Power tool ratings: Watts out is what it is

If you use tool ratings as your sole criteria to select power tools, you may be cheating yourself or the workers who use the tools, leading power tool manufacturers concur.

Instead, tool experts say you should look at the ratings as a way to classify the tool’s power and capabilities. They caution users not to base tool selection on a tenth more horsepower or a few tenths more amps than a similar model of another brand.

“It’s unfortunate how tool users look to ratings as a true indication of how much work a tool may do,” says Bob Wanke, trainer at Milwaukee Electric Tool. “It’s much more important to look at the range of jobs a tool can do, then get opinions from other heavy-duty users about what works well and what lasts.”

Ratings in general
However, tool manufacturers do not follow the same protocol when developing tool ratings. That’s what makes using ratings alone as a guide for tool selection a bad practice.

The best rating to use to compare tool power is maximum watts out, says Vinny Lupenski, director of product management/saws at DeWalt. “Most professional tool users look to amps to compare tools, but two tools with the same amp rating may not perform the same. The watts coming out of the tool is a better measure of usable power.”

Why not amps?
Wanke says the amp ratings of drills, drivers and saws only gives you an idea of how much heat the unit can handle before excessive heat buildup will damage the motor. It should not be the sole criteria upon which to select these tools.

Horsepower a poor guide
Like amp ratings, horsepower ratings are not an accurate guide of tool power. “In most cases, a tool with a higher amp or horsepower rating should be able to handle heavier loads. But this isn’t always the case because the ratings do not consider how effectively the tool’s mechanical components transfer power from the motor to the accessory,” says Wanke. “Technically, horsepower is a measurement of mechanical power and figured by multiplying speed and torque. It is a measure of motor power and does not account for how the power is transferred to the blade or bit,” he says.

According to Milwaukee Electric’s Tool Fundamentals reference guide, mechanical power, or horsepower, is the product of RPM and torque. RPM is a straightforward measurement, but torque may not be.

Torque is the amount of force applied to a system multiplied by the distance of that force from the rotational axis. That means the further you get from the axis, the greater the mechanical advantage. How tool manufacturers measure torque can greatly affect subsequent rated horsepower.

External factors also affect true amp and horsepower ratings. Accessory type and size, the work material, tool and ambient temperature affect tool ratings. To accurately compare tools from different manufacturers, these variables must be held constant. Since power tool companies have unique methods to assign power ratings, just taking specs out of the tool catalog sets you up for apples-and-oranges comparisons.

Recently, power tool manufacturers have started listing horsepower ratings as peak or maximum horsepower. That’s because there has been some controversy as to whether a 4-hp. tool can indeed produce 4 hp.

“We have found that professional tool users rarely look at horsepower as a measure for tool power,” says Rich Hurn, director of engineering at DeWalt. “But they still look at amps. Again, the watts-out rating is the best measure of tool power.”

Measuring the watt difference
So if the total or maximum watts-out rating is the best measure, at what point does it make a difference when comparing two tools?

“I’d suggest users look at amps first to broadly classify tool power then drill down to the watts-out ratings to compare similar amp-rated tools more carefully,” says Lupenski. “You won’t see much performance difference in a circular saw with 2,000 watts vs. a saw with 2,075 watts, but you will see a difference in a saw that has only 1,700 watts out,” he says.

Look at the total unit
Experienced users know there is more to a tool than its specifications, and tool manufacturers are eager to point that out.

In your final selection process, the tool manufacturers suggest you base your final decision on how the following components stack up:
• Motor windings – the more copper, the better
• Ball or roller bearings – can withstand more force and abuse than sleeve bearings
• Heat-treated and machined gears – for long life and more efficient power transfer
• Quality cords – long, chemical-resistant cords that stay flexible in all weather conditions
• Quality switches with amp ratings that meet or exceed the tool’s amp rating
• Interlocking tool housings – they hold drive components in alignment and help the tool withstand drops and heavy loads
• Ergonomics – how the tool feels in your hand, considering the jobs you’ll do with the tool
• Warranty – the longer, the better
• Access to service and repair

Tool manufacturers are constantly improving tools, so when you are replacing a tool, look at what the latest models offer, suggests Lupenski.

“Word of mouth is one of the best ways to learn about what works and doesn’t work for contractors, but always look at the new tool models. You’re going to continue to see more powerful units in more compact, easier-to-use designs,” he says.

DeWalt’s Hurn agrees. “We design tools for a five-year minimum life with the most demanding user and find that contractors, on average, replace tools every two years because they get lost, stolen, run over or dropped. The tools are changing dramatically.

“The new power tools will have the same amp rating as older models, but the watts-out rating will continue to increase. That’s why you need to look at watts-out ratings to measure a tool’s power,” he says.

Published in the March/April 2001 issue of Contractor Tools and Supplies magazine.

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