The method of mounting saws of small size, such as are suited to be worked by the treadle of a foot-lathe, is shown in [Fig. 183]. E is a steel spindle, of which the diameter equals that of the central hole in the saw B. At F, about the middle of the spindle, is a fixed flange, at the base of which is a short feather or inlaid key, X [184], which fits the small slot seen in the centre of the saw and reaches also within a similar slot in the movable flange, G, but it must not be so long as to come through to the back of the latter. This flange and nut H having been removed, the saw is slid upon the spindle till it rests against the fixed flange; the movable one is now to be brought against it and clamped by the nut. The spindle is sometimes made with a square end to fit the square hole chuck, and centred at the other, or it is drilled at both ends, so as to be driven by the carrier or driver chuck, C, D. It must be so placed as to run towards the operator. The above arrangement must now be made complete by the addition of a platform, B, on which to lay the work that is to be sawn, and on which some contrivance can be adjusted to guide the passage of the saw through the same, so as to cut the work in parallel pieces, or at any desired angle, such as would be necessary for mitred joints. For the general uses of the amateur a mahogany or hardwood platform is as good as any, and such as is delineated in vol. ii. of Holtzapffel's valuable work is perhaps the best arrangement. The saw table rests on the opposite ends of a kind of open box, which is represented without the two sides, although they may be added if desired, and the whole when removed from the lathe would then form a case for the saws, or serve other similar purpose. The platform is hinged, so as to overlap, as seen in the [Fig. 184A], and there is in the middle of it a slit cut by the saw itself, which, when it is mounted on its centres will be in the position shown. If sides are added a notch must be made in the upper edge of both for the passage of the spindle. The fillet B fits between the bearers of the lathe, securing the parallelism of the whole. When made with four sides the box must first be placed on the lathe bed and loosely held by the bolt beneath. The saw is then mounted, and the box adjusted to its place and fixed. The cover is then (if for the first time) brought carefully down upon the saw, and the lathe being put in motion the slit is made, and its position will be truly at right angles with the spindle and the lathe bed. Of course, in future operations the platform is lowered over the saw before the holding down bolt is permanently screwed up. The sides of the saw-kerf may be edged with brass if preferred, but on the whole the plan is not to be recommended, for if, as will occasionally happen, the saw should get slightly out of truth, or vibrate a little when in use, the teeth will come into contact with the metal and be blunted or broken. If the saw-kerf by constant wear should widen too much, the whole platform is renewable at little cost, or a new piece can be let in, and a fresh saw-kerf made. There are several guides for parallel work. The one shown in [Fig. 185] is precisely such as is to be seen in the ordinary parallel ruler—A is the back bar screwed to the platform at the right-hand edge; B the guide or fence which, when the connecting links C, C are perpendicular to A, should touch the saw; D, D are arcs of circles of which E, E are the centres. They may be arcs of brass pivoted to the links and passing through a slot in the bar, A, A, or may themselves be cut as mortises in the platform, in which fit a pair of bolts with thumb-nuts passing through the links, by which to clamp the fence in any desired position. This form of parallel guide is not very substantial, and is not correct in practice unless the pins are very nicely fitted, and the links precisely of a length. The second figure shows the sectional form of the fence G, the links being represented at H, and the fixed bar at K. The following is a more solid and unyielding guide, and much to be preferred. Holtzapffel attributes it to Professor Willis. It is merely a modification of the T-square as used with the ordinary drawing board with an arrangement for fixing it in the required position. The present arrangement differs from that in Holtzapffel's work in the manner of fixing it and the addition of a second T-piece on the side next the workman. In [Fig. 186] A is the upright part of the fence, B the bottom or sole, to which is attached at each end the T or cross pieces, E, E, which slide along the straight edges of the platform and secure the constant parallelism of the fence to the surface of the saw; C is the groove or slot, in which a screw, D, traverses, and the fence is thus fixed by a turn of the thumb-nut, D. This fence can by no possibility get out of truth; it is easily removed by taking out the single screw, and it is far more simple and more easily made than the one previously described. The nearest edge of the platform may be marked in inches and eighths, and the fence can then be instantaneously adjusted for sawing pieces of any desired width. It is not always, however, that straight, rectangular, or parallel strips are required, and an additional arrangement is needed to form a guide for sawing angular pieces. Now it is not sufficient to lay the guide fence at a given angle, for if the latter were arranged for that adjustment by taking off the tees and causing it to turn upon the screw which secures it in place, and a piece of board were placed against it to be sawn, the latter would press against the saw sideways as seen in [Fig. 187]. The guide fence for angles must itself therefore travel in a line parallel to the saw and carry with it the piece to be cut. The simplest and usual arrangement is that given in Holtzapffel's work. A dovetailed groove in the platform running in a direction parallel with the saw carries a sector attached to a bar which fits the groove, and this bar is free to move forward or backward without lateral movement. The piece to be sawn is thus rested against the fence forming the straight face of the sector, and the whole is moved forward together against the edge of the saw. [Fig. 188] explains this. It will be seen that several grooves are made side by side, all of which fit the slide alike, and by moving the latter into either of these a lateral adjustment is effected to suit pieces of different widths. The sliding strip should be made of hard wood and nicely fitted, and may be lubricated with soap, or polished with black lead, either of which will cause it to slide with diminished friction. [Fig. 189] shows a somewhat different arrangement, by which more lateral adjustment may be given. The sector is replaced by a T-square, the blade of which has a slot through which a screw passes into the sliding bar. A second jointed rod is added, passing through a staple in the slide, and by a screw in the latter the T is fixed as required. The staple must turn on a centre to accommodate itself to all positions of the T-square, and a second eye may be placed on the opposite arm to allow the guide rod to be removed to that side, which is sometimes more convenient. The sector also may be made adjustable as in [Fig. 190], and clamped by a simple screw in the slot. Either of the above methods will allow sufficient range for small work, such as is likely to be the object of amateurs or those who add small saws to the foot lathe. The guide for angular pieces may indeed be in many cases dispensed with by making use of patterns of wood chiefly in the form of triangles; these sliding against the parallel guide, and carrying the work with them, will answer well in a number of cases where other provision for such work has not been made in arranging the saw table. It must be remembered, however, that in this case the length of the piece (supposing it to be the side of a picture frame to be mitred) is limited to the space between the fence and the saw, which in the more perfect arrangement is an evil plainly avoided. It may sometimes be necessary to cut pieces with various angles not in the same plane. By using the hinged platform, and adding a screw attached to the front of the box, and standing perpendicularly, the front of the table can be raised to a given angle, but those who are likely to enter extensively into the cutting mathematical figures are referred to vol. ii. of Holtzapffel's work, where the subject is fully explained and illustrated. The following remarks upon the proper speed of saws and sizes of teeth are copied from that work, and may therefore be relied on:—
"The harder the wood the smaller and more upright should be the teeth, and the less the velocity of the saw.
"In cutting with the grain the teeth should be coarse and inclined, so as rather to remove shreds than sawdust.
"In cutting across the grain the teeth should be finer and more upright, and the velocity greater, so that each fibre may be cut by the passage of some few of the consecutive teeth rather than be torn asunder by the passage of one tooth only.
"For gummy or resinous woods and ivory, the saw teeth must be keen, and the speed comparatively slow, to avoid the dust becoming adhesive (by reason of the heat engendered by friction), and thus sticking to, and impeding the action of the saw."
Fig. 186.
Fig. 187.