Abstract: A portable slotting device is used to cut a conical slot in a propellant grain of a rocket motor. A telescoping arm having a cutter thereon is mounted at an angle upon a rotating shaft held in position by a housing attached to said motor. Pressurized fluid is fed to the telescoping arm for providing the motive force to extend the cutter. A control cable is attached to one of two extension arms in the telescoping arm and to an adjusting knob. As the drive shaft is rotated, the adjusting knob is unthreaded from a rod having the control cable attached thus allowing the control cable to extend the telescoping arm. The pressurized fluid forces the extension arms out while the control cable restrains movement. The cutter thus moves in a spiraling conical motion paring out propellant grain.