[Fig. 955] represents a diamond point tool much used by eastern tool makers. The sides are ground flat and the point is merely oil-stoned to take off the sharp corner. This tool is used with very fine feeds as, say, 180 work revolutions to an inch of tool traverse, taking very fine cuts, and in sharpening it the top face only is ground; hence as the height of the tool varies greatly before it is worn out, the tool elevating device must have a great range of action.
Fig. 956.
Fig. 957.
In [Fig. 956] is shown a side tool for use on wrought iron; it is bent around so that its cutting edge a may be in advance of the side of the steel, and thus permit the cutting edge to pass up into a corner. When it is bent to the left as in the figure, it is termed a right-hand side tool, and per contra when bent to the right it is a left-hand tool. The edge a must form an acute angle to edge b, so that when in a corner the point only will cut, or when the edge a meets a radial face, as in [Fig. 957], the cutting edge b will be clear of the work as shown.
If the angle of a to b is such that both those edges cut at once, the pressure due to such a broad cutting surface would cause the tool to spring or dip into the work, breaking off the tool point and perhaps forcing the work from between the lathe centres.
This tool may be fed from right to left on parallel work, or inwards and outwards on radial faces, but it produces the truest work when fed inwards on radial faces, and to the left on parallel work, while it cuts the smoothest in both cases when fed in the opposite direction.