An easy-to-implement design concept shows promise for improving the performances of impact tool bits used in abrading surfaces, drilling, and coring of rock and rocklike materials. The concept is especially applicable to tools actuated with a combination of ultrasonic and sonic vibrations, as in the cases described in “Ultrasonic/Sonic Drill/Corers With Integrated Sensors (NPO- 20856), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 38. Such tools were originally intended to be used in scientific drilling and coring of rock; they might also be useful for drilling, coring, and surface grinding of rock for art and construction.

The Asymmetry of the Teeth of an Abrasion Bit typically gives rise to a torque that, averaged over time, causes the bit to rotate as indicated. On hard rock, the direction of rotation could change to the opposite of that shown here.
When teeth of a tool of this type are symmetric, the tool tends not to rotate. In the absence of rotation, the hammering action of the tool against the rock face causes the tool to dig a footprint that includes holes that mate with the teeth. A footprint is generally undesired for two reasons: (1) usually, one seeks uniformity of the abraded or drilled surface; and (2) once the tool settles into the footprint, the impact forces become spread over the tooth and footprint surfaces, with consequent reductions in tooth impact stresses and, hence, reduction in the rate of removal of rock.

The present design concept is simply to make the teeth asymmetric, so that the hammering action of the tool against the rock face gives rise to a net torque that causes the tool to rotate, even in the absence of a rotary actuator (see figure). The rotation prevents the formation of a footprint, thereby helping to ensure that contact between the tool and the rock takes place predominantly at the tooth tips, with consequent concentration of impact forces at tooth tips and, hence, higher impact stresses resulting in a greater rate of removal of rock.

This work was done by Benjamin Dolgin, Stewart Sherrit, Yoseph Bar-Cohen, Stephen Askins, Deborah Sigel, Xiaoqi Bao, and Zensheu Chang of Caltech for NASA’s Jet Propulsion Laboratory.