Fig. 2146Fig. 2146.
Fig. 2146.
Cast iron is more rapidly affected by pening than either wrought iron or steel. One of the most useful applications of pening is in the case of moulding patterns, which in time may become warpedfrom the rapping of the pattern in the mould, and this warping may be corrected by judicious pening, or suppose that a number of plates, such as represented inFig. 2146, having been cast, it is found that the ends of the tonguesa bcurl up when cooling in the mould, then the tongues may be pened as atc d, throwing them down to the requisite amount, and thus moulding the pattern to accommodate the curling in cooling.
The riveting usually performed by the machinist is generally upon cold metal. The blows in this case should fall dead and the riveting be performed with a view to stretching the metal uniformly and evenly over the surface to be riveted.
Fig. 2147Fig. 2147.
Fig. 2147.
Fig. 2148Fig. 2148.
Fig. 2148.
An excellent example of cold riveting is given in the crank pinpinFigs. 2147and2148.cis the crank (both being shown in section). The end of the pin should be recessed as shown ata, so that it may be the more readily riveted outward to fill the countersink shown in the crank atb,b. The crank-pin is rested upon a piece of copperdinterposed between it and the iron blocketo prevent damage to the finished face of the crank-pin.
The riveting blows should be given with a ball-faced hammer, and delivered with a view to stretch the whole end face of the crank-pin evenly. Otherwise the riveted surface will be apt to split as shown. This usually occurs from not riveting the area at and near the circumference sufficiently, although it may occur from riveting that part of the area too much. The line of travel of the hammer should not be directly vertical, but somewhat lateral in a direction from the centre towards the circumference. If the countersink is a deep one, it is desirable to leave the crank-pin sufficiently too long, so that after the riveting has proceeded some time the surface of the metal which has become condensed and crystallized from the direct impact of the hammer blows, may be chipped away, leaving a surface that is swollen by the riveting without being so much condensed. This enables a much greater spreading of the metal without splitting it.
If in this class of work the riveted piece (as the crank-pin) is not driven in very tight before riveting, the riveting blows will be apt to jar the pin back. Hence, it is necessary to occasionally drive the pin home. The riveting should proceed equally all over, as if one side be riveted in advance of the other it tends to throw the pin out of true. When, however, the riveting begins to bed the pin, four equidistant places may be riveted home in advance so as to bring the pin home and hold it firmly.
Fig. 2149Fig. 2150Fig. 2151Fig. 2149.Fig. 2150.Fig. 2151.
Fig. 2149.Fig. 2150.Fig. 2151.
The Chisel.—The machinist’s cold chisel is made from the two forms of steel shown inFigs. 2149,2150, and2151, and of these the former is preferable because it has two broad flats diametrally opposite and these form a guide to the eye in holding the chisel on the grindstone, and aid in grinding the facets that form the cutting edge true. Furthermore, as the cutting edge is in the same plane as these flats they serve as a guide to denote when the chisel edge lies parallel to the work surface, which is necessary to produce true and smooth chipping.
Fig. 2152Fig. 2153Fig. 2152.Fig. 2153.
Fig. 2152.Fig. 2153.
The width of the chisel may be made greater, as inFigs. 2152and2153, for brass or cast-iron work than for wrought iron or steel for the following reasons. On account of the toughness and hardness of wrought iron and steel the full force of a 13â„4lb. hammer, having a handle 13 inches long, may be used on a chisel about7â„8inch wide without danger of causing the metal to break out below the chipping line, but if such a chisel be used with full force blows upon cast iron or brass the metal is apt to break outin front of the chisel, the line of fracture often passing below the level it is intended to chip down to. Hence if a narrow chisel is used lighter blows must be delivered. But by using a broader chisel the force of the blow is distributed over a longer length of cutting edge, and full force blows may be used without danger of breaking out the metal.
Fig. 2154Fig. 2154.
Fig. 2154.
Fig. 2155Fig. 2155.
Fig. 2155.
Fig. 2156Fig. 2156.
Fig. 2156.
Fig. 2157Fig. 2157.
Fig. 2157.
Fig. 2158Fig. 2158.
Fig. 2158.
