This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Common lathe tools may be few or many, according to the requirements of their owner, and tools for wood working or for metal working may predominate, according to taste. A workman is always adding to his stock of tools, until by-and-by he almost insensibly finds himself in possession of a very varied assortment, each member of which has a special use and a special history. From among a set of lathe tools we will select and describe those which are either absolutely essential or of very general adaptability; all the rest beside are merely modifications of these few and simple types. Excellence in the production of plain turned work, whether of wood or metal, does not necessarily follow from the possession of a large number of tool depends entirely upon skill in their manipulation. In the hands of a professional woodturner a simple gouge is a marvellous tool, producing hollows, ogees, and mouldings of various shapes with swift dexterity, aided only by the chisel where sharp corners arc-concerned. Those who handle the gouge with confidence and skill can turn out work quicker, cleaner, and better than those who, dreading a disastrous "kick" or "catch," scrape away cautiously with round nose and chisel and diamond point.
Therefore, plenty of practice with the gouge is essential to the acquirement of a perfect command of that tool, and he who has acquired this mastery is, to a very great extent, independent of the rest.
The turning of metal is effected by a slow motion, comparatively speaking, with respect to the turning of wood; yet wood-turning tools require a less obtuse angle to form the cutting edge than the tools employed to turn iron, brass, or steel. The planes forming the cutting edge of metal-turning tools make a solid angle which generally exceeds 60°. Figs. 1197 to 1213 are a set of turning tools for metal, Figs. 1212, 1213 being especially for screw cutting.
A writer in the English Mechanic says that metal-turning tools are made from "tool steel," different kinds of which are in the market, and may be purchased in square bars of various sizes. Few tools, except scrapers, can be used indiscriminately for cast iron, wrought iron, and brass; each metal needs its particular set of tools, differing, not so much in the shape of their cutting edges, as in the angles which they make with the surface of the work to be turned. Thus, Figs. 1214, 1215, 1216, are each intended to represent in profile the ordinary roughing-down tool; but their angles are very different the one from the other, Fig. 1214 being only suitable for wrought iron, Fig. 1215 for cast iron, and Fig. 1216 for brass. In all these, everything (temper of course excepted) depends upon the angle at which the tools are ground. The brass tool with the flat face would not cut the iron, but would simply abrade it; while the iron tools would hitch in the brass, and manifest a tendency to chatter or to " draw in." Neither would the tool ground at an acute angle for wrought iron cut cast metal, but would itself become broken off at the tip, while the thicker cast-iron tool would not take clean shavings off wrought iron, but would possess more of a scraping action.
Men accustomed to metal turning know exactly how to grind their tools, so that they shall either cut or scrape wrought iron, cast iron, or brass; but to assist others in the matter, the cutting edges of various tools are drawn to a large scale.
Taking the iron-turning tools first, Fig. 1217 is a common roughing tool for cast iron. The side view gives the proper angle to ensure a clean cut, without breaking the top across in the direction of the dotted line. The angle is drawn on the supposition that the tool is held horizontally, as indeed it ought to be. But a tool that will not cut nicely in a horizontal direction will often work by inclining it at a slight angle; hence, less care is often taken in the grinding of hand tools than in those used with the slide-rest. Neither is the angle at which a tool should be ground, in order to cut well horizontally, necessarily quite constant. It should be about 65° with the vertical for cast iron, but may vary slightly either way. In fact, not one workman in ten could say what angle he grinds his tools to: he simply judges the proper angle by the experienced eye which seldom betrays him. The angle which the front of the tool makes with the work may vary somewhat more than the upper face, depending on the diameter of the work to be turned, but should not slope more than 4° or 5° from the vertical for cast iron (Fig. 1215). If it becomes excessive, the tool is weak, and soon abrades or breaks off.
Attention to these matters, apparently so trivial, is really of the utmost importance. The angles given on sketches are taken from tools in actual use, doing their work well.
Fig. 121S shows a round nose; Fig. 1219 a parting tool; Fig. 1220 a knife tool for finishing edges and faces of flanges, and ends and sides of work, which latter will of course be required right- and left-handed (Fig. 1221), just as we require right- and left-handed side tools in wood turning. The end views of these tools show the upper and clearance angles, which are about the same as in Fig. 1215, but may vary somewhat more without detriment to the work.
Figs. 1222 are boring tools for hollow cylinders - tools capable of much modification, their cutting edges not only taking the forms of all the other tools, but each form also being often required right- and left-handed. In reference to the more usual shape - that of the round nose for boring, when used simply as a roughing tool, the shape B showing it in plan, with the axis of the cutting angle in the direction of the dotted line is preferable to A, because in the former the true cutting edge is carried forward.