Sharp points

Precision’s role in band saw blades

he first time I ever cut anything with a band saw blade was at a public-use shop, where I had a monthly membership. I thought I was there to invent the next industry-leading CNC milling machine. In retrospect, however, I was doing a lot of learning by trial and error.

The shop had a vertical saw and a horizontal saw. The instructor showed me a chart with feed pressure settings and speed settings, listed according to material types. He said, “These are some rough guidelines, but finding the right cutting rate is really more of an art than a science.” I was surprised to hear him say that—and I didn’t believe him.

“There must be a formula that will allow me to cut through a piece of metal faster than this,” I thought, as I waited about an hour for the rickety horizontal band saw to trudge its way through a piece of 4-inch-round scrap aluminum.

As I later found out, I had been wasting my time tinkering with a dull blade. I still have that piece of aluminum eight years later. It serves as a reminder that there’s more to saw cutting than tweaking the machine settings. Even at a small shop, the quality of the saw blade is paramount. At a steel service center, where tons of metals are being processed, a high-quality band saw blade makes a tremendous difference in productivity and profits.

Blade quality starts with precision manufacturing. Not only does the blade need to start sharp but it also needs to stay sharp. The band (blade) needs to be straight and flat. The teeth need to be centered and they must be the same height. These are the basic requirements for any band saw blade.

a high-quality band saw blade makes a tremendous difference in productivity and profits.

Starrett Advanz carbide-tipped band saw blades are one example where Starrett’s precision expertise is being applied to the blade manufacturing process. I told one of our saw techs a few years ago, “Don’t think of a carbide-tipped saw tooth as a normal saw blade—think of it as a cutter.”

It’s a cutting tool and we should view the carbide saw teeth as a series of tiny milling or turning inserts. Aside from the obvious cost limitations of this concept, there are many ways we can envision a saw blade as being just like any other high-precision cutting tool.

Geometric tolerances

Each tooth is precision-ground individually, going through several grinders to achieve the complex geometries necessary to imbue the blade with both strength and efficiency. The weld between the carbide tooth and the steel band needs just the right amount of current, heating time and cooling time.

Every tooth in any given blade must pass inspection; even one defective tooth can adversely affect all the teeth behind it. The geometric tolerances must be precise because the amount of material each tooth removes is much smaller than that of a turning or milling tool. The chip load in saw cutting is measured on the order of 10-4 inches. If some teeth are cutting while others are not, blade life decreases.

The Starrett Saw Division uses Starrett-made precision micrometers and dial gages and other advanced Starrett-made metrology equipment to ensure the highest quality blade manufacture. This includes measuring critical components such as the height of each tooth, the kerf, the bow of the band and the weld strength while the blade is still in production.

For every saw blade coil it produces, Starrett uses its own force gage to measure the strength of the carbide welds. A Starrett optical comparator is used to analyze the rake angle, clearance angle and other important features that cannot be determined using a mechanical device.

At Starrett’s Mt. Airy, North Carolina, plant, the latest processes and dedicated employees churn out high-quality carbide tipped band saw blades with innovative tooth geometry designed for the production cutting of today’s exotic alloys.

Final product inspection after machining can identify any problems, but using precision measurement solutions together with knowledgeable expertise at the start of the blade manufacturing process is critical.