Fig. 2303Fig. 2303.
Fig. 2303.
The finishing marks, if any, should be in a line with the bore of the nut, which gives the neatest appearance. The process is the same for a bolt head, such as shown inFig. 2295, as for a single nut, with the exception that the gauge must be applied as inFig. 2303, when testing the truth of the flats with the axial line of the bolt, this being necessary because of the roundness of the end facea, inFig. 2303. The distancesdandcwill be equal when the flat is true in that direction.
A pair of outside calipers form an excellent example in vice work. The material should be good cast steel of an even thickness, and therefore (unless for very large ones) saw blade will answer the purpose. It should be well softened by being made to a low red heat and buried in fine cinder ashes or lime, and allowed to cool there; the proper width of this piece of steel being sufficiently greater than the size of the caliper washer, to allow room for a chisel cut and leave a little to file off in truing up the joint. The length should be somewhat more than that required to make the legs, because a piece will be required to be cut off the narrow end to give substance enough for the points. The size of the washer should be drawn at each end of the steel, the centre of the washer should be centrepunch-marked, and a line should then be drawn to set off the two legs. The steel is then severed along this line, thus getting out the two rough legs. When shears are not at hand, or when it is not designed to use them for this purpose, three methods of dividing may be pursued: First, we may drill small holes along the line, and cut between the holes with a chisel. The objection to this is that the blade is sometimes veryhard to drill. Secondly, we may make centrepunch marks along the line, and then cut along the line with a chisel; and thirdly, we may drill a few holes at each end, and cut the middle with the centrepunch and chisel. The entire drilling is the safest, and the centrepunching the most hazardous, but it can be accomplished if the centrepunching is done lightly and gone over several times, with the chisel applied between the centrepunch marks, which will be much the quickest plan of the three.
The hole is next drilled for the rivet, care being taken to make it about1⁄32inch smaller than the proper size, because the drill will not make a sufficiently true and parallel hole, and the latter must be reamed or trued out; and again because the legs have to go into the fire to be bent, and hence the holes may become damaged. There is another consideration, however, in determining the size to drill this hole, which is that the two legs require to be riveted together to bend them, and it is as well to drill the hole to suit the piece of metal intended to be used for this temporary rivet, which should be of brass or copper, so as to drive out easily after the bending is done. During the bending process the points should be thickened, care being taken not to twist them in the process. If the vice hand does the bending, the following instructions are pertinent: Heat the steel slowly and turn it over and over in the fire so that the points may not get burned before the wider parts are sufficiently heated. Let the fire be a clean one, that is, with no gaseous or blazing coal about it, or the coal will stick to the sides of the calipers, and they will get cool while being cleaned of adhering coal after being taken from the fire. Begin the bending from the thick end, carrying it forward by degrees. Strike light but rapidly succeeding blows, placing the steel upon the round point of the anvil.
The bending completed, and the points being thickened, the edges of the legs are trimmed upon an emery wheel or with a file, using the latter lengthwise of the edges if a new one, or crosswise if an old one. A full1⁄32inch may be left to trim off after the calipers are put together. The temporary rivet may next be driven out, first, however, gripping the legs firmly and near to the rivet end with a hand vice, putting a piece of sheet brass between each jaw of the hand vice and the steel; otherwise the teeth of the latter will mark the steel, entailing a great deal of extra labor to file the marks out. The rivet hole is then reamed out to the required size, the two legs being held together by the hand vice to render the reaming more steady and true by making the hole longer when the two are together.
The next operation is to turn the rivet and washers. It is a very common practice to turn two separate washers and a rivet. On account, however, of the small amount of bearing in the washer holes, such washers are apt to rivet up out of fair one with the other, making an unsightly joint and causing them to be out of round when the edges of the joint are filed up. A better plan is to turn a pin and washer, taking care to make the diameters of the two exactly equal and the flat faces of each quite level. The pin should be turned about1⁄64inch taper, the small end being made a neat fit to the holes in the caliper legs, and should be made of cast steel properly annealed. When finished, the head of the pin should be gripped by a pair of lead clamps in the vice, the end being left protruding so that the legs can be put upon it and revolved back and forth with a good supply of oil and under hard pressure, so that the pin will be forced a good and rather tight fit into the holes. This process will also smooth out the holes and condense the metal around both the holes and the pin. It is well to leave the pin to fit about one half as tight as the finished joint requires to be. The washer should be countersunk about three-quarters of the way through the hole, the latter being left a close working fit to the pin.
The legs should be rough filed, second-cut filed, and smooth filed before being draw-filed, care being used to keep the files clean, so as to avoid scratches. During this filing, however, the pin should be tried in the hole to see if the head comes fair down upon the face; thus the pin forms a guide and test in facing up the joint of the leg, and this is one of its advantages over the two-washer plan. After carefully draw-filing and polishing the sides of the legs the fitting of the joint is finished as follows: Place the two legs upon the pin in their proper position, and then put the washer into its place. Then behind the washer place another temporary one that will protrude beyond the end of the pin; then grip the whole tightly between a pair of lead clamps or pieces of thick leather in the vice; this will bring all parts of the joint home. Take hold of one leg in each hand and move them backward and forward as far as the vice will let them go, repeating the operation about a dozen times or more. This will mark the high spots upon the legs, which may then be taken apart again and have the bright parts removed by a scraper. It is also well to place the flat face of the washer upon a smooth file and rub it backward and forward under finger pressure, which will tend to correct any defect in its flatness. When the faces of the joint bear all over, it may be put together with oil and placed in the vice as before. Work it well back and forth, take it apart again and cut off the rivet to the required length, taking care very slightly to recess the end to assist the riveting. The whole joint should then be wiped quite clean, freely oiled, and put together ready to rivet. The head of the pin should be rested upon a block of lead, so that it will not get damaged. The riveting should be done with a small light ball-pened hammer, the blows being delivered very lightly and evenly all round the edge. As the riveting continues it is necessary to move the legs occasionally to see how the tightening proceeds, and when the legs are sufficiently tight, one of them may be gripped between pieces of leather in the vice, while the other is well worked and lubricated with oil. Then the riveted end should be filed off to very nearly its proper height and shape, and the joint well worked back and forth and round and round in the hand until it gets quite warm, when it may be cooled in water and tried for tightness. If too tight, it may be either worked until easy, or the riveted end of the pin may be tapped with a hammer to loosen it slightly. The riveting being completed, and the end filed smooth, the rounded part of the washer and the pin head should be draw-filed with a very fine file moved in varying directions, and then the polishing may be done with emery paper.
Fitting Keys.—Keys that have been planed or milled will still require fitting with the file to insure that they bed properly. If the key to be fitted is taper and intended to fit top and bottom, the sides should first be filed true to a surface plate, and fitted into the keyway in the shaft, so that it can be slid up and down a good working fit. While fitting it, however, it is well to try it once or twice in the keyway in the wheel, as well as in the shaft, so as to see by the marks whether the keyways in the shaft and wheel require any fitting at all, either to make them quite square with the outside face, supposing it to be turned off, or to give them a good even bearing surface. The key being fitted sideways we must give the two keyseats a coating of red marking just sufficient to show that the surface is of a red tint, and then put the wheel in its place on the shaft. Then we bevel off the edges of the key at each end, leaving a chamfer of1⁄16inch, and after facing off the top of the key with a bastard file, we place it in the keyway and tap it very lightly to a gentle bearing. After driving the key lightly home and taking it out again, we may file it on the top and bed it on the bottom, according to the indication of the marking, and re-insert it, tapping it up until it is home, top and bottom, without being a driven fit at all; on taking it out we file it according to the marks again, and if we continue this process until the key is a good fit, it will not spring the wheel the least out of true, no matter how tight, reasonably, it is finally driven. The key must never be driven in or out dry, for it will, in that case, inevitably cut during the first part of the operation; the marking put on the keyway is sufficient lubrication, but after two or three insertions the key also should be itself given a light coat, which will serve as lubrication, as well as denote the fit.
The bearing or contact marks upon a key driven home very lightly may show at one end or on one side only, while if the key was driven farther in those marks may show all over, making the key appear to fit much better than it actually does. This occurs from the elasticity and compression of the metal of the keyway and key, the metal giving most where the contact is hardest; from this it is apparent that a wheel truly bored and a good fit may be set out of true by the key.
Fig. 2304Fig. 2304.
Fig. 2304.
Fig. 2305Fig. 2305.
