Fig. 11. Cylinder turned around for Machining Valve Seats
The next operation is that of boring and milling the opposite end of the cylinder. This end is turned toward the spindle (as shown in [Fig. 11]) without unclamping the work or fixture, by simply turning the circular table T half way around. This table is an attachment which is clamped to the main table for holding work that must be turned to different positions for machining the various parts. Its position is easily changed, and as the work remains fixed with relation to the table, the alignment between different holes or surfaces is assured, if the table is turned the right amount. In this case, the casting needs to be rotated one-half a revolution or 180 degrees, and this is done by means of angular graduations on the base of the table. The illustration shows the casting set for boring the inlet and exhaust valve chambers. The different cutters required for boring are mounted on one bar as shown, and the casting is adjusted crosswise to bring each valve chamber in position, by using the micrometer dial. The single-ended cutter c forms a shallow circular recess or seat in the raised pad which surrounds the opening. The cover joint directly back of the cylinders is finished by milling.
Fig. 12. Boring Differential Gear Casing
Examples of Boring, Radial Facing and Milling.—Another example of boring, in which the circular table is used, is shown in [Fig. 12]. The work W is a casing for the differential gears of an automobile. It is mounted in a fixture F which is bolted to the table. The casting has round ends, which are clamped in V-blocks, thus aligning the work. This fixture has a guide-bushing G which is centered with the bar and cutter in order to properly locate the casting. There is a bearing at each end of the casing, and two larger ones in the center. These are bored by flat cutters similar to the style illustrated at A in [Fig. 3]. The cutter for the inner bearings is shown at c.
Fig. 13. Facing and Turning Flange of Differential Gear Casing