Fig. 2. Views illustrating Use of Various Types of Lathe Tools
Turning Tools for General Work.—The tool shown at A is the form generally used for rough turning, that is for taking deep cuts when considerable metal has to be removed. At B a tool of the same type is shown, having a bent end which enables it to be used close up to a shoulder or surface s that might come in contact with the tool-rest if the straight form were employed. Tool C, which has a straight cutting end, is used on certain classes of work for taking light finishing cuts, with a coarse feed. This type of tool has a flat or straight cutting edge at the end, and will leave a smooth finish even though the feed is coarse, provided the cutting edge is set parallel with the tool's travel so as to avoid ridges. Broad-nosed tools and wide feeds are better adapted for finishing cast iron than steel. When turning steel, if the work is at all flexible, a broad tool tends to gouge into it and for this reason round-nosed tools and finer feeds are generally necessary. A little experience in turning will teach more on this point than a whole chapter on the subject.
The side-tools shown at D and E are for facing the ends of shafts, collars, etc. The first tool is known as a right side-tool because it operates on the right end or side of a shaft or collar, whereas the left side-tool E is used on the opposite side, as shown in [Fig. 2]. Side-tools are also bent to the right or left because the cutting edge of a straight tool cannot always be located properly for facing certain surfaces. A bent right side-tool is shown at F. A form of tool that is frequently used is shown at G; this is known as a parting tool and is used for severing pieces and for cutting grooves, squaring corners, etc. The same type of tool having a bent end is shown at H ([Fig. 2]) severing a piece held in the chuck. Work that is held between centers should not be entirely severed with a parting tool unless a steadyrest is placed between the tool and faceplate, as otherwise the tool may be broken by the springing of the work just before the piece is cut in two. It should be noted that the sides of this tool slope inward back of the cutting edge to provide clearance when cutting in a narrow groove.
At I a thread tool is shown for cutting a U. S. standard thread. This thread is the form most commonly used in this country at the present time. A tool for cutting a square thread is shown at J. This is shaped very much like a parting tool except that the cutting end is inclined slightly to correspond with the helix angle of the thread, as explained in [Chapter IV], which contains descriptions of different thread forms and methods of cutting them. Internal thread tools are shown at K and L for cutting U. S. standard and square threads in holes. It will be seen that these tools are somewhat like boring tools excepting the ends which are shaped to correspond with the thread which they are intended to cut.
A tool for turning brass is shown at M. Brass tools intended for general work are drawn out quite thin and they are given a narrow rounded point. The top of the brass tool is usually ground flat or without slope as otherwise it tends to gouge into the work, especially if the latter is at all flexible. The end of a brass tool is sometimes ground with a straight cutting edge for turning large rigid work, such as brass pump linings, etc., so that a coarse feed can be used without leaving a rough surface. The tools at N and O are for boring or finishing drilled or cored holes. Two sizes are shown, which are intended for small and large holes, respectively.
The different tools referred to in the foregoing might be called the standard types because they are the ones generally used, and as [Fig. 2] indicates, they make it possible to turn an almost endless variety of forms. Occasionally some special form of tool is needed for doing odd jobs, having, perhaps, an end bent differently or a cutting edge shaped to some particular form. Tools of the latter type, which are known as “form tools,” are sometimes used for finishing surfaces that are either convex, concave, or irregular in shape. The cutting edges of these tools are carefully filed or ground to the required shape, and the form given the tool is reproduced in the part turned. Ornamental or other irregular surfaces can be finished very neatly by the use of such tools. It is very difficult, of course, to turn convex or concave surfaces with a regular tool; in fact, it would not be possible to form a true spherical surface, for instance, without special equipment, because the tool could not be moved along a true curve by simply using the longitudinal and cross feeds. Form tools should be sharpened by grinding entirely on the top surface, as any grinding on the end or flank would alter the shape of the tool.
