Know Rotary Saw Blades

Understanding the blades used in rotary saws can improve fireground effciency

By Peter F. Kertzie
Published Tuesday, September 30, 2008 | From the October 2008 Issue of FireRescue

I had a freezer full of pork tenderloin that I needed to divide up without thawing it. Not being a butcher, or even someone who’s comfortable in the kitchen, I was not equipped to handle this task. I looked around my workshop, which is located near my freezer, and my eyes fixated on my 12" motorized miter saw. Not knowing if this would work, I took my time with the first cut and, to my surprise, it cut great. I finished cutting the meat and rewrapped it.

For the record, there was nothing on my carbide-tipped finish blade that indicated this saw could be used to cut meat (although these types of blades have been known to claim fingers). What’s the point to all this? We carry several blades on our rigs, and although they may not be designed for the material we need to cut, they may work just fine. (Note: Consult your owner’s manual and/or the manufacturer before attempting to cut any non-rated materials.)

Know the Basics
This month’s column focuses on the blades we use in our rotary saws. Most truck companies include a rotary saw in their power tool cache, and most of these saws are equipped with a carbide-tipped blade. My company doesn’t use the rotary saw at every fire. The majority of our responses involve wood-framed, peaked-roof structures on which we normally use a chainsaw. But we do use rotary saws fairly often for an assortment of other tasks at different types of emergencies (i.e., cutting through the trunk or hood during a car fire, opening garage doors, cutting through metal doors, cutting flat roofs made from of an assortment of building materials). The saw consists of a gasoline/oil-fed power head, similar to that found on a chainsaw, a belt drive and a blade that can be similar to those found on a household circular saw.

Household electric circular saws can be purchased with an electric brake that stops the blade from rotating when you take your finger off of the trigger. Ventilation chainsaws have a clutch that will stop the chain when you release the throttle. The rotary saw doesn’t have a braking mechanism for the blade. The blade will rotate freely after turning the saw off or releasing the throttle, so keep your digits and appendages a safe distance away.

A handful of manufacturers supply these saws to the fire service. You can also get them from industrial equipment suppliers, which call them “cut-off” saws—their common name in the construction industry.

Testing the Blades
I decided to take a closer look at the blades we carry on our rigs, all of which are issued to us by the department. These blades include a couple of carbide-tipped, wood-cutting blades of various design, and two different abrasive discs—an aluminum oxide disc for metal and a silicon carbide disc for concrete.

In addition to what my fire department supplies, a couple manufacturers have allowed me to test their diamond blades. Several years ago, I had the opportunity to do some hands-on training at the Cutters Edge facility in Julian, Calif. I was familiar with the company’s ventilation saws and was surprised to learn that they had a rotary saw, too. This saw comes with a diamond blade that can cut through a whole bunch of stuff.

Based on my experiences with our department’s blades, as well as those I’ve been able to test, I will break down the blade assortment.

Carbide-Tipped: We carry carbide-tipped blades for cutting wood products and the roofing materials attached to them—often some type of asphalt or rubber coverings. I would use this saw and blade on structures of ordinary construction: flat roofs. You’d probably run into this type of roof fairly often in big cities like New York and Los Angeles. In my mostly peaked, wood-frame roof response district, I may open this type of roof only a couple times a year. But as long as there’s even one of these roofs in our district, we must be prepared to open it.

We use the chainsaw on peaked roofs, but when our chainsaws have been down, I’ve used the rotary saw with the carbide-tipped blade. Some of my pals in Milwaukee don’t use ventilation chainsaws on the roof, so it’s common practice for them to open a wood-frame peaked roof with a rotary saw—and they’ve had great success with it.

Even when we don’t need to open flat roofs with a saw equipped with a carbide-tipped blade, we still have plenty of need for it. We’ll often use the carbide-tipped blade to expose boarded-up windows and doors. Using it for this purpose is very similar to using a standard electric circular saw, with the obvious difference being that our rotary saw is gasoline-powered. Additionally, with this saw, you can open wooden floors for ventilation, for rapid-intervention team operations, to expose hidden fire or for any other application where you need to open both thin and relatively thick areas of wood.

Carbide-tipped blades are often found in lumber mills, and many are marketed as specialty blades for demolition or for the fire service. None of the carbide-tipped blades are good for everything, even if they’re billed as such. A standard carbide-tipped blade used by carpenters will be rendered sub-par if it hits a nail. It will cut, but not as designed. These blades are designed to cut wood fibers and will be quickly damaged if brought into contact with masonry or metal.

Carbide-tipped blades sold as demolition or rescue blades will hold up after coming in contact with many materials other than wood; however, they are not designed to cut through these materials. The primary targets of these blades are wood, asphalt, tar or even rubber. Some will do well on masonry or concrete, too, but will not cut through steel rebar, a common item found inside concrete. An example of this is the Warthog blade, a formidable blade with an intimidating appearance that will hold up under most conditions; however, the manufacturer doesn’t warrant the blade if it comes in contact with metal or masonry objects (www.thewarthog.com/Merchant2/merchant.mvc).

Another formidable blade is the Piranha blade, which is designed to cut through an impressive list of materials, but a warning on the company’s Web site states that the blades aren’t intended to be used on masonry, concrete or stone (www.diasharp.com/demolition-blades.html). These blades are both great carbide-tipped products and will hold up to a lot of abuse.

Abrasive Discs: Let’s now turn to abrasive discs and the various materials they are designed to cut. Silicon carbide discs are made to cut concrete, as well as stone, brick, soft aggregate and masonry—materials we encounter when performing forcible entry and often on flat roofs. These discs are fairly inexpensive (usually under $20) and, as with all abrasive discs, wear out rather quickly and will need to be replaced during an emergency if many cuts are required.

Aluminum oxide abrasive discs are for cutting through non-ferrous metals—steel, angle iron and rebar. For example, they can cut through steel gates, locks, bars on windows, roll-up doors and two of my favorites: the engine compartments and trunks of burning vehicles.

These discs are also usually under $20. Like discs for concrete, the downside is that they wear quickly, so be prepared to change blades if you’re making several cuts. When opening a trunk and hood at a car fire, I often have to change blades in the middle of the operation.

There were times when I had the wrong disc or saw or we ran out of either of the previously mentioned abrasive discs and were forced to use the wrong one. Oddly, it didn’t appear to make a difference. I called the manufacturer to discuss this and was told nothing that would negate our actual findings. As we discussed the exciting world of abrasive discs even further, I posed the question, “Do you have a disc that’s good on both metal and masonry?” The answer was yes. There’s a Ductile disc that’s a combination of aluminum oxide and silicon carbide. I then asked about the price and was told that they all cost about the same. Brilliant! One disc that does two things—what more could you ask for? I’m sure that there are many suppliers of these types of blades; however, I’ve only talked to ours—United Abrasives (www.unitedabrasives.com). They were easily reachable, available to answer questions and supplied me with a couple samples of their “ductile” blade to try out.

A warning: Don’t store your discs in wet or humid areas, and don’t let oils, fuels or even water come in contact with them, as this may degrade the materials that bond the discs together.

Diamond Blade: Blades using industrial diamonds have expanded in the past few years. Both Cutters Edge (www.cuttersedge.com) and Supervac (http://supervac.com) gave me rotary saws equipped with diamond blades to test, and I have an offer to try one from Team Equipment (www.teamequipment.com). Additionally, I examined various companies’ diamond blades on display at this year’s FDIC, and I have to say that I like this type of blade. They’re made to cut through concrete and metal, but are sometimes promoted as being able to cut through anything. That may be a bit of a stretch. Although they will cut through wood, they don’t do it in the most efficient way, and if wood was my primary target, I would use a blade that’s made for wood.

Diamond blades will do what the abrasive blades do and more. They cut through concrete, steel, steel-reinforced concrete and limited amounts of wood. The big advantage: The blade will not easily wear out. As a matter of fact, I tried to wear out the blades that were loaned to me and was unsuccessful. I wasn’t purposely trying to damage the blades, but rather determine how long the blades would last.

Fire service diamond blades come in different quality levels and price ranges. For a couple hundred dollars, you can find one that will last as long as 25 abrasive discs. Up the price a hundred or so and you’ll have a blade that will last as long as 50 abrasive discs. I have successfully used the diamond blade on concrete, reinforced concrete, wood garage doors with steel structural components, steel roll-up doors, metal doors and cars.

Slice & Dice
When determining which blade to run with on your saws, first figure out what you need to cut most often and keep the appropriate blade on the saw. Keep your other blades nearby, and be trained and ready to do a quick change if needed. Whatever blades you have, make sure you’re familiar with the materials that they will cut and how to safely use them. This will come with personal research and hands-on training cutting actual masonry, steel and wood.

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