Bandsaw blades are more than just consumables. Sawing is often the first step in a lengthy list of operations that eventually turn out a finished product. Therefore, the quality of the sawing cuts sets the pace and tone for the entire production process.
Manufacturers depend on their blades to make quality cuts, but they must also know how to use them if they’re going to reach the maximum expected blade life. Replacing blades can get costly, especially where downtime is concerned.
Manufacturers need to perform due diligence in selecting the right blade for the material they’re cutting. This is an important step. However, all that research is for nothing if the blade isn’t used correctly. For instance, most bandsaw blades require a breaking in period if you’re going to get the most out of them.
Ellis Mfg. Co. Inc. specializes in producing quality blades, but the company also educates customers about how to get the most out of their blades. Here are some general recommendations from the company.
The first order of business in blade selection is determining the size of your blade, which includes its length, width and thickness. Users can find this information in the bandsaw user’s manual. Note that the size and blade material affect the price of the blade.
The second step is to determine the proper teeth per inch (TPI) for the application. To measure TPI, start 1 in. or 2 in. along the blade from the center of the gullet. Count the number of teeth in that space. This is the TPI. When counting the teeth, note that a blade’s TPI may not always be a whole number.
It’s important to understand that the blade TPI to use is determined by the size and type of material to be cut and the desired finish. Typically, a courser TPI – 2 to 3 – is used with thicker material, whereas a finer TPI – 18 to 32 – is used with thinner material.
The next step in selecting a bandsaw blade is determining if you should use a bi-metal or carbon-tipped blade.
One of the advantages of using a bi-metal blade is the high-speed steel toothed strip of material that has been electron-beam welded to a fatigue-resistant spring backing. In a production setting, it’s more economical in the long run to use a bi-metal blade than a carbon-tipped blade even though the bi-metal blade costs more, because it will outlast carbon by up to five times.
While carbon-tipped blades are used for mild steels and other nonferrous metals, bi-metal blades tackle tough materials, including carbon steel, tool steel, structural steel, stainless steel, pipes and tubes, die steel, angles and flat stock and mixed metals.
Break in and Settings
Ellis recommends breaking in a new blade by running it at the recommended cutting speed, but only at one third the normal feed rate for 10 min. Gradually, you can increase the feed to the normal rate. This essentially primes the blade, prepping it for more efficient cutting.
The perfect analogy to demonstrate the effectiveness of this process is to think about how you use a newly sharpened pencil. You carefully press down as you write to gently wear down the sharp point, and gradually increase pressure as the tip becomes more rounded and stable.
Also important are the settings related to the bandsaw itself provided by the manufacturer. For instance, blade tension is critical to the quality of the cut and the life of the blade. Saw head pressure and guide bearings must also be tweaked for proper operation. This means the operator must have a regular maintenance schedule so the wear and adjustments are monitored. Most diligent operators check guide bearings with every blade change.
The best setting for a guide bearing is to set it 0.001 in. wider than the thickness of the blade being used.
The most accurate way to determine this is by using a feeler gauge set to the thickness of the blade plus 0.001 in. If you’re not able to use a feeler gauge, you can look down the blade with enough light to determine if there is any space between the guide bearings and the blade. If you do see a gap, adjust the guide bearings until the gap disappears. You can tell if the guide is too tight if there is scoring along the surface of the blade.
To check the proper alignment of the guides, grasp the blade between the guide and the housing and give it a twist. A correctly adjusted guide will show no movement on the cutting portion of the blade. Simply repeat this procedure between the other guide and the housing on that side.
To make sure the blade is held in place during cutting, a pressure bearing rides at the top edge of the blade. This will wear out over time, so it must be checked and replaced when necessary.
The pressure bearing must also wear evenly, so take a straight edge and hold it against the side of the bearings. It should sit flush. If there is a gap at the top or the bottom, the bearing needs to be replaced.
Saw head pressure is another aspect of sawing that affects blade life and cut quality. Periodically, you should use a pull scale, commonly called a fisherman’s scale, to check the head pressure.
Before doing this, open the hydraulic valve, then connect the scale to the saw head handle and lift until the blade is an inch off the cutting table. As you’re bringing the saw head down, read the scale. If the saw head weighs more than 8 lbs. over the last inch of travel, you need to adjust the compensating springs.
The adjustment for the springs is under the pulley box on the back of the saw head. Simply turn the head weight adjustment knob clockwise and recheck the weight of the saw head until it reads 8 lbs.
For long life and the ability to cut a variety of materials, consider the Ellis General Purpose blade (GP), which has a distinct tooth style for a variety of cutting needs. The GP is a bi-metal blade that offers a long blade life yet has the ability to cut a variety of materials. It’s available in widths from 1/4 in. to 2 in. and thicknesses from 0.025 in. to 0.063 in. The GP is commonly used to cut cold-rolled steel, hot-rolled steel, aluminum, stainless steel and cast iron.
Ellis recommends having at least three teeth in the work surface at all times and no more than 24. The optimum number is six to 10. Also, be sure to never run bi-metal blades faster than 500 sfm. Overly aggressive cutting rates can damage the material being cut and reduce the life of the blade.
Furthermore, while using your new blade, monitor chip formation. For burnt, heavy chips, reduce the feed and speed; for thin, fine or dusty chips, increase the feed; and for curled, shiny and warm chips, use the bandsaw’s optimum feed.
As a final general rule for choosing the cutting speed for your bandsaw blade: The harder the material, the slower the speed; conversely, the softer the material, the faster the speed. The faster the speed, the finer the finish produced on the cut surface.