A surgical instrument. Example surgical instruments include a cutting member being at least partially positioned within the outer member. A drive member coupled to the cutting member such that in response to only a rotational force applied to the drive member in a single direction, the cutting member (i) rotates and (ii) moves linearly in a back-and-forth motion. The drive member having a continuous helical groove including a first helical channel and a second helical channel that are blended at their ends. The first helical channel having a first helical angle that causes the cutting member to move in a first direction at a first linear speed and the second helical channel having a second helical angle that is smaller than the first helical angle that causes the cutting member to move in a second opposing direction at a second linear speed that is slower than the first linear speed.
