Fig. 1029.
When the tool requires to preserve its exact shape it may also be made circular with the required form for the cutting edge formed round the perimeter. Thus [Figs. 1028] and [1029], which are extracted from The American Machinist, represent tool holders with circular cutting tools.
The holder a fits the lathe tool post, carrying the cutting tool b, which is bolted to the holder and has at f a piece cut out to form the cutting edge.
To facilitate the grinding, holes are drilled at intervals through b. A plan view of this tool and holder is shown at c, the shape of the cutting edge being shown at d. The cutting edge is shown in the side view to be level with the centre of the tool holder height, but it may be raised to the level of the top of the tool steel by raising the hole to receive the bolt that fastens the cutter, as is shown at e; or the cutter may be mounted on top of the holder as shown at h, having a stem passing down through the holder, and capable of being secured by the taper pin i. A plan view of this arrangement is shown at j.
Fig. 1030.
Another form of circular cutter is shown in [Fig. 1030]. It consists of a disk or cutter secured to a holder fitted to the tool post, the cutter edge being formed by a gap in the disk, as shown in the figure, which represents a cutter for a simple bead or round corner. The front end of the holder has a face a, whose height is level with the line of lathe centre when the holder is set level in the tool post. Hence the top face of the cutting edge may be known to be set level with the line of centres when it is fair with the face a of the holder. The bottom clearance is given by the circular shape of the cutter, while side clearance may be given by inclining the face b of the holder (against which the face of the cutter is bolted) to the necessary angle from a vertical line. The face c is ground up to resharpen the cutting edge, and may be reground until the circumference of the wheel is used up.
