Part 8

The remarks of the above eminent mechanic upon this subject, as also those of Professor Willis and Mr. Babbage have been embodied in a very excellent paper by Dodsworth Haydon, Esq., an amateur, and will be found in the Appendix to this work. The whole principle of the formation and application of cutting tools is explained in that paper, so that it only remains to treat briefly of a few special _forms_ of tools which are required for metal-turning in the lathe, whether by hand or by the aid of the slide-rest. In the first place, however, a word or two may be necessary as to the kind or quality of steel required for such tools. What is called Blister steel may be at once passed over as unfit for the formation of tools--it is, however, the raw material (so to speak) from which, by the process of reheating and welding, the next quality, called Shear steel, is made. When bars of this are similarly heated and again welded into a homogeneous mass under the tilt-hammer or between rollers, double shear-steel is made, which is of extensive use for cutting tools, and must, moreover, of necessity be used in almost every case where there is to be an iron shank, for economy's sake, the steel being then welded to the iron, and forming that part of the tool intended for the edge. The third and best kind of all is Cast-steel, formed of blister steel, melted at an intense heat and run into iron moulds. This, however, can be welded only with great difficulty, and hence the whole tool, whatever its length, must be of the same material. This can be purchased in bars of a convenient size of round, triangular, square, or other section, and needs only the careful use of the hammer, file, and grindstone to become a tool of any required pattern. It would be very advantageous to an amateur to master the art of forging in a small way to enable him to make his own tools, for he may sometimes require them of unusual form, and if he lives far from a manufacturing town he will find it very difficult to get them fashioned to his liking. Cast-steel will not allow of the welding heat applied to iron--it will burn, and cannot then be made to recover its proper consistency, and is for ever useless for the purpose in question. Double shear will take a moderate white heat, while cast-steel must not be brought to a higher temperature than that indicated by bright red--a point never to be forgotten when shaping a tool at the forge. There are in every workshop a number of files laid aside as worn out. These being made of the best cast-steel, are invaluable to the turner in metal, as they supply the best material for his tools at no cost whatever. To begin with the saw files (called, by a horrible perversion of mathematical definition, "three square"). Here you possess a tool at once for the mere trouble of grinding off the teeth and reducing the sides to a smooth surface. Each angle is equally useful--each 60°, which, as the paper above alluded to demonstrates, is the best angle for cutting iron. On brass, however, its use is by no means to be recommended, being, as Holtzapffel remarks, "too penetrative and disposed to dig into the work." It is to be used upon iron in the position shown in Fig. 110, where A is the rest, B the cross section of the tool, C the diametrical line. The side, of which D is a continuation, is to form very nearly a tangent to the circumference of the work, being, as explained in the Appendix, only 3° from that position. Worn out square files being of rectangular section, are exactly suited for brass turning, for which metal a cutting edge is required of 80° to 90°, the former for the first or roughing down cut, the latter for finishing. The position of such tool is shown in Fig. 111.

The flat files are not altogether so useful for making turning tools as those alluded to; they are too thin in proportion to their breadth. Their sides, moreover, generally speaking, are not rectilineal, but curved, so that they are more fit for grinding off at the ends to form brass-turning tools with rectangular edges. They may, however, by careful forging, be made to assume a square section, and thence be formed as desired; but a rectangular bar of steel, ready-made, is then to be preferred. A round or rat's tail file is of far greater service than the last-named--not, indeed, in its own shape, for the reasons stated by Mr. Haydon, but as being capable, with very little labour at the forge, of being converted into a bar of square section. The first tool to be made from such a bar is the graver, _the_ tool of the watchmaker, and not less useful to the general mechanician. This is formed by grinding the end of a square bar diagonally, so as to produce a lozenge-shaped face. The angle to be preferred in this operation is 45°, which will give two cutting edges of 60°. The latter may be varied at pleasure by varying the angle at which this face is ground, as explained in the chapter which treats upon this question. The graver will do all kinds of outside work, light or heavy, as it may be made of any size. It is represented in Fig. 112. Fig. 113 is the heel-tool shown in position for work; 114 and 115, two forms of nail-head tool very commonly used, but both requiring great attention to the angles of the cutting edge to become effective. All the above are for outside work, and are to be so held that the side next to the work--the _sole_ of the tool in Fig. 113--forms very nearly a tangent to the work--a position, as Holtzapffel remarks, strangely similar to that required by the soft wood chisel and similar tools. The heel-tool, indeed, if more keenly sharpened, will cut soft wood (on the face) with great rapidity, and is in principle similar to the broads used for that purpose. It is, however, an unsafe tool, owing to its great tendency to dig into the work. It is a good plan to make extensive use of various shapes of hand-tool before passing to the slide-rest, because the hand feels exactly the _resistance_ which the tool meets with, and the best form and position is thus _practically tested_, and will be found to bear out to the utmost the theory advanced in this work, and founded on mathematical truths worked out and applied by Willis, Babbage, and others.

