and Inconel because cutting them generates a high level of heat.

Behringer has developed a system for applying multiple coolants—flood coolant, spray mist and air mist—for its HCS series circular saws. “Those three can be used individually or in any combination,” Klipp said. “Because circular sawing is typically performed at high speeds (up to 1,100 sfm), you want to make sure you are cooling effectively for good blade life and excellent cutting. The ability to cool effectively when cutting more difficult materials, such as chrome molybdenum and nickel, has been a hurdle in increasing the cutting speed. But by being able to utilize flood coolant in this typical spray-mist application, you are taking more heat away from the blade and material, and allowing for faster cutting.”

Bandsaw Blade Characteristics

Most metalcutting bandsaw blades are bimetal, featuring a thin strip of HSS that is welded to a wide strip of spring-steel backing material. The spring steel makes the blade flexible so it can bend around the machine’s wheels and twist into the guides. Different types of HSS are used, but M-42 is the most common because it is said to be the most versatile for bandsaw applications.

Once the two types of steel are welded together, the teeth are milled or ground into the HSS edge. “The teeth are then set before the final heat-treating process,” said Glenn Tatro, director of sales for Lenox, Industrial Products & Services, East Longmeadow, Mass. “This means the teeth are bent left and right in a pattern.” Various set patterns are used by different manufacturers.

Tooth setting prevents the bandsaw blade from binding in the cut. “The set provides a slot (kerf) for the back of the blade to move through the cut freely,” Tatro said. “For example, on a 1 “×0.035 ” blade, if you set the teeth 0.011 ” on each side, the total slot you can cut would be 0.057 “. If the slot is the same width as the thickness of the blade (0.035 “), the material can expand or stress-relieve itself and close in on the blade, and the blade can get hung up in the cut.”

Variable-tooth bandsaw blades are the most common type used for metalcutting. Variable tooth means there is a variable number of teeth on the blade in a designated length of that blade and the tooth pitch changes from one tooth to the next. This helps eliminate vibration, one of the major enemies of blade life.

Knowing how many teeth to have on a bandsaw blade depends on a variety of factors, but there is a simple rule of thumb that can be a good starting point.

“The 3, 6, 12, 24 rule is very simple,” Tatro said. “You want at least three teeth on the work all the time, you don’t want more than 24 teeth on the work at any one time, and what you’d like is between six and 12 teeth on the work all the time.”

Take, for example, cutting a 2 ” solid square with a 6/10 variable-tooth blade. “The average amount of teeth per inch on a 6/10 variable tooth is around eight teeth,” Tatro said. “So if you have an average of 8 tpi and you have 2 ” of blade in that 2 ” square material, that would put about 16 teeth on the work. But the rule says ideally you want between six and 12. So go down to the next size. A 4/6 variable tooth, with an average of about 5 tpi, would be a great choice for the application because you would have 10 teeth on the work.”

Courtesy of Lenox

Lenox’s Armor Black bandsaw blade has an AlTiN coating that allows it to withstand high levels of heat.

Carbide-tipped bandsaw blades are also available. A carbide blade retains its sharpness longer and imparts a finer surface finish than a bimetal blade.

Blade coatings, which can be applied on bimetal and carbide-tipped bandsaw blades, also play an important role in bandsaw cutting. A coating shields against heat. “Heat is another major enemy of saw blade life,” Tatro said. “When the teeth on the blade get hot, they lose their hardness to the point where they are no longer effective. When that happens, the operator tends to push the blade harder to make it cut and eventually the blade can strip the teeth off.”

Courtesy of Behringer