Fig. 2094Fig. 2094.
Fig. 2094.
Fig. 2095Fig. 2095.
Fig. 2095.
Fig. 2096Fig. 2096.
Fig. 2096.
Fig. 2097Fig. 2097.
Fig. 2097.
Fig. 2098Fig. 2098.
Fig. 2098.
The machinists’ hand hammer is usually made in one of the three forms shown inFigs. 2094,2095and2096, and varies in weight from about 13⁄4lbs. for heavy chipping to about1⁄2lb. for light work, the handle being about 15 inches long for the heavy, and about 10 or 12 for the light business. The round face is usually somewhat convex on its surface with its edge slightly rounded or beveled. The pane or penea,Fig. 2097, is usually made in European practice to stand at a right angle to the axis of the handle as shown, while in the United States it is usually made to stand parallel with the handle as inFig. 2096. The face end is sometimes given taper as inFigs. 2094and2095, and at others parallel as inFigs. 2097and2098, or nearly so. The pene is mostly used for riveting purposes, and it is obvious that with the pene at a right angle to the handle axis as inFig. 2097, it will not matter whether the pene meets the work quite fair or not, especially as the pene is made slightly curved in its length, and it is easier to hold the hammer level sideways than it is to hold it so true lengthways that the pene, when forward, as inFig. 2096, will meet the work fair.
Fig. 2099Fig. 2099.
Fig. 2099.
Fig. 2100Fig. 2100.
Fig. 2100.
Fig. 2101Fig. 2101.
Fig. 2101.
Fig. 2102Fig. 2102.
Fig. 2102.
The proper shape for the eye of a hammer is that shown inFigs. 2099and2100, a representing the top of the hammer. The two sides of the eye are rounded out from the centre towards each end, while the ends of the eye are made parallel. The form of the eye as viewed from the topais as shown inFig. 2102, whileFig. 2101represents a view from the bottomb. The handle is fitted a driving fit and is driven in from sideb, and is shaped as inFigs. 2103and2104which are side and edge views.
Fig. 2103Fig. 2103.
Fig. 2103.
Fig. 2104Fig. 2104.
Fig. 2104.
Fromctodthe handle fills the eye, but fromdtoeit fills theeye lengthways only of the oval. A saw-slot, to receive a wedge, is cut in the handle, as shown inFig. 2104. The wedge is best made of soft wood, which will compress and conform itself to the shape of the slot. To drive the handle into the eye, preparatory to wedging it permanently, it should be placed in the eye held vertically, with the tool head hanging downward, and the upper end struck with a mallet or hammer, which is better than resting the tool head on a block. The wedge should be made longer than will fill the slot, so that its upper end may project well, and the protruding part, which may split or bulge in the driving, may be cut off after the wedge is driven home.
The wedge should be driven first with a mallet and finally with a hammer. After every few blows on the wedge, the tool should be suspended by the handle and the end of the latter struck to keep the handle firmly home in the eye. This is necessary, because driving the wedge in is apt to drive the handle partly out of the eye.
Fig. 2105Fig. 2105.
Fig. 2105.
The width of the wedge should equal the full length of the oval at the top of the eye, so that one wedge will spread the handle out to completely fill the eye, as shown inFig. 2105. Metal wedges are not so good as wooden ones, because they have less elasticity and do not so readily conform to the shape of the saw-slot, for which reasons they are more apt to get loose. The taper on the wedge should be regulated to suit the amount of taper in the eye, while the thickness of the wedge should be sufficiently in excess of the width of the saw-cut, added to the taper in the eye, that there will be no danger of the end of the wedge meeting the bottom of the saw-slot.
Fig. 2106Fig. 2106.
Fig. 2106.
By this method, the tool handle is locked to the tool eye by being spread at each end of the same. If the top end of the tool eye were rounded out both ways of the oval, two wedges would be required to spread the handle end to fit the eye, one wedge standing at a right angle to the other. In this case, one wedge may be of wood and one of metal, the one standing across the width of the oval usually being the metal one. The thin edge of the metal wedge is by some twisted, as shown byFig. 2106, which causes the wedge to become somewhat locked when driven in.
Fig. 2107Fig. 2107.
Fig. 2107.
In fitting the handle, care must be taken that its oval is made to stand true with the oval of the tool eye. Especially is this necessary in the case of a hammer. Suppose, for example, that inFig. 2107the length of the oval of the handle lies in the planea b, while that of the eye lies in the planec d, then the face of the hammer will meet the work on one side, and the hammer will wear on one side, as shown in figure ate. If, however, the eye is not true in the hammer, the handle must be fitted true to the body of the hammer; that is to say, to the linec d. The reason for this is that the hand naturally grasps the handle in such a manner that the length of the oval of the handle lies in the plane of the line of motion when striking a blow, and it is obvious that to strike a fair blow the length of the hammer should also stand in the plane of motion.
Fig. 2108Fig. 2108.
Fig. 2108.
The handle should also stand at a right angle to the plane of the length of the hammer head, viewed from the side elevation, as shown inFig. 2108, in which the dotted line is the plane of the hammer’s length, whilebrepresents a line at a right angle toa, and should, therefore, represent the axial line of the hammer handle. But suppose the handle stood as denoted by the dotted linec, then the face of the hammer would wear to one side, as shown in the figure atd.
In the operation of straightening iron or steel plates by hammer blows, the process when correctly carried out is one of liberating the strains (whose existence throws the plate out of a true plane) by stretching those parts that are unduly contracted. Every hammer blow should, therefore, be directed towards this end, forone misdirected blow entails the delivery of many others to correct its evil influence; hence, if several of such misdirected blows are given, the plate will have upon it a great many more hammer marks, or “hammer sinks” or chops, as they are sometimes termed, than are necessary. As a result, not only will the painter (in fine work) be given extra trouble in stopping the hollows to make a smooth surface, but the following evil will result: Every blow struck by the hammer compresses and proportionately stiffens the small surface upon which it is delivered, and creates a local tension upon the surrounding metal. The misdirected blows then cause a tension acting in opposition to the effect of the properly delivered ones; and though the whole plate may be stiffened by the gross amount of blows, yet there will be created local tensions in various parts of the plate, rendering it very likely to spring or buckle out of truth again. If, for example, we take a plate of iron and hammer it indiscriminately all over its surface, we shall find it very difficult to straighten it afterwards, not only on account of the foregoing reasons, but for the additional and most important one that the effect of the straightening blows will be less, on account of the hammered surface of the plate offering increased resistance to the effects of each blow; and after the plate is straightened, there will exist in it conflicting strains, an equilibrium of which holds the plate straight, but the weakening of any of which will cause the preponderance of the others to throw the plate out of straight; for the effects of the blows cannot be permanent unless the whole body of the iron is acted upon to an equal extent by the hammer. Suppose, for example, that we take a flat plate, and deliver upon it a series of blows round about its centre. The effect will be to make it hollow on one side and rounding on the other, the effect of the blows being, not only to indent the plate in the spots where they fell, but to carry the whole body of the middle out of true; because, the area of the iron being increased by the stretching effect of the blows, the centre leaves the straight line to accommodate the increased area. Thus, if we mark off a circle of, say, a foot in diameter, in the middle of a plate, and hammer it so as to stretch it and increase its area1⁄8inch each way, the form of the plate must alter to suit this added area, and the form of a dish or curve is the only one it can assume.
The skilful workman, so soon as he has ascertained where the plate is out of true, sets to work to stretch it, so as to draw the crooked place straight, taking care that the shape and weight of the hammer and the weight of the blows delivered shall bear a proper relation to the thickness of the plate and the material of which it is composed. If it is of consequence that the finished work shall bear no marks of the hammering (as in the case of engravers’ plates), an almost flat-faced hammer is employed; but for other work the shapes, as well as the weights, of the hammers vary.
Fig. 2109Fig. 2109.
Fig. 2109.
Fig. 2110Fig. 2110.
Fig. 2110.
Fig. 2111Fig. 2111.
Fig. 2111.
Fig. 2109represents what is called the long cross-face hammer, used in saw straightening for the first part of the process which is called the smithing. The face that is parallel to the handle is called the long one, and the other is the cross-face. These faces are at a right angle one to the other, so that without changing his position the operator may strike blows that will be lengthways in one direction, as ata, inFig. 2110, and by turning the other face towards the work he may strike a second series standing as atb. Now, suppose we had a straight plate and delivered these two series of blows upon it, and it will bend to the shape shown inFig. 2111, there being a straight wave ata, and another across the plate atb, but rounded in its length, so that the plate will be highest in the middle, or atc; if we turn the plate over and repeat the blows against the same places, it will become flat again. Both faces of this hammer are made alike, being rounded across the width and slightly rounded in the length, the amount of this rounding in either direction being important, because if the hammer leaves indentations, or what are technically called “chops,” they will appear after the saw has been ground up, even though the marks themselves are ground out, because in the grinding the hard skin of the plate is removed, and it goes back to a certain, but minute, extent towards its original shape. This it will do more in the spaces between the hammer blows than it will where the blows actually fell, giving the surface a slightly waved appearance.
The amount of roundness across the face regulates the widths, and the amount of roundness in the face length regulates the length of the hammer marks under any given force of blow. As the thicker the plate the more forcible the blow, therefore the larger the dimensions of the hammer mark.
Fig. 2112Fig. 2112.
Fig. 2112.
The twist hammer, shown inFig. 2112, is used for precisely the same purposes as the long cross-face, but on long and heavy saws or plates, and for the following reasons, namely: When the operator is engaged in straightening a short saw he can stand close to the spot he is hammering, and the arm using the hammer may be well bent at the elbow, which enables him to see the work plainly, and does not interfere with the use of the hammer, while the shape of the smithing hammer enables him to bend his elbowand still deliver the blows lengthways, in the required direction. But when a long and heavy plate is to be straightened, the end not on the anvil must be supported with the left hand, and it stands so far away from the anvil that he could not bend his elbow and still reach the anvil. With the twist hammer, however, he can reach his arm out straight forward to the anvil, to reach the work there, while still holding up the other end, which he could not do if his elbow were bent. By turning the twist hammer over he can vary the direction of the blow the same as with the long cross-face.
Fig. 2113Fig. 2113.
Fig. 2113.
Fig. 2114Fig. 2114.
Fig. 2114.
It is obvious that by slightly bending the elbow and turning either of these hammers over the blows may be caused to be in any required direction, as shown inFig. 2113. These two hammers are used for the straightening or smithing processes, and not to regulate the tension, because the effects of their blows do not extend equally around the part struck, but follow the form of the hammer marks, whose shapes are shown inFig. 2114, ataandb, the radiating lines denoting the directions in which the effects extend; obviously the size of these marks depends upon the shape of the hammer face and the force of the blow.
Fig. 2115Fig. 2115.
Fig. 2115.
Fig. 2116Fig. 2116.
Fig. 2116.
An inspection of hammered saw plates, however, will show that the marks (which are scarcely visible, having a merely dulled surface), are usually about one-half wider than the thickness of the plate, and about four or five times as long as they are wide. Obviously, also, the direction of the effects of a blow follow the direction in which the hammer travels. If, for example, the long cross-face falls vertically its effects will extend equally all around the hammer mark, as atainFig. 2115, but if the hammer moved laterally to the left while falling its blows would have more effect on the left-hand side of the mark as atb, or if it moved away from the operator its effects would extend most in front as atc, the amount increasing with the force of the blow, and it may be remarked that quick blows are not used, because they would produce indentations or chops; hence, the force of the blow is regulated by the weight of the hammer rather than by the velocity it travels at. On account of the oval shape of the blow delivered by the long cross-face and by the twist hammers, the dog-head hammer, shown inFig. 2116, is used to regulate the tension of the plate or saw, the effects of its blow when delivered vertically being circular, as ata, inFig. 2117; obviously, however, if in falling it moved vertically in the direction of arrowcthe effects would extend as atb. But while the dog-head is used entirely for regulating the tension, it may also be used for the same purposes as either the long cross-face or the twist hammer, because the smith operates to equalize the tension at the same time that he is taking down the lumps; hence he changes from one hammer to the other in an instant, and if after regulating the tension with the dog-head he should happen to require to do some smithing, before regulating the tension in another, he would go right on with the dog-head and do the intermediate smithing without changing to the smithing hammer. Or, in some cases, he may use the long cross-face to produce a similar effect to that of the dog-head, by letting the blows cross each other, thus distributing the hammer’s effects more equally than if the blows all lay in one direction.
Fig. 2117Fig. 2117.
Fig. 2117.
In circular saws, which usually run at high velocity, there is generated a centrifugal force that is sufficient to actually stretch the saw and make it of larger diameter. As the outer edge of the saw runs at a greater velocity than the eye it stretches most, and therefore the equality of tension throughout the saw is destroyed, the outer surface becoming loose and causing the saw to wabble as it revolves, or to run to one side if one side of the timber happens to be harder than the other, as in the case of meeting the edge of a knot.
The amount of looseness obviously depends upon the amount the saw expands from the centrifugal force, and this clearly depends upon the speed the saw is to run at; so the saw straightener requires to know at what speed the saw is to run, and, knowing this, he gives it more tension at the outside than at the eye; or, in other words, while the eye is the loosest, the tension gradually increases towards the circumference, the amount of increase being such that when the saw is running the centrifugal force, and consequent stretching of the saw, will equalize the tension and cause the saw to run steadily.
Fig. 2118Fig. 2118.
Fig. 2118.
If the eye of a circular saw is loose, or, in other words, if it is rim bound when running, it will dish, as inFig. 2118, and the rounded side rubbing against the side of the saw slot or kerf, will cause the saw to become heated and the eye to expand more than the outer edges, thus increasing the dish. But if the saw strikes a knot on the hollow side it may throw the dish over to the other side of the saw in an instant. The remedy is to hammer the saw with the dog-head as shown in the figure, not touching the eye,and letting the blows fall closer together towards the circumference.
Fig. 2119Fig. 2119.
Fig. 2119.
Fig. 2120Fig. 2120.
Fig. 2120.
Fig. 2121Fig. 2121.
Fig. 2121.
Fig. 2122Fig. 2122.
Fig. 2122.
Fig. 2123Fig. 2123.
Fig. 2123.
Fig. 2124Fig. 2124.
Fig. 2124.
On the other hand, if the eye is tight and the circumference loose the saw will flop from side to side as it runs, and the remedy is to stretch it round about the eye, letting the blows fall wider apart as the outer edge of the saw is approached. The combinations of tight and loose places may be so numerous in circular saws that as the smith proceeds in testing with the straight-edge he marks them, drawing a circular mark, as atg, inFig. 2119, to denote loose, and the zig-zag marks to indicate tight places. To cite some practical examples of the principles here laid down, suppose we have inFig. 2120a plate with a kink or bend in the edge, and as this would stiffen the plate there, it would be called a tight place. To take this out, the hammer marks would be delivered on one side, radiating from the top of the convexity, as on the left, and on the other as shown radiating from the other end of the concavity, as on the right, the smithing hammer being used. This would induce a tight place atawhich would be removed by dog-head blows delivered on both sides of the plate. Suppose we had a plate with a loose place, as atginFig. 2121. We may take it out by long cross-face blows, as ataandb, delivered on both sides of the plate, or we might run the dog-head on both sides of the plate, both ataand atb, the effect being in either case to stretch out the metal on both sides of the loose placeg, and pull it out. In doing this, however, we shall have caused tight places ateandf, which we remove with dog-head blows, as shown. If a plate had a simple bend in it, as inFig. 2122, hammer blows would first be delivered on one side, as ata, and on the other side, as atb. A much more complicated case would be a loose place atg, inFig. 2123, with tight places ath,j,k, andl, for which the hammer blows would be delivered as marked, and on both sides of the plate. Another complicated case is given inFig. 2124,g gbeing two loose places, with tight places between them and on each side. In this case, the hammering with the long cross-face would induce tight places atdande, requiring hammer blows as denoted by the marks.
Fig. 2125Fig. 2125.
Fig. 2125.
The saw or plate straightener’s anvil or block is about 12 by 18 inches on its face, which must be very smooth and is slightly convex, because it is necessary that the plate should be solid on the block, directly beneath the part of its surface which is being hammered, otherwise the effect of the blows will be entirely altered. If, for instance,a, inFig. 2125, represents the straightening block, andba plate resting thereon, then the blows struck upon the plate anywhere save over the very edges of the anvil will have but little effect, because of the spring and rebound of the plate; and the effect of the blow will be distributed over a large area of the metal, tending to spring it rather than give it a permanent set. If the blow is a quick one, it may indeed indent the plate without having any straightening effect. On the other hand, by stretching the skin on the upper side of the plate, it will actually, under a succession of blows, become more bent. In fact, to use a straightening block, so large in proportion to the size of the plate that the latter cannot be adjusted so that the part of the plate struck lies solid on the block, renders all the principles above explained almost valueless, and is a process ofpounding, in a promiscuous way, productive of hammer marks, and altogether fatal to the production of true work.
Fig. 2126Fig. 2126.
Fig. 2126.
To straighten the plate shown inFig. 2125, we place it upon the anvil, as shown inFig. 2126, striking blows as denoted ata, and placing but a very small portion of the plate over the anvil at first; and as it is straightened, we pass it gradually farther over the anvil, taking care that it is not, at any part of the process, placed so far over the anvil as to drum, which will always take place if the part of the plate struck does not bed, under the force of the blow, well upon the anvil.
The methods employed to discover in what parts a plate requires stretching, in order to straighten it and to equalize its tension, are as follow: Suppose we have a plate, say 18 inches by 24, and having a thickness of 19 gauge, and we rest one end of it upon the block and support the other end in the left hand, as shown inFig. 2127; then with the right hand we exert a sudden pressure in the middle of the plate; and quickly releasing this pressure, we watch where its bending movement takes place. If it occurs most at the outer edges, it proves that the plate is contracted in the middle; while, if the centre of the plate moves the most, it demonstrates that it is expanded in the middle. And the same rule applies to any part of the plate. This way of testing may be implicitly relied upon for all plates or sheets thin enough to be sprung by hand pressure.
Another plan, applicable for either thick or thin plates, and used conjointly with the first named, is to stand the plate on edge with the light in front, as inFig. 2128; we then cast one eye along the face of the plate upon which the light falls, and any unevenness will be made plainly visible by the shadows upon the surface of the plate. The eye should also be cast along the edges to note any twist or locate any kinks.
We may take a thin piece of plate in the hands, and if it is loose in the middle and we lay a straight-edge upon its upper surface, and try to bend the middle of the plate downward with the fingers, it will go down under the finger pressure, the straight-edge showing a hollow place in the middle; and the same thing will occur if the straight-edge be tried with either side of the plate uppermost. But if the piece be tight in the middle and we test with the fingers and straight-edge in the same way, the middle instead of bending downwards, appears to rise up, the straight-edge showing it to be rounded. In the first case the middle moves because it is loose, and in the second the edges move because they are loose.
Fig. 2129represents a plate for a circular saw that is loose in the middle, and if we bend the middle down it will become concave on the top, as shown in the figure. But if it were tight in the middle and loose at the outer edge, it would become, under the same pressure, convex on the top, as inFig. 2130, and here again the part that is loose moves the most.
In thin saws, such as hand saws, the workman takes the saw in his hands, as inFig. 2131, and bends it up and down so that by close observation he may see where it moves the most, and then discover the loose places, or he may watch for the tight places, since these are the places he must attack.
Fig. 2135Fig. 2135.
Fig. 2135.
The sledge hammer used by the machinist is usually made in one of the two forms shown inFigs. 2132and2133, the latter being the most serviceable because it has two faces which may be used for driving purposes, which is the only use the machinist has for the sledge hammer. The coppersmith varies the shape of his hammer faces to suit the nature of the work, thusFig. 2134represents a coppersmith’s hammer, its two faces being of different sizes and of different curvature, and both being used to form convex surfaces having different degrees of curvature, it being noted that the curvature of the hammer face is always less than that of the work. In other forms of coppersmith’s hammers there are two penes and no face, one being at a right angle to the other, as inFig. 2135, the penes being rounded as in the figure, or sometimes square.
Fig. 2136Fig. 2136.
Fig. 2136.
Fig. 2136represents a coppersmith’s hammer with a square nosed pene, which is sometimes made to stand at a right angle to the handle as in the figure, and at others parallel to it.
Fig. 2137Fig. 2137.
Fig. 2137.
Fig. 2137represents the file cutter’s hammer, whose handle is at the angle shown because the chisel is held at an angle, the point or cutting edge being nearest to the workman; hence if the handle were at a right angle to the hammer length his arm would require to be considerably elevated in order to let the hammer face fall fair on the chisel head, whereas by setting the handle at the angle shown the arm need not be elevated, and the blow may be given by a movement of the wrist.
Fig. 2138Fig. 2138.
Fig. 2138.
Fig. 2139Fig. 2139.
Fig. 2139.
Figs. 2138and2139represent hammers used by boiler-makers for riveting boiler seams. The faces are made small so that if the blows are properly directed the edge of the face will not meet the boiler plate and indent it. These hammers are made long and narrow so that the weight may lie in the same direction as the hammer travels in when delivering the blow, and thus cause the effects of the hammer blows to penetrate deeper than if the hammer was wider.
Fig. 2140Fig. 2140.
Fig. 2140.
In the cooper’s hammer, shown inFig. 2140, the face extends flush up to the head, thus enabling it to strike a hoop upon abarrel without danger of the extreme end or top of the hammer meeting the barrel, and preventing the hammer face from meeting the edge of the barrel hoop when driving it on the barrel. The face is square and its front edge therefore a straight line, which is necessary on account of the circular shape of the hoop of the barrel.
Fig. 2141Fig. 2141.
Fig. 2141.
The mallet is made in various forms to suit the nature of the work and the tools it is to be used upon. Thus the carpenter’s mallet is a rectangular block, such as shown inFig. 2141. It is composed of wood, because the carpenter’s tools are held in wooden handles, and a metal hammer would split them in course of time. It is rectangular in shape so that it may be applied to tools held in a corner of the work, where a round mallet could not, if of sufficient diameter, give the necessary weight. For such carpenters’ or wood-workers’ tools as are for heavy duty, and the tools for which have ferrules at the head of their handles to prevent them from splitting, the mallet is made cylindrical or round, as it is termed, and has an iron band at each end to prevent the face from spreading or splitting.
The stonemason’s mallet is also of wood, and is disk-shaped, with the handle in the centre, the circumferential surface forming the face. The reason for this is that his tools are of steel and have no handles; hence if the blow continually fell on the same part or spot of the mallet face it would sink or indent holes in it, which is prevented by utilising the whole circumference of the mallet for the face.
An excellent mallet for the machinist’s use, for driving finished work without damaging it, is formed of raw hide secured in a metal eye that receives the handle. Or for the same purpose a lead hammer is used, being especially serviceable for setting work in machines.
What is known as pening, or paning, consists of hammering the skin of metal to stretch it on the side that is hammered. It may be employed either to bend or to straighten. Suppose, for example, we have a piece of metal that is bent to a half circle, and if we take a light hammer and hammer it on the concave side and all over its surface the piece will straighten out to an amount depending on the amount of pening. Or if he hammers the convex side the piece will bend to a smaller circle. The principle involved is, that if one side of a piece is elongated and the other remains of its original length, the only shape it can assume to accommodate or permit the elongation is that of a curve of which the convex side is the longest. It follows, therefore, that the hammer blows must in pening be sufficiently light to condense or stretch the metal on one side only of the metal, and not forcible enough to effect it all through.
In order to accomplish this stretching as rapidly as possible it is necessary to use a light hammer, with sufficient force to be expended in condensing the metal at its surface, and to so form the hammer that it shall expend its force upon the work with a dead blow, that is, with as little rebound as possible. These results are best accomplished with a ball pened hammer, such as shown inFig. 2108and weighing about1⁄2lb. The blows should fall dead; that is, the hammer should fall, to a great extent, by its own weight, the number rather than the force of the blows being depended upon; hence, the hammer marks will not be deep. This is of especial importance when pening has to be performed upon finished work, because, if the marks sink deeply, proportionately more grinding or filing is required to efface them; and for this reason the force of the blows should be as near equal as possible. Another and a more important reason, however, is that the effect of the pening does not penetrate deeply; and if much of the pened surface is removed, the effects of the pening will be also removed. The work should not be rested upon metal, but upon wood.
Fig. 2142Fig. 2142.
Fig. 2142.
Fig. 2143Fig. 2143.
Fig. 2143.
The following are examples of pening.Fig. 2142represents a shaft bent as shown, the arms being too wide ata, which may be corrected by pening atb. If the error was in the arms themselves and not in the stem, the side faces of the arms would require to be pened. Thus inFig. 2143the distanceais too short, and the pening must be atb c.
Fig. 2144Fig. 2144.
Fig. 2144.
Fig. 2144represents a strap requiring to be closed acrossa, the pening being atcord. But as pening atdwould bend the crown and unpair the bed of the brasses, it is preferable to pene atc. In either case the jaws will close as denoted by the dotted lines.
Fig. 2145Fig. 2145.
Fig. 2145.
Fig. 2145represents another common form of connecting rod strap, and in this case the pening may be most quickly and effectively done at the crown as denoted by the dots; and as this would alter the inside curve, the brass or box fitting into it must be refitted. In case the pening should be overdone it is better to modify it by filing away some of the pened surface.