Big power, small package

Small grinders gain power without gaining weight

Which would you rather use: A 15-lb. grinder, or one that can get the job done and weighs about half that amount? It’s a no-brainer, and contractors are taking smaller, 4"- to 6"-diameter grinders onto jobs where up to 9"-diameter grinders have been used in the past.

“Users have seen the power of 4.5" and 5" grinders increase 40 percent in the last few years with not much change in weight,” says Terry Tuerk, Metabo USA’s technical services manager.

That increase in power takes these grinders into jobs that were large grinders-only territory in the past. But it also puts these smaller tools in extremely demanding work.

“The smaller grinders on the market today are the most abused tools on the jobsite, flat out,” says Dave Duecker, grinder product manager at Milwaukee Electric Tool. But because of greater power, they are being pushed into bigger jobs.

Couple that with the relatively low price of the units, and workers push them until they burn up, says Dmitri Lvov, Hitachi marketing manager for accessories. “Grinder prices have come down over the last 10 years, so users replace them instead of repairing them,” he says.

Not one-handed wonders anymore
The increase in power means these tools can’t be safely used with one hand anymore. “Smaller grinders come with a side handle and it’s important to use it because with the extra power these tools have, it takes two hands to control them safely,” says Tuerk.

“Operators must respect these tools because of the kickback they can cause, especially when used for working in corners or cutting. With the amount of torque these tools offer, it takes two hands to control the kickback,” Tuerk says. Metabo’s grinder features a clutch that helps the operator maintain control of the tool and can help prevent the motor from burning out in a kickback or stall situation. “The clutch allows the motor and fan to spin, moving air through when there is a tremendous heat rise in the tool. Because of the size of the universal motors used in these tools, a seized motor from a kickback can burn up the tool in less than two seconds.”

Although these tools pack more power in the past, they should not be fitted with larger wheels than what their guards allow. “Although a grinding wheel seems harmless, if it is used on a grinder that runs too fast for the wheel’s rated speed, it can burst into shrapnel-like pieces. With the wheel’s peripheral speed close to 180 mph, the pieces can injure anyone in the area, especially the user,” says Kurt Honaker, product specialist at Bosch Accessories. “Make sure the rpm rating of the grinder does not exceed the wheel’s rating.”

With a tremendous amount of torque, these tools can feel like they could jump out of your hands when they start. To counteract that start-up jerk, some of the tools have soft-start capability that smoothly ramps the tool up to operating speed.

“The electronic controls also adjust the tool’s voltage draw to maintain optimum speed under varying loads and will even cut power to the tool without shutting it down if the motor overheats. That’s important because it allows the fan to pull air into the tool and cool it, preventing motor burn-out. Having the motor shut off if it overheats doesn’t help cool the tool. Pulling air through it without a load will help cool the tool,” says Tuerk.

Hard-working tools need air
Look for grinders that are designed to suck air through the tool without sucking in high levels of abrasive wheel grit or metal chips. “Heat kills these tools, so make sure the vents in the tool remain unobstructed, which will allow proper air flow,” says Duecker.

Lvov recommends looking at grinders that use a metal or combination metal and plastic housing. “An all-plastic housing that’s used to hold the armature will get hot and melt over time. That creates additional wear and higher temperatures and will burn out the tool.

“Also, make sure the motor’s fan pulls in the clean, cooler air efficiently. If the air comes into the tool and only creates turbulence instead of swiftly moving through the tool, it will not cool as well,” Lvov says.

“Having epoxy-coated field windings to protect the tool’s inner workings and a sealed switch that avoids contamination will help the tool withstand the demanding work environment,” says Mitch Burdick, grinder product manager at Bosch Tools and Accessories.

Use trial to improve productivity
Grinders continue to evolve, and so do the accessories that can be used on them. “Manufacturers are constantly improving their abrasive wheels to make the selection process easier and users more effective on the job. Try new abrasive wheels and understand the various solutions available so you can achieve the best results possible,’ says Honaker.

Published in the November/December 2004 issue of Contractor Tools and Supplies magazine.

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