By this title I wish to distinguish this Ventilator from all such as act by the mere centrifugal force of the air: and to make this distinction the more palpable, I would add that this Machine acts like a pump, that is by means of a space alternately contracted and expanded, into which the air enters, and from which it is expelled by force as water is from a pump. The means are the following: A B (fig. 4 of Plate 20) is a hollow cylinder, of a diameter proportioned to the effect wanted to be produced. C is a cylinder closed at both ends, which fills that just mentioned as far as the length goes, excepting a play of about 1⁄8 of an inch. This interior cylinder revolves in the former; but not on its own centre. It revolves on an axis E eccentric to itself, but exactly concentric with the outer cylinder A B. The centre therefore, of the inner cylinder C, describes a circle within the outer one, which is always parallel to its circumference. On the axis of motion of this cylinder C, and outside of that A B, are fixed two cranks E F fig. 5, which exactly reach from its centre of motion to its centre of figure: so that whatever circle the latter describes in the large cylinder, the former describe the same line without it. And hence any slide or valve D, driven by these cranks, will always touch, or be equally near, the circumference of that interior cylinder C. The valve D then, worked by the bars G from without, forms a constant separation between the right and left hand parts of the lunular space left between the fixed and moveable cylinders; and if the latter turns from C by B to D, the right hand space C B G is the plenum, and the left hand space C A D is the vacuum of this Instrument; or in other words the air will flow in, through the passage H, and flow out through the passage I: and by a contrary motion of C, it would do the contrary—but I prefer the first process because any pressure within the valve D is not liable, then, to press the valve upon the drum C, and produce contact and friction; which in the second case it might do. Suffice it to add, that the quantity of air displaced at each revolution of C round its centre of motion, is the difference between the area of the drum C and that of the cylinder A B: and that its quantity at each part of the revolution is proportionate to the curvilinear triangle G B, multiplied by the length of either cylinder.
In the prospectus, this Machine was said to be good as “a gas meter,” which I still think it is. For such a purpose however, friction and eccentricity of weight should be obviated, by placing the axis E, in a perpendicular position: when I doubt not it would measure flowing gas better than many of the machines that have been proposed for that purpose.
This mode of raising water in its simplicity, is I think called the Persian wheel. The buckets hang upon centres, dip in the under water, fill themselves there, and by meeting an obstacle above which turns the buckets aside, they empty themselves into the upper back, from which the water is conveyed to the general reservoir prepared for it. This present Machine is such an extension of the above principle as to make it applicable to considerable degrees of elevation, and to many situations where a single wheel would be of no service. Having observed that in every train of wheels, the circumferences of any two wheels, have motions towards each other, as well as from each other; I perceived that, in a vertical train, this circumstance might be laid hold of to compose a machine for raising water. Be therefore, (Plate 21, fig. 1) A B C D four of a set of wheels thus intended: on the left of the lowest wheel the buckets move upward, as indicated by the arrow; while those at B move downward, coming thus to meet the former. The buckets A are full, and those B are empty; and as the latter, by the motions of the equal toothed wheels on which they are hung will infallibly meet the former, and even plunge into them at I K and L, it is only to put a clack of leather or a valve, in the bottom of all the buckets, and we have a machine that will raise water to the top-most wheel, be it ever so high, and there the water will be poured out into the vessel M, as in the common Persian wheel above alluded to. On this principle the first change of buckets will take place at I; where the lower bucket belonging to the wheel B G will take the water from the upper bucket of the wheel A H; when the bucket I will go down, nearly empty, by H and fill itself again in the under water; But the bucket of the wheel B G having now got the water, will rise by G to K, where another bucket belonging to the wheel C F will come empty, and plunging itself into that, take its water and go upward by way of C to L, where a similar change will take place and the water from L will rise by E to M, into which vessel it will be poured by the canting of the bucket as seen in the figure. Thus it appears that any number of toothed wheels geering together, surrounded with buckets valved at bottom, and receiving power from any one of their number, will raise simply and effectually a quantity of water not small in proportion to the power employed, and by means that promise great durability to the Machine.