The cutting end of the chisel should be kept thin, as in that case it cuts both easier and smoother. The total length of a chisel should not when new exceed 8 inches, for if made longer it is not suitable for heavy or smooth chipping, as it will bend and spring under heavy blows, and cannot be held steadily. The forged part should not exceed about 21â„2or 3 inches in length, as a long taper greatly conduces to springiness, whereas solidity is of great importance both to rapid and smooth work. The facets forming the cutting edge should be straight in their widths, as atbinFig. 2154, and not rounded as ata, so that the face next to the work may form a guide in holding the chisel at the proper angle to maintain the depth of the cut. This angle depends upon the nature of the material to be cut; the facets forming an angle one to the other of about 65° for cast steel and about 50° for gun metal or brass. The more acute these angles the nearer the body of the chisel lies parallel with the work and the more effective the hammer blows. Thus inFig. 2155chiselcis the position of the chisel for wrought iron, and positiondis for steel. The angles should always be made, therefore, as acute as the hardness of the material will permit. If they are too acute the cutting edge will be apt to bend in its length, while if not sufficiently acute they will not cut keen enough; hence the object is to make them as acute as possible without causing the cutting edge to bend in its length. For copper and other soft metals the angle may be about 30° or 35°, the chisel end being kept thin so that it may not become wedged between the work and the chipping, which will bend but little, and is, therefore, apt to grip the wedge end of the chisel. The cutting edge should be slightly rounded in its length, which will strengthen it and also enable a fine finishing clip to be taken off, as inFig. 2156, the width of the chip not extending fully across the chisel width so that the corners are not under duty and are not, therefore, liable to break, or dig in and prevent smooth chipping. In some practice the edge is made straight in its length, as shown inFig. 2149, which is permissible in heavy chipping when a cape chisel has been used, but in any event an edge rounded in its length is preferable. If the edge is hollow in its length, as shown inFig. 2157, and magnified inFig. 2158, the chip acts as a wedge to force the corners outwards as denoted by the arrows, causing them to break under a heavy cut, and, furthermore, a smooth cut cannot be taken when the corners of the chisel meet the work surface.
Fig. 2159Fig. 2160Fig. 2159.Fig. 2160.
Fig. 2159.Fig. 2160.
If the facets are ground under on one side, those on the other, as inFig. 2159, the edge will not be parallel with the flats of the chisel, so that in holding it the flats will not form a guide to determine when the edge lies parallel to the work surface as it should do. The edge should also be at a right angle to the length ofchisel, as denoted by the lines, as inFig. 2160, for if not at a right angle the chisel will be apt to move sideways after each blow, and cannot be held steadily.
The chisel should be held as close to its head as possible, so that the hand will steady the head as much as possible, and should be pushed forward firmly and steadily to its cut, which will greatly facilitate rapid and smooth chipping, and for wrought iron and copper it is found better to occasionally moisten the chisel with oil or water, the former being preferable.
Fig. 2161Fig. 2161.
Fig. 2161.
Messrs Tangye, of Birmingham, have introduced the employment of chisel holders, such as shown inFig. 2161, the object being to fit to each holder a number of short pieces of steel for chisels so that a number can be ground or forged at one time; obviously chisels of different shapes require different forms of handle.
Fig. 2162Fig. 2163Fig. 2164Fig. 2162.Fig. 2163.Fig. 2164.
Fig. 2162.Fig. 2163.Fig. 2164.
When a heavy cut is to be taken the cape (Fig. 2162) chisel is used, first to carry through grooves or channels, such as shown inFig. 2176ata,b, andc, the distance apart of these grooves being slightly less than the width of the flat chisel, whose cut is shown partly carried across atdin the figure. The width of a cape chisel should gradually decrease fromatobinFig. 2163, so that its side will be free in the groove it cuts, and the chisel head will be free to be moved sideways, and the direction of the groove may be governed thereby. If the chisel end be made parallel, as atcinFig. 2164, it will have no play in the groove and the head cannot be moved; hence if the groove is started out of line, as it is apt to be, it will continue so.
Fig. 2165Fig. 2166Fig. 2167Fig. 2168Fig. 2165.Fig. 2166.Fig. 2167.Fig. 2168.
