| 摘要 |
A valve seat is cut in a cylinder head or other engine cast-ing in concentric relation to a valve stem opening therein. A boring head, driven from outside the cylinder head, rotates on a cylindrical arbor concentrically mounted in the valve stem opening. Three tool bits are precisely positioned on the boring head so as to make a three face cut having the exact profile desired with reference to the axis of the valve stem.
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