This press (see Plate 21, fig. 2) is indefinitely powerful. It was invented for the use of my late beloved brother, then contractor with government for cleansing the sea bedding. It is composed of a centre piece A, strongly fixed to a post in the ground, the bars A B A C being suspended above it, so as to remain horizontally moveable, while describing 1⁄4 of a revolution round the general centre A. The blankets (or other goods) are put into the space s, (on a net nailed under the bars) while in the position A B; and the whole is then thrown with force towards B C; the length A C being so calculated as to cease pressing at the desired moment: for such is the power of this Machine, even without this projectile force, that were the stress not moderated, nothing could remain whole under its operation. It is clear however, that, when this operation begins at s, the relative motion of the jaws s and B is assignable, and even visible, as shewn by the dotted circles; but as the whole approaches toward B C that relative motion becomes insensible, the circles parallel, and consequently the power infinite: which is all I shall say on the theory of this Machine.
This Machine is delineated in fig. 3 of Plate 21. It has several properties which I think important in the process of grinding colours, either in a wet state or a dry. It consists of a frame A B, which has a hollow centre, through which the axis of the bevel wheel C D is brought in such manner as to geer with the bevel pinion P, in whatever position the frame A B may be placed. The axis of the pinion P carries a vessel of which E F G is a section, and in which rolls a well turned and heavy ball H, upon the colour to be ground: which it crushes in the line of direction of its centre, and to a greater or lesser width according to the diameter of the ball, as compared with the section of the groove E G, in which it rolls. Now as the motion of the vessel E G F, is oblique to the perpendicular, the contact between it and the ball does not take place in any great circle of the latter: but is constantly varying by a twist in its motion dependent upon the angle of the vessel’s inclination to the horizon. From hence arises the impossibility of any colour remaining on the ball unground: and in order likewise, that none may remain uncrushed in any part of the vessel E F G, the frame A B gives it constantly new positions, one of which is represented by the dotted lines I K: where it is seen that the ball bears on a different line of the vessel’s bottom than it did before. This also adds still greater change of action to the ball itself, and occasions (taking both these properties together) an unbounded variety of effect, which necessarily brings every particle of colour under the ball by the mere continuance of motion: and thus grinds it all without any care on the part of the attendants. It may be added, that this vibrating motion of the frame A B, is easily made to result from an eccentric stud and proper connecting rods behind the frame; all which is too easy to require further description.
In Plate 21 fig. 4, there is a representation of this Instrument. It is composed of a frame A B, containing a strong shaft C D, on which are placed the three following objects. First, a fixed pulley E, working by a strap, the Machine whose resistance is to be measured. 2ndly, a loose pulley F, receiving the power from the mover whatever it be. And 3rdly, a barrel G, which is the acting pulley, when the strap is put on it from F in the common method. But this barrel G acts by means of a barrel-spring within it, which is hooked by one end to the boss of the shaft, and the other to the rim of the barrel, as is usual for barrel-springs in general. Now the power produces the desired motion by coiling this spring to the necessary degree: and to make that degree visible, there is fixed to this barrel G a spiral s, which as the spring bends, drives outward the stud t, and with it the finger v, which, pointing to the graduated scale, shews at once the number of pounds with which the spring acts on the shaft C D to turn it. By these means the stress on the straps and on the Machine turned is known; of which also the velocity is easily determined by counting the number of revolutions performed by either of the pulleys E F G, which are alike in diameter.
In ending the first part of this work, I gave my readers room to expect this part “within three months,” and am happy now to fulfil that engagement. Although these pages contain fewer errors than the former—an apology is due for those that have crept in: to which I add the promise that every thing shall be done to lessen them further in the future parts, and wholly to correct them before the work closes.