Fig. 2305.
InFig. 2304, for example, is a wheel hubw, assumed to be a good fit to the shafts, while the keykfits at the endaonly. Ifthe key be driven tightly home, the wheel will spring over, so that instead of the plane of its diameter standing at a right angle to the axial line of the shaft as atdinFig. 2305, it will stand at an angle as ate, throwing the wheel out of true in that direction. This would occur not only on account of the elasticity and compression of the metal of the keyway, but also because the surface of the bore of the wheel and of the shaft is not, even under the best of turning, smooth enough to come into close contact all over, but are covered with slight projections or protuberances, which may occur in spirals because of the turning tool marks, or in localities because of differences in the texture of the metal. In driving the key home these protuberances give way, and they do so most where the contact pressure is greatest, which would be atginFig. 2305, causing the wheel to cant over. If the wheel is not a good fit to the shaft it will not in this case touch the shaft atc,Fig. 2305.
Fig. 2306Fig. 2306.
Fig. 2306.
Now suppose the key to bear ataandb,Fig. 2306, only, then the wheel would be thrown out of true in a direction at a right angle to the length of the key as denoted by the linee, which should stand as atd.
A properly bedded key binds the opposite half of the circumference of the wheel bore to the corresponding half circumference of the shaft; but if the key binds at one end only, as inFig. 2304, the contact will be at the endhonly; hence the surfaces will soon compress, on account of all the strain of the key falling on a small area, and the key will get loose.
It is obvious then that if a wheel has not been bored to run true the error may be to some extent corrected in fitting the key, but in this case the key must be driven well home, and the wheel rim tried for running true during the fitting process, the key being so bedded as to true the wheel as far as the elasticity and compression will permit; but a key thus bedded will not hold so firmly.
The distance a key of a certain length, breadth, and thickness, and of a given taper, will drive after being pushed home by hand or lightly tapped in with a hand hammer depends upon how closely it fits to its seat, and upon the elasticity of the metal, as well as upon the force with which it is driven. The workman usually, while fitting the key, drives it well home occasionally, to see how much of its length to allow for the final driving, and while doing so, if the key is a small one, a hand set chisel or a piece of copper should be interposed between the key head and the hammer (a blacksmith’s set chisel is used for large keys) to prevent the hammer from damaging the key.
In fitting keys to old keyways the key is made too long, and cut off after being driven home. A long key is apt to bend in the driving, hence it is not unusual to support it by holding a second hammer beneath and against it to support it while being driven. In driving a key out, especially if it is fast home, a quick heavy blow is best, as it is less likely to burr, swell, or bulge the end of the key. But after the key has started lighter blows will answer.
To make a key for an old sunk keyway, it is as well to fit a piece of wood thereto as a guide in forging and fitting the key. If afastrunning grindstone or emery wheel is at hand, many will forge the key a trifle large and then grind it as near as possible, and finish by filing. This, however, does not produce good work; it is better to plane the key all over, leaving a little in size for fitting. In preparing the piece of wood referred to, it should not in the fitting be driven or even forced in and out to try the fit, for the wood will compress and the marks mislead as to the actual fit. The proper way is to chalk the piece of wood and push it up the keyway just tightly home, then withdraw and fit it again.
In cases where the key is forged to very nearly the finished size, and is finished by the file, as sometimes occurs when away from the shop, it is best to forge the key with a gib head, as inFig. 462, to assist in extracting it, especially when it is difficult to drive the key out from the back end, or when the keyway does not pass entirely through. The key should be finished with a smooth file and with the file marks lengthways; it is, in fact, better to use a small smooth file and draw-file it, taking care to ease the high spots the most; and before driving it home both it and the keyway should be oiled.
If a keyway is to be cut by hand through a bore, as in a pulley or gear-wheel bore, its width should be marked with aT-square. If its width does not exceed1⁄2inch a cape chisel a little less (say1⁄32inch less) than the finished width of keyway should be used, which will leave a little metal for the sides to be filed true. If the keyway be an inch wide it is better to take a cape chisel about1⁄4inch wide and cut a groove along each side of the keyway (keeping close to the marked line), and then cut out the middle with a flat chisel. The sides and bottom of the keyway should be surfaced true with the file.
