The concave saw shown in Fig. 3080, is employed for barrel heads. The three pieces for a barrel head are clamped together and fed in a circular path, so that the saw cuts out the head at the same time that it bevels the edge.
The advantage of the circular saw lies mainly in the rapidity of its action, whether used for ripping or cross-cutting purposes. In order, however, that it may perform a maximum of duty, it is necessary that the teeth be of the proper shape for the work, that they have the proper amount of set, that they be kept sharp, and that the tension of the saw is uniform throughout when running at its working speed.
The centrifugal force created by the great speed of a circular saw is found to be sufficient to cause it to stretch and expand in diameter. This causes the saw to run unsteadily unless it is hammered in such a way as to have it rim bound when at rest, leaving the stretching caused by the centrifugal force to expand the saw and make its tension equal throughout. The saw obviously stretches least at the eye, and the most at its circumference, because the velocity of the circumference is the greatest, and the amount of stretch from the centrifugal force is therefore the greatest.
It is obvious that the amount of centrifugal force created will depend upon the speed of the saw, and it therefore follows that the hammering must be regulated to suit the speed at which the saw is to run when doing cutting duty, and in this the saw hammerer is guided solely by experience.
A circular saw may have its tension altered and impaired from several causes as follows:
1. From the saw becoming heated, which may occur from the arbor running hot in its bearings, or from the work not being fed in proper line with the saw.
2. From the reduction in diameter of the saw by frequent resharpening of the saw, this reduction diminishing the amount of centrifugal force generated by the saw, and therefore acting to cause the saw to become loose at the eye.
3. From the saw teeth being allowed to get too dull before being sharpened, which may cause the saw teeth to heat, and thus destroy the tension.
4. From stiffening the plate at the throats of the teeth when gumming the saw, an effect that is aggravated by using a dull punch.
5. From the saw teeth having insufficient set, and thus causing the saw to heat.
The methods of discovering the errors of tension in a saw, and the process of hammering to correct them, have already been explained with reference to the use of the hammer on pages from 68 to 70 of volume 2 of this work.
Before hanging a saw on a mandrel, it is necessary to know that the mandrel itself runs true in its bearings or boxes. In a new machine this may be assumed to be the case, but it is better to know that it is so, because if the mandrel does not run true several very improper conditions are set up. First, the saw will run out of true circumferentially, and therefore out of balance, and the high side of the saw will be called upon to do more cutting duty than the low side. Second, the centrifugal force will be greatest on the high side, and the saw will be stiffer, thus setting up an unequal degree of tension. Third, the saw will run out of true sideways, cutting a wider kerf than it should, thus wasting timber while requiring more power to drive.
The collar on the saw arbor should be slightly hollow, so that the saw will be gripped around the outer edge of the collar, and the arbor or mandrel should be level so that the saw will stand plumb. The boxes or bearings of the arbor should be an easy working fit to the journals, and there should be little, or what is better, no end play of the arbor in its bearings.
If a saw arbor becomes heated enough to impair the tension of the saw, it has been hot enough to impair its own truth, and should be examined and trued if necessary.
The most important point in this respect is that the face of the collar against which the saw is clamped should run true, bearing in mind that if it is one hundredth of an inch out of true in a diameter of, say 3 inches, it becomes twenty hundredths or one-fifth of an inch at the circumference of a saw that is 60 inches in diameter.
In cases of necessity, a saw that wabbles from the collar face of the mandrel running out of true, may be set true by means of the insertion of pieces of paper placed between the saw and the face of the collar.
The first thing to do in testing the saw is to take up the end motion of the saw arbor, or if this cannot be done, then a pointed piece of iron or wood should be pressed on the end of the mandrel so as to keep it from moving endways while the saw is being tested.
The saw should be revolved slowly, and a piece of chalk held in the cleft of a piece of wood should be slowly advanced until it meets some part of the face of the saw just below the bottom of the saw teeth.
As soon as the chalk has touched and the saw has made one or two revolutions the chalk should be moved a trifle farther on from the teeth, and another mark made, and then moved on again, and so on, care being taken to notice how much space there is between the high and low sides of the saw. It will be found, however, that the shorter the chalk marks are the more the saw is out of true.
A more correct method is to chalk the face of the saw and use a pointed piece of iron wire of about one-quarter inch in diameter, but in any case the saw should only be touched lightly.
The pieces of paper should be portions of rings or segments, and should extend an equal distance below the circumference of the collar, because the same thickness of paper will alter the saw more in proportion, as it is inserted farther in toward the eye of the saw.
If it should happen that two thicknesses of paper are necessary to true the saw, one should be made about half the length of the other, and the long one may extend farther in toward the eye of the saw. Thus one ring of paper may be an inch deep and the other one-half inch deep.
If but one piece of thin paper is needed, it may be simply a straight piece inserted half way down the collar and trimmed off level with the collar. In placing the paper, the middle of its length should be on that side of the saw that is diametrically opposite to the marks left by the chalk on the face of the saw.
When the saw is trued and is started it will be loose on the outside, but as its speed increases it should stiffen up so as to run true and steadily when running at its working speed.
If the saw is to be tried by actual work, it must be borne in mind that the tension of the saw must be right for its speed when in actual use, and not when running idle. If the machine has belt power enough to maintain the same speed whether the saw is cutting at its usual rate of feed, or whether it is running idle, the tension will not be altered by putting on the feed, but if the saw has been hammered to run at the full speed of the machine when not cutting and the feed is heavy enough to slacken the speed, then the tension of the saw will not be correct for its working speed.
The eyes of small saws are either made to fit the mandrel an easy sliding fit, or else the mandrel is provided with cones to accommodate various sizes of holes, an ordinary construction being shown in Fig. 3081, in which a is the saw arbor, fast on which is the collar b, s representing a section of the saw, w a washer or loose collar, and n the nut for tightening up w. The cone c is screwed upon a and passed through the saw until it just fills the hole, and thus holds the saw true.
In putting on the saw, it should be passed up to the collar, and c screwed home until it binds in the saw eye with enough force to bring the threads of c fairly in contact with those on the mandrel a, but if screwed home too tightly it may spring the saw, especially if the saw is a very thin one.
As c must be removed from the arbor or mandrel every time the saw is changed, the wear on its thread is great, and in time it becomes loose, which impairs its accuracy.
This objection is overcome in the construction shown in Fig. 3082, which is that employed by the S. A. Woods Machine Company. It is seen in the figure that the cone c fits externally in a recess in the collar b, and at the coned end also upon the plain part e of the arbor. The cone is hollow and receives a spiral spring s, s. When the saw is put on it first meets c, and as nut n is screwed up, the saw s and cone are forced along arbor e until the saw meets the face of b, and the clamping takes place. The strength of the spring s is sufficient to hold the saw true, and as the motion of cone c is in this case but a very little, therefore its wear is but little, which makes this a durable and handy device, while the saw cannot be sprung from over-pressure of the cone. Circular saws of large diameter, as from 40 inches upwards, are made a fair sliding fit upon their arbors or mandrels, and are provided with two diametrically opposite pins that are fast in the arbor collar.
The pins should be on diametrically opposite sides of the arbor, and an easy sliding fit to the holes in the saw, but they should not bind tight. Both pins should bear against the holes in the saw, and if both the pins and the holes in the saw are properly located, the saw will pass up to the collar with either side against the arbor collar, or in other words, the saw may be turned around upon the arbor.
If the pins, or either of them, bind in the holes of the saw, and the latter is forced on the arbor, it will spring the saw out of true, and when this is the case care should be taken in making the correction to discover whether it is the pins or the holes in the saw that are wrongly located. If it is the pins, the error will show the same whichever side of the saw is placed next to the arbor collar, while if the error is in the holes, the error will show differently when the saw is reversed on the arbor.
When a saw becomes worn, and its teeth require sharpening, the first thing to do is to joint it, that is to say, bring down all its teeth to the same height, which may be done by holding an emery block or file against it while the saw is running, care being taken to hold the block or file firmly, and to continue the process until the tops of the teeth run true.
The next operation is to gum and sharpen the teeth. Gumming a saw is cutting out the throats, or gullets between the teeth, so as to maintain the height of the tooth, and it follows that on saws that have sharp gullets (or in other words, saws in which the back of one tooth and the face of the next tooth join in a sharp corner), the sharpening process with the file may be made to also perform the gumming.
In the case of teeth of coarse pitch, however, this would entail too much labor in filing, and furthermore, as the height of the teeth increases with the pitch or distance apart of the teeth of circular saws, and as the higher the tooth the weaker it is, therefore coarse pitched teeth are given round gullets so as to strengthen them as much as possible. The gumming of a saw should always be performed before the sharpening, and the sharpening before the setting.
When the sharpening is to be done with the file, the cutting strokes of the file should be in the same direction as the teeth lean for the set, as this leaves a sharper cutting edge, and it follows that the proper plan is to file every other tooth first, going all around the saw, and to then turn the saw around in the vise, and file the remaining teeth.
The height of the teeth and the diameter of the saw will be best maintained by filing the front face of the tooth to bring it up to an edge, but in filing the front face the spacing of the teeth should be kept as even as possible.
If the front face has been filed until a tooth is as widely spaced as those already filed, and the edge is not brought up sharp, then the edge may be brought up by filing the back of the tooth.
A saw gumming, gulleting or chambering machine to be operated by hand, and constructed by Henry Disston & Sons, is illustrated in Fig. 3083. It consists of a frame spanning the saw, and having screws b b, b b, to adjust to the saw thickness; 4 and 5 are two saw teeth, and 6 the cutter, k is a wheel for the feed screw g, and c and d gauges for regulating position and depth of the gulleting.
The cutter 6 is driven or revolved by means of the handles h h, but an important point in the construction is, that a pawl and ratchet wheel is used to drive the cutter, so that if the handles h h were revolved in the wrong direction, the cutter would not be revolved. This saves the cutter teeth from breakage. The machine is operated as follows:
Run the cutter back by means of screw g as far as necessary, then place the machine on the saw, with the cutter close up in the chamber of the tooth to be gummed.
If the teeth are regular and the same distance apart, start the cutter in any chamber; but if they are irregular, make them even by commencing in the smallest space. After gumming the saw a few times the teeth must become regular. f is a set-screw to regulate the depth of gullet. Fasten the machine to the saw by means of the screws b b, and proceed to gum the first tooth, one of the points of the star being struck at each revolution by a projection on the handle, steadily feeding the cutter until arrested by set-screw f. Remove the machine to the next tooth towards you, after having run the cutter back, and proceed as before until the whole of the teeth are gummed.
The cutter is so arranged as to slide on its axis, and when one portion becomes dull, remove a washer from back to front, and thus present a new sharp cutting surface; and so continue changing the washers until the whole face of the cutter becomes dull.
Set is given to saw teeth in two ways: first, by what is called spring set, which is applied to thin saws and to cross-cut saws; and second, swage set, which is given to thick saws and to inserted teeth. Spring set consists of bending the teeth sideways so as to cause the saw to cut a passageway or kerf, as it is termed, wide enough to permit the saw to pass through the timber without rubbing on its sides.
Swage set consists of upsetting the point of the tooth with a swage, thus spreading it out equally on both sides of the body of the saw plate, as shown at a, Fig. 3084.
The set of the teeth, whether given by swaging or upsetting, or by spring set, should be equal throughout the saw, so that each tooth may have its proper share, and no more, of duty to perform.
If spring set is employed, it should not extend down more than half the depth of the teeth, and this point is one of considerable importance for the following reasons. The harder the saw is left in the tempering the easier the teeth will break, but the longer they will keep sharp. Now a tooth that is hard enough to break if it is attempted to carry the set down to the root or bottom, will set safely if the set is given to it for one-half its depth only.
If a saw is to be sharpened by filing, it should be made as hard as it can be to file properly, even at the expense of rapidly wearing out the file, because the difference in the amount of work the saw will do without getting dull enough to require resharpening is far more than enough to pay the extra cost of files.
Circular saws with inserted teeth are made of thicker plate than solid saws of corresponding diameters, which is necessary in order that they may securely hold the teeth. The principal difference in the various forms of inserted teeth lies in the method of locking or securing the teeth in the saw.
Figs. 3084 and 3085 represent the chisel tooth saws of r. Hoe and Company. The No. 2 tooth is that used on gang edging machines and for bench work. No. 3 tooth is that used in miscellaneous sawing, for hard woods and for frozen lumber. No. 4 is the shape used in the soft and pitchy woods of southern and tropical countries.