| Page | 100, | line | 2, | for | “:”, | read ∷; |
| „ | 126, | „ | 4, | „ | “on its surface” | read at its pitch line. |
| „ | 126, | „ | 17, | „ | “its height f g,” | read the length required. |
| „ | 129, | „ | 16, | „ | “2,” | read 4, |
| „ | „ | „ | 20, | „ | “imperfect,” | read homely. |
| „ | 144, | „ | 7, | take away “alone.” | ||
| „ | „ | „ | 8, | for | “usually” | read chiefly. |
| „ | 146, | „ | 23, | for | “the friction,” | read it. |
| „ | 147, | „ | 1, | for | “nothing,” | read little or nothing. |
| In fig. 7 of Plate 19, slope the groove of both faces the same way. | ||||||
A few words seem wanting to complete the description of the Cutting Engine above given. They relate principally to the cutter-frame and cutters. Although, with a view to celerity, I have shewn the cutter out of the frame (fig. 4) yet a common frame, carrying the arbor on points, may be used with propriety; and would often be an eligible substitute for the frame above described. In cutting bevel wheels however, either on this Machine or that to be described, there is a form of the cutter frame which leaves less freedom of choice, as the cutter itself must have a peculiar form and position. To return to the cutter for spur wheels, their form (or section) depends on the degree of finish which the wheels require. For rough work they may be cylindrical on the face, the sides being under cut, so as to leave them thickest at the circumference—whence a certain coarseness of cut ensues, but without any injury to the spiral form. But, generally speaking, the cutters are best, when made a little tapering towards the edge, and toothed on both sides as well as on the circumference. The teeth should be tolerably fine, but not very so, unless great smoothness of surface were required: and we have seen above that, in this System, great smoothness is very seldom necessary, provided the obliquities be correct. I may add, that those cutters used on common engines, whose great rapidity compensates for the small number of their teeth, would not answer here, on account of the twisting motion in the wheel. But nothing prevents using cutters, so formed on the sides, as to round off the teeth in the act of cutting—only the cutter must be so thin as that its thickness, added to the aforesaid twist, may not make the spaces too wide. A little observation will render these things familiar to an attentive observer: nor shall this work conclude before all that I have gathered from long observation on this subject, be fully known to my readers.
J. W.
5, Bedford-street, Chorlton Row,
20th. November, 1822.
A NEW CENTURY OF
Inventions.
It has been observed and regretted by a well-known writer, that “a periodical work resembles a public carriage—which must depart at the usual hour, whether full or empty;”—and having undertaken to deliver this work at stated periods, I have found myself in a situation not unsimilar: the consequence of which has been a too cursory view of some of the subjects. I feel however, that this is not a sufficient apology for any essential defect: nor would it be more so to say that, although verging to old age, I am still a young author. Yet I may claim the privilege of supplying, in the latter parts of the work, what is most deficient in the former; and thus of proving that I do not intentionally neglect any thing that might make it practically useful.
With these views I commence this third part: intending first to continue the description of the Cutting Engine given at page 121, and here applied to Bevil Wheels; and then to re-consider, shortly, one or two other objects, that were too rapidly passed over in their proper places.
Plate 22, repeats at fig. 1, the first figure of Plate 15; by way of shewing the additions required to extend this method of cutting teeth, to Bevil Wheels. These additions are first, a disk n n, concentrically fixed to the main axis A B of the engine. And, second, an inclined plane o, of variable obliquity, connected by a joint with the forked sliding bar p q, by which the plane o is put in contact with the disk, at whatever distance the cutter-stand e f may be from the common centre, which distance depends, of course, on the diameter of the wheel to be cut; and to secure which is the office of the fixing screw r, in the figure.
It is now evident that for the disk n n, and the shaft A B to rise, the slide p q and the cutter-stand e f must recede: and this more or less according to the degree of obliquity of the inclined plane o, that is according to the slope of the bottom of the teeth in the wheel w: see the dotted line w p.
A circumstance presents itself, that should be here explained: when the bevil of the wheel w, or the cone of which the wheel is a part, is very obtuse, the cutter-stand e f, can not be driven back by the action of the disk n n on the plane o, without too great a stress being applied from below, to the axis A B. (See the apparatus I M O N, Plate 16, fig. 2.) In this case therefore, the handle R is not used: but a weight is suspended to the end N of the lever M N, sufficient to give the whole System A B, a tendency to rise; and the operator now acts on the screw g, so as to draw back the plane o; by which motion the disk m n with it’s axis A B is suffered to move upward, and the wheel is cut, as desired. But on the other hand when the wheels are portions of acute cones, they are cut by means of the aforesaid handle; by which the plane o and the cutter-stand are forced backward as before intimated.
