Selecting a Band Saw Blade

Proper blade selection starts with a review of material composition and shape

December 1, 2010

The three main choices for blade type in metal cutting applications are carbon steel, bimetal, and, more recently, carbide-tipped.

Selecting a band saw blade involves many variables, but blade type and tooth configuration largely depend on the material being cut. By first examining the part being cut, you can choose the correct type, size, and width of blade, as well as the proper tooth shape and pitch.

Unfortunately for most band saw users, no single blade can cut every material encountered in daily shop life. While production cutting shops typically have several saws, and therefore the ability to have different setups for particular materials or shapes, the majority of shops have to switch out blades as necessary.

“Even if the shop is constantly cutting different materials and shapes, we generally recommend that they switch out the blades when needed,” explained Gene Ramsdell, a sawing expert and metallurgist for the L.S. Starrett Co.

While some may view this setup time as downtime, the key indicator in band saw cutting is always band life.

“If you keep the same blade on your saw for every cut and end up stripping the teeth from the blade, you will be switching out blades anyway,” said Ramsdell. “By selecting the proper blade initially, you can eliminate this waste.”

Band life should not be measured by the number of shifts or days that the band remains on the saw, said Ramsdell, but rather by how many square inches of material it cuts before it must be replaced. A qualified operator will get the maximum life out of saw blades, which maximizes productivity and reduces downtime. Many good operators can tell how well the sawing operation is proceeding by the sound the saw is making while cutting, the look of the chips, and how the machine is reacting.

For example a motor that’s drawing more amperage than normal can mean a speed or feed problem; if the chips are changing color, it can be an indication that the blade isn’t cutting properly.

“Do not ignore the importance of the operator,” said Ramsdell. “A good, experienced operator and a quality saw are keys to successful sawing. If the band saw operation was treated the same way as a CNC machine, we would see better life and better productivity from the blades.”

Tracking cost per cut over time, including blade cost, labor, downtime, and other wastes, is a good way to judge the success of a new blade that is put on the saw.

“Treating sawing as part of the manufacturing process as a whole, rather than an outside operation that is done before the real manufacturing begins, creates the best environment for success,” said Ramsdell. “Process improvement is important for every part of the manufacturing process, and sawing should be no different.”

The Blades

Band saw blades differ by type, length, width, tooth shape, and tooth pitch.

Each is chosen based on the part being cut and the type of sawing machine doing the cutting.

Blade Type

Band saw blades are chosen based on the part being cut and the type of sawing machine doing the cutting.

The three main choices for blade type in metal cutting applications are carbon steel, bimetal, and, more recently, carbide-tipped.

“Blade type will always be based on the material you are cutting and the amount of that material that you want to cut,” said Ramsdell.

Carbon steel blades are suitable for cutting carbon steels and aluminum.

“Carbon blades are a good, economical entry point for sawing, especially if the production rates are very low. This type of blade is used in many DIY applications as well,” added Ramsdell.

Bimetal blades are made with a high-speed steel tooth structure attached to a flexible alloy steel backing material. They are the most common blade used in metal sawing applications because of their ability to cut a variety of materials.

“Bimetal blades are the predominant choice for many production and industrial applications,” said Ramsdell. “They are the real workhorses when cutting metal.”

Carbide-tipped blades, a relative newcomer, have a steel backing and teeth made from carbide grades. They generally are to cut hard materials. Carbide-tipped blades are becoming increasingly popular for cutting prehardened tool steels and exotic alloys, such as titanium, Waspaloy®, and HASTELLOY®.

Material that has a high nickel or high cobalt content produces a lot of heat during the cutting process, and usually is a good candidate for a carbide-tipped blade.

In these cases, a rigid machine and experienced operator are also needed to produce the best results.

“For this type of blade we weld carbide tips onto the backing material, and then through a grinding process, we generate a tooth form,” said Ramsdell.

Blade Length and Width

The blade length, preset by the saw manufacturer, is determined by how far apart the band wheels have been placed.

The choice of blade width, however, is based both on the material that will be cut and the type of cutting that will be performed. For example, if scrolling or tight-contour cutting is being done, a thin blade (e.g., 1/4 in.) is recommended.

Some machines, typically vertical saws, have adjustable guides that can accept different blade widths.

Band life should not be measured by the number of shifts or days that the band remains on the saw, but rather by how many square inches of material it cuts before it must be replaced.

Tooth Shape

Until the mid-1970s a standard tooth shape had a zero-degree rake with a 35-degree relief angle. New shapes now can enable better cutting, especially in harder materials.

“In bimetal blades a positive rake of 5 degrees was developed, and since that time we have moved to even higher positive rakes on some teeth,” said Ramsdell. “Different tooth profiles can now make a 10-degree-rake tooth very strong, and we are seeing less strippage and less tooth chipping, especially at the tip.”

Tooth geometry, back angle, and the radius approaching the gullet have all evolved, giving us today’s cutting form, which for steels and exotic alloys usually is a positive rake from 10 to 16 degrees.

“If you get to a point where there is too much positive rake, the blade will start to skate over the material rather than dig into it, which leads to work hardening,” said Ramsdell.

Tooth Pitch

Pitch hasn’t changed much over the course of time, except in larger machines, which can now handle wider blades.

These wider blades – those wider than 3 in. -- are meant for billets approaching 30 to 40 in. wide. These large sawing machines have high-HP motors and drive the wide blades down into the cut while pulling the teeth through at the same time.

“For a long time 3 TPI [teeth per inch] was standard, but now we are seeing tooth pitches of 2-3, 2-1, and even 0.8-1,” said Ramsdell. “These types of pitches are beneficial when you are cutting a wide section. The fewer number of teeth in the cut allow the teeth to penetrate easier and therefore create a chip easier.”

The more teeth that are in the cut, the harder it is to pull the blade through. This is because there are more chips in the gullets, and it actually becomes more difficult to cut, even though there are more teeth in the work zone.

For more information, visit www.starrett.com.