Fig. 2165.Fig. 2166.Fig. 2167.Fig. 2168.
The round-nosed chisel,Figs. 2165and2166, may be straight fromhnearly to the pointg, but should be bevelled at and nearg, so that the chisel head may be raised or lowered to govern the depth of the cut. Its round nose should also be wider than the metal higher up, so that the chisel head may be moved sideways to govern the direction of the cut as in the cape chisel. The cow mouth chisel,Figs. 2167and2168, should be bevelled fromgtothe point to enable the governing of the depth of the cut, and should be of greater curvature than the corner it is to cut out, so that its corners cannot wedge in the work.
Fig. 2169Fig. 2169.
Fig. 2169.
Fig. 2170Fig. 2170.
Fig. 2170.
The oil groove chisel,Figs. 2169and2170, should be wider at the cutting edge than atafor reasons already stated, and of less curvature than the bore of the brass or bearing it is to cut the oil groove in.
Fig. 2171Fig. 2172Fig. 2173Fig. 2174Fig. 2175Fig. 2171.Fig. 2172.Fig. 2173.Fig. 2174.Fig. 2175.
Fig. 2171.Fig. 2172.Fig. 2173.Fig. 2174.Fig. 2175.
The diamond point chisel,Figs. 2171and2172, may be made in two ways. First, as inFigs. 2173and2174, for shallow holes, and as inFigs. 2171and2172for deep ones. In shallow holes the chisel can be leaned over, as inFig. 2176aty, whereas in deep ones it must be held straight so that the chisel body may not meet the other side of the hole, slot, or keyway. The form shown inFig. 2172is the strongest, because its point is brought into line with the body of the steel, as shown by the lineq. The side chisel,Fig. 2175, for cutting out the sides of keyways or slots, should be bevelled fromwto the cutting edge for the reasons already given, and straight fromwtov, the linev wprojecting slightly above or beyond the bodyu. An application of the cow mouth chisel is shown atl, and one of the side chisel is shown atzinFig. 2176. All these chisels are tempered to a blue color.
Fig. 2176Fig. 2176.
Fig. 2176.
The chisel that is driven by hammer blows may be said to be to some extent a connecting link between the hammer and the cutting tool, the main difference being that the chisel moves to the work, while the work generally moves to the cutting tool. In many stone-dressing tools the chisel and hammer are combined, inasmuch as that the end of the hammer is chisel shaped; an example of this kind of tool being given in the pick that flour millers use to dress their grinding stones. On the other hand we may show the connection between the chisel and the cutting tool by the fact that the wood-worker uses the chisel by driving it with a mallet, and also by using it for a cutting tool for work driven in the lathe. Indeed, we may take one of these carpenter’s chisels and fasten it to the revolving shaft of a wood-planingmachine, and it becomes a planing knife; or we may put it into a carpenter’s hand plane, and by pushing it to the work it becomes a plane blade. In each case it is simply a wedge whose end is made more or less acute so as to make it as sharp as possible, while still retaining strength enough to sever the material it is to operate upon.
Fig. 2177Fig. 2177.
Fig. 2177.
In whatever form we may apply this wedge, there are certain well-defined mechanical principles that govern its use. Thus when we employ it as a hand tool its direction of motion, under hammer blows, is governed by the inclination of the face which meets the strongest side of the work, while it is the weakest side of the material that moves the most to admit the wedge and therefore becomes the chip, cutting, or shaving. InFig. 2177, for example, we have the carpenter’s chisel operating ataandbto cut out a recess or mortise, and it is seen that so long as the face of the chisel that is next to the work is placed level with the straight surface of the work the depth of cut will be equal; or in other words, the line of motion of the chisel is that of the chisel face that lies against the work. Atcanddis a chisel with, in the one instance, the straight, and in the other the bevelled face toward the work surface. In both cases the cut would gradually deepen because the lower surface of the chisel is not parallel to the face of the work.
If now we consider the extreme cutting edge of chisel or wedge-shaped tools it will readily occur that but for the metal behind this fine edge the shaving or cutting would come off in a straight ribbon, and that the bend or curl that the cutting assumes increases with the angle of the face of the wedge that meets the cutting, shaving, or chip.
Fig. 2178Fig. 2178.
