Cordless Reciprocating Saws - Part 3

Understand Reciprocating Saw Bi-Metal Blade Design and Function.Subject:  Cordless Reciprocationg Saws, Part 3Topic:  Selection and Use of Bi-Metal Blades for Reciprocating Saws at Vehicle Rescue IncidentsObjective:  Understand Reciprocating Saw...


Fine-tooth 18 or 22 tpi reciprocating saw blades serve no useful purpose for vehicle rescue applications. The cutting teeth are too small and too fine for the thickness and layering of metal being cut through at extrication scenes. An 18-tpi blade will not last long enough at a crash scene to perform effective cutting. Using a blade that is too fine for the job also causes it to cut more slowly and to wear out rapidly.

For the majority of vehicle rescue applications, a medium tpi blade is the best to use. Extrication crews should consider standardizing on using the new bi-metal blades rated between 10 and 14 tpi.

To make it even easier to standardize on blade choice for rescue applications, manufacturers now produce "variable tooth" blades. These are very versatile for our vehicle rescue applications. A typical “vari-tooth” blade has a rating of 10/14 tpi. This means that throughout the length of the blade, the tpi changes back and forth from the finest setting of 14 tpi to a coarse setting of 10 tpi. These variable-tpi blades are the most efficient all-around fire rescue blade available. If you only had one blade style to stock in your inventory for vehicle rescue, they should be variable tooth 10/14-tpi blades.

To cut through wood such as a tree limb or structural lumber, a coarse-tpi saw blade with a tpi of 6 or less would be used. I have also used 6-tpi blades for cutting sheet metal along the side panel of a vehicle. With a 12-inch-long, 6 tpi blade, I can completely cut out the "third door" of a two-door vehicle along with the B-pillar. This aggressive cutting allows the entire sidewall, B-pillar and door to open on the front door’s hinges.

Cutting vehicle metal with a blade designed for wood, however, causes a lot of saw vibration and is noisy. But with a well-prepared and properly trained rescuer, it results in an aggressive attack that will quickly open up the entire side of a damaged vehicle. This is not the blade of choice for tubular metal, pipes or even narrow roof pillars. For sidewalls or the base area of a B-pillar however, the 6-tpi blade is an exciting alternative. Grab hold, hang on and be impressed!

Besides the routine metal cuts through vehicle components such as roof pillars with 10/14-tpi blades, a reciprocating saw can be very effective in totally removing a vehicle’s windshield. When cutting laminated glass, a coarse-tpi blade is better. Use a 6-tpi or a variable tooth 10/14 for best results on the windshield. The finer teeth of a straight 14- or 18-tpi metal cutting blade dulls quickly as the glass is cut. Any reciprocating saw blade that is used to cut out a windshield should be discarded after the windshield evolution is completed because the cutting edges of the teeth will be significantly dulled.

Recommended Lengths For Extrication Blades

Crews using reciprocating saws for any of a wide variety of fire-rescue applications should stock three basic lengths of saw blades in their inventory. The shortest blades should be six-inch-length units. These would be used only when there is limited clearance or when a longer blade cannot fit into an opening.

The most effective length blade for all purpose vehicle rescue applications is the eight- or nine-inch blade. Fire departments should make the eight- or nine-inch blade their standard rescue attack blade and pre-blade their saw with this length. This versatile length blade cuts best through the multiple layers of material found in vehicles today; thick rear roof pillars, side B-pillars, door panels, etc.

For unique circumstances, rescue teams should stock a minimum number of 12-inch-length blades also. These special-purpose blades are useful when cutting through some thick object such as the base of a B-pillar on a full-size sedan, the entire sidewall panel of a two-door coupe or the side of a van. With the longer length blade, it is possible to cut through all layers at the same time. The protruding end of this blade, however, may be too long to be used near a patient. There is one more caution when using this long length blade. If a 12-inch blade is used to cut through a thin wall material, the extra length of the tip causes the blade to "wag" back and forth. This wagging causes the material being cut to also vibrate and reduces the cutting efficiency of the saw.