We proceed now to describe the perpendicular part of the cutter stand e f; which is made double, as shewn at i k in fig. 4 of Plate 15; and is also perforated at various heights to receive the bolt which forms the centre of motion of the arm m u, the latter having a cylindrical boss u, fitted into the fork of the stand e f, and so graduated as to determine the angle of it’s obliquity to the horizon, or it’s parallelism to the dotted line w p, which indicates the slope of the bottom of the teeth on the wheel. Finally, the cutter-frame x is fastened to this arm at right angles to it, and thus forms a right angle (or nearly so) with the surface of the wheel: and is, moreover, directed to the centre, produced, of the shaft A B. This latter fact is strictly true, only when the teeth required are of so common a kind as not to require greater exactness: for in theory the sides of the cutter (supposed cylindrical) must alternately direct to that centre—namely, that side which is actually cutting: so that a provision must be made to shift the cutter spindle sideways, a distance equal to it’s diameter; this being no more than what is necessary in every system of wheel cutting.
We may also consider here, the form of the cutter itself, v, fig. 1. It is slightly conical, (more or less so according to it’s use) and of no greater diameter than the smallest width of the spaces between the teeth of the wheel. A common disk-like cutter would not produce perfect, nor even tolerable teeth on a bevil wheel. The reason of this will appear by considering that a spiral line, either on a cone or it’s base, turns more the further it is from the centre, and less the nearer it comes to it. So that a flat cutter placed at any angle, is parallel to the curve at one place only; whence the propriety of using a cutter of the kind represented in this figure. It is however true, that the first opening of the spaces may be made with a common cutter; but it should be very thin comparatively with the spaces required: and it’s cut would serve only as a sketch of such space, serving principally to permit the metal to escape while finishing the teeth with the cutter just described.
I proceed now to the examination of the plates, and the manner of adapting their length to the process of cutting spiral teeth on bevil wheels. But before entering on this subject, I would explain a kind of inadvertency into which I fell at the close of my former description of this Engine (see page 129). In my zeal to be candid in stating the properties of my Machines, I have suffered it to appear that I thought this an “imperfect” one:—an expression which, although modified among the errata, may still cause it to be looked upon as radically defective; than which nothing could be further from the idea I wished to convey. I intended merely to express the want of absolute connection between the two movements of the shaft—the rotatory and longitudinal motions. I meant that the process by this Machine was not theoretically certain, because dependent on the action of a weight (Plate 16, fig. 1 and 2) and an unforced obedience to the direction of the plates. But this small remove from rigourous principle is in my opinion much overballanced by the facility of cutting good wheels of all diameters, by the sole change of a morsel of tin, which leaves untouched every other part of the Engine.
Entering then on this branch of the subject, I first observe that if we chuse for the teeth an inclination of 15 degrees (in imitation of the cylindrical wheels) it can only be for one point of such wheels—as observed above. This point therefore I have placed at r in the middle of the face. And supposing now that at this point the wheel O were 4 inches in diameter and the wheel S two inches, these plates would be found as before by these analogies:
(1) wr, or 2 inches : 11 inches (rad. of plate rim) ∷ 26.8 : 294.8⁄2 = 147.4 plate required.
(2) vr, or 1 inch : 11 inches (rad. of plate rim) ∷ 26.8 : 294.8⁄1 = 294.8 2d. plate required.
But it is plain that the conical face, b C, (common to both wheels) is broader than the supposed cylindrical ones b e and b d: and therefore that the above plates must be made longer (to furnish the said obliquity) in the following proportions, namely: for the wheel O in the ratio of b e to b C; and for the wheel s in that of b d to b C: that is, these plates should be lengthened as the tabular cosines of the angles B A C and D A C to radius (for b e : b C ∷ A B : A C; and b d : b C ∷ A D : A C.) Thus then,
(1) Cos. 63°27′ : radius ∷ 147.4 (present plate) : required plate x, = 147.4 r⁄Cos. 63°27′; and
(2) Cos. 26°33′ : radius ∷ 294.8 (present plate) : required plate y, = 294.8 r⁄Cos. 26°33′.
Now, by the tables, cosine 26°33′ = 894, and cosine 63°27′ (it’s complement) = 447, when radius is 1000: whence dividing the two equations by r, and substituting these values of cosines 63°27′ and 26°33′ we shall find the two quantities x and y, equal. Whence it appears that for every pair of bevil wheels, whose shafts lie at right angles, the same plate serves for both wheels: only turning it once to the right, and once to the left hand on the plate rim.
And if now we measure on a scale of equal parts, the line A r and call it 100, we shall find the line w r (near enough for practice) to be 90, and the line v r to be 45, and these numbers respectively, put for rad. for cos. 26°33′, and for cos. 63°27′, will make the first equation x = 147.4 × 100⁄45 and y = 294.8 × 100⁄90 or x = 327.55 and y = 327.55, &c. confirming the above deduction that the same plate serves for both wheels; and giving, withal, the length of the plate required.
In performing this operation by actual measurement of the lines, I have had in view to trace a path for those of my readers who may not have the tables, or may be unaccustomed to use them. The process, generally, is to take the diameter of any bevil wheel O fig. 4, in the middle of it’s face; and supposing it a spur wheel, to find it’s plate by the method above given: and then to multiply the length of that plate by the line A r and divide the product by the line A w, both measured on the same scale of equal parts.
It may be well to observe, likewise, that the same method of finding the plates, applies to bevil wheels of every description or angle: but that it does not give equal plates for every pair, except in the above case of wheels placed at right angles to each other.
I would just remark that by the figure near B, is shewn a section of the Machine on which I centre the wheels to be cut on this Engine. It is an inverted cup s t, into which the arbor is screwed in a true position; and this cup is fixed on the top of the shaft A B, by the three pressure screws near s t, which enter a triangular neck made round the shaft, against the upper slope of which, the screws press so as to draw the cup downward in the act of centering it. This I say is my present method; but it is in a measure accidental, the shaft not having been perforated to receive arbors of the usual kind. Mine, however, have their utility in the ease with which they are varied in size, and changed on the Machine: but on their comparative usefulness I give no opinion. The other is the most solid method.
In the description of my differential Steel-yard, (see page 163) I stated that the load P was wholly collected in the point o; and that dividing the line A C by the line A o, the power of the Machine was known. But I should have shewn that this line (A o) is equal to one half the difference between the arms A D and A E. To do this, here, (see Plate 23, fig. 4) I take the Machine in the state of infinite power, before mentioned; and observe, that in moving the point of suspension from o towards A, I at once lengthen the arm A E, and shorten the arm A D: by which process, (supposing each arm to have been called a) that which I lengthen by any quantity d becomes a + d, and that which I shorten by the same quantity becomes a - d, and the difference of these quantities, is 2d: so that the line A o is in reality one half the difference between the two arms A D and A E as was required to be shewn.
But we may go a step further: The two arms of the equibrachial lever x y may likewise be made unequal: and the line s a be subdivided in any ratio: which division will augment still more the power of this Machine. If for example, we hang the load on the point v, halfway between a and s, that power will be doubled; for the line c v (representing the space moved through by the load in this case) is only one half of that w s, or o q, and might be still less at pleasure. Thus the whole power of the Machine is now found by dividing the length of the long arm, beyond D, by the line a v, instead of the former line A o, or dividing the motion of it’s extremity upward, by the line c v, the motion downward, of the load P.
It has been further suggested, that the description of my excentric Bar Press was not sufficiently explicit. I have therefore added the figure 2 of Plate 22, to assist in elucidating that description. I had, perhaps made an undue use of the principle of virtual velocities by saying, too concisely, (page 174) that “as the whole approaches toward B C, the relative motion (of the cheeks s and B) becomes insensible, the circles parallel, and consequently, the power infinite.” It is however vulgarly said that power cannot be gained without losing time—which implies that if time is lost, power will be gained: and the principle of virtual velocities says the same thing, though in more appropriate terms—that if a small movement be given to a system of bodies actually counterpoising each other, the quantity of motion with which one body ascends, and the other descends perpendicularly, will be equal: so that, as remarked in page 50, by “whatever means a slow motion is obtained, dependent on that of a moving force, the power is great in the same proportion.” Now, in the eccentric Bar Press, (see fig. 2) this is so in an eminent degree: for when the bars are in the position A B, the distance of the cheeks is equal to B s; and they must move, circularly, as far as A f, to bring them closer to each other by the quantity s a: dividing therefore, the distance B g by the line s a, we find (near enough for practice) the power of the Machine within the limits A g B. It is nearly as 10 to 1. In like manner this power at A e g, is equal to the arc e g divided by the line f b; and at A l n to the arc l n divided by the line d k, namely by the difference of the lines k l and m n. From the above it appears that the nearing motion of the cheeks of the press, becomes slower and slower as the bars A and C come nearer to the point C: insomuch that the difference between the lines m n and o p is nearly imperceptible, and that between the lines o p and C q entirely so. But according to the above process, the distance p C should be divided by this imperceptible line, to find the power of the press at the point C; which therefore is immense. Another proof of this may be drawn from the supposition (see fig. 3) that the small lever a d is turned round the centre o by a bar o C fixed to it, and of equal length with the line A C fig. 2. Fig. 3 shews that the lines or bars C d, and a C are moved endwise by the circular action of the points a and d; and therefore (by statics) their motion is the same as though caused by the perpendiculars b o and o c let down from the centre o, on each of them. Hence the power of this Machine is found by dividing the distance o C by the sum of the lines b o and o c; which sum (when these lines vanish by the union of the bars over the centre) becomes infinitely small: the quotient of which division therefore is infinitely great—as was to be shewn.
The usual method of making Punches for engraving Copper Cylinders, (otherwise than by the milling system) is to cut the desired pattern on a die, and then to transfer that pattern by blows or pressure to the punch, from which it is again transferred to the cylinder. My Machine in this operation, unites motion to the needful pressure; and thus renders the result more easy and complete. This effect I could the better ensure, because the surfaces of my punches are essentially convex, or rather cylindrical; as will appear when my engraving Machine comes to be described. Their convexity however, can be diminished at pleasure—whence this Machine is capable of offering useful assistance to a maker of flat punches.
In Plate 23, A B fig. 1 and 2, is the body of the Machine, with the vibrating bar C D laid upon it; reposing especially on the correct and level parts of the body at a b; this bar contains the die c, with which it vibrates between the cheeks B R, as impelled by the screws E F, it’s centre of motion being the pin P, duly supported by the strong shoulder A. In a line with the bar C D, is placed a second vibrator G, containing the steel d, that is to become a punch, already rounded into the cylindrical shape it must have when finished. This vibrator has it’s centre of motion at e fig. 1, and it need not be added that the curvature of the punch depends on it’s distance e d from that centre: for the centre of the long bar C D is so distant as to have little influence on it’s formation. Further, the cap or bridge H I, which furnishes a centre for the smaller vibrator G, can be brought forward to any useful position by the nuts K L: that cap sliding horizontally between the cheeks M N as directed by the small arms m n. This motion, then, taken from the nuts K L, serves to impress the work of the die on the steel prepared for the punch; and this being done to a first degree, both the handles O Q, are laid hold of: and by turning the screws the same way one of them goes forward and the other recedes, until the punch and die have been in contact over half their surface. At this moment both screws are turned backward, and the motions of the two vibrators reversed: by the repetition of which alternate motions accompanied by the needful pressure, the whole pattern is transferred from the die to the punch—when the latter is taken out of the Machine, and filed up in the usual method.
It should be observed, that the smaller vibrator G can be displaced with ease when the nuts K L are withdrawn: and this should be frequently done to examine the progress of the impression. Nor is there any difficulty in re-entering the figures. In a word, the perfection of this process depends more on much motion than on violent pressure: whence this facility of re-entering is a desirable property. This Machine is usually laid on a bench or tressel, with a long mortice in it, into which the feather x of this Machine enters so as to be firmly fixed.
I was the rather induced to attend a second time to the differential Steel-yard, because I had it in contemplation to apply that principle to the present purpose; since, to make flat punches, is to some engravers a more desirable thing than to make cylindrical ones. I am not fully persuaded that it is even possible to transfer a large pattern, from a flat die to a flat punch, by any pressure acting simultaneously on the whole surface. In those cases, if there is much work, the whole surface goes down; and the parts that form the pattern do not rise. But, all that can be done in this case, is, I believe, feasible by the Machine now to be described.
Plate 23, gives in fig. 3 and 4, a representation of this Machine; A B and C D, are two slides, having wedge-formed ends above A and below D, well made, well steeled, and well tempered. One of these slides contains the die and the other the steel prepared for the punch (see B C). These wedge-ended slides are embraced by two levers E F, G H, which are themselves connected by two stirrups I K and L M, better shewn at fig. 3. These latter are supposed in fig. 4 to be broken at L M, to leave the levers E F and G H more visible. They are formed, at the turning below, into wedge-like edges a b; well hardened, that clip the nicks c d of the lower lever: and at the top of the Machine their arms e f, pass through the caps m n, above which they are nutted like a common bolt, and made to press strongly on the main lever E F. The stirrup placed to the right hand, presses in particular, by it’s cap n, on the moveable step o, exactly in the notch q: this step having a backward and forward motion communicated by the regulating screw p. Before beginning to use this Machine, I make all it’s arms A E, A g, D e, D d, equal, when it’s power (see page 162) is infinite; and to put it in a working state, I turn the screw p backward, say one half round: which motion (if the screw has 20 threads to the inch) makes a difference in the two arms A r and A q of 1⁄40 of an inch, and the virtual centre of the Machine is therefore 1⁄80 of an inch from the former point A, that is from the edge of the slide A in this fig. 3. Supposing now, the whole working lever E F to be 3 feet, and the workman’s force to be 100lbs. in each arm, then by displacing the lever to any proper distance from F towards f, he will produce a pressure between the die and the punch of 200lbs. multiplied by 1440, the number of times that 1⁄80 of an inch is contained in 18 inches.—That is, a pressure of two hundred and eighty-eight thousand pounds!
I have been seduced, by the anticipated brilliancy of this result, from the regular course of description,—and the plate w x, y z, which forms the base or frame of this whole Machine has not yet been spoken of. But that plate is supposed screwed down to a horizontal bench, at or near the height of a man’s breast; the slides or cases are fastened to it, and the man is supposed to work the Machine nearly as he would a die-stock in tapping a screw. This however is not indispensable; the Machine might be placed vertically, and these motions given by any proper mover; or a weight may be suspended to the arm F, so as to add continuity to pressure. It is however important, that the position should comport with the frequent extraction of the punch in order to examine the progress of the work, or cut away any redundant metal. I have before given it as my opinion that much could not be expected from mere pressure: but this is a pressure of a peculiar kind, consisting of immense powers with very short motions. In this respect it is just what was wanted, as it can be renewed and repeated frequently, without loss of time. And the more to facilitate this delicate operation, the hollow slides or cases B C, are made slightly pyramidical, to be furnished with set-screws on the four sides, by which to change the place of bearing; and thus to meet the case of a flat punch with the advantage of impressing it by portions, so as to have only to finish it by brute pressure.
The foregoing application of the principle of the differential Steel-yard, is, I think, important, and founded on unobjectionable principles; for although by changing alone the place of the step o, we disturb a little the parallelism of the stirrups I K, and L M; we do it not enough to produce, any material change in the theoretical result. With respect then to the lesser properties of this Machine, I leave them with confidence in the hands of those whom they most concern—who doubtless, will treat them with greater practical utility than I could myself hope to do.