3. Platforms or tables, and benches. - Wooden platforms em-ployed for supporting the work have sometimes iron stems, and are in fact, extensions of fig. 733, except that they are placed above the center, so that one-third the saw-plate protrudes perpendicularly through the center of the platform. But a large platform thus constructed is very weak, from being attached only at one point; and every time the platform is fixed, there is the trouble of placing the saw-kerf exactly parallel with the saw, otherwise great friction ensues.
The saw platform and apparatus in fig. 735, are made almost entirely in wood; they are applicable to the ordinary turning lathe, and to saws not exceeding about 8 to 10 inches in diameter. The wooden platform is supported at the front and back, nearly throughout its width, upon the edges of the wooden box, the position of which is defined by a tenon fitting between the lathe bed, and secured by a bolt passing through the same. The platform is hinged to the back of the box, thus constituting as it were, a large and overhanging cover. The last process in the construction of the apparatus, is to fix it upon the lathe bearers, and to allow its own circular saw to cut the saw-kerf or slit in the platform, which thence becomes exactly parallel with the saw.
In refixing the apparatus ready for work, the wood frame is first placed loosely on the bearers, and the platform is turned up; the saw spindle is then adjusted between the centers, and lastly, the platform is shifted sideways until the saw enters the kerf, the entire wood frame is then secured by its bolt and nut; but owing to the tenon beneath, there is no risk of the groove being otherwise than parallel with the saw. Occasionally that part of the platform which is contiguous to the saw, is covered with a thin plate of brass to increase its durability.
The sawing apparatus, fig. 735, although made principally in wood, will be found a very convenient appendage to the turning lathe; or the same parts may be used independently of the lathe, upon a wooden bench or frame with a wheel and treadle, much the same as that partly represented in the succeeding figure, except that the wooden standards are then required to extend above the bearers, so as to carry the center screws for the saw spindle. The back board for receiving any parts of the work under progress, and the drawer for the saws, are convenient for their respective purposes, but by no means important.
The sawing machinery represented in fig. 736, although generally similar to the last, is made entirely in metal, except the wooden frame. The principal piece in fig. 736, or the bed piece, is planed fiat on its underside, and has a fillet to adapt it to the lathe bearers or other frame; the ends of the casting are formed as popit heads, and are tapped for the reception of the center screws, which support the saw spindle. The middle of the bed piece is formed as the box or trough, to which the platform is hinged by two center screws, tapped into projections on the underside of the platform, the front part of which rests upon the supporting screw, fitted into the bed piece.
In general construction the iron machine fig. 736 is a great improvement on that in wood, fig. 735, in respect to strength and permanent accuracy; and an the supports for the spindle and platform, are all united in one iron casting, the mechanism is not subject to derangement, and is quite independent of the frame or beneh, which may be cither that partly represent. in the figure or the frame of an ordinary foot lathe after the removal of the headstocks; or on any bench whatsoever, provided mot power from any source can be conveniently applied to the saw spindle. And in the course of the following descriptions it will be seen, that the latter machine, with certain additional mechan-ism, is capable of performing, within the limitation of its size, almost any kind of work to which the circular saw is applied.
4. Stops to prevent the vibration of flexible saws. - When the diameter of the circular saw is considerable, compared with the diameter of the flange on the spindle, the blade becomes very flexible, and may be easily diverted sideways from the true plane; the prevention of this is accomplished in many ways.
The saws used for slitting the thin wood of which cedar pencils are made, are from about 4 to 6 inches diameter, and very thin, so as to act rapidly and with little waste; such saws have frequently supplementary collars, or thick flat plates of brass, fitted to the cylindrical neck of the spindle, and extending to within 1/2 or 3/4 of an inch of the edge of the saw, which thereby nearly acquires the stiffness of the collars themselves. But as saws are in general required for thicker wood, such large flanges are mostly inadmissible, and other methods must be employed.
For small saw machines having wood platforms, it is generally considered sufficient, that the saw should work in a narrow cut or groove made by the revolving blade in the platform, and which allows the saw but very little lateral play; as the teeth can no longer cut when the smooth part of the blade rubs against the slit. The friction will in time wear away the wood until the slit becomes inconveniently wide, but a fresh piece of wood can be then inlaid, and another notch made by the saw as at first.
Metal platforms arc sometimes made in two parts for the convenience of forming the slit for the saw, but friction against the metal would blunt the teeth, and should be avoided. In such cases, the inner edges of metal platforms made in two pieces are usually tapped for small screws, which are adjusted very nearly to grasp the smooth part of the saw, just within the line of its teeth. The platform fig. 736, is made in only one piece, with a wide shallow groove in its upper surface, which is again filled up flush with a bar of iron, in the end of which is a deep notch to admit the saw, and at right angles thereto the stop screws are inserted laterally in the bar. The latter can be adjusted in the groove, to place the stop screws just within the line of the teeth, after which they are twisted by their capstan heads until they nearly touch the saw plates.
But stop screws, howsoever constructed, give rise to noise, and are somewhat liable to wear the saw into grooves. A preferable mode for small saws, is to inlay a piece of ivory or hard wood in the groove on the top of the platform, and allow the saw to cut its own slit; or else to fit two pieces of ivory into dovetail grooves, made transversely in the under sides of the platform, and to advance them to the saw by adjusting screws, but which, although a more costly method, is no better, as in every case the stops should be as nearly as possible flush with the platform; various other stops will be described in speaking of large sawing machinery.
5. Parallel guides for small circular saws. - Saw machines of every kind, depend very materially for their usefulness on the various guide principles introduced into their several constructions, and upon the advantage of which principles, as applied to cutting tools generally, some preliminary observations were offered in pages 463 to 471 of the volume now in the reader's hands.
In circular sawing machinery, the table or platform being a flat surface, and the saw-blade at right angles thereto, all pieces that lie tolerably flat on the saw-bench are sure to be so guided as to be cut out of winding, and square with the face on which they lie. But to guide them across in a right line, it is requisite to have some kind of rectilinear guide parallel with the saw; the width of the piece sawn off' then becomes equal to the distance between the saw and guide, and any number of succeeding pieces may be produced exactly of the same width.
The guides for parallelism are constructed in many ways, three of which, available for small sawing machines, will be noticed at this place; the jointed parallel rules are also used, and will be described in subdivision 5 of the next section.
The most simple parallel guide, is a straight bar of wood fixed to the platform by a screw clamp at each end, or by two screws passing through transverse mortises in the ends of the bar; but two sets of guaduations are then required on the platform, to place the straight fence or bar exactly parallel with the saw.
Sometimes a shallow groove, inclined 30 to 40 degrees with the saw, is made in the top of the platform, and fitted with a slide, the overhanging edge of which is also inclined 80 to 40 degrees, so as to be always parallel with the saw; the variation of width arises from placing the guide in different parts of the groove. This may be considered a modification of the principle employed in the Marquois scales and parallel rule, but as a saw-guide the range is rather too limited.
A more convenient guide was suggested by Professor Willis of Cambridge, and is shown in figs. 735 and 736. The first is simply a square, the two bars of which are not in the same plane, as the one bar lies upon the platform, the other is flush with it, and fitted to the back edge of the platform by a groove and tongue joint: a screw-clamp is there situated, to fix the one bar of the square to the platform, after the position of the other bar has been adjusted to the width required in the works. This parallel guide may be allowed to extend altogether beyond the sides of the platform, so as to have fully twice the range of the jointed parallel rules, to be described hereafter, and is besides steady alike in every position, provided the surfaces by which the two bars are united are sufficiently large, and firmly joined. The parallel guide in fig. 736, is made in iron, and also after Professor Willis's plan; but the back bar, then lies in a rebate in the platform, and is secured by a small clamp and screw, partly seen.
6. Sawing the tides of rectangular pieces. - Before commencing to saw a piece of wood with the circular saw, it is desirable, in order to ensure accuracy in the result, that two neighbouring faces of the work should be moderately straight, to serve as the basis from which to commence; otherwise as the work is thrust past the saw with the hand, it may assume different positions in its course, and thereby give rise to enormous friction against the saw, and may also present, when finished, curved instead of flat surfaces.
Round wood is in general too large to be cut up with the small saw-machines here referred to, but particulars of the mode adopted in large machines, are given in the corresponding sub-division of the next section. It may however be observed, that when the first cut is diametrical, small round wood may be held with tolerable facility to the saw, and it is sometimes sawn at twice, or with two radial cuts, from opposite sides, but which cannot be expected exactly to meet. When the first cut is required to be on one side the center, it is much the best plan to flatten some part of the wood with the hand-saw or plane, to serve as the bed on which the work may rest upon the platform.