Abstract: A boring head for use in machining the inner surface of a vertical work piece wall having inner and outer surfaces and a central opening therethrough to produce a flat, plane, discoid surface where a boring machine and a boring bar to which the boring head is to be attached are situated adjacent the outer surface of the vertical work piece wall. The boring bar and work piece are positioned to have the boring bar axis of rotation coincident with the axis of the desired final machined discoid surface. A taper shank extending outwardly from a main body of the boring bar projects through the work piece wall opening to fasten to the boring bar to position the boring head in adjacent relation to the inner surface of the work piece wall. A tool slide extends longitudinally outwardly from the main body radially of the axis of rotation of the boring bar.