If a keyway is to be cut in a shaft the cape chisel should be used in the same manner as above. But in both cases it is best, when filing, to occasionally ease out the corners with the edge of a half-round file, for reasons which will be explained presently.
In chipping a keyway in a bore the cut must not be carriedentirely through from one side, or the metal at the end of the cut will break out, and even in wrought iron this is apt to occur, so that it is necessary to cut the keyway from each end, or, at least, nick it in at one and cut it from the other end. In long key ways it is handiest to cut them half-way from each side, using, in the absence of anything better, a piece of planed wood and red marking or chalk to try the keyway with.
Fig. 2307Fig. 2307.
Fig. 2307.
In cutting out through keyways by hand the location of the keyway is marked off by lines on both sides of the stub end of the rod, and then the mass of the metal is removed by drilling through as many holes as can be got in the size of keyway required, as shown inFig. 2307, in whichwis the work,b c d ethe location of the keyway, and 1, 2, 3, 4 are the holes, taking care to have the drill rather smaller than the width of requisite keyway. The holes are drilled half-way through from each side, which is done to keep the keyway true; for if the drills were to run a little to one side, as they are apt to do from a variety of causes, a great deal of work would be required to correct the error.
If the keyway is of sufficient dimensions to admit of the use of a chisel, the pieces left between the drilled holes are chipped out, and for this purpose a side chisel is found very useful, not only to nick the sides of the pieces left by the drilling, but also to take the finishing chipping cuts on the sides of the keyway. To cut out the square corners of the keyway, the diamond-point chisel shown inFig. 2171is employed.
Fig. 2308Fig. 2308.
Fig. 2308.
If, however, the keyway is a very deep one, requiring long and slight chisels, the chipping process may be greatly reduced, or in fact entirely dispensed with, by plugging up the holes first drilled in the stub end by driving pieces of round iron tightly into them, and then drilling new holes, having their centres midway between the pieces so driven in, as atainFig. 2308. After the latter drilling, the remaining pieces of plugs are driven out, leaving the centre of the keyway cut clear through and the sides with a series of flutes in them, as shown atb,Fig. 2308(in which1 2are the plugs andais a centre for the new hole at that end), which should be filed away with a file as thick or strong as the clear space will allow. These plugs must be of the same metal as that in which the keyway is cut, otherwise the drill will be apt to run to one side.
To insure truth in the surfaces, a surface plate to test with is an absolute necessity, while to test the parallelism, a small sheet iron gauge is used, which gauge may afterwards be employed as a guide whereby to plane the thickness of the gib and key.
In cases where a slotting machine is at hand, it is sometimes the practice to cut out one end of the keyway to a sufficient length to admit a slotting tool, and then to slot out the remainder. This plan is often resorted to in getting out keyways of unusually large dimensions.
A much more usual method, however, is to employ slotting or keyway drills.
It is obvious that the ends of the keyways cut by drills are half round; hence, if square corners are required, they must be cut out square with the chisel shown inFig. 2176, and afterwards filed out true. As a general rule, keyways cut with these drills require filing on the sides to get proper smoothness and bearing for the keys; and here it may be remarked that, in filing the corners of the keyway, a safe-edge file must be used, so that the two faces forming the corner will not be operated upon simultaneously, because that would require that the file be used in a straight line laterally as well as horizontally, and this is impracticable even in the hands of the most skilful.
Even the square file should have a safe edge upon it, and such an edge is usually produced by grinding the teeth off one face of the file. In selecting the face to have the teeth ground off, choose a face that is hollow in its length, or, if none of the faces is hollow, then select a face that is at a right angle to a good face of the file. It will be noted that with one safe edge only the square file will require turning over in order to operate upon both corners and maintain in each case a safe edge of the file against the flat sides of the keyway. For this reason many workmen select the two best parallel faces of the file and grind off the two other faces, giving to the file two safe edges, one opposite to the other. In this case either of the cutting faces of the file may be used upon the whole end face of the keyway operating close up to the corner, or if the file is much narrower than the keyway it may be used with a side sweep that will prevent the file from pinning, and produce much truer filing.
It is useless to attempt to cut out a square corner with a square file unless one edge of the latter is ground safe, because the teeth of the file itself do not form a square corner, and it is therefore only by grinding the teeth off one side that the points of the file teeth can be brought full up to a sharp angle. Here, however, it may be noted that even if the filing is performed with the best of safe-edge files, and as carefully as possible, it will still be necessary to square out the fine corners with the edge of a fine smooth half-round file.
