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The shriek of the circular saw is the most familiar sound associated with the sawmill, but many other types of saw are used to cut up the timber in preparation for the ingenious planing and finishing machines used by the woodworker


INDUSTRIAL MACHINERY AT WORK - 2


THE CROSS-CUTTING CIRCULAR SAW at the wagon-building works of the London and North Eastern Railway


































THE CROSS-CUTTING CIRCULAR SAW at the wagon-building works of the London and North Eastern Railway at Darlington, Co. Durham. An 8-tons overhead travelling crane brings the logs into position. They are then cut into suitable lengths and carried to other types of saw for further cutting. The limit of thickness to which the circular saw will cut is rather less than half its diameter.




OF all the tools which have been devised by man to serve him in. his countless and varied activities, those connected with the craft of woodworking have the widest application.


The essential basic principles of the hand-operated saw, the plane and the drill as used in nearly all parts of the world for thousands of years are still retained, and remain the foundation of even the most modern woodworking machines. Yet modern machines are in striking contrast to those of even a generation ago. Speeds have increased greatly, and the power still more so.

Almost all the preliminary rough work is done by the saw. Saws are the first and the most numerous woodworking implements, and there are several kinds — great multiple-frame saws, circular saws and band saws.


A big and powerful mechanical saw, generally driven by steam because it is the most easily produced form of power in the dense forests, fells the tree. Another saw, working on similar lines, cuts the long trunk up into suitable lengths for transport. On arrival at the sawmill the log is loaded on to the bed or carriage of another machine, either to be suitably squared or to be cut up into planks of various thicknesses. This may be done on either of two types of machine, the one being fitted with a single band saw running over two large pulleys, the other being known as the frame saw.


The vertical frame saw derives its name from the form of its construction. Across the main upright columns, straddling the log table or carriage, is a strong moving frame which carries a number of gigantic saw blades stretched tightly to the ends. This saw frame is driven up and down by a crank motion, which derives its power from a driving belt pulley or from an electric motor. The sawing action is similar to that of the ordinary hand saw, as it is of a reciprocating nature. The band saw gives a continual cut during its traverse of the whole length of the log, but the frame saw has an idle stroke for each cutting stroke. The maximum linear speed of the reciprocating saw is only about 600 feet a minute, but the band saw will run as fast as 9,000 to 10,000 feet a minute. The inertia of the heavy frame of saws working up and down requires rigid construction. A log frame saw capable of dealing with logs up to 4 feet in diameter and fitted with eight saws would require about 30 horse-power.


The horizontal log band saw has a rigid framework, consisting of two massive cast-iron upright columns placed far enough apart for the log to pass between them, and tied together at the top by a crosspiece. The saw itself, which is made from a continuous steel band, is in the largest sizes perhaps 10 in. wide and 60 feet long, with the teeth running along one side.


The saw is carried by two large pulleys, one at either end. The saw and its pulleys are mounted on a rigid horizontal column which is arranged to slide up and down the two upright columns of the main frame, so that the saw can be lowered or raised to accommodate the part of the log that. is being cut.


The pulleys run on ball or roller bearings, as the speeds are high. One of the pulleys is driven from the belt pulley of the machine, or from an electric motor mounted on the frame, and pulls the saw band round. The other pulley is turned by the band while it runs. A straining mechanism on the saw frame automatically adjusts the tension on the band to suit the work and to keep the band tightly stretched.


As the band saw runs in a definite position the log is fed up to it, as the cut proceeds, by mechanism on the log carriage. The rate of this feed can be varied from zero up to about 80 feet a minute while cutting, with a quick return traverse up to a speed of 200 feet a minute, as on this return stroke no cutting takes place. Such a machine of the largest size would take about 75 horse-power to drive it.


Another form of log band saw is made with the band running in a vertical position. This arrangement occupies less floor space, but half of the saw mechanism is below ground, and therefore not quite so accessible or convenient for inspection. These two forms of band saw are more effective than the vertical frame saws for dealing with timber of every size and quality. They do better work, waste less in the cutting and absorb less power for a given amount of work done.


The band saw is used extensively for much smaller work than logs, and has become increasingly popular. Though the principle has been used for many years, the idea was patented by William Newberry as far back as 1808.


Cambered Pulleys


Two great difficulties confronted the earlier makers of band saw machines.