Inside tools must of course be made upon the same principles as the last, the particular form alone being modified to enable the cutting edges to penetrate into the various nooks and corners that may occur in such work. The inside tool for iron (Fig. 116), with cutting angles of 60°, is of a general and useful pattern. It must be so curved and so placed that _both_ cutting edges come into action, one on the face and one on the side of the cut, a condition explained in the Appendix as _essential_ to all good work. It being quite impossible to cut metal like wood, and necessary to allow sufficient time for such work, a pointed tool is in most cases preferable to one of a semicircular or rectangular form of edge, and the greater part of the heavy work done in large factories is thus executed. Inasmuch, however, as such a tool, well formed on correct principles, may be made to take a tolerably deep cut, the shaving detached will be of sufficient _thickness_, and consequently sufficient width to reduce work a satisfactory quantity at each cut. The cut, too, must be continuous wherever possible, the tool being slowly and steadily advanced the whole of the acquired distance without being removed, and then re-entered for a second cut. The result should be a smooth, even surface, and that great exertion is not required when thus working with hand-tools is sufficiently evidenced by a remark of Mr. Haydon to the writer, "I have often detached, with a graver alone, a tolerably thick shaving of iron, two feet and more in length." From what has been said, it will be understood that in hollowing out a piece of metal such as a chuck, the tool should not be made with a _long_ cutting edge, such as would be used if it were intended to scrape the whole depth of the side. A _broad_ shaving is not to be thus aimed at, nor is the _inside only_ to be thus attacked, but the tool advanced gradually inwards from the face of the work till it reaches the bottom, thus (to repeat the important point again) cutting at the same time the front and side of the shaving. The half-round or cylinder-boring bit already described is, of course, an inside turning tool, but is used with the aid of the back centre. In principle it follows other inside tools, the end being bevelled or sloped off 3°, and the side being 90°. The latter is to be regarded as a blunt cutting tool, being the largest angle that can be used; but, nevertheless, this bit must be regarded as cutting in the two required directions--forward and sideways. If a regular Goniometer for measuring angles is not to be obtained, nor any apparatus for grinding a tool to the required bevel, an addition to Nasmyth's tool-gauge, described in the Appendix, may be made by constructing in tin a set of templates, with the angles marked upon them. The easiest way is to mount on the lathe a few round sheets of tin, and mark the degrees by the division-plate, the outer circle of which contains 360°. The tin may then have pieces cut out, as shown in Fig. 117, to be applied as gauges over the ends of the tool, or _solid_ pieces of the required sections (those which are removed in forming the above) may be retained. It will, perhaps, be as well to finish up both neatly, taking care to mark the angles on each. The degrees most required are, as explained, 90°, 60°, 80°, and 3°; but intermediate numbers may be prepared, and will often be found convenient. An inside tool for brass must retain the angles 80° to 90°, the latter acting as a scraping tool to put a finish to the interior of work roughed out by a tool of the lesser angle. There are not many forms in general vogue, for brass work, whether internal or external. The round, the flat, and the point tools (Figs. 118 to 121) are more or less capable of hollowing out work, as well as surfacing. With the first ground to an angle of 80°, brass chucks can be hollowed, and, with the second at 90°, finished; and if there chance to be any internal angles out of reach by the point-tool, it is only necessary to use a similar one bent round at the end towards the left. Much of the turner's success in brass work depends upon the quality of the metal, which is often very hard and unequal in texture and perhaps blown and honey-combed. It is always the best plan to send patterns of any work of importance to some well-known firm, instead of trusting to a country foundry, whose business, if worthy the name, is generally iron work, and who only run brass once in a way, and make a terrible mess of it, too. The same may be said respecting iron castings. It is worth while, as an experiment, to test with turning tools the quality of a country casting, pulley, or what not, by the side of a similar work really made of malleable iron, such as is now so extensively used by the sewing-machine makers. Tools that will stand the first and make good work deserve a place in the British Museum, with a portrait of the turner!

For light brass work, such as small model engines now so generally sold, a description of lathe may be used of which no mention has yet been made--namely, a bar lathe Fig. 122. Such a tool may be made for £3 or £4, and will be found sufficient for such work as specified.