If the edges of the keyways are rounding, as they are sometimes made where strength is required in the strap, it is better to take a file nearly or about1⁄8inch larger in diameter than the width of the keyway, and grind two safe edges on it, otherwise the round file is very apt to go astray and cut the sides as well as the edge of the keyway.
An equaling file is much better for keyways than one actually parallel.
Fig. 2309Fig. 2309.
Fig. 2309.
Another way employed to finish small keyways is by the aid of the tools shown inFigs. 2309and2310, which are termed drifts, because they are driven through with a hand hammer. That shown inFig. 2309is intended for holes having but little depth and not requiring to be very true, such, for instance, as those cut in the ends of keyways or bolts to receive cotters; the thickness ata ais made greater than atb cto give the cutting edge clearance.
Fig. 2310Fig. 2310.
Fig. 2310.
The form shown inFig. 2309is for use by hand, the teeth being cut diagonally instead of across, as ata a, to preserve the strength.This end may also be attained by making the serrations round at the bottom, as shown in the figure.
The slant of the teeth on one side of the drift should cross the slant of the teeth on the diametrally opposite side, because if the teeth on opposite sides were parallel one to the other the drift would have a tendency to move over to one side, and crowd there during the process of drifting.
In using these drifts the keyway should first be filed out to very nearly the finished size, leaving very little duty for the drift to perform, although the drift may be driven a short distance into the keyway occasionally during the filing, so as to show where filing is requisite. The work must lie flat and level upon a metal block, lead being preferable, and oil freely supplied to the drift. “If the hole is a deep one, and the cuttings clog in the teeth, or if the cut becomes too great (which may be detected by the drift making but little progress, or by the blows sounding solid) the drift must be driven out again, the cuttings removed, and the surplus metal, if any, removed by filing. The drift must again be freely oiled, and driven in as before, and the operation continued until the drift is driven through the keyway. After the drift has passed once through it should be reversed (or, if a square one, turned a quarter revolution) and again driven through, so that each side of the drift will have cut on each side of the hole, which is done to correct any variation in the size of the drift” (“Complete Practical Machinist”).
The great desideratum in using these drifts is to drive them true, and to strike fair blows, otherwise they will break. While the drift is first used, it should be examined for straightness at almost every blow; and if it requires drawing to one side, it should be done by altering the direction in which the hammer travels, and not by tilting the hammer face.
Fig. 2311Fig. 2311.
Fig. 2311.
InFig. 2311, supposeato be a piece of wood andbandcdrifts which have entered the keyways out of plumb, as shown by the dotted linesdande. If, to right the driftc, it was struck by the hammerfin the position shown, and travelling in the direction denoted byg, the driftcwould be almost sure to break; but if the driftbwas struck by the hammerh, as shown, and travelling in the direction denoted byi, it would draw the driftbupright without breaking; or, in other words, the hammer face should always strike the head of the drift level and true with it, the drawing of the drift, if any is required, being done by the direction in which the hammer travels. When it is desired to cut a very smooth hole, two or more drifts should be used, each successive one being a trifle larger in diameter than its predecessor. Drifts slight in cross-section or slight in proportion to their lengths would be tempered evenly all over to a blue, while those of stout proportions would be tempered to a deep brown, bordering upon a bright purple.
For cutting out long narrow keyways, that are too narrow to admit of a machine cutting tool, and for very true holes, not to be cut out in quantities all of the same dimensions, it has no equal.
Fig. 2312Fig. 2312.
Fig. 2312.
Hand drifts are sometimes used to cut keyways in small bores, as in small hubs, the method being shown inFig. 2312, in whicharepresents a pulley with a keyway to be cut in the hubb;cis a plug, anddslips of iron placed betweencand the drifteto press the latter to its cut. It is obvious that in this case the keyway in the pulley will be cut parallel, and the taper must be provided for in the key seat in the shaft. Keyways cut in this way are more true than those filed out. It is also obvious that the sides of the keyway, as well as its depth, may be finished by a drift, and this is very desirable (on account of insuring parallelism) when the key is to act as a feather that is to have contact on the sides and not bind top and bottom.