The method of inserting the teeth is shown in Fig. 3084 on the left, the pin wrench being shown in position to move the socket whose projection at c carries the tooth d home to its seat and locks it there.
The sockets for the numbers 3 and 4 tooth are, it is seen, provided with a split, which gives to them a certain amount of elasticity that prevents the sockets from getting loose.
Swing-frame saws are made in various forms, generally for cross-cutting purposes or cutting pieces to length.
Fig. 3086 represents a swing-frame saw that is mounted over a work bench, and can therefore be used without necessitating carrying the work from the bench. It consists essentially of a frame pivoted at the upper end to the pulley shaft and carrying below a circular saw driven by belt over pulleys on the upper shaft and the saw arbor. In this machine the iron hubs carrying the frame have sockets fitting over the outer diameter of the hanger hubs, so that the frame hangs upon those hubs and not upon the pulley shaft. The advantage of this plan is that the frame joint is relieved of the wear which would ensue were it hung upon the revolving spindle, while at the same time the movement of the joint is so small as to induce a minimum of abrasion. To counterbalance the frame while it is placed out of the perpendicular, there is provided a compensating weight as shown in the engraving.
Fig. 3087 represents an example of that class of cutting-off saw bench in which the length of the work is determined by the width apart of the saws.
This machine is constructed by Trevor and Company, and is designed for cutting barrel staves to exact and uniform lengths.
The stave is laid upon the bars of the upright swing-frame (which is pivoted at its lower end), and the latter is vibrated by hand, which may obviously be done both easily and quickly on account of the lightness of the swing-frame and its vertical position. A dimension sawing machine, by G. Richards and Company, is shown in Fig. 3088. This machine is designed for general fine work, such as pattern making, and its general features are as follows:
It carries two saws (a cross-cut and a rip-saw), mounted on a frame that can be quickly revolved by a worm and worm wheel to bring either saw into position as may be required.
There is a fixed table and adjustable fence on one side of the saw, and a movable table and fence on the other.
| VOL II. | DIMENSION SAWING MACHINE. | PLATE XVIII. |
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Large image (100 kB). Fig. 3089 |
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| Fig. 3089. | ||
The saws are ground thin at the centre, as shown in Fig. 3089, so that but little or no set need be given to the saw teeth; hence the cutting edges of the teeth are more substantial and true, and as a result the work is cut very smoothly, and if the machine is kept in thoroughly good order, the sandpaper may follow the saw.
In Fig. 3088, a is a substantial box frame, to which is bolted the fixed table t. t′ is the movable table which runs on rollers, and is guided by the ∧ slideway at e. This table the workman pushes to and fro by hand, the work being adjusted upon the table or to the fence, as the case may be. At w is the wheel for swinging the frame to bring the required saw into position.
In Fig. 3089 the worm gear for swinging the saws into position is shown, and also a sectional view of one saw arbor and of the movable table. a is the main frame, and f the disc frame carrying the two saw arbors. The disc d is turned to fit a seating formed in the base, while the other end of the disc frame fits through a substantial bearing b; w′ is the worm wheel, and w′′ the worm for swinging the disc frame. The worm teeth fit closely to the worm wheel teeth, and backlash or play is prevented by means of the spring bearing shown at d, the spiral springs forcing the worm teeth into the worm wheel teeth. Thus a is the bearing for the worm carried in the box c, upon which is the spiral spring whose tension is regulated by the screw g.
The end of the worm is therefore held in a swivel joint that causes it to operate very easily.
Fence f, Fig. 3088 is for slitting, and is made to swing back for bevel cutting, while f′ is for cross cutting, and is adjustable for angle cutting. Fence f is fitted to a plate p, Fig. 3090, which rests on the table top, and also rests on the long slide g. This slide fits in a beveled way h, and contains a ⊥ groove. A tongue likewise beveled fits in the top of this groove, the tongue being permanently fast to the fence plate. The ⊥ bolt passes through the tongue and fence plate, having at its upper end a milled or knurled thumb wheel r, which when tightened up fastens the fence plate and the slide together.
Upon slacking the thumb wheel r, the fence plate and ⊥ bolt may be readily shifted, setting the fence as near to gauge as possible by hand, and the thumb wheel is then tightened, and the slide (which carries the fence bodily with it) is adjusted by means of the hand wheel h and its screw which threads into a lug from the table.
The fence f is pivoted to plate p at p, and the angling link which holds it in position is secured by a hand nut m.
The front journal of the saw arbor has a double cone, and by means of the nuts n n′, Fig. 3089, can be regulated for fit independently of the back bearing and journal, the latter being also coned and capable of independent adjustment by means of the adjustment nuts m m′.
The countershaft for driving the saw arbors is below the machine, so that the saw that is not in use remains stationary.
Examples of the work done on this machine are shown in Fig. 3091, the various sections shown being produced by the vertical movement of the saw through the table and the cross movement of the fence. For example, for cutting out a core box, such as shown at 6, small grooves are cut through to remove the bulk of the wood, and the saw marks at the bottom of each saw cut serve as gauge lines for the workman in finishing the circular bore with the gouge, etc.
An example in which the table is fixed to the frame and the saw is adjusted for height above the table is shown in Fig. 3092. The saw arbor is here carried in a frame that is pivoted at one end to the main frame, while at the other end is a handle through which passes a locking screw for securing that end of the saw arbor frame to the arc slot shown on the main frame.
In a more expensive form of this machine an adjusting screw is used for regulating the height of the saw, and an iron table is employed instead of a wooden one.
A double saw machine constructed by P. Pryibil is shown in Fig. 3093. In this machine each saw is carried in separate frames, that are pivoted at one end to the main frame and secured at the other to segments, so that either saw may be elevated to the required distance above the work table.
One saw is for ripping and the other for cross cutting, and the arbor of the latter is provided with an adjusting screw operated by the hand wheel shown on the right hand of the machine.
As the saws are on independent arbors, they can be speeded differently to suit different saw diameters, which is an advantage because, as machines of this class are for the lighter classes of work, the ripping saw will rarely be required for work of more than about 3 or 4 inches thick, and a rip saw of large diameter is not therefore necessary.
The cross cut saw however requires to be of larger diameter, as its work includes cross cutting up to 8 or 10 inches diameter, and the saw being larger does not require so high a speed of revolution.
Both saws are provided with ripping gauges and with right and left hand mitre fences, adapted to the application of either short or long work, and provided with length gauges.
Fig. 3094 illustrates the various gauges in place upon the table of a machine. The table is provided with a slideway, or slot, on each side of the saw, and parallel with it, and also with a slideway at one side of the table. In the figure, the mitre gauge, or gauge for sawing at an angle, is shown in two positions.
The gauge a a a is for cutting work to length, and for cropping the ends at the same time, an extension frame being used, as shown for unusually long work.
Fig. 3095 illustrates the method of employment of the mitre gauge. The pointer is set to the degree of angle the work is to be cut to, and is fastened to its adjusted position by the set screw h. The stop is set to the required length, and the work is held by hand against the face of the gauge, and at the same time endways against the stop, and the gauge is then moved along the slot, feeding the work to the saw. When the work is sawn and is to be withdrawn, care must be taken to keep the work fair, both against the gauge and against the stop.
Figs. 3096 and 3097 show the application of the gauges for cropping off the ends of work and cutting it to exact length. There are two stops, s and t, each of which is secured in position by a set screw, and has a tongue that may be thrown over, as occasion may require—thus, suppose it is desired to merely crop off the end of the work—and both stops may be set for the work to rest against as in Fig. 3096, and the end of the work may be cut off or cropped to square it or remove a defective part. Stop s may then be thrown over as in Fig. 3097, and the squared or cropped end of the work rested against stop t, to gauge the length to which the work will be cut. This is a simple and convenient method of cropping and gauging.
Fig. 3098 represents a circular saw machine, constructed by the Egan Company, in which the table is carried on a vertical slide, and may be raised or lowered by means of the hand-wheel, bevel gears, and screw shown, and may be set at any required angle to the saw for cutting bevels.
The saw arbor or mandrel is carried by the main frame, and is therefore rigidly held.
The fences can be used on either side of the saw, which is very convenient when the table sets out of the level.