One difficulty was that of making a steel blade in the form of a continuous band of considerable length, with the ends joined together so that it would stand up to the heavy work it had to do and run at fairly high speeds. There was also the trouble of getting the band to remain on the pulleys without continually running off sideways.


Modern progress in steel manufacture and improvements in the technique of brazing the ends together have overcome the former trouble. By a combination of certain features in the construction of the band and of the pulley, the second difficulty has been satisfactorily surmounted in a simple but ingenious manner.


To make a leather belt keep its place on its driving or driven pulley, the pulley is generally made with a slight camber in the centre of the pulley rim. In other instances the pulley has been provided with a flange or flanges to effect the same end. The function of the flanges is obvious. The camber method is based on the fact that a belt always tends to ride on, or towards the largest diameter of the pulley; if, therefore, the central portion of the track is made slightly bigger in diameter, the middle part of the belt automatically keeps in the middle of the pulley.


This feature does not apply, however, to the steel band saw. New factors affecting the running have been discovered. The tightest part of the saw band has to be the toothed side, so that side is made slightly shorter than the plain, or back edge. Then again, the central strip of the steel band is now hammered or pressed so that it is a little thinner than the rest. This has the effect of making that portion slightly longer than either side of it.



VERTICAL FRAME SAW used for cutting up logs into planks. A strong frame to which several saws can be attached is driven up and down by a crank motion whose power is derived from a driving belt pulley or from an electric motor. A log frame saw suitable for 4-feet logs and fitted with eight saws requires about 30 horse-power. The maximum linear speed of the saw is about 600 feet a minute.



The pulleys of the smaller sizes, with bands up to about 3 in. wide, are generally covered with a thin layer of rubber vulcanized on to the. steel. This forms a relatively soft cushion for the steel band on the pulley. On the larger band saws the teeth are made to project over the edge of the pulley. The vulcanized rubber also gives the band a better grip on the pulley. With all these improvements, and also by making provision for adjusting the angle of the one pulley in relation to the other, it is now possible to get extremely good results with this type of saw. Another feature of a band saw is that, in passing over the pulleys and then straightening out again between each, the band is subjected to continual reversal of stress due to the bending back and forward which takes place many thousands of times an hour. Only the best steel, therefore, may be used. The linear speeds of saw bands are high, and reach 10,000 feet a minute, so that the cutting is done rapidly. For cutting wood at various angles the table is made to cant to the desired degree.


Here again automatic tensioning provision is made to keep the band taut while running. Saw guides are fitted as close above and below the job as possible. These guides are sometimes in the form of hardwood held in a grip, and having a slot cut in them through which the saw runs just clear. If the saw is inclined to jump the pulley the guide will prevent its doing so, and yet will not maintain a continuous pressure on the saw and so overheat it. Some modern band saws are fitted with ball or roller bearing guides. An adjustable brush also is provided to keep the face of the bottom saw pulley free from dust and chips. A dust chute may also be embodied in the main frame of the machine for the collection and easy disposal of dust and chips. The pulleys and saws are always carefully provided with guards. The smaller sizes of band saws, where the band is relatively narrow, can be used for doing curved work, that is, cutting to almost any curved line of form, merely by feeding the wood to the saw as required to get the desired shape of cut. Much depends on the skill of the operator.


The type of saw which is familiar to most people is the circular saw, so frequently heard, if not seen, and known by its hum, which gradually increases to a shriek as the wood is pushed up against the rapidly rotating teeth. It is also the most versatile of woodworking machines.


Rigidity of the Blade


The circular saw will do roughly the jobs which in more specialized workshops are allocated to special machines. It has its own sphere of ripping — cutting along the grain of the wood — or cross-cutting; it is capable of cutting grooves; with its canting table it will cut to any angle. Several of these saws can be mounted on one spindle and made to cut a number of pieces at once, especially for such work as light laths.


The saw blade must be carefully made of great rigidity. Its cutting edge is at a greater distance from the point where the power is supplied (at its centre) than in the band or frame saw, so that the disk must be capable of standing up to this stress. The disk has to pass through the wood again on the second half of its revolution and thereby tends to widen the cut, unless carefully set, whereas the band saw passes through the wood only once as it cuts it. This tends to leave the wood with a better surface and causes less waste.


The limit of thickness to which the circular saw will cut is rather less than half its diameter. As the largest practicable size of such a saw is about 7 feet, the maximum depth of cut is about 3 feet. A 7-feet circular saw is rated to cut up to 35 in., and a 36-in. saw up to 14 in. It is possible to deal with larger logs by using two saws, one above the other, but this is not always desirable.


Because of its speed the saw spindle runs in ball bearings, and is rigidly supported in two, or sometimes three bearings to secure absolute rigidity, for if it is allowed to wobble in the least it will make a wider cut than necessary (but see below).


The saw is generally mounted vertically and at right angles to the table or bench carrying the wood, but some machines are fitted with a canting spindle so that the saw can be placed at any suitable angle to the wood. The angle used at the time is indicated by a scale, generally marked on the frame of the machine. The operation of feeding the wood to the saw may be done by hand, as in the smaller and jobbing machines, or it may be done by screw or rack mechanisms and worked automatically. A small hydro-electric feed system has been used in some machines. The table generally has a fence against which the wood presses as it passes along, keeping it in line, and this fence can be adjusted to any angle as required.



VERTICAL BAND SAW in the L.N.E.R. wagon-building works at Darlington. Less floor space is occupied by a vertical than by a horizontal band saw, but half of the mechanism is below floor level. The saw may run as fast as 10,000 feet a minute.



For cutting grooves on the underside of a plank or baulk the fixed circular saw can be lowered in the table until it projects just to the depth of the groove to be cut. The wood is then fed along over the saw. Sometimes a wide groove can be cut by the use of a wobbling saw. This is mounted on its spindle at an angle slightly off the right angle, so that at each revolution the outer edge of the saw carrying the teeth wobbles from one side to the other and cuts a groove in width equal to the amount of double departure from the vertical centre line.


A useful type of circular saw for cross-cutting is the pendulum saw. As its name implies, the saw is mounted on a long frame which is supported from bearings overhead, and so can be moved backwards or forwards at will across the job to be done. A counterbalance weight keeps the saw to the rear out of the way of the work while the job is being placed on the table or changed.


Over Two Miles a Minute


When the cut has to be made the operator pulls the frame forwards towards him, drawing the saw across the job, which is generally a short cut. When he lets go the frame is automatically pulled back to the rear and clear of the table.


The speed at which the teeth of a circular saw travel is amazing, varying from 8,000 feet to 12,000 feet a minute, that is, nearly 2| miles a minute. The power absorbed is considerable. With an 84-in. saw it amounts to about horse-power. Even a moderate size bench saw of 36 in. diameter will require up to 35 horse-power. Because of these speeds individual electric motor drive is now common. The motor may be coupled direct to the saw spindle or, as is more common, the drive may be transmitted from the motor to the spindle by a number of V-shaped belts. Being formed of a deep V section and running in a correspondingly grooved pulley, these belts retain a powerful grip on the pulley with no appreciable slip. In all instances guards are provided over the saw and other fast moving parts.



WOODEN COREBOX made by a pattern miller for the casting of a machine-tool gearbox. Either half of the corebox measured 3 ft. 3 in. by 2 feet, and was worked out of a solid piece of wood. Except for the bosses, the whole job was completed in about three hours by the pattern miller illustrated to the right.

PATTERN MILLER for forming the wooden moulds used for casting metal (see above). A strong arm projects from the vertical pillar and is made to move up and down it as required. Through the arm runs the main driving spindle. At right angles to this, at the spindle head, is the cutter spindle. By moving the head the cutter spindle can be set at any desired angle.



The form of the teeth of saws is determined by the nature of the work they have to do. In a circular saw, which is used for ripping up timber or for cutting with the grain, the cutting edge or point is inclined well forwards. A saw used for cross-cutting, however, has teeth of a different shape. The teeth may have a backward rake or they may be of a regular inverted V shape with equal rake on either side. The space between the teeth, known as the gullet, should be of ample size to accommodate the cuttings until the adjacent tooth is clear of the cut and the cuttings fall out. Otherwise the sawdust will be inclined to get jammed between the sides of the saw and the wood, causing unnecessary friction and heat. The teeth are set, preferably by hammering them on a setting anvil, to alternate sides, so as to give a little clearance to the body of the saw while cutting through the wood. For ripping work the top face of the tooth is made square to the sides, with the edges slightly projecting beyond the body of the disk. For cross-cutting the face may be ground so as to have a slight bevel, first to one side and then to the other. If the disk is hollow ground, or the disk centre has been hammered thin, as is sometimes done, no setting of the teeth is necessary.