The most improved form and method of using this class of tool, however, is as follows:—If a keyway is to be cut out of solid metal, holes are drilled as closely together as the length of the keyway will admit, their diameter nearly equaling the required width of keyway, after these holes are drilled through the metal remaining between them.
Templates.—Templates for vice work are used for two purposes: first to serve as guides in filing work to shape and size, and secondly to test the finished work. When used as guides to file the work they are mainly used to work of irregular, curved, or angular form, to which the square and other ordinary vice tools cannot be applied.
Fig. 2313Fig. 2313.
Fig. 2313.
Fig. 2313represents a template for filing out a square hole. The edgesa,bare at a right angle to each other, the wire simply serving as a handle.
There are two methods of applying this template; the first is to file out two opposite surfaces of the hole to the required diameter, making them true and parallel one to the other, and to then employ the template while filing out the remaining two sides; theother is to file out one side and apply the template from that as a base for the other sides. The first is preferable because the liability to error is a minimum.
When work is to be from a template, the latter obviously becomes the original standard, and in many cases the best method of forming it so as to insure correctness and enable its proper application to the work is a matter of great consideration. The shape of the template must, of course, be marked by lines which should be as fine and as deep as possible. But it does not matter how closely the template may be filed to these lines, it will still have some error, and this can in many cases be discovered and corrected during its application to the work. In the following examples there are principles which will be found of generalapplication:—
Fig. 2314Fig. 2314.
Fig. 2314.
Fig. 2315Fig. 2315.
Fig. 2315.
Fig. 2316Fig. 2316.
Fig. 2316.
Fig. 2317Fig. 2317.
Fig. 2317.
Let it be required to make or test a piece of work such as inFig. 2314, the teeth to be equally spaced, of the same angle, and of equal height. A template must be made of one of the two forms shown inFig. 2315. To begin with, take a piece of sheet metal equal in width to at least two teeth, and, assuming that the template is to have two teeth, file its sidesp q, inFig. 2316, parallel, and make the width equal to twice the pitch of the teeth. We next divide its width into four equal parts by lines, and mark the height, as shown inFig. 2316. If we desire to make the template such as ata, we cut out the shaded portion; or for the template atb, the shaded portion. It will be observed, however, that in templateathere are two cornerscanddto be filed out, while atbthere is but onee, the latter being the easier to make, since the corners are the most difficult to file and keep true. The best method of producing such a corner is to grind the teeth off the convex side and at the edge of a half-round file, producing a sharper corner than the teeth possess, while giving at the same time a safe edge on the rounded side that will not cut one angle while the other is being filed. But when we come to apply these templates to the work, we shall find thatais the better of the two, because we can apply the squares,Fig. 2317, to the outside of the template, and also to the edgefof the work, which cannot be done to the edgesgof the work andhof the template, because the template edge overhangs. We can, however, apply a squares′to the other edge ofb, but this is not so convenient unless the tops of the teeth are level.
Fig. 2318Fig. 2318.
Fig. 2318.
Fig. 2319Fig. 2319.
Fig. 2319.
Assuming, therefore, that the templateais the one to be made, we proceed to test its accuracy, bearing in mind that for this purpose the same method is to be employed whatever shape the template may be. Consequently, we make from the male templatea,Fig. 2318, a female templatek, beginning at one end ofkand filing it to fitauntil the edges ofaandkare in line when tested by a straight-edges. We then move the templateaone tooth to the right, and file another tooth ink, and proceed in this way until a number of teeth have been made, applying a square as ats,Fig. 2319, to see that the templateais kept upright uponk. Whenkhas been thus provided with several teeth that would fitain any position in which the latter may be placed, we must turn templateaaround uponkto test the equality of the angles. Thus, suppose at the first filing the edgesa,b,c,d, uponaaccurately fit the templatek, and the straight-edge shows the edges fair; then if we simply turn the templateaaround, its angles, which were before on the right, will now be on the left, as is shown at the right ofFig. 2318.Thus in one positionafits toe, in the other it fits toh, orbfits tof, and when turned around it fits tog, and so on. Supposing that when thus turned around the angles do not coincide, then half the error will be in the teeth ofaand one-half in those ofk, and the best plan will be to correct them onato the necessary amount as near as judgment will dictate, and then to applykas before, continuing this process untilawill fit anywhere ink, and may be turned around without showing any error. But at each correction the straight-edge must be applied, and finally should be tried to prove if the teeth tops are level. We thus have two interchangeable templates, of whichamay be used on the work andkkept to correctawhen the latter becomes worn. It may be as well to add, however, that in first applyingatokit is best to press the straight-edgesagainst the edge ofk, and hold it there, and then to placeaagainsts, and slide it down intok.
