Understanding Sawing

Blade selection, cutting parameters, coolant, and maintenance are all important factors in any sawing job

October 1, 2009

Selecting the proper band saw blade is much like any other manufacturing decision. You start with an understanding of the work that needs to be done, and then simply select the correct tool for the job.

Today however, there are many blade choices, new technologies, and uncontrollable circumstances such as the economy that can affect the selection process.

The first and easiest step is to determine the blade you need, which the band saw machine basically specifies. Important numbers here are the length, width, and thickness of the blade.

The next steps are to select the cutting edge material, tooth pitch, and tooth form.

The Cutting Edge

“The material to be cut determines the cutting edge material,” explained Juergen Meckle, general manager for sawing supplier TecSaw. “Carbon steel blades; bimetal blades; and coated and uncoated, carbide-tipped blades are widely used for the cutting of wood, steels, and nonferrous metals, while carbide-grit and diamond-grit blades are used for more exotic applications like the cutting of abrasive building materials, fiberglass, and silicon.”

According to Meckle, the majority of blades used today are bimetal, because of their versatility. But for even higher cutting performances and longer blade life, he recommends carbide-tipped blades.

Tooth Pitch

Selecting the correct tooth pitch is crucial for good cutting performance and long blade life. Contact length determines the tooth pitch. The contact length is either the width of the material on a horizontal machine, or the height of the material on a vertical machine.

The tooth pitch is measured in teeth per inch (TPI). A blade with a TPI of 3-4 has a minimum of 3 and a maximum of 4 teeth within an inch. The higher the number, the finer the tooth pitch.

“While there are charts for the selection of the proper tooth pitch, the rule of thumb says that it’s best to have no fewer than 3, but no more than 24 teeth in the workpiece,” said Meckle. “Obviously, this gives some room to play, and the final selection of the TPI depends on cutting time and the desired surface finish. The more coarse the tooth pitch, the rougher the finish, but the faster the cut, and vice versa.”

Tooth Form

The material to be cut and the shape of the material dictate tooth form – the tooth angles (zero degrees, positive, or negative cutting angle) and the tooth shape.

“Structural applications require a more stable tooth that can handle constant impact better,” said Meckle. “Material with a lot of inner stress tends to close the cutting kerf while cutting and can pinch the saw blade. Therefore, a blade with a wider set should be used.”

A lot of factors can influence blade selection. Apart from certain factors that are a given, it is also important to know what should be achieved. Many fabricators need a universal blade that can cut many different kinds of materials and shapes without the need for extremely high performance.

Others want to achieve the shortest possible cutting time, and others still desire long blade life. The price of a blade is obviously a big factor as well.

“It is a common mistake to think that a cheap blade results in less production costs,” explained Meckle. “In many cases, it is better to spend more for a blade that lasts longer and cuts faster, because the price of the blade itself is only a small part in the whole cutting operation.”

Of course, the machine itself plays a big role in the cutting process too.

“It certainly doesn’t make sense to put a very expensive blade on a cheap machine that is not capable of running the parameters that the blade needs in order to function properly,” he added.

And, there is no such thing as the “best” blade. The best blade for one application might not work at all for another.

The blade and the saw are not the only variables in the cutting process. Cutting parameters and coolant usage also affect cutting performance.

“Each application has different requirements regarding the cutting parameters, and it is obviously very important to use the proper speeds and feeds,” said Meckle.

Using incorrect speeds and feeds can damage a blade, which prevents it from working properly.

However, it is not always easy to ensure the proper speeds and feeds are being used because many machines don’t have all the necessary features.

“In the ideal situation, the machine has an infinitely variable cutting speed adjustment, a feed rate regulator, and an automatic feed force regulator,” said Meckle. “In this case it is fairly easy to make sure that the proper parameters are used.”

In other cases, however, the saw may have only two speeds, may not have a feed rate regulator, and the feed force control is basically the weight of the saw head.

The three main coolant choices are: water-soluble oils, semisynthetic cutting fluids, and synthetic cutting fluids.

“The proper [coolant] selection depends on the application, but, semisynthetics will work for most applications and are also easier to maintain than water-soluble oils,” said Meckle. “They basically combine the advantages of water-soluble oils and synthetic cutting fluids. Therefore, semisynthetic cutting fluids are used in the majority of band saw cutting applications.”

As important as product choice is, the operator is perhaps the most important variable in the cutting process.

“The operator is very important because he has to ensure that the proper cutting parameters are used,” said Meckle. “There can be huge differences regarding cutting performance and blade life depending on how well the operator knows how different materials have to be cut.”

Every time the application changes parameters should be changed accordingly; sometimes this also includes blade change. Without the necessary knowledge, an operator can destroy a blade in seconds.

Machine Maintenance

Good cutting results can be achieved only if the band saw is in good working order. Certain components of the saw can influence the performance, accuracy, and blade life tremendously.

“Worn-out carbide guides or guide rollers not only reduce accuracy, they also reduce blade life,” said Meckle.

Because of increased friction, a worn-out guiding system can lead to premature blade breakage. Worn-out wheels can have the same effect, especially on wheels with shoulders. On a worn-out wheel the tracking changes and the blade can rub against the shoulder. As a result, the back of the blade gets damaged and can break prematurely.

“One of the most neglected components of a band saw is the chip brush,” added Meckle. “However, this is actually a very important part. Without the chip brush, the chips are not removed out of the gullet of the blade, and the next time the blade comes around all the chips are pulled back into the material.”

This means that the gullet has no more room for additional chips, so the blade is lifted off the material and cannot penetrate the material. As a result, the cut quality can be poor and the risk of tooth breakage high.

For more information, visit www.tecsaw.com.