The hammering process is not primarily to make the disk thin in the centre but to enable it to adapt itself to the expansion due to the heat generated when cutting. For large saws, which would be costly if wholly made of the expensive quality of steel that is required, it is usual to insert separate teeth, so that the body of the disk may be made of a less expensive steel but still perfectly satisfactory for the work it has to do in carrying the teeth and transmitting the power to them.


Planing Machines


For feeding the timber to the saw, rollers are generally used in the larger sizes. Where the wood is fairly rough these rollers are grooved so as to get a good grip, but if the timber is in a finished state, then smooth rollers are necessary so as not to mark the wood as they press on it.


Another type of machine which is extensively used is the planing machine in its various forms. Planing may be done either by a fixed knife against which the wood is fed or, as is more common, by fast rotating cutters. The action of a rotating cutter does not leave a perfectly flat cut, as would a fixed knife plane (such as a hand plane), but a curved one.


The smaller the diameter of the rotary cutter the greater the relative amount of curvature. Thus the surface of the wood will be a series of hollows and ridges. The closeness of these ridges depends on the rate of feed in relation to the rate of cutting. The slower the relative feed speed the more these ridges will be eliminated, but fast feed speeds are wanted. So the number of cuts made for a given length of travel of the wood is increased by using more cutters on each spindle.


Suppose the wood is being fed at the rate of 200 feet a minute (speeds of 350 feet a minute and higher are reached), with a single rotary cutter running at 2,000 revolutions a minute. This would then produce ten curved cuts with their corresponding ridges along each foot of the wood surface, which would be noticeably not flat.


Even a moderate cutter speed of 4,000 revolutions would double the number of cuts and halve the number of ridges. By mounting four cutters, however, on the spindle block, or six, as is sometimes done, four or six times as many cuts would be obtained for each revolution of the cutter spindle. With the spindle running at 4,000 revolutions the four cutters would produce eighty cuts per foot length with a feed at 200 feet a minute. This would give a much more level surface to the wood, leaving little smoothing to be done by sandpapering or by other means. On the latest planing machines cutter spindle speeds have reached a rate of over 7,000 revolutions a minute with a correspondingly fine finish to the surface.



A SMALL- BAND SAW is similar to a fret saw and will make a curved cut, according to the way in which the work is fed by the skilled operator. The steel band saw, less than 2 in. wide and about 20 feet long, is carried on two disk pulleys. The electric drive is self-

contained, the motor being mounted on the bottom saw spindle.



Most of the large planing machines are, however, also fitted with other cutters which operate on the edges. With cutters working on the top and bottom sides of the plank, and others working on the two edges, all four surfaces can be finished in one operation. Apart from straight planing, this type of machine is used extensively for producing mouldings such as window sashes, door frames and skirting boards. Shaped cutters can be attached to each of the revolving cutter blocks and any given profile or mould can thus be reproduced in the wood on all four sides. Big planing machines consume much power, due to the high speeds of cutting and feeding elements. In a large machine the necessary power amounts to as much as 100 horse-power.


Because of the enormous capacity of some of these machines and of their high speeds, the question of vibration is important if good results are expected. The main frames are of solid construction, and they may be over 30 feet long. Individual electric motor drives are now common, a separate motor being used for each of the spindles as well as for the feed mechanism. By either direct drive or by short V-belt drives, these motors can be neatly stowed in the machine, thus saving floor space, economizing power and giving a pleasing appearance to the whole machine. They are greedy machines, however, and to get the most out of them it is necessary to make special provision for maintaining the supply of boards as fast as they can be planed. This may be at a rate of fifteen or twenty 12-feet boards a minute, and they could not be lifted continuously and placed in position by hand. An automatic feeding table, therefore, is provided.


Automatic Feeding Table


This generally consists of a frame table up to about 15 feet long and 30 in. wide, across which are placed four or five spirally grooved rollers projecting slightly above the table surface. At the front end of the main table is a sloping side table on to which the rough boards are placed. They slide down this on to the cross rollers, which carry them forward at the required speed.


