Orbital Sander Interface
One of the tasks that was identified as a priority in the casegoods surveys was sanding. An analysis of the jobs
requiring the continuous use of the random orbital sander highlighted two principle risk factors for hand/wrist/forearm
fatigue and discomfort. In using this handtool, the operator would forcefully grasp the sander and hold this hand
posture statically for extended periods of time. Further, due to the nonsymmetrical nature of the rotation of a random
orbital sander, significant vibration exposure exists. In many cases, this is the only task that the workers perform,
indicating an extended exposure.
To reduce the vibration reaching the operator’s hand, a sheet of Viscolas padding was applied to the
circumference of the tool’s gripping surface and was also sewn into a glove, covering the palm and lower parts of the
fingers. In an attempt to reduce or eliminate the need for prolonged static gripping forces, a harness was fabricated
that attaches to the orbital sander. Two adjustable velcro straps hold the hand to the sander, providing for a secure
hand position without constriction of blood flow. The new device allows the worker to maintain a neutral, extended
hand position while sanding without exerting continuous gripping forces. A butterfly valve allows the worker can turn
the air supply on and off with the non-dominant hand. This feature allows the worker to change the sandpaper while
the hand is still attached to the sander. The valve also allows the worker to adjust the speed of the sander, so that the
sander can begin in the ‘off’ position if necessary.
LABORATORY TESTING
To simulate the conditions of operators using orbital sanders in the furniture manufacturing industry, a wooden box
was placed on a workstation. The subjects were instructed to hold the orbital sander with their dominant hand and
move it in a circular motion on the top of the box and then on the side of the box. This procedure was completed
using two conditions involved gripping the orbital sander with the standard grip and with the new interface consisting
of a vibration absorbing glove that is strapped to the sander.
These pictures show the testing set-up. In the left-hand picture, the subject is using the glove and ergonomic interface while sanding the top of the box. In the right-hand
picture, the subject is sanding the side of the box using the standard grip.
Results
The results of this study showed considerable reduction in the muscle activities of the extensor muscle group and
the flexor muscle group with the use of the sander interface.
FIELD TESTING
We had workers try the interface for approximately 30 minutes each. This allowed them to become comfortable
with the interface and provide more detailed feedback concerning its use. Also, we were able to watch each worker’s
sanding method. We found that many of the workers use both their right and left hands to sand on each piece of
furniture in order to sand the front and both sides of the piece as it moves down the assembly line. In order to address
this need, we had one worker wear a glove on each hand and switch the interface as needed. This frequent movement
required some extra time, but the speed of the assembly line allowed for this, so the worker kept up the same
productivity levels. The workers liked the design of the interface and stated that they would use it if it was available. In
addition to increased comfort while sanding, one worker liked the fact that the interface allowed her hand to fully
depress the palm control at all times. She said that her hand sometimes moves off the control, thereby slowing the
sander down. The interface kept the sander at a constant speed.
For more information about ergonomic interventions for the furniture manufacturing industry, please contact:
Dr. Gary Mirka, Professor of Industrial Engineering at North Carolina State University