Making the cut

Abrasive wheels can make short work of steel cutting. Here’s how to cut with greatest efficiency and safety.

Whether you are using an angle grinder or a chopsaw to cut metal, always keep in mind the most expensive part of the operation is usually the hourly wage of the person operating the tool, says Rick Lawson, product manager for abrasives and accessories at Metabo Corporation. “It’s not uncommon for the purchasing department to buy wheels based on wheel life without considering the amount of time it takes to complete a cut or to remove a weld. They should consider the effects of increased labor costs due to the extra time needed by the operators to complete their tasks with a harder wheel,” he says.

To fully understand the metal-cutting process, abrasive experts report that the person making the wheel selection needs to look at three factors: The material being cut; the type of abrasive wheel and the grinder or tool used to make the cut.

“What do you want to do?” asks David Dorantes, Makita senior accessory marketing manager. “Are you cutting tubes or solid stock? What is the material? Mild steel or cast iron? And what tool do you plan to use to make the cut? If you don’t ask these questions before selecting the cutting or grinding wheel, you may not achieve optimal working results,” he says.

Material makes the difference
“Many contractors use a general-purpose wheel because they cut or grind a variety of materials. Their equipment may be used on rebar, sheet metal, heavy channel or stainless steel all in the same day. For this type of use, a general purpose abrasive is ideal. If you’re going to be cutting a large amount of a particular type of material, there is probably a more effective or efficient wheel than the general-purpose one,” says Lawson. “From calls I get, it’s apparent that many contractors don’t take advantage of the specialized abrasives products now available to make some of their projects more effective and profitable. They often don’t consider a specialized abrasive until they get into a situation where they must be more competitive than usual, they have a wheel failure or a new employee brings their experience to the workplace.”

Wheel selection: Tried and true or new to you?
Contractors fall into the rut of using the same tool or product even when there is something out there that can do the job better. The same is true for cut-off wheel selection. “Try different wheels and compare them to what you have been using,” says Peter Chiello, accessories product manager at Milwaukee Electric Tool.

Chiello has taken a variety of cutting wheels into Milwaukee’s testing facility and measured the number of cuts the wheels can make before they are worn out. From brand to brand, there were huge differences in number of cuts, even though the wheels are built to cut the same material. “In our tests of cutting 1/2" black pipe, we had some wheels cut as few as three to more than 15 before the wheel was worn out. With these types of cut-off wheels, the speed of the cut was about the same, but the wheel life varied greatly. That’s why it’s important to try new or different wheels to make sure you are using the best wheel for the job,” he says. “We tested wheels that cost between $1.29 and $1.99 each, and there was only a slight correlation between price and quality,” he says.

Terry Tuerk, Metabo Corporation’s technical services manager, concurs. “There are ongoing formulation changes in wheels. You want to balance the amount of work a wheel can do against its longevity. Although contractors don’t do time studies, they can go by the gut feel and comments from workers who use the wheels. From time to time, take a look at what’s out there.  Encourage your people to evaluate products in the work environment, not just some three-minute test.  There may be a better wheel out there than the one you have used for 20 years,” he says.

Typically, metal-cutting abrasive wheels are made out of aluminum oxide grain held together with resins and reinforced with fiberglass. Aluminum oxide is best for cutting ferrous metals and small-diameter stainless steel. For extremely hard or thick metals, zirconia alumina wheels can offer better performance, but cost more. Silicon carbide wheels cut non-ferrous metals as well as low-tensile metals such as cast iron or ductile iron.

“There is a good rule of thumb to remember with abrasive wheel use,” says Phillip Benincaso, product support specialist at Pferd. “Use a hard wheel to cut a soft material and a soft wheel to cut a hard material. This also correlates with the power tool being used. Lower-powered tools, such as a chopsaw, should be used with wheels with a softer bond. Higher-powered stationary saws should be matched with wheels with a harder bond. If you use a hard bond on hard material, you will get wheel glazing and even workpiece discoloration,” he says.

The 12" or 14" cut-off wheels are either single-reinforced or double-reinforced with fiberglass mesh. “Use a double-reinforced wheel to cut angle iron or rebar. It will last longer, is more rigid and can take more downward force than a single-reinforced wheel. You will notice a slower speed of cut. You can tell a double-reinforced wheel by the mesh fibers visible on the outside of the wheel,” Chiello says.

Single-reinforced wheels will do a better job cutting solid stock. More grain is exposed and it is less likely to glaze. Under heavy load, these wheels don’t last as long and are more likely to flex.

Wheel thickness also plays a role in cutting efficiency, says Lawson. “In thin wheels, a thicker wheel tends to have a longer life and the best cutting performance. Thin-cutting wheels vary from .040" to 1/16"- thick. The first wheels made for the thin cut category were manufactured and labeled as .040". However it soon became evident that the life and performance could be improved by making them slightly thicker,” says Lawson. “Now, most thin cutting wheels, although slightly thicker than the first ones on the market, are still labeled as .040" because it is the recognized identifier for the thin cut wheel family.”

Consider the tool
The tool greatly affects wheel selection, and improper matching of the wheel and the tool can create an ineffective or even dangerous scenario.

Never put a lower speed-rated wheel on a higher speed tool. That can lead to the wheel flying apart and could injure the operator or bystanders,” says Tuerk. “The rpm may not always be legible on the tool. The guard on the angle grinders helps assure the proper size wheel is used. Be aware that the physical size of most 4 1/2", 5", and 6" grinders is similar. If the tool is not equipped with a guard, the wrong size wheel could easily be mounted on the machine. If you are ever in doubt about a wheel being compatible with tool, don’t hesitate to call your distributor or the tool or abrasive wheel manufacturer.”

Although 14" wheels are available for chopsaws and portable gas or electric saws, the wheels are not interchangeable, says Benincaso. “The chopsaw wheel doesn’t have the double reinforcement to take the lateral load that a portable saw can exert. The lateral forces can delaminate the wheel and it could shatter in the cut,” he says.

Horsepower is key to cutting materials. Typically, higher horsepower is needed with harder wheels because the wheel needs power to cut through the metal and wear away the bond to expose abrasive. “If the wheel chatters when it’s put against the workpiece, the bond is not breaking away and the wheel will glaze. It’s a ‘Catch-22’ situation because that means the user puts more pressure on the wheel to make the cut, which creates more heat and leads to wheel glazing and even marring and discoloration of the workpiece from thermal overload,” Benincaso says. “Horsepower is a good indicator of the saw’s ability to provide the power for heavy loads.”

Cutting caveats
The experts offer some helpful tips on making metal cuts with abrasive wheels:

Clamp the material. “If you don’t clamp the material, you run the risk of it jumping which could damage the wheel,” Dorantes says.

Know how the wheel was used and who used the wheel last. “If you don’t know who used the cutting or grinding wheel last, or how it was used, you should replace it with a new one,” says Lawson. Abrasive wheels can have hidden cracks from being dropped or hit which can result in wheel failure.

Don’t force the saw. “This is a common mistake contractors make. They try to force the wheel into the material. Let the tool and the wheel do the cutting,” Dorantes says.

Keep up your guard. “Never operate an angle grinder or chopsaw without the guard and make sure your guards are in proper working condition. When using Type 1 wheels, a Type 1 guard should be installed on your power tool,” says Chiello.

Use the right wheel. “Using the right wheel on the right tool is key to cutting success and safety,” says Tuerk. “Never use a wheel with a different sized arbor on a tool and never bore out or modify the arbor hole to make it fit your tool.”

Published in the January/February 2004 issue of Contractor Tools and Supplies magazine.

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