The spiral grooves on the rollers cause the planks to work their way diagonally forward and towards the main fence placed right along the one side. Having reached the end of the feeding table the plank strikes against a butting, or angle fence which directs it beneath the top rollers of the planer, which have already been adjusted to suit the thickness of plank being dealt with. Another stop prevents two boards from entering the machine at once.


When one or more surfaces of the board, after having been planed, require a finer finish, they are passed on to a drum roller-feed sander. This is a machine which comprises one or more long drums, each of which is covered with a layer of sandpaper tightly stretched over it. These drums may be placed to work above or below the boards, or they may be on both sides if the two sides of the board are to be polished simultaneously.


As the board is fed through the machine the sandpaper rollers revolve at a high speed over the surface, and are also given a small oscillatory movement endways so as to avoid marking the surface by any slight projection caused in the paper at any particular spot. When more than one drum is used the sandpaper is graded in its degree of coarseness or roughness, getting finer towards the last drum.



TWO LARGE STEEL PULLEYS carry the band of a horizontal band saw. The pulleys are mounted on a strong horizontal frame which can be moved up or down the upright columns to suit the height of the cut required. The log is moved up to the saw at speeds up to 80 feet a minute.



In all classes of woodwork there are many forms of mouldings used, cut to innumerable designs. These may be on the edges of boards, or they may be in long laths, and either straight or curved. For this work the spindle moulding machine is invaluable. In principle it is similar to the side rotary cutters on the planing and matching machines. The chief difference is in the form of the cutters. Instead of these being parallel with a straight face or cutting edge, the spindle moulder cutters are shaped to produce the required moulding.


The spindle speeds are high, being from 4,500 to 9,000 revolutions a minute. The spindles, therefore, have to be rigidly mounted to avoid any vibration which would tend to spoil the finish of the work. Being made specially for this work, and generally having plenty of it to do, the machine has no other operating parts than the cutting spindles. These spindles project through the table vertically, and are provided with the usual adjustable fence and suitable guards. Patent feed mechanism is rapidly coming into use for spindle moulding work.


Many objects of box or cabinet form have the corners of the adjacent sides or ends mortised and tenoned, or dovetailed in some way, to keep them rigid. Mortises, or the rectangular slots into which the tenoned (or projecting) parts are fitted, may be cut by several methods. A simple way is to drill a number of holes equal in diameter to the width of the mortise, and to square the ends with a chisel. For much repetition work of this kind, however, special mortising machines are used.


The main principle of operation is that of a drilling machine, but the tool used for cutting the slot is called a hollow chisel. This is a four-sided hollow square chisel, inside which a fast running auger drill works. As the combination tool is fed into the wood, the auger drills a hole nearly the size of the width of the slot, and the sharp edges of the chisel clean out the corners square.


Another form of machine uses a chain cutter. This is an endless steel link chain, on the links of which are fixed cutting teeth. A rectangular tension bar, placed vertically between the two side portions of the chain, carries a small pulley at the bottom end. The top end of the chain runs over another pulley fixed in the headstock frame. This tension bar provides adjustment to keep the chain taut.


With the chain running at a high speed, driven by a small electric motor embodied in the head stock, the headstock is fed downwards by a hand lever and pressed through the wood. The thickness of the chain and its width determine the size of slot cut, and narrow mortises, down to {-in. wide, can be cut with this tool. This is the only machine which will cut a complete mortise in a single operation. Making the corresponding tenon is a fairly simple operation, but there are also special machines for this work.


Pattern Millers


For dovetailing an ingenious machine is used. This consists mainly of two disks mounted on a spindle at an angle to each other. This angle is maintained by gears. On each disk are mounted round its circumference a number of small sections of saws. As the disks rotate and the wood is fed up to them those saws on one disk cut one side of the dovetail; those on the other disk cut the opposite side at the same time. The bottom of the dovetail is cut by shoulder saws on certain segments. The position of the saws can be adjusted for varying sizes. Lathes are used in woodworking shops, but the functions for which they are generally required are still much the same as as they have been for hundreds of years. Ornamental lathes are extremely complicated mechanisms for producing all kinds of ornamental turning in wood or in metal.


