Abstract: A hand tool for trimming a window frame including a corner clamp assembly for detachably clamping right angularly disposed coplanar trim members to right angularly related window frame members with the plane of the trim members being perpendicular to the plane of each frame member. The clamp assembly includes a frame mounting a pair of right angularly disposed clamp members each including an outer clamp face for clamping against an outer edge of one of the trim boards and a relatively moveable inner clamp face for clamping against one of the frame members.