Fig. 2320Fig. 2320.
Fig. 2320.
Fig. 2321Fig. 2321.
Fig. 2321.
Fig. 2320represents an example in which, the form being a curve, it would be best to have the template touch more than two teeth, as shown in the cut. By letting the sidea,Fig. 2321, of the templatetterminate at the centre line of the two curves, and the endbterminate at the top of a curve, turning the template around would cause endato envelop sidecof the middle curve, thus increasing the scope of the template. Suppose, however, that the base curvedrequired to be true with the teeth, then a second templatet′must be used, its ends ateandfmeasuring an equal length or height, so that when they are placed even with the ends of the work, the distancesg hbeing equal, the corrugations will be true to the curved d. Now let it be supposed that, instead of making a template to test a piece of work such as inFig. 2321, it is required to make a template for use in making another piece of work that is to fit to piecew, then templatetinFig. 2321will not answer, because it is a female template, whereas a male one is required, so that the edge of the template may coincide with that of the work. But we may convertt,Fig. 2321, into amale templateby simply cutting off the edgeaas far as the linej, and causing its right-hand edge to coincide with the edge of the work so that the latter, after being fitted to the template, may be turned upside down and fit upon the piece of work.
Fig. 2322Fig. 2322.
Fig. 2322.
Fig. 2323Fig. 2323.
Fig. 2323.
Fig. 2324Fig. 2324.
Fig. 2324.
InFig. 2323is an example in which the forms of both sides of a piece require to be exactly alike, and the easiest method of accomplishing this is as follows:—The faceashould first be made true, and facebmade parallel toa. A centre linecmay then be drawn, and from it the linese,emay be marked. The linesdare then drawn parallel toa a, linesebeing made square todand toa. The sidesemay be calipered to width and parallelism, and all that will then remain is to file the anglesf,fand the endsg,gto their required lengths. Forf,fall that is necessary is a template formed as inFig. 2324. The object of dressing the endsg,glast is that if they were finished before, their facesewould have to be made at exactly correct distances from them, which would render the job considerably more difficult.
Fig. 2325Fig. 2325.
Fig. 2325.
Fig. 2326Fig. 2326.
Fig. 2326.
Fig. 2325represents a sketch for a piece of work whose two sides are to be shaped exactly alike, requiring a template of the form of the work, as shown. From this a second template,Fig. 2326, is made, and to this latter the work may be filed. To make the template inFig. 2325, which represents the work, the edgex xmust be made straight, and the edgedparallel to it at the proper height. A centre linesis then marked, and the edges atemay be filed equidistant fromsand square tod; hence they will be parallel to each other. The side sectionsfshould then be filed equidistant fromsand parallel to each other. They should be the proper width apart and square tod, being tested in each of theserespects. The line joiningeandfshould be left full, as denoted by the dotted line ataon the right. The edges atc,cshould then be filed, calipering them from the edgex x. Edgesg,gare obviously equidistant fromsand parallel tos, or, what is the same thing, at a right angle tox x, from which they may therefore be tested with a square, and, finally, the edgesbare made parallel tox x, and the endshmade square toxand equidistant froms. We have now to file the angular groove ata, and to get this true after marking its depth from the lines ata, we file it first to the lines as near as may be by the eye and very nearly to the full depth. We then make a small supplemental male templatet,Fig. 2327, equal in width to the distancee f, or, in other words, to the width of the step ata, and having its edges quite parallel. Its end is then filed to fit the groove ata, when its edge meets and coincides with edgee, as inFig. 2327,trepresenting the supplemental template. It is clear that when theV-grooveais so filed thattwill fit it with either of its edges againste, the angles of the groove will be alike, and we may then make a male gauge, as inFig. 2326, that may be used to mark or line out the work and to use as a template to file it to, its edgehbeing kept parallel to faced,Fig. 2325, of the work.