In using hand-tools the instrument rests immediately upon the face of the work under formation; and in repeating any one result, the same careful attention is again required in every successive piece. But it was explained in the last chapter, that in the machines acting by cutting, the accuracy is ensured far more readily, by running either the work or the tool, upon a straight slide, an axis, or other guide, the perfection of which has been carefully adjusted in the first formation of the machine; and the slide or movement copies upon the work, its own relative degree of perfection. The economy of these applications is therefore generally very great, and they are frequently most interesting, on account of the curious transitions to be observed from the hand-processes to the machines, in some cases with but little, in others with considerable change in the general mode of procedure.
The first planing machine for wood is supposed to have been that invented by General Bentham, who took out a patent for it in 1791; it was based on the action of the ordinary plane, the movements of which it closely followed. This contrivance reduced the amount of skill required in the workman, but not that of the labour; it appears to have been but little used. The board to be planed was sometimes laid on a bench, at other times fixed by long cheeks having teeth which penetrated its edges; the iron of the plane extended the full width of the board, and the stock of the plane had slips to rest on the bench and check the cutting action, when the board was reduced to the intended thickness, much the same as in the reglet plane, fig. 310.
For feather-edged boards, the two slips were of unequal thicknesses; for those intended to be taper in their length, the guide rails had a corresponding obliquity, and were fixed to the bench. The plane was moved to and fro by a crank, it was held clown to its work by weights, and the plane was lifted up in the back stroke to remove the friction against the cutter.*
The scale-board plane, abbreviated into scabbard-plane, for cutting off the wide chips used for making hat and bonnet boxes, is, in like manner, a plane exceeding the width of the board; it is loaded with weights, and dragged along by a rope and windlass, the projection of the iron determines the thickness of each shaving or scale-board. This construction is also reversed, by employing a fixed iron, drawing the wood over it, and letting the scale-board descend through an aperture in the bench; each of these modes is distinctly based on the common plane. See Appendix, Note A. N., page 981.
The late Mr. Joseph Bramah took out a patent in 1802 for a planing machine for wood; one of which may be seen in the Gun Carriage Department, Woolwich Arsenal. The timber is passed under a large horizontal wheel, driven by the steam-engine at about ninety revolutions per minute; the face of the wheel is armed with a series of twenty-eight gouges, placed horizontally and in succession around it; the first gouge is a little more distant from the center, and a little more elevated than the next, and so on. The finishing tools are two double irons, just like those of the joiner, but without the advantage of the mouth.
Mr. Bramah employed the principle of his famous hydrostatic press (patented in 1791), both for raising the cutter wheel to suit the different thicknesses of wood, and also for traversing the timber under the cutters upon guide rails; the latter, by means of an endless chain connected with the piston of the pump, by a rack, pinion, and drum. The bottom of the axis of the cutter wheel is cylindrical to the extent of its vertical adjustment, and is fitted in a tube terminating at its upper part, in a cupped leather collar, impervious to oil or water, as in the hydrostatic press. The injection of water into the tube by a small force-pump, lengthens the column of fluid, upon which the wheel is supported as on a solid post; the descent of the wheel is effected by allowing a portion of water to escape by a valve. †
* See the Encyclopedia Metropolitana, etc. etc. † Mr. Bramah's patent includes many modifications of fixed and revolving
A more recent machine for planing looting boardS, and other wood works, consists of a series of knives placed parallel with, and around the axis of, a small cylinder; the hoard is passed underneath the cutter whilst it is in rapid motion; this may he called an adzing machine, and the knives are of the full width of the board.
In Mr. Muir's patent planing machine for flooring boards, a rotary adze roughly planes the bottom, another operates on the top of the hoard; afterwards, two oblique fixed cutters, like the skew-rebate irons, but with top irons, remove each a shaving of the full length and width of the deal; two cutters make the sides parallel, and two others groove the edges for the tongues, or in fact, these are four revolving planes or saws in order to expedite their effect. The board enters the machine as left from the saw-mill, it is thrust forward by the engine, and comes out wry speedily in a condition nearly ready for fixing, the eight operations being simultaneous; but sometimes a little finishing with the hand-smoothing plane is required at those parts where the grain is unfavourable to smooth cutting. Other machines, by Paxton, by Burnett and Poyer, and others, are used for preparing sash-bars, and similar works.* See Appendix, Notes A.O, & A.P., pages 981 & 982.
The preceding machines are mostly intended to work with the grain; and I am only acquainted with one rectilinear planing machine that is exclusively intended for cutting across the grain, namely, the mortising engine, one of the series of machines erected at Portsmouth in 1807, by Mr. Brunei, for the manufacture of ships' blocks.†
A hole is first bored through the block at the commencement of the intended groove for the sheave, and it is extended by the successive action of a mortising or paring tool, which rides cutters, for planing and cutting wood and metal works; also a machine for turning spheres, and for cutting wooden bowls one out of the other, and likewise other mechanical contrivances. See Specification, Gregory's Mechanics, vol. ii. p. 415.
* See the description of Paxton's machine, Trans. Soc. of Arts, vol. liii. p. 97; see also specification of Burnett and Payer's patent.
The reader is likewise referred to the foot-note, page 32, vol. i, on Taylors patent machine for chopping out the stares for casks; a similar mode was previously employed forchipping into fragments the dye-woods, the logs of which fell against the revolving disk through an inclined shoot.
† Now Sir Mark Isambard Brunel.
perpendicularly up and down; just before the tool descends, the block is traversed a quantity equal to each cut or shaving.
The cutter is made cylindrical, and is formed just like a quill pen, but solid and with an elliptical cutting edge instead of the points. "The chisels are provided with small teeth, which are fitted into dove-tailed notches formed in the blade of the chisel. These are called scribers, they have a sharp edge projecting a short distance beyond the inside edge of the chisel, and therefore in descending through the mortise, the scribers cut the sides of the mortise fair, and make two clefts which separate the chip (which will be cut out at the next stroke), at its edges from the inside of the mortise, so that the chip comes out clean without splitting at the edges, and this makes the inside of the mortise as clean and smooth as possible."* A hole is drilled nearly in the axis of the cylinder, for the insertion of a pin, by which the shavings are thrust out when they happen to clog the hole.
By forming the tool of a semicircular section and with two small fins, or edges projecting at right angles from the ends of the diameter, and then sharpening it so that the diameter becomes a straight chisel-edge, the scribing points are formed in the solid with the chisel, and are continually restored as the tool is sharpened. The tool is then perfectly analogous to fig. 334, page 485, if we suppose the plane condensed into a long chisel of semicircular section, equal to the diameter of the hole, the progressive elongation of which it has to effect.
There are many useful applications of revolving figured planes, moving through curved paths, by which we obtain figures of double curvature, as explained in the theoretical diagram, fig. 317, page 464. Mr. Brunei introduced an example of this in the scoring engine, one of the machines recently adverted to, for the manufacture of ships' blocks.
It is intended to form the groove around the block, for the rope by which it is attached to the rigging. The revolving plane is a disk of brass with a round edge and two cutters, inserted at an angle of about 30° with the radius; it traverses around the one side of the block, and receives its direction from a shaper plate or pattern placed parallel with the block, by which
* Rees's Cyclopedia, article "Machinery for manufacturing Ships' Blocks." arrangement the cutter makes the groove deep at the ends, but shallow where it passes the pin or axis of the sheave. The same method has been subsequently extended to shaping the entire block with cutters of the full width, applied at four times.*
These several machines are compounds of slides and guides, and of fixed or revolving planes: the relative degrees of perfection attained, depend on the stability of the machines, and their respective agreement with the principles of the ordinary hand tools which are generally themselves, the last stages of a long series of gradual improvements.
But the absence of some of the true characters of the plane, in nearly the whole of the machines for wood, namely, the proper obliquities of the iron, the frequent want of the mouth of the plane, and of the top or breaker iron, which so greatly restrains the splitting and tearing up of the fibres, prevent the machines from producing, in the softer woods, the smooth finished work of hand tools, in the management of which the judgment of the operator can be employed to combat the peculiarities of fibre. But the enormous productive powers of such machines, out-weigh these drawbacks, and the more especially so, as the general forms or outlines are repeated by them in a most exact manner, and a little after-trimming by hand imparts the necessary finish.
In speaking of the apparatus for ornamental turning, there will be occasion to show that these same principles are strictly embodied in miniature, in the various parts of the complex lathe for ornamental turning; but as the hardwood and ivory therein generally used, admit of the employment of scraping-tools, not requiring either the obliquity of the cutter, or the mouth of the plane, the above objections do not apply to them, and their several results exhibit a much nearer approach to perfection.
* In revolving planes for wood, the cutters should always present an obliquity of about 30° to the radius, otherwise, or when the cutters are placed radially, they only scrape, or act like saws. Some of these planes are made of one disk of steel, in which ease there are four, five, or six openings, like the mouths of rebate planes; the one side of each wedge or cutter is now a part of the circumference, the other is elevated some 20 or SO degrees, thereby resembling the spokeshave iron. This form of cutter, although nearly perfect, is very expensive, and difficult to maintain in order.