Fig. 3223 represents a horizontal boring machine such as used in furniture and piano factories. The spindle feeds through the driving cone, being operated by the treadle shown. The work table is adjustable for height by the hand wheel and elevating screw. The usual fences, stops, and clamping devices may be applied to the table, which is on compound slides to facilitate the adjustment of the work.

Fig. 3223a shows a double spindle horizontal boring machine, in which the table and work are fed up to the boring tools by hand. The spindles are adjustable in their widths apart, and may also be set at an angle. The work table is adjustable for height, and the spindle carrying head is adjustable across the machine.

Fig. 3224 represents a machine by J. A. Fay & Co., for heavy work, rollers taking the place of the work table. The drill spindles are fed by hand from the stirrup handles shown, which are weighted to raise up the spindles as soon as they are released.

MORTISING MACHINES.

The mortising machine for wood work consists essentially of an ordinary auger, which bores the holes, and a chisel for cutting the corners so as to produce the square or rectangular mortise that is usually employed in wood work.

The chisel is reciprocated and its driving spindle is provided with means whereby the chisel may be reversed so as to cut on either the sides or the ends of the mortise. The chisel is fed gradually to its cut.

Fig. 3225 represents a mortising machine for the hubs of wheels.

The auger spindle is here fed vertically by a hand lever, the depth bored being regulated by a rod against which the hand lever comes when the hole is bored to the required depth.

Fig. 3226 represents a mortising machine in which the mortising tool consists of a hollow square chisel containing an auger, and having at its sides openings through which the cuttings escape.

The chisel is rectangular in cross section, but its cutting edges are highest at the corners, as may be clearly seen in the figure.

The work is firmly clamped to the work table and simultaneously to the fence, the upper hand wheel being operated to bring the work-holding clamp down to the work, and the lower one to clamp it so as to press it to both the table and the fence at the same time.

The chisel bar is mounted horizontally in a slide way on a substantial bed that is mounted on a vertical slideway, which enables the chisel bar to be set for height from the work table. It has a horizontal traverse motion or feed, the amount of this motion being governed by the horizontal rod with its nuts and check nuts as shown.

The auger runs continuously, and works slightly in advance of the cutting edge of the chisel, which is passive except when making the mortise.

The chisel bar and auger have a slow, reciprocating motion, and will complete a hole the size of the chisel used. An inch chisel will cut an inch-square hole, consequently a mortise 1′′ × 4′′ would only require four strokes forward to complete it. It has a capacity to work mortises from ³⁄₄′′ to 3′′ square, and 5′′ in depth, and any length desired. The boring spindle is driven by an idler pulley, direct from the countershaft.

The bed upon which the timber is placed to be mortised is gibbed to a sliding frame, which allows it to be set to any position, with the chisel straight or at an angle. It is adjustable to and from the chisel bar, to suit the size of material, the under side of which always remains at one height. Adjustments are provided for moving the carriage forward, for regulating the depth of the mortise, the position of the chisel from the face of the material, and the adjustment of the chisel bar, controlling the mortises to be made in the timber.

Two treadles are used upon the side of the machine; the pressure upon one carrying the chisel bar attachment forward, completing the mortise, while the other will instantly force it back when it is desired to withdraw it from the wood, without allowing it to cut its full depth. Provision is made by stops for regulating the length of the stroke as well as the depth of the mortise.

TENONING MACHINES.

In tenoning machines, the lengths of the pieces usually operated upon render it necessary that the work should lie horizontally upon the table, while the shortness of the tenon makes an automatic feed unnecessary.

The revolving heads carrying the cutters in tenoning machines are so constructed that the cutting edges of the cutters are askew to the sides of the heads, but so set as to produce work parallel to the axis of the cutter shaft.

This causes the cutting action to begin at one end of the cutter edge, and pass along it to the other, which enables a steady hand feed, and reduces the amount of power required to feed the work.

Fig. 3227 represents a cutter head for a tenoning machine, a, a and b, b being the cutters and c, c, d, d spurs which stand a little farther out than the cutter edges, so as to sever the fibre of the wood in advance of the cutter edges coming into action, and thus preserve a sharp shoulder to the tenon, and prevent the splitting out at the shoulder that would otherwise occur.

To bring the outer edge of the shoulder in very close contact with the mortised timber, the cutters are for some work followed by what is termed a cope head, which is a head carrying two cutters bent forward as in Fig. 3228, to make them cut very keenly, as is necessary in cutting the end grain of wood.

The cope head undercuts the shoulder, as shown at a, a, in Fig. 3229, which is a sectional view of a mortise and tenon.

