Understand Reciprocating Saw Bi-Metal Blade Design and Function.
Subject: Cordless Reciprocationg Saws, Part 3
Topic: Selection and Use of Bi-Metal Blades for Reciprocating Saws at Vehicle Rescue Incidents
Objective: Understand Reciprocating Saw Bi-Metal Blade Design and Function
Task: Select the correct bi-metal blade for rescue use and demonstrate proper use of the blade in a reciprocating saw.
The fire service is becoming increasing familiar with the operating capabilities of reciprocating saws. They are being used in unique ways at incidents such as structure fires, building collapse rescue incidents and vehicle extrications. To use these saws effectively, however, we must also keep abreast of advances made recently in the design and manufacturing of the reciprocating saw blades themselves.
The most important action a fire department can take to dramatically improve the capabilities of its reciprocating saw is to stop using consumer-grade blades and begin immediately to only utilize break-resistant, bi-metal blades specifically designed for the rugged use and abuse of fire-rescue applications. This new family of super-heavy-duty blades, commonly known as demolition blades within the industry, are such a vast improvement in what we have used in the past that they make the standard hardware store variety saw blades obsolete.
Manufactured by companies such as DeWalt, Milwaukee and American Saw & Manufacturing Co., the demolition blades reduce tang breakage, a common problem with lightweight consumer-grade blades. The new rescue blades also bend rather than snap or break and minimize tooth chipping compared to standard blades.
Bi-metal demolition-type blades are sold to professional contractors through industrial supply houses and are now even available through nationwide outlet stores such as Home Depot and Lowe’s. The cost per blade is more than a consumer-grade blade but the advantages and capabilities of these blades far outweigh their cost factor. Fire/rescue teams should not use anything but industrial-grade, bi-metal demolition reciprocating saw blades specifically designed for fire and rescue applications. Contact information on three manufacturers of demolition-type rescue blades is offered at the end of this article.
Bi-metal reciprocating saw blades have actually been manufactured for many years: the original bi-metal blades were first introduced in the 1960s. These blades work so well for rescue applications because of their special rugged construction. They consist of two types of metal (thus the term bi-metal): a high-speed steel cutting edge that is welded to a strong, flexible spring steel back.
The thin high speed steel edge contains all the teeth that do the cutting while the thicker main body of the blade, called the back, is specifically designed to help resist breakage during sawing operations.
Blade Thickness Matters!
Another difference with the new demolition blade is apparent when one compares the standard blade to a new fire-rescue blade. Most hardware-store-variety reciprocating saw blades are .035 of an inch thick or less. Blades this thin may be acceptable for weekend jobs around the house, but they fail miserably for fire-rescue applications.
The new TORCH and AX blades from Milwaukee, for example, are .042 of an inch thick. Both the DeWalt and the Lenox line of Demolition blades are .062 of an inch thick. When using these rescue blades, you will feel more resistance because the thicker blades is actually cutting more metal. You simply increase your pressure on the tool to offset this resistance.
Manufacturers produce blades with different numbers of cutting teeth because of the various types of materials that must be cut through. The number of teeth along each inch of the blade is the referred to as the blade’s tooth-per-inch (tpi) rating. A high tpi number such as 18 or 22 indicates a fine-tooth blade, one with many small teeth along its cutting edge. This blade is used by builders or contractors to make detailed cuts in thin metal, plastic or laminate materials.