Sherri Singer
Associate Editor
Acomfortable handle makes the difference between a well-designed hand tool and one that’s poorly designed. Engineers at The Stanley Works, New Britain, Conn., carefully reengineer the handles of many popular hand tools, producing ergonomically correct versions for the human hand.
Redesign there relies on extensive testing. Stereolithography (SLA) models from CAD drawings get replicated via rubber molds into functioning prototypes. The prototypes are tested in Stanley Work’s ergonomics lab. According to Gary VanDeursen, director of industrial design for The Stanley Works, before the company created its ergonomics lab, it used outside labs to prove out designs. “It was almost to quantify how good we were against competition,” he says. “Now we use them internally during development. Every time we test a tool in the ergo lab, we can make modifications immediately and retest the product. This greatly shortens the time cycle for product development.”
HAMMERING OUT A NEW DESIGN
The AntiVibe framing hammer has a carbon-steel shank to absorb as much vibration as possible. Measurements in trial tests showed the hammer transmits less energy to its user than comparable tools.
The handle design arose out of rigorous testing and analysis. Infrared photography captures the trail of reflective dots placed on key points of the hammer. For example, developers stick dots to the wrist, elbow, knuckles, and put two on the hammer. A split second stroke of the tool is captured on the computer. Engineers play it back in slow motion to see the interrelationships of the wrist, hammer, and arm. They size up the relationships to make sure they fall within the norm of wrist flexation.
Another test determines what muscle strains occur as a person hammers, through sensor readings fed into a computer. If there is overextension or if a tester grips the handle too hard, the shock travels from the hammer into the wrist and arm. For example, traditional hammers produce a lot of shock that the handle shaft transmits into the arm. Over time, this affects muscles and joints, particularly those of professionals who hammer daily.
Using test results from traditional hammers, a team of engineers set out to reduce shock. Gary VanDeursen claims the key to the success of an antivibration hammer lies in the materials and shape of the handle, particularly where it meets the head. The steel hammerhead extends into a steel shaft encased in a polymer jacket. The steel handle doubles as a tuning fork to absorb vibration. The tuning fork is buried in a soft durometer elastomer, further reducing the transmission of shock into the arm.
NEW TWIST ON SCREWDRIVERS
An ergonomic screwdriver arose from changes in materials and a better shape for the handle. Designers also considered other factors such as hand size, fit, and torque capabilities. The end result is a dual material trilobe handle that screwdriver users find easy to use and comfortable.
A diamond texture on the handle promotes a good grip without forcing a user to squeeze to the point of hand pain. A soft elastomer is used for the diamond pattern and provides the grip. A hard polypropylene layer under the soft elastomer gives a solid foundation to withstand torque, pressure, and impact. Polypropylene on the ball end of the grip helps keep the handle in the palm of a hand and lets it spin and twist without damaging skin.
ANATOMY 101 FOR HAND TOOLS
All in all, designing hand tools that work harmoniously with the human anatomy is becoming increasingly popular. Ergonomically designed tools let workers be comfortable while boosting safety and productivity.