In place of the double bed a triangular bar of cast iron is used, on which the poppets slide, and are clamped. D shows one of two sockets with feet which hold the ends of the bar, and by which the lathe can be mounted on any stout plank or on the window sill. The pulley A is made for a strap, because this allows of a plain flywheel, which is much cheaper than those which are bevelled and turned. The rest is shown at E and F. The part E slides upon the bar like the poppet--at the top is a dovetailed groove to receive the slide F, which carries the socket for the tee, and is fixed by a turn of the screw seen on the top of it. There is much to be said in favour of triangle bar lathes, they are very stiff, and can be fixed anywhere. The flywheel can be supported on a separate frame, which is an excellent plan, for the jerk of the treadle and crank is not communicated to the poppets and mandrel. In Maudslay's triangle bar lathe, which was made for amateurs, a slide rest was attached, and the whole work was first class--of late they have gone out of fashion, but are nevertheless good tools.

Fig. 123 represents another very simple form of lathe for turning small articles of brass. It may be said to be one remove from the watchmaker's bow lathe, as it has no true mandrel or treadle; the small flywheel being attached to an arm at the back and worked by hand. The left hand is used for the latter purpose while the tool is held in the right. Through a tapped hole in the left hand poppet passes a steel pin shown at E, on a larger scale; this screws into the poppet after passing through a brass pulley B; this bolt ends in a point, and an arm fixed into the pulley becomes a dog to act against a carrier screwed on to the work as in turning iron. Thus the mandrel and point are fixtures, and the pulley only turns when motion is communicated to it by a catgut from the flywheel behind it. The back poppet and rest, which last is shown separately, slide on the rectangular bar; the latter is about two inches wide, and three eighths thick, and is made with feet to screw to any convenient support. This lathe is especially adapted for work of small size which can be centred at both ends, and on which a carrier can be fixed to bear against the pin, E, of the pulley; nevertheless it is even possible to use chucks, if cast in metal with a pulley to each like G. A spindle must in this case be made like H, on which the chuck must be slipped, and fixed by the nut in the hollow of the chuck. Although however this form of lathe is sometimes met with, and may be used as a makeshift, a small triangle bar or 3in. lathe of the usual form is far preferable.

In centering a bar of iron in the lathe too much care cannot be exercised in causing it to run evenly. The ends should be drilled, first with a small, and afterwards with a larger drill, so that a countersunk hole may be obtained in order _to keep the point of the lathe-centre from touching the bottom of the hole_. If this is not done the friction of the work upon its bearing will soon spoil the lathe-centre, and the work itself will speedily get out of truth, and it will not be possible to screw up the spindle of the back poppet so as to correct this. Of course in turning up very small work this drilling cannot be done. A simple hole must then be made, sufficient for the safe support of the work while being turned, but even in this case the angle of the drill point should be less than that of the conical centre of the lathe, the point of which will then run free. To mark the true centres of a round bar of metal a punch has been devised like Fig. 124. This is figured in Bergeron's work, and is very serviceable. To insure its working truly be careful that the bar of metal is filed flat on the ends, and that the surface of the latter is at right angles to the length of the bar. It is then only necessary to place the end of the piece in the conical part of the cup (which will be best effected by fixing the bar in a vice) and by raising the spring and letting it go sudden by a sufficient mark will be made to guide the point of the drill.

The proper place at which to commence turning an iron bar is at one end, the rest being placed so as to bring the tool just upon the line of centres; if applied lower the tool would take too deep a hold, and would either be broken or lift the bar out of the lathe, damaging the centre points. The ends of the bar should be squared up before the circumference is turned, and on no account must a file be used after the turning tool has done its work. It is only at the commencement before a cutting tool has been applied, that an old file may be made use of to take off the scale and roughness left from the forging or casting.

Brass may be attacked upon or just below the line of centres, because the form of tool is such as cannot penetrate deeply. This metal is perhaps easier in some respects to turn, but the tool is apt to form undulations on its surface (is apt to chatter). This is due, partly to the impossibility of obtaining continuous shavings, and partly to the vibration of the tool, and when once this has taken place there is a tendency to deepen these channels, which makes it difficult to produce a plane and even surface. If a rectangular tool is used in the position already shown and described under the head of tools for metal turning, this chattering will be avoided. If it takes place, the undulations should be worked off by gentle usage of the angle of the tool, the rest being placed close to the work, and only a light cut taken.