In this machine, which is shown in Figs. 3099, 3100, and 3101, the construction permits of the saw being set so as to revolve at other than a right angle to the work table, which is rigidly secured to the frame of the machine.
Fig. 3099 is a general view, while Figs. 3100 and 3101, are sectional views of the machine.
This machine is constructed by J. S. Graham & Company, and its action may be understood from the following:
The table is firmly bolted to the frame, and is fitted with the necessary groove slides and fences for rip sawing and cross cutting. It is also provided with a removable piece, which allows the use of wabbling saws, dado heads, etc.
The sides of this machine a, a, Fig. 3099, are cast with an extension for countershaft. Referring now to Figs. 3100 and 3101, the upright piece i, i, with arms b b, and g, g, is bolted to the frame as shown. The arbor frame m, m, is gibbed to t, t, by the circular piece u, and is moved to any angle by the hand wheel z, which operates the worm w, which in turn moves the arbor frame m, m. This arrangement does not require any locking device to hold the saw in position. As the centre upon which the arbor swings is in the intersection of the planes of the saw and table top, the opening in the table needs not be larger than for the ordinary saw. When cutting a mitre the saw takes the position j, Fig. 3101. When cutting at a right angle the saw takes the position j′ and the arbor takes the position p′ n′.
The saw arbor can be raised and lowered by the use of the hand wheel which operates the screw b (Fig. 3100.)
There is an accurate index located in front of the machine in sight of the operator, marked from 0 to 45°.
The iron table is of one piece 4 feet by 3 feet and fitted with the necessary groove slides for ripping and cross cutting gauges. It is also provided with removable piece e, Fig. 3101, allowing the use of dado head, etc. The table is provided with a bevel slitting gauge s′, and cross cut or mitering gauge x′, Fig. 3099, which in connection with the angular adjustment of the saw enables the operator to get every conceivable plain or double mitre ever required. The pulleys a′, b′, are made wide to allow the belt to travel as the saw is inclined. The pulley b′ takes up the slack of the belt. The countershaft and tightener are a part of the machine and can be run wherever a belt can be brought to them.
Figs. from 3102 to 3105 represent a roll feed circular saw, by J. Richards.
Fig. 3102 is a side elevation, Fig. 3103 a plan, and Fig. 3104 a cross-sectional view through the rolls.
In Fig. 3102, p is the saw-driving pulley, t a stand for carrying the saw guides a, b, c, d, which are adjustable for height by means of the arm whose set screw is shown at u; at w is the spreader for opening out the board after it has been cut by the saw, and thus prevent its binding against the saw and heating it.
The construction of the feed motion is shown in Figs. 3103, 3104, and 3105.
On the saw arbor is the feed cone c, Fig. 3103 having four steps so as to give four rates of feed. This cone connects by belt to feed cone d, whose shaft drives feed pulley e, which drives f by belt connection. f drives two worms shown by dotted lines at h and i, and these drive the worm wheels which drive the feed rolls, one of these worm wheels being shown at k, in the side view, Fig. 3102.
The feed roll l (Fig. 3103) is supplemented by a fence or gauge face p, which guides the work closer up to the saw than would be possible with a roll, and a supplemental roll is provided at m, thus affording a guiding surface for the work from m to the end of p. The stand for guide roll l fits in a slideway, and is adjustable along it by means of the screw s. Similarly the stand for roll n is fed along its slideway by screw r. There are three separate sets of saw guides, all of which are shown in the plan view Fig. 3103, and of these the top ones, a, b, c, d, e, f, g, and h are adjustable by nuts. The front ones, l, m, n, o, p, q, and the back ones, i, j, k, and r, s, t, are adjustable by means of the wedges w. At z is a wedge for adjusting the spreader w so as to keep it close to the saw whatever the diameter of the latter may be.
Fig. 3105 is an end view of the machine showing the feed worms h and i, and the belt tightener v, which is carried on the arm u on whose shaft is the weight y, attached to which is the handle x.
A segmental circular saw is one in which the saw is composed of segments secured by screws to a disc, the construction being such as shown in Fig. 3106, in which a is the saw arbor, d the disc, and e, f, g, h, i, j, etc., the segments.