One particular class of woodcraft is that of making patterns from which metal parts are cast in sand moulds. Pattern making is a highly skilled job and formerly much laborious handwork was involved. Much of this has, however, been eliminated by the introduction in recent years of an ingenious machine known as the pattern miller.



MANUFACTURE OF PLYWOOD from a log of birch. The log is fixed in a rotary lathe and is rotated against a knife edge, which strips the log into a long roll or ply. The ply, as it leaves the lathe, is wound into a reel. It is then subjected to special processes and the required number of plies is cemented together under hydraulic pressure. The strength of plywood lies mainly in the fact that each ply is laid with the grain across that of its neighbour.



Projecting horizontally from a rigid vertical pillar is a strong overhanging arm, which is arranged to slide up and down on machined guides on the face of the pillar. Through the centre of this arm runs the main driving spindle. The electric motor driving it is sometimes mounted on the spindle end. At the outer end of the arm is the spindle head, which can be turned round to any desired angle in a vertical plane, the angle being registered by a spring plunger. Carried in the head is the cutter spindle, placed at right angles to the axis of the arm, and driven by suit able gears inside the head and frame. Thus, the head, being rotated, the cutter spindle can be set at any desired angle.


The table on which the work is placed is of the universal type, it being possible to turn the job in any direction in a horizontal plane The combination of these two variable movements enables the most complicated surfaces to be cut. the cutter being rotated at a high speed and being of a contour suitable for the particular form of cut desired.


That part of the pattern known as the corebox involves recessed cutting, that is in each half of the corebox a number of semi-cylindrical forms, both straight and curved, which have to match or pair when assembled, will have to be cut. Straight grooves might be bored in a lathe, but curved recesses need to be done by hand The pattern miller can save the pattern-maker many laborious hours.


The manufacture of plywood is another branch of woodwork which is extending with the modern tendency to use more of this material. Plywood is a series of laminations of what, in the ordinary way, would be called veneer wood, strongly cemented together with the grain of each alternate layer placed across the grain of its neighbour. It is this feature which contributes mainly to its strength.


The cutting of such thin layers — from about one-hundredth of an inch up to about three-eighths of an inch — is done by a special machine. Imagine a long strip of stout paper which has been coiled or rolled up tightly until it is virtually a thick tube or even a solid cylinder. Place the almost solid tube horizontally and make it rotate as in a lathe


Metal-Coated Plywood


If a long straight knife blade is placed under the top lamination and if the tube is rotated, the paper will be unrolled again into a long strip. Substitute a round log for the paper tube, and a gigantic knife held in a powerful machine, and one of the chief processes of plywood manufacture will be fairly clear.


Not all woods are suitable for this treatment. those which are suitable are generally steamed or otherwise treated to condition the fibres before cutting. The thin sheet of wood, as it is peeled off the cutting lathe, can be rolled up in the same way as a carpet The sheet is then conditioned by a carefully regulated drying system, and then cut to the size required. The required number

of plies is then coated with suitable cementing composition, and placed in a powerful heated hydraulic press, where the plies are subjected to great pressure for a few minutes.


The composite board is allowed to cool again, its edges are trimmed, and it then undergoes a further drying or conditioning period. Where desirable the surfaces are smoothed or sandpapered to complete the process.


Plywood can now be made with a thin metal coating of various kinds, which not only increases its existing great strength in relation to weight, but enables it also to stand some climatic conditions which the bare wood will not stand.


There are many other adjuncts of a modern sawmill or woodworking shop. Special features include the abstraction of sawdust and chippings from the various machines, and their conveyance through pipes and dust cyclone separators to boilers for fuel where steam power is used, leaving a clean and healthy atmosphere for the workers.


The systems for drying the timber, the methods of handling the timber about the works, and the workshop where the tools are repaired, set, ground or adjusted — these all contribute their share to the successful operation of a large woodworking establishment.


A CONTINUOUS STEEL BAND, sometimes as much as 10 in. wide and 60 feet long, is used in the larger horizontal and vertical band saws. At the L.N.E.R. wagon-building works at Darlington these saws are sharpened in a special department. The form of the teeth depends can the nature of the work that the saw is called upon to do.



You can read more on “Ball and Roller Bearings”, “Electric Motors and Generators” and “From Timber to Newsprint” on this website.


Machinery of the Saw Mill