A machining tool forms a first relief surface, a valve seat surface, and a second relief surface by cutting the inner periphery of a valve seat blank having an opening. The machining tool is provided with: a tool body rotationally driven about an axis; a plurality of cutting tools rotating with the tool body; a cartridge mounted to the tool body so as to be capable of moving forward and backward along the axis; and a cam in contact with the base end surface of the cartridge and moving the cartridge forward and backward. At least one of the plurality of cutting tools is mounted to the cartridge.

The present invention provides, in an embodiment, a gear-shifting structure of power equipment, the gear-shifting structure comprising: first and second gears having shafts concentric with a first shaft, respectively, the first and second gears being positioned at different locations along the axial direction of the first shaft, the first and second gears having protrusions formed thereon, respectively, and the first and second gears freely rotating with regard to the first shaft; a clutch disposed concentrically with the first shaft between the first and second gears, the clutch being spline-coupled to the first shaft, and the clutch having engaging members formed thereon so as to protrude toward the first and second gears, respectively; an adjustment member configured to move the clutch toward the first gear or the second gear; a second shaft; and third and fourth gears having shafts concentric with the second shaft, respectively, the third and fourth gears being disposed to engage with the first and second gears and to rotate together with the second shaft. The engaging members of the clutch engage with the protrusion of the first gear or the second gear by means of the adjustment member.

The present invention provides, in an embodiment, a gear-shifting structure of power equipment, the gear-shifting structure comprising: first and second gears having shafts concentric with a first shaft, respectively, the first and second gears being positioned at different locations along the axial direction of the first shaft, the first and second gears having protrusions formed thereon, respectively, and the first and second gears freely rotating with regard to the first shaft; a clutch disposed concentrically with the first shaft between the first and second gears, the clutch being spline-coupled to the first shaft, and the clutch having engaging members formed thereon so as to protrude toward the first and second gears, respectively; an adjustment member configured to move the clutch toward the first gear or the second gear; a second shaft; and third and fourth gears having shafts concentric with the second shaft, respectively, the third and fourth gears being disposed to engage with the first and second gears and to rotate together with the second shaft. The engaging members of the clutch engage with the protrusion of the first gear or the second gear by means of the adjustment member.