Fig. 2178.
I may, for example, take a piece of lead, and with a penknife held as ata,Fig. 2178, cut off a curl bent to a large curve, but if I hold the same knife as atbit will cause the shaving to curl up more. Now it has taken some power to effect this extra bending or curling, and it is therefore desirable to avoid it as far as possible. For the purpose of distinction we may call that face of the chisel which meets the shaving the top face, and that which lies next to the main body of the work the bottom face. Now at whatever angle either face of the chisel may be to the other, and in whatever way we present the chisel to the work, the strength of the cutting edge depends upon the angle of the bottom face to the line of motion of the chisel, and this is a principle that applies to all tools embodying the wedge principle, whether they are moved by a machine or by hand.
Fig. 2179Fig. 2179.
Fig. 2179.
Thus, inFig. 2179we have placed the bottom face at an angle of 80° to the line of tool motion, which is denoted by the arrow, and we at once perceive its weakness. If the angle of the top face to the line of tool motion is determined upon, we may therefore obtain the strongest cutting edge in a hand-moved tool by causing the bottom angle to lie flat upon the work surface.
Fig. 2180Fig. 2180.
Fig. 2180.
But in tools driven by power, and therefore accurately guided in their line of motion, it is preferable to let the bottom face clear the work surface, save at the extreme cutting edge. The front face of the wedge or tool is that which mainly determines its keenness, as may be seen fromFig. 2180, in which we have the wedge or tool differently placed with relation to the work, that in positionaobviously being the keenest and less liable to break from the strain of the cutting process.
If we now turn our attention to that class of chisel or wedge-shaped tools in which the cutting edge is not a straight line, but may be stepped or curved—as, for example, the carpenter’s plane blade—we shall find that so long as the blade stands at a right angle to the surface it is operating upon, as inFig. 2183atb, the shape of surface it cuts will exactly correspond to the shape of its cutting edge; but so soon as the tool is inclined to its line of motion its cutting edge will, if curved, produce a different degree of curvature on the work.
Fig. 2181Fig. 2181.
Fig. 2181.
Fig. 2182-2183Fig. 2182.Fig. 2183.
Fig. 2182.Fig. 2183.
Suppose, for instance, that we have in the figure a piece of mouldingmand a plane bladeb, and the length of the cutting edge is denoted bya,Fig. 2182; now suppose that the blade is inclined to its line of motion (as in the case of carpenters’ planes) and stands atc,Fig. 2183: we then find that the cutting edge must extend to the length or depthd, and it is plain that the depth of the curve on the moulding is less than the depth of the cutting edge that produces it; the radiusebeing less than ofd, so that if we place the cuttercupright on the moulding it will appear as shown inFig. 2181. If, therefore, we are required to make a blade that will produce a given depth of moulding when moved in a straight line and presented at a given angle to the work, we must find out what shape the blade must be to produce the given shape of moulding, which we may do as follows:
Fig. 2184Fig. 2184.
Fig. 2184.
InFig. 2184letabe a section of the moulding, and if the blade or knife is to stand perpendicular, as shown atb,Fig. 2183, and if it is moved in a straight line in the direction of the length of the work, then its shape would necessarily be that shown atb,Fig. 2184, or merely the reverse ofa. In the position mentioned it could be used only as a sweep applicable to some few uses, but not adapted to cutting. To become a cutting tool it must be inclined and stand at some angle of less than 90° to its line of motion.
Fig. 2185Fig. 2185.
Fig. 2185.
Fig. 2186Fig. 2186.
Fig. 2186.
Thus inFig. 2185d b erepresents the bottom of the moulding and line of motion of the cutter, anda bthe cutter perpendicular to it, the highest point of the cutting edge, ascofFig. 2184, being atc,Fig. 2185. The height or thickness of the moulding cut would be the space between the linese b dande c f, but the cutter assuming the positionb cat an angle of 30° froma b, the pointcis brought tod; consequently the highest line of the moulding would now beg d h, and its thickness less. This is further exhibited inFig. 2186, wherearepresents the original depth section ofFig. 2184that would be formed by knifebofFig. 2184when standing perpendicular; andgshows the depth with the same knife when placed asb c,Fig. 2185, or at 30° inclination, andhshows the depth that would be cut with the same knife or cutter at 45°. It is now evident that every change in the inclination of the same cutter would effect a change in the shape of moulding which it cuts, and to produce a given style of moulding the shape of the cutter must be decided by its inclination, or the angle at which it is used.
Fig. 2187Fig. 2187.
Fig. 2187.
The method of projecting a given section of moulding in order to exhibit the form that the curve of the opening should assume on the face of the knife, is shown inFig. 2187. Upon a horizontal linea b c ddraw a section of the required style of moulding, as shown ata e b. To the right of this draw a line, asf c, to meet the base linea b c d, and asf crepresents the cutter, it must stand at the same angle that the proposed cutter is to have—in this particular example 30° from the perpendicular. From the highest point of the sectiona e bdraw a horizontal linee g, meetingf cing. From pointsgandcdraw lines, asc jandg h, of any convenient length, at right angles tof c. At any distance fromg hdrawk lparallel tog h, and uponk ltrace the section of mouldinga e b, ask m l. Draw lines from the extreme edgeskandlofk m l, ask n, l j, perpendicular tok l, cuttingg hand meetingc jatnandj.e gbeing parallel toa b c d,gwill be the point on the cutter where the topeof the moulding will come on the highest point of the cutting edge, andc gwill be the entire length of cutting edge or height of opening measured on the face of the cutterf c.c jbeing drawn from the lowest pointcof the cutter andg hbeing drawn fromg, the highest cutting point, both lines at right angles tog c, then their distance from each other, asp o, must obviously represent the extreme height of opening in the cutter in its new position or front view, andk l, representing the width of moulding transferred ton jby the parallel linesk nandl j, will show the width of opening in the cutter. Having now the height and width, it only remains to project an indefinite number of points and trace the curve through them. Dividea binto a number of parts, andto avoid confusion mark the points of division thus obtained upona b—1, 2, 3, 4, &c. Dividek lin an exactly similar manner and into the same number of parts, and mark the divisionsi.,ii., iii.,iv., &c. Erect perpendiculars from points 1, 2, 3, 4, &c., meeting the curvea e b, and from the points thus found ona e bdraw horizontal lines tof c; from the termini of these horizontals onf cdraw the remaining lines parallel to and betweeng handc j. From the divisionsi.,ii.,iii.,iv., &c., onk l, let drop the perpendiculars, cutting the other series of lines at right angles. A point of the curve will then be at the intersection of the line from 1 ona b, with lineionk l; another at the intersection of the line originating at 2 with that fromii, and so on, and the proper curve is found by tracing fromnthrough the intersections top, and fromptoj. Thenk nbeing one side of the cutter andl jthe other,n p jis the curve that the opening or cutting edges must have to cut the profilea e b, with the cutter set atf c, or 30°.
Fig. 2188Fig. 2188.
Fig. 2188.
The same method is shown inFig. 2188, except that in this case, instead of dividinga bandk l, the divisions are made directly on the peripheriesa 6 bandk vi. lby stepping round with the dividers. The cutterf cis shown in this case at an angle of 45°, in order that the change in form which the curve assumes with the cutter at different angles may be clearly seen by comparing the curven p jofFig. 2187with the same inFig. 2188. The two figures are similar in other respects, and as the lettering is the same on each, the description ofFig. 2187will apply equally toFig. 2188.
Fig. 2189Fig. 2189.
Fig. 2189.
There remains one more case of cutters moving in right lines, and that is where, besides having an inclination backward, as atf c,Fig. 2187, making a vertical angle to the line of motion, they are placed at an angle across the guiding piece also, or “skewing,†thus making an angle to the line of motion on a horizontal plane as well as on a vertical one. Thus, suppose an ordinary carpenter’s plane to have the cutter or “iron†turned partly round and placed so that the cutting edge, instead of lying at a right angle across the body, crosses it at some other angle.Fig. 2189represents an ordinary carpenter’s plane with the blade so placed. Here the edge, or rather side,d b, of the blade inclines back at an angle, asa b d, which is 45° in this case, to the perpendicular linea bon the side of the plane. For convenience calla b dthe vertical angle. The lower or cutting edgee bof the blade also crosses the bottom of the plane at an anglee b c—30° in this instance—to a lineb c, crossing the bottom at right angles. Now, it is evident that this latter anglee b cwill influence the form of the cutter, if, instead of being a flat plane, as represented for clearness inFig. 2189, it had a cutting edge of curved outline for cutting mouldings or similar work. But in either case the angle thatd bor one side of the blade makes toe b, or the cutting edge—that is, the angled b e—must be found in order to cut off the blank for the cutter or knife at the right “slant.â€
Fig. 2190Fig. 2190.
Fig. 2190.
The method given inFigs. 2187and2188of determining the form of cutter to produce a moulding of given profile now undergoes a modification where there are two angles to be taken into consideration instead of one. As an example, suppose a cutter is required that is to be fixed in such a position in its carrier or block that the handlea b d, or “vertical angle,†ofFig. 2189is, say, 45°, and the anglee b c, or “horizontal angle,†ofFig. 2189shall be 30°. Required the angle at which the bottom of the blank for the cutter must be cut off; or the angle that the sided band lower edgeb eofFig. 2189would make to each other, measured on the face of the cutter, and required the outline of cutting edge to be traced on the face of cutter to cut the section of mouldinga e b,Fig. 2190: draw a horizontal line, asa b c d, and erect a perpendicular, asc r. Fromcdrawc f, making an angle toc requal to the “vertical angle,†or anglea b d,Fig. 2189, which is 45° in this case. Draw a profile of the required moulding, asa e b, with its backa bcoincident to the horizontal linea b c d. Draw a horizontal line from the highest point of the profile, ase, to meetf cing. Draw parallel linesc jandg h, fromcandgrespectively, of any convenient length and making right angles tof c. At right angles tog handc j, and parallel tof c, drawk h jto represent one side or edge of the cutter, but the angle of the lower end or angled b eofFig. 2189must now be determined; to do this, draw an indefinite horizontal line,a b c,Fig. 2191, and from any point, asb, drop a perpendicularb d; now, frombset off ona b cthe distancecbofFig. 2190, obtaining pointe, and fromeextend a perpendicular above and belowa b c, asf e h. Fromeone fset off distancegbofFig. 2190, obtainingjone f. Frombdraw a line, making the same angle tob dthat the anglee b cis inFig. 2189, or 30° in this case, and cuttinge hink. Set off distancee kfromeona c, obtainingl; drawl j. Now, onFig. 2190, with centre ath, and radiusl jofFig. 2191, describe arcw x, and fromjas centre, onFig. 2190, andb kofFig. 2191as radius, describe arcy z. Through the intersectionvof arcsy zandw x,j l mmust be drawn, making the proper angle to the sidej h kof the cutter; this angle is 69° in this case, as found by construction. Fromhdrawh nparallel toj l, and fromhdrawh oat the same angle toh nthatb kis tob d,Fig. 2191, or anglee b c,Fig. 2189. Place a duplicate ofa e b, with its base coincident toh oand corneraath, ash p r. Fromrdrawr nat right angles toh rand cuttingh natn; throughndraws n lparallel tok h j. Then whilek h jrepresents one edge of the cutter,s n lwill be the other, andj lthe cutting edge before the opening is cut out. Divide the curvese bandp rsimilarly, obtaining points 1, 2, 3, &c., andi.,ii.,iii., &c., respectively. From points 1, 2, 3, &c., lines are to be drawn parallel toe g, meetingg c, continued fromg cparallel tog h, and meetingh j, and fromh jparallel toh n, meetingn l. From pointsi.,ii.,iii., &c., lines are to be drawn perpendicular toh r, meetingh nand continued fromh n, parallel toh j, toj l, thus intersecting the first series. Lines from points 1, 2, 3, &c., then determine the height of different points of the curve, and those fromi.,ii.,iii., &c., their location laterally; hence, by tracing through the intersections of 1 withi., 2 withii., &c., the curveh t lis obtained. The two outside linesk h jands n lmay now represent the edges of a piece of steel of which the cutter is to be made, andh t lwill be the contour of cutting edge that must be given it in order that when, fixed for use at the angles named, it will form the required mouldinga e b.