With regard to the method of mounting a piece of brass in the lathe, any convenient chuck may be used, but sometimes the piece is short or irregular and requires to be bored out. In this case use solder and firmly attach the piece to a face plate of brass. The easiest way is to smear the two faces to be joined with sal-ammoniac made into a paste with water, and laying a piece of tin-foil between the surfaces, which must be quite clean and bright, apply heat. The tin will melt and a perfect union will be effected. When the piece is finished it is re-heated and detached. This may be considered a wrinkle worth knowing. The flat flanges of brass spoken of under the head of chucks are just suited for this method of working, and they are not damaged by the process, as the solder can be wiped off quite clean when the chuck is made hot. This is a good way to mount small cylinders of brass for model engines, as they can be bored and turned on the outside at one operation with great ease and certainty. If a piece is to be drilled or bored in the lathe, the following is the arrangement to be adopted. Fig. 125, A is the face plate, B, the piece to be drilled, C the drill, which is advanced by screwing up the point, E, of the back centre; D is a hand vice or similar article to prevent the drill from revolving with the work. If it is more convenient to fix the drill itself in a chuck, the point of the back centre is to be removed, and a flange of brass or iron substituted, as A, Fig. 126. If the drill is to penetrate quite through the work a piece of wood must be interposed between the latter and the flange to receive the point of the drill and protect it from injury. The pressure should be so regulated as to be constant and equal without being excessive, or the drill will be bent or broken. Boring is simply drilling on a larger scale, and is of such general use as to require detailed notice. In the first place there are several tools used for the purpose, according to the size of the work. The first is the cylinder bit, Fig. 127. This is a most excellent tool, as it will work very truly, and can hardly get out of place if properly directed at starting. The cutting part A is half a cylinder, the centre being just left visible, the end is not quite at right angles with the length of the tool, but is sloped off a little and bevelled also slightly below.[7] This forms the cutting edge. The other end of the tool has a central hole, drilled to receive the point of the back centre by which it is kept to its work. To use this tool, let the piece to be drilled be placed in a chuck, and a recess turned in it of the same diameter as the cylinder bit, the latter is then placed in this recess B, and when screwed up it cannot possibly rise or shift its position; a hand-vice or spanner is then fixed as shown in Fig. 125, and the lathe put in slow motion, oil or soap and water being freely used to lubricate the tool. Either a solid piece of metal, or a hollow casting can be thus bored.

[7] To an angle of 3°. See Appendix.

These cylinder bits can be had of all sizes, from one-eighth of an inch upwards.

Pipe stems are bored with the smallest of these tools. For this purpose they are made of round steel wire, which is sometimes merely flattened with a hammer at one end to spread and enlarge it, this part being afterwards rounded on the underside with a file, and with the same tool finished on the upper flat face. These slender drills require to be delicately used, and are conveniently held in a pin vice or pair of pin pliers, the handle of which being hollow, allows the greater part of the drill shank to lie within it, a small part only being drawn out at a time for use; thus the drill will be kept from bending, and will work quickly and well.

Of recent inventions in the matter of drills, the most important is the Morse American twist drills sold, in sets, at 30s. on a neat stand with a self-centering chuck, complete. The form is that of a cylinder with spiral grooves cut round it of extended pitch. The cutting edge is as difficult to draw as it is to describe, and must be seen to be understood. It is chiefly formed by the meeting of the spiral grooves and the solid end, the latter forming a blunt angular point rendered cutting by the edge of the grooves. They should have a place in every workshop.

The next tool to be described is also much used, especially in agricultural implement manufactories, for boring out the brasses, or bearings. It is called a rose bit, or grinder, and is shown in Fig. 128 A and B. In this case also a recess is cut in the work as a guide, and as the tool fills up the whole interior as it proceeds, no change of position can occur. The rose bit is used as shown in 125. A bit of this pattern is very useful for brass work of all kinds, such as the cylinders of small engines, bosses of wheels, bearings and collars, and one of these tools of the exact size for hollowing out the sockets of brass chucks, previously to their being tapped, will be found serviceable. The third kind of boring tool is made with movable cutters, which can be removed at pleasure, to be sharpened or replaced by more convenient ones. The simplest consists of a cutter bar, A, Fig. 129, with a slot in it to hold the tool, which is fixed by driving a wedge at the back of it. The tool here shown has two cutting edges, _b_ and _c_ which should be shaped according to the principles already enunciated respecting hand tools for iron and brass. The cutter bar is usually fixed between the lathe centres, and turned by a driver chuck and carrier, while the cylinder to be bored is clamped to the slide rest, and thereby advanced against the cutting edge. This form is chiefly used upon work that has been cast hollow, or drilled.