Abstract: An improved adjustable sharpener for self-sharpening feed chopping knives. The sharpener provides a stone housing having a sharpening stone mounted therein for the sharpening of the edges of the knives mounted on a rotating cutter head. The stone is manually adjustable in a direction toward the axis of the cutter head. The stone is prevented from lateral movement by rigidly securing the length of the stone inside the stone housing. The sharpener is provided with a cutter bar for the more efficient cutting of the crop material and for protecting the stone from breakage.