Fig. 3230 represents a tenoning machine for heavy work, constructed by J. A. Fay & Co., adjusted for cutting a double tenon, the upper and lower heads revolving in a vertical plane, and the middle head in a horizontal plane.

a is a vertical slideway for the heads c, d, carrying the shafts for the cutter heads a, b. At b is the hand wheel for adjusting d, and at e that for adjusting c. The pulley d is for driving the cope heads, one of whose cutters is seen at c. The work carriage h is provided with rollers which run on the slide on k, and is supported by the arm i, which rises and falls to suit the cross motion of h. The fence g, for the work, is adjustable by means of the thumb nuts.

SAND-PAPERING MACHINES.

Sand-papering machines are of comparatively recent introduction in wood working establishments, but are found very efficient in finishing surfaces that were formerly finished by hand labor.

Fig. 3231 represents a sand-papering machine, by P. Pryibil, in which a spindle has three stepped cones on one end, and a parallel roller or cylinder at the other. The steps on the spindle are covered with a rubber sleeve, and the sand paper is cut to a template, and the edges brought together and joined by gluing a strip of tough paper under them. When this has become dry the paper is slightly dampened everywhere except at the joint, and is then slipped on the taper drums. In drying it shrinks and becomes tight and smooth upon the rubber covering with which the drums are provided. These are of different sizes to fit different curves in the work.

Flat work is done upon the table, which is hinged and provided with an adjusting screw to regulate its height, and it can be raised to give access to the drum.

When sand paper is applied in this way, every grain is brought into contact with the work, whereas at first only the larger grains cut when it is used on the faces of revolving discs, as in some machines of this class. Furthermore, when used on drums it is offered ample opportunity to clear itself of dust; it therefore does not become clogged, and, as a consequence, it lasts longer and does more and better work than when used on discs.

Fig. 3232 represents a similar machine, but having a spindle vertical also, so that one face of the work can be laid on the table, which acts as a guide to keep the work square, the table surface being at a right angle to the vertical spindle.

The vertical cylinder or drum is split on one side, and provided with internal cones, so, that by screwing down the nut shown the drum can be expanded to tightly grip the sand paper, which is glued and put on as already described.

Besides these rotary motions, these drums receive a slow vertical motion, the amount of which is variable at the operator’s pleasure. This provides for using the full face of the drum on narrow work, while it prevents the formation of ridges or grooves in the work.

For sand-papering true flat surfaces the flat table is provided, there being beneath it a parallel revolving drum, whose perimeter just protrudes through the upper surface of the table. The surface of the table thus serves as a guide to steady the work while the sand-papering is proceeding.

By using sand paper in this manner, every grain of the sand is brought into contact with the work; furthermore, a small area of sand paper is brought into contact with the work, and the wood fibre can fly off and not lodge in the sand paper; while at the same time the angles of the grains of sand or glass are presented more acutely to the work, and therefore cut more freely and easily. Hence the sand paper lasts much longer, because a given pressure is less liable to detach the sand from the paper.

The machine is constructed entirely of iron, and the drum is intended to revolve at about 800 revolutions per minute.

Fig. 3233 represents a sand-papering machine in which a long parallel cylinder is employed, the work resting on the surface of the table and being fed by hand. In using a machine of this class the work should be distributed as evenly as possible along all parts of cylinder, or one end of the cylinder may become worn out while the other is yet sharp; this would incapacitate the machine for wide work unless a new covering of sand paper were applied.

Fig. 3234 represents a sand-papering machine constructed by J. A. Fay & Co., for finishing doors and similar work. The frame constitutes a universal joint enabling the sand paper disc to be moved anywhere about the door by hand. An exhaust fan on the top of the main column removes the dust from the work surface. The head carrying the disc is moved vertically in a slideway to suit different thicknesses of work.

Fig. 3235 represents a self-feeding sand-papering machine constructed by J. A. Fay & Co. It is made in three sizes, to work material either 24′′, 30′′, or 36′′ wide by 4′′ thick and under; it has a powerful and continuous feed, and gives to the lumber a perfect surface by once passing it through the machine.

The feeding mechanism consists of six rollers, in three pairs, driven by a strong train of gearing. The upper feeding rollers, with the pressure rollers over the drum are lifted together in a perfect plane by the movement of four raising screws, operated by a chain and hand wheel. The lower feeding rollers always remain in perfect line with the drums.

It is supplied with two polishing cylinders, placed in the body of the machine, on which the upper frame rests, both having a vibratory lateral motion for removing lines made by irregularities in the sand paper. The finishing cylinder is placed so that the discharging rollers carry the lumber from it, thus running through and finishing one board, if desired, without another following, and these rollers are arranged for a vertical adjustment to suit the dressed reduction on the material to be worked. The roughing cylinder carries a coarse grade of sand paper, and the finishing one a finer grade. They may be driven in opposite or in the same direction, as may be necessary. The lower frame is hinged at each end to the upper frame, so that by removing a pin, either cylinder can be reached by raising the frame with the screw and worm gear, operated by a hand wheel at the end of the machine.

A brush attachment (not shown in the cut) is now placed at the end of the machine just beyond the finishing cylinder, which is a most complete device for brushing the material clean after it leaves the sand-papering cylinders.

Fig. 3236 represents a double wheel sanding machine by J. A. Fay & Co.

This machine is intended for accurately finishing the tread of the wheel ready for the tire, and is one of the most useful and labor-saving machines that can be placed in a wheel shop.

The frame is built entirely of iron, and has a heavy steel arbor running in long bearings, with tight and loose pulleys in the centre. On each end of the arbor is a large sand paper disc for polishing the tread of the rim.

The wheel to be finished is laid on a rotating carrying frame, having two upright drivers. These are attached to a jointed swinging frame, with flexible connections, adjustable to suit wheels of varying diameters.

The first section of the jointed frame is driven by a shaft and bevel gears, and swings upon it. The second one has the wheel-carrying frame, and swings upon the extreme end of the first one, and is driven from it by a chain connection.

A roller wheel is secured at the bottom of the leg, affording a floor support; also a chain to regulate the proper distance of the wheel from the discs.

A wrought iron supporting frame is attached upon each side of the sand paper discs, adjustable for different sizes.

The wheel when placed in the machine is carried by the gearing against the sand paper discs, which finishes the tread in the most accurate and perfect manner.

Machines are made both single and double. The latter are the most desirable, as the operator has only to place a wheel in position on one side, when it feeds and takes care of itself.

By the time this is done, the wheel on the opposite side will be finished and ready to be removed, when a fresh one is put in, and the operation continued, the only care required being to put in and remove them. Its capacity is 150 set of wheels per day, and it will do the work better than can be done by hand.

Chapter XXXVI.—BOILERS FOR STATIONARY STEAM ENGINES.

The boiler for a steam engine requires the most careful usage and inspection, in the first case because a good boiler may be destroyed very rapidly by careless usage, and in the second case because the durability of a boiler depends to a great extent upon matters that are beyond ordinary control, and that in many cases do not make themselves known except in their results, which can only be discovered by careful and intelligent inspection. All that the working engineer is called upon to do is, to use the boiler properly, keep it clean, and examine it at such intervals as the nature of the conditions under which it is used may render necessary.

The periods at which a boiler should be cleaned and inspected depend upon the quality of the water, whether the feed water is purified or not, and to a certain extent upon the design of the boiler; hence these periods are variable under different circumstances.

The horse power of a boiler is estimated in various ways, and there is no uniform practice in this respect. Some makers estimate a boiler to have a horse power for every fifteen square feet of heating surface it possesses, while others allow but 12 square feet.

The heating surface of a boiler of any kind is the surface that is exposed to the action of the fire on one side, and has water on the other; hence the surface of the steam space is not reckoned as heating surface, even though it may be exposed to the action of the heat. The effectiveness of the heating surface of a boiler obviously, however, depends upon the efficiency of the fire, and this depends upon the amount of draught, hence the estimation of horse power from the amount of its heating surface, while affording to a certain extent a standard of measurement or comparison while the boiler is not in use, has no definite value when the boiler is erected and at work.

Thus whatever amount of steam a boiler may produce under a poor or moderate draught, it will obviously produce more under an increased draught; hence the efficiency of the same boiler depends to a certain extent upon the draught, or in other words upon the quantity of fuel that can be consumed upon its fire bars.

The amount of water required in steam boilers varies from 16 lbs. to 40 lbs., per horse power per hour, and it has been proposed to compute the horse power of boilers from the water evaporation, taking as a standard 30 lbs. of feed water at a temperature of 70 degrees, evaporated into steam at a temperature of 212 degrees, at which temperature the steam is assumed to equal the pressure of the atmosphere.

[49]“The strength of the shell of a cylindrical boiler to resist a pressure within it, is inversely proportional to its diameter and directly, to the thickness of the plate of which it is formed.

“For instance, take three cylindrical boilers each made of ¹⁄₂ inch plate, the first one 2 feet 6 inches in diameter; the second twice that, or 5 feet in diameter; and the third twice that again, or 10 feet in diameter; and if the 2 foot 6 inch boiler is fit for a safe working pressure of 180 lbs. per square inch, then the 5 foot boiler will be fit for exactly one-half that amount, or 90 lbs. per square inch; and the ten foot boiler will be fit for half the working pressure of the five foot boiler, hence we have:

“The reverse applies to the thickness of the plate. For instance, if we take two cylindrical boiler shells, each 5 feet in diameter, the first one made of plate ¹⁄₂ inch thick, and the second twice that, or 1 inch thick, and if the first is equal to a safe working pressure of 90 lbs. per square inch, then the second is equal to a safe working pressure of twice as much, or 180 lbs. per square inch, providing, of course, that the riveted seams are of equal strength in each case, and that both boilers are allowed the same margin for safety; hence we have:

“These principles (namely, that the strength of a boiler is, all other things or elements being equal, inversely proportional to its diameter, and directly proportional to its thickness) afford us a groundwork upon which we may lay down rules for determining by calculation the strength of the solid part[50] of any boiler shell, and the bases of these calculations are as follows:

“If the shell plate of a cylindrical boiler is ¹⁄₂ inch thick, there is one inch section of metal to be broken before the boiler can be divided into two pieces, that is to say there is ¹⁄₂ inch on each side of the shell, as shown in Fig. 3237, and the two together will make 1 inch. If we take a ring an inch broad, as, say, at a in Fig. 3238, we shall obviously have a section of 1 square inch of metal to break before the ring can be broken into two pieces.

“The next consideration is, what is the average strength of a plate of boiler iron? Now suppose we have a strip of boiler iron 2 inches wide and ¹⁄₂ inch thick, or, what is the same thing, a bar of boiler iron 1 inch square, and that we lay it horizontally and pull its ends apart until it breaks, how many lbs. will it bear before breaking? Now for our present purpose we may assume this to be 47,040 lbs., and if this number of lbs. be divided by the diameter of the boiler in inches, it will give the bursting pressure in lbs. for any square inch in the ring, or any other square inch in the cylindrical shell of the boiler.

“The reason for dividing by the diameter of the boiler is as follows:

“Of course the steam pressure presses equally on all parts of the interior surface of the shell, and may be taken as radiating from the centre of the boiler, as in Fig. 3239, which represents an end view of a strip an inch wide, of one half of a boiler. Now leaving the riveted seam out of the question, and supposing the shell to be truly cylindrical, and the metal to be of equal quality throughout, it will take just as much pressure to burst the shell apart in one direction as it will in another, hence we may suppose that the boiler is to be burst in the direction of arrow a, and it is the section of metal at b b that is resisting rupture in that direction.

“Now suppose we divide the surface against which the steam presses into six divisions, by lines radiating from the centre c, and to find the amount of area acting on each division to burst the shell in the direction of arrow a, we drop perpendicular lines, as line e, from the lines of division to the line b b, and the length of the line divided off (by the perpendicular) on the diameter represents the effectiveness of the area of that division to burst the boiler in the direction of arrow a; thus for that part of the boiler surface situate in the first division, or from b to line e, the area acting to burst the boiler in the direction of a is represented by the length of the line k, while the general direction of the pressure on this part of the shell is represented by arrow m.

“Similarly, for that part of the shell situate between vertical line e and vertical line f, the general direction of the steam pressure is denoted by the arrow l, while the proportion of this part that is acting to sever the boiler in the direction of a is represented by the distance n, or from the line e to line f measured on the line b b.

“By carrying out this process we shall perceive that, although the pressure acts upon the whole circumference, yet its effectiveness in bursting the boiler in any one direction is equal to the boiler diameter. Thus in Fig. 3240, the pressure acting in the direction of the arrows a (and to burst the boiler apart at b b) is represented by the diametral line b b, while the pressure actually exerted upon the whole boiler shell is represented by the circumference of the boiler.

“To proceed, then, it will now be clear that the ultimate strength of the boiler material, multiplied by twice the thickness of the boiler shell plate in inches or decimal parts of an inch, and this sum divided by the internal diameter of the boiler, in inches, gives the pressure (in lbs. per square inch) at which the boiler shell will burst.”

We have here only considered the strength of the solid plate of the shell, and may now consider the strength of the riveted joints, because, as the boiler cannot be any stronger as a whole than its weakest part is, and as the riveted joints are the weakest parts of a cylindrical boiler,[51] therefore the strength of the riveted joint determines the strength of the boiler.

[52]“The strains to which a riveted joint is subjected are as follows: That acting to shear the rivet across its diameter is called the shearing strain. But the same strain acts to tear the plate apart; hence, when spoken of with reference to the action on the plate, it is called the tearing strain.

“The same strain also acts to crush and rupture the plate between the rivet hole and the edge of the plate, and in this connection it is called the crushing strain.

“Thus, Fig. 3241 represents a single riveted lap joint, in which the joint at rivets a, b, and c is intact, the metal outside of d has crushed, the rivets e, f have sheared, and the plate has torn at h, leaving a piece j on the rivets k l.

“It is obvious that, since it is the same strain that has caused these different kinds of rupture, the joint has, at each location, simply given way where it was the weakest.

“If a riveted joint was to give way by tearing only, the indication would be that the proportion of strength was greatest in the rivets, which might occur from the plate being of inferior metal to the rivets, or from the rivets being too closely spaced. If the rivets were to shear and the plate remain intact, it would indicate insufficient strength in the rivets, which might occur from faulty material in the rivets, from smallness of rivet diameter, or from the rivets being too widely spaced.

“The object then, in designing a riveted joint is to have its resistance to tearing and shearing proportionately equal, whatever form of joint be employed.”

The English Board of Trade recommends that the rivet section should always be in excess of the plate section, whereas, in ordinary American practice, for stationary engine boilers, the plate and rivet percentages are made equal.

The forms of riveted joints employed in boiler work are as follows:

Fig. 3242 represents a single riveted lap joint. Fig. 3243 represents a double riveted lap joint, chain riveted; and Fig. 3244, a double riveted lap joint, with the rivets arranged zigzag.

Fig. 3245 represents a single and Fig. 3246 a double riveted butt joint, so called because the ends of the boiler plate abut together. The plates on each side of joint are called butt straps.

The advantages of the butt joint are, first, that the boiler shell is kept more truly cylindrical, and the joint is not liable to bend as it does in the lap joints, in the attempt of the boiler (when under pressure) to assume the form of a true circle, and second that the rivets are placed in double shear. That is to say, if in a lap joint the rivet was to shear between the plates, the joint would come apart, whereas, in a butt joint, the rivet must shear on each side of the plate, and therefore in two places.

Fig. 3247 represents a form of joint much used in locomotive practice in the United States. It is a lap joint, with a covering plate on the inside of the joint; rivets e and f are in single and rivets d in double shear.

[53]“When we have to deal with comparatively thin boiler plates, there is no difficulty in obtaining a sufficiently high percentage of strength in the joints, by using the ordinary double riveted joint, but when we have to deal with thick plates, as in the case of large marine boilers, as 1 inch or upwards, a more costly form of joint must be employed, in order to obtain the required percentage of strength at the joint; hence the ordinary double riveted joint is replaced by various other forms as follows:

“First, a triple zigzag riveted lap joint, such as shown in Fig. 3248, or a chain riveted joint as in Fig. 3249, in both of which the third row of rivets enables the rivet pitch to be increased, thus increasing the plate percentage, while the third row of rivets also increases the rivet percentage.

“Second, by employing butt joints with butt straps, either double or treble riveted.

“A double riveted butt joint with double straps is shown in Fig. 3250, and a treble with double straps in Figs. 3251 and 3252.

“Third. By various arrangements of the rivets in conjunction with butt joints and double straps, with which it is not necessary, at this point, to deal.

“One of the great advantages obtained by the use of the double strap is that of bringing the rivet into double shear (or in other words, the rivet must shear on each side of the plate, or in two places, instead of between the plates only, before the joint can give way by shearing), and thus obtaining an increased calculated strength of 1³⁄₄ times the ordinary or single shear, the rule being to find the rivet strength in the ordinary way (as before explained), and then multiply the result by 1.75.

“The Board of Trade rules for spacing the rivets of these joints are as follows:

“Dimension e is the distance from the edge of the plate to the centre of the rivet hole. Dimension v is the distance between the rows of rivets, dimension p is the pitch of the rivets, which is always measured from centre to centre of the rivets, and dimension pd is the diagonal pitch of the rivets.

“The rule for finding dimension e, whether the plates and rivets are either of steel or iron, is as follows:

“Multiply the diameter of the rivet by 3 and divide by 2, the formula being as follows:

“To find the distance v between the rows of rivets in chain riveted joints. This distance must not be less than twice the rivet diameter, and a more desirable rule is four times the rivet diameter plus 1 divided by 2, thus:

“To find the distance between the rows of zigzag riveted joints:

that is, multiply 11 times the pitch plus 4 times the rivet diameter, by the pitch plus 4 times the rivet diameter, then extract the square root and divide by 10.

“To find diagonal pitch pd, multiply the pitch p by 6, then add 4 and divide by 10, thus: