Purchase by Torque

In the 26 months that I’ve been working at Popular Woodworking, we’ve studied and discussed drills in most ways imaginable. We’ve examined batteries moving from 12 volts through 18 volts and even up to 36 volts in power. (Now we’re moving back down the scale to see manufacturers develop 10.8-volt drill/drivers and even a handful of tools with 4-volt or lower batteries.)

And we’ve traversed the chasm from Nickel-cadmium to Lithium-ion batteries. We’ve even divided Lithium batteries into a number of sub-categories. So what’s next?

Torque! That’s the next measurement manufacturers want us to use to decide which drill/driver to purchase. Is this something meaningful to woodworkers? I can see torque being important when you drive 3″ screws into a deck, but when I use my drill under normal circumstances, I cannot see where one tool with more measurable torque is better. But, I don’t adjust my drill torque. I tend to leave the setting at the “drill” mode and simply release the trigger when the screw is set to my required depth. I do, however, have to agree that providing a given measurement that would allow us to directly compare apples to apples , or drill to drills in this case , is a good idea.

To that end, most manufacturers have agreed upon a set of accepted guidelines to measure torque. These guidelines are set forth by the Power Tool Institute (PTI) , to which most major tool manufacturers belong. (Click here for a list of members.) This method for measuring relative output torque does not apply to hammer drills, rotary drills and impact drivers.

The Relative Torque Measurement (RTM) is reported to a 95 percent degree of confidence. The test is made on five normal production samples that have not been modified, and each sample is tested five times with a minimum three-minute cool down between tests. This, according to PTI, ensures more consistent readings.

Cordless tools use the same battery for all five trials without recharging. A properly conditioned battery ,in PTI terms, a battery that consists of five charges and discharges completed on the supplied battery charger , is used.

Corded tools are tested with a regulated power supply circuit that matches the voltage and frequency numbers on the tool’s nameplate.

All tools will be supported in a torque fixture (See the PDF below) to prevent any movement from applied torque and if there’s a clutch on the drill/driver, that clutch is set to a full-lock position. (If the tool slips, the test results are considered invalid and will be repeated.) If the tool has changeable gears, it will be tested in the gear that results in the greatest torque.

The results of the 25 tests are tabulated and put through a number of mathematical calculations to find the “Lower 95% Confidence Limit” and the “Upper Confidence Limit.” The rating released falls somewhere within these two boundaries.

If you would like to read the exact process for yourself, open the PDF below.

First to adopt and publish results from these tests is Makita. On the company’s web site, a couple of Makita drill/drivers have the torque numbers listed.

Any comments?

-Glen D. Huey

Torque Fixture.pdf (347.12 KB)

PTI Test.pdf (308.26 KB)

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