Concave Attachment in Lathe
A concave attachment is a versatile one to cut concave-convex profiles. A set of rotating plates have T-slots for the T-bolts that hold the boring bar. These plates are rotated by a train of gears. The bar is held roughly yet free enough to rotate. When the tool is built, the boring bar is first clamped with both pivots at lead center. So, the tool describes a zero radius when the crank is turned. At this time, one set up pin hole is drilled in each of the rotating plates, as indicated so that the pin touches the boring bar.Then to set the tool, for a desired radius, it is merely necessary to place a piece of flat stock the same thickness as the desired radius between the bar and the set up pins while securing the bar in position. At this point, data the flat stock and set up pin can be removed.