Choosing and using band saw blades to meet diverse fab shop requirements
October 15, 2012
It’s not difficult to choose the right blade for your application; all you need to do is carefully consider and understand tooth shape, blade width,and teeth per inch.
The band saw is a useful tool for metalworking due to its versatility and precision, and one can be found in almost every shop. Its usefulness, however, depends on the blade. If you choose the wrong blade, teeth can dull prematurely, damage your material, or break.
It's not difficult to choose the right blade for your application; all you need to do is carefully consider and understand tooth shape, blade width, and teeth per inch.
Choosing the correct blade to satisfy a range of cutting requirements and applications is critical in a fab shop.
Performance, durability, and cost are all important factors in deciding which band saw blade is right for all of your various applications. Getting the lowest cost per cut, while maintaining acceptable levels of surface finish, is the optimal solution for ensuring continued productivity and profitability. Thinking about these factors is the first step in selecting blades that optimize metal cutting production and profit.
The demands and cutting needs in a fabrication shop require a variety of band saws to cut solid materials and heavy-walled tubing, structural shapes, bundles, and hard materials such as tool steels.
Since no single blade can satisfy all those requirements, you need to decide whether to purchase a dedicated band saw blade for each type of cut needed, change the band saw blade after each application, or choose a band saw blade that works for multiple cutting applications in your fabrication shop. The last option is the most common choice.
Choosing the correct blade is only the first step in the decision-making proc-ess. Using the blade appropriately for each type of cutting you do is important to prolonging the operational life of the blade. Understanding how the blade will stand up against the cutting of various metal materials is the next step in ensuring better productivity.
When blades cut a large, continuous area of solid material, the stresses on the teeth after initial impact tend to be consistent in terms of intensity and direction. The teeth proceed all the way through the cut, maintaining unending contact with the metal. Since no additional impact shocks occur after initial contact, there is no excessive stress on the teeth as they cut through the material. The blade's longevity and ongoing performance in this type of application are based on the blade's wear resistance, which is largely dependent on its hardness and tooth geometry, or rake angle—the angle of the cutting face relative to the work.
For cutting structural steels or bundles, the band saw blade teeth are subjected to multiple forces from different directions. For example, when cutting a piece of tube steel, the blade is required to cut through two walls, thereby causing a destructive action where the tooth is being released in a forward motion by both the speed of the blade and a downward feed pressure. Similar shocks occur when cutting other shapes such as angles, channels, and I-beams.
In the case of bundles, solids, or shapes, the number of strikes per pass increases substantially. These repeated impacts, and the stresses that are generated by the cutting of heavy-duty metal, can cause the teeth to crack.
The No. 1 reason band saw blades fail in fabrication shops is the repetitive shocks or impacts on the blade, not excessive use.
It is impossible for one blade to work well for every purpose. What you need to determine is what band saw blade will be durable enough to withstand these forces while quickly providing a smooth cut without the need for secondary operations such as filing and grinding.
To determine the band saw blade that best suits your shop's cutting requirements, you must examine the materials being cut. Most blades are bimetal, which means they are composed of two separate metals joined together.
Bimetallic blades consist of layers of different metals. These blades can withstand the punishment of cutting shapes and bundles, yet possess the hardness for continuous use with solids and heavy-walled tubing and the occasional cutting of high-alloy steels.
Bimetal band saw blade teeth, which are made of high-speed steel, are bonded by various methods to the high-strength carbon steel base. Such construction makes for blades with a better combination of cutting speed and durability than shown by nonbimetal blades in certain applications.
A recent advancement in bimetal band saw blade production replaced electron beam welding with a diffusion bonding process that has resulted in blades that are more resistant to tooth strippage and also able to withstand operating temperatures up to 1,100 degrees F. These blades now can cut materials with 40/45 HRC.
Some bimetals have coatings such as titanium nitride, often used on components to improve surface properties, making them more suitable for custom applications in which neither conventional bimetal nor carbide-tipped blades work well. Heat treatments are also applied to bimetals, providing the right combination of rigidity and strength.
For cutting large volumes of high-nickel-alloy steel, you should use a carbide-tipped blade or tungsten carbide that is 78-80 HRC.
Cutting these hard materials requires more shear break for the material to form the chip, creating a considerable amount of heat at the face of the tooth. Carbide is recommended over high-speed steel because it offers more resistance to heat. Therefore, carbide-tipped blades hold their edges longer than bimetal blades for cutting of such materials as INCONEL®, MONEL®, Hastelloy®, and titanium.
The optimum tool is not necessarily the least expensive or the most expensive, but the one that has been carefully chosen to get the job done quickly, efficiently, and economically. A cutting tool must have the following characteristics in order to produce good-quality parts economically:
The blade's properties also must be chosen based on the type of cutting that is being performed.
Blade width, which is measured from the tips of the teeth to the back edge of the blade body, is an important factor. Use the widest blade your machine will accommodate, except when cutting contours.
Tooth rake, the angle formed by the tooth face and a line perpendicular to the back of the blade, needs to be chosen based on the material and shapes that will be cut. A positive rake angle increases the tilt of the tooth face and is best-suited for thick solids and heavy-wall tubing.
Straight or less positive rakes are preferred for most structural and bundle cutting.
Band saw tooth blades are available in different shapes, each with their own characteristics.
Pitch is the distance between one tooth tip and the next. Cutting thin sections of material requires a fine pitch (more teeth), and thicker sections require a coarse pitch (fewer teeth). Strive for a minimum of three teeth in the cut. Having six to 12 teeth in the cut at any time is optimal.
On a constant-pitch blade, the distance from one tooth tip to the next tip, gullet depth, and rake angle are uniform throughout the full length. It is typically used for general-purpose cutting.
A variable-pitch blade has various tooth sizes and gullet depths to reduce noise and vibration when cutting structurals, tubing, and solids. The lowest/highest pitch on the blade is signified by two numbers as follows: 10/14, for example.
One of the most common problems in band sawing is stripping the teeth from the blade. Usually this is due to overload of forces on the blade caused by repeated impacts with the material, especially while cutting structural shapes and bundles.
In addition to the blade itself, other factors should be considered when selecting a band saw blade.
Equipment Condition and Type. As is always the case, keeping your equipment well-maintained and vibration-free will ensure accuracy and longer blade life. Blade wear patterns may be a sign that a wheel adjustment is needed or guides are worn and are causing problems.
Coolant. It is important to choose the right coolant for your cutting applications. Choosing the proper coolant will help you improve the cut and also the life of your saw blades.
Operator Skill. Like with any job, knowing your equipment and understanding the operation and processes, as well as being able to troubleshoot or get service when equipment fails, are vital to the success of your company. Being properly trained and having the correct resources are also contributing factors to the success of your company.
Following are just a few skills necessary to ensure continued productivity: