Factors That Affect The Cost Of Cutting
There are several factors that affect band sawing efficiency: tooth design, band speed, feed rates, vise loading, lubrication, the capacity and condition of the machine, and the material you are cutting.
LENOX® has developed planning tools that help you make intelligent decisions about these many variables so that you can optimize your cutting operation. Ask your LENOX® Distributor or Sales Representative about the SAWCALC® computer program.
How Chips Are Made
If you were to look at a blade cutting metal under a microscope, you would see the tooth tip penetrating the work and actually pushing, or shearing, a continuous chip of metal. The angle at which the material shears off is referred to as the “shear plane angle.” This is perhaps the single most important factor in obtaining maximum cutting efficiency.
Generally, with a given depth of penetration, the lower the shear plane angle, the thicker the chip becomes and the lower the cutting efficiency. The higher the shear plane angle, the higher the efficiency, with thinner chips being formed.
Shear plane angle is affected by work material, band speed, feed, lubrication and blade design as shown in the following sections.
Feed refers to the depth of penetration of the tooth into the material being cut. For cost effective cutting, you want to remove as much material as possible as quickly as possible by using as high a feed rate/pressure as the machine can handle. However, feed will be limited by the machinability of the material being cut and blade life expectancy.
A deeper feed results in a lower shear plane angle. Cutting may be faster, but blade life will be reduced dramatically. Light feed will increase the shear plane angle, but increase cost per cut.
How can you tell if you are using the right feed rate? Examine the chips and evaluate their shape and color.
Gullet capacity is another factor that impacts cutting efficiency. The gullet is the space between the tooth tip and the inner surface of the blade. As the tooth scrapes away the material during a cut, the chip curls up into this area. A blade with the proper clearance for the cut allows the chip to curl up uniformly and fall away from the gullet. If too much material is scraped away, the chip will jam into the gullet area causing increased resistance. This loads down the machine, wastes energy and can cause damage to the blade.
Band speed refers to the rate at which the blade cuts across the face of the material being worked. A faster band speed achieves a higher, more desirable shear plane angle and hence more efficient cutting. This is usually stated as FPM (feet per minute) or MPM (meters per minute).
Band speed is restricted, however, by the machinability of the material and how much heat is produced by the cutting action. Too high a band speed or very hard metals produce excessive
heat, resulting in reduced blade life.
How do you know if you are using the right band speed? Look at the chips; check their shape and color. The goal is to achieve chips that are thin, tightly curled and warm to the touch. If
the chips have changed from silver to golden brown, you are forcing the cut and generating too much heat. Blue chips indicate extreme heat which will shorten blade life.
The new LENOX® ARMOR® family of products create some exceptions to this rule. These products use coatings to shield the teeth from heat. This ARMOR®-like shield pushes the heat into the chip.
Getting Around Blade Limitations
Once you understand how feed and gullet capacity limit cutting action, you will be able to choose the most effective feed rate for the material being cut. Here is an example. Assume you are cutting a piece of 4" round. There are actually three cutting areas to consider: