A support arm for a cutter drum carried on a longwall mining machine characterized in being formed from two telescoping parts, at least one of which is movable axially relative to the other to change the length of the arm. This enables the mining machine to cut material from a coal seam with one support arm length and roadways at opposite ends of the seam face with longer support arm lengths without the necessity for raising the mining machine on its support tracks in the roadway areas or otherwise adjusting the vertical heights of the support arms.