The hack-saw attachment shown in elevation and plan as Figs. 1 and 2 can be removed and replaced as quickly and easily as a face plate and T-rest, and is of a size to suit a 6 in. center lathe; but the dimensions may be altered to suit any other size of lathe if necessary.
The first thing to do is to get out the patterns and send them to the foundry. In all, six iron castings will be required, these being for the driving plate A, the saw frame guide B, the collar C, the vice D, the movable jaw E and the counterweight (Fig. 3), which is 6 in. long and 3 in. in diameter. Patterns for the driving plate and collar should be made to the dimensions given in Fig. 4, where the separate collar is shown on the left; this illustration being a section on the line X X (Fig. 2), with the saw-frame guide omitted. The guide pattern should be made to the dimensions given in Figs. 1, 5 and 6. Attention must be paid to the circular-bearing part of the casting, which is continued along the lines in the form of a rib. Fig. 5 is a section on the line Y Y (Fig. 1). The boss at the back of this casting carries a 3/4-in. iron rod, on which the counterweight is clamped.
The vice is a hollow casting as far as the dotted line HH (Fig. 1), the remainder being solