The Right Blade for the Right Bandsaw Cut
“You need that chunk of metal cut in half? No problem—I’ve got a bandsaw in the corner of my shop that’ll rip right through it.”
Unfortunately, a one-size-fits-all approach to metal cutting isn’t usually the wisest plan. Different metalworking projects require different methods, whether it be shearing, laser cutting, sheet metal slitting, or sawing. Even with saw cutting, there are times when a cold saw or an abrasive saw would be more appropriate to use than a band saw, so it’s important to thoroughly understand the project and the desired outcome.
When it’s determined that a bandsaw is the right machine for the job, there’s still the matter of using the correct blade. While there are general-purpose blades that may be adequate for most of your work around your shop, swapping out blades that are specific for the job can be wise (such as when cutting stainless steel) or even critical (such as when cutting aluminum). Factors affecting blade selection include:
- The material to be cut.
- The material the blade is made from.
- The length, width, and thickness of the blade.
- The style and pattern of the teeth on the blade.
- The speed of the blade.
- The feed rate and feed pressure.
While it’s important to understand the basics of proper blade selection, keep in mind that the essential rule of thumb is to simply follow the manufacturer’s specifications. Every quality blade maker will provide charts designating which blades do what, and there are programs, apps, and online tools to streamline the process. Many saws today feature NC and even CNC control units that further take the guesswork out of the equation.
How the teeth are arranged on a bandsaw blade are key to getting a proper cut as well as increased blade life. Two of the most important variables in tooth selection are TPI and tooth pitch.
- The abbreviation TPI stands for “teeth per inch”—literally the number of teeth or portions of teeth found in one inch along the bandsaw blade, as measured from one gullet to the next (gullets are the curved areas at the bottom of each tooth).
- Tooth pitch is the distance between the tip of one tooth to the tip of the next one.
Both measurements are important, since many blades will have a variable tooth pitch, meaning that several teeth in a row will have different spacing between them. These non-uniform distances help reduce blade vibrations, especially when cutting hollow workpieces like tubing.
Some general principles governing the selection of tooth pitch and TPI include:
- The minimum number of teeth that should be in contact with the workpiece at a time is three (preferably six to twelve).
- A thinner workpiece usually requires a finer tooth pitch with a larger TPI.
- A thicker diameter solid workpiece requires a courser tooth pitch with a smaller TPI.
- The higher the TPI, the better the finish following the cut.
- The lower the TPI, the faster the cutting can go.
- If there are too few teeth, they may wind up straddling the workpiece and getting broken off.
- If there are too many teeth, their gullets could overload with swarf (chips) that can’t escape until they reach the other side of the cut. This can lead to undo pressure on the teeth, allowing parts of them to get stripped off.
- If at least three teeth can’t be maintained in the cut, decreasing the feed rate can help prevent the teeth getting snagged.
- If the material being cut allows it, increasing the speed of the blade may compensate for too few teeth.
- If too much swarf is accumulating in the gullets, decreasing the feed rate can reduce the build-up.
- When cutting bundled loads, determine the proper TPI for a single piece, then go slightly coarser.
- Tooth pitch may have to be altered depending on how the material is loaded in the vise.
Using the literature provided by the bandsaw blade manufacturer, match the tooth pitch and TPI to the job at hand to achieve the lowest cost per cut and the longest possible blade life.
Even with the correct TPI and pitch, a bandsaw blade won’t cut efficiently if it isn’t well-maintained.
The first step is to break in the blade before it is put into full production. Simply put, brand-new bandsaw blades are generally too sharp to work effectively. By running the blade for a period at a reduced feed rate, the sharp points on the tips of the teeth will be smoothed down to a radius that is less likely to get caught and broken off during normal operation. The first few cuts (perhaps 50 to 75 square inches of material) should be cut at three-quarters of the normal feed rate in hard metal or half of the normal feed rate in softer metal, then slowly increased to the normal feed pressure.
Ongoing maintenance of your bandsaw blades include:
- Checking the chips. Something may be wrong in the cutting process if the chips are hot, a different color than the material being cut, or not coming off in little curls.
- Ensuring correct blade tension during cutting and removing the tension when the saw will be idle for an extended period.
- Keeping the blade cleaning brush in good order.
- Inspecting band wheels and other parts for chips or other debris.
- Properly positioning and clamping workpieces.
- Positioning guides as close to workpieces as possible.
- Using coolant as directed and in the correct mix.
- Paying attention to any strange noises arising during the cutting cycle and determining the cause of them.
- Handling blades carefully when not in use.
- Applying anti-rust treatments if needed when storing blades.
Choosing the Best Blades
When it’s time to buy new blades for your bandsaw, a good course of action might be to check with your fabrication machinery provider. They will likely have good recommendations for which blades from which manufacturers will work best with your various applications. They may also be able to give you some additional pointers on how best to adapt TPI and tooth pitch for any specialized projects you might be starting.
Taking the time to match the right blade to the right project will always improve the productivity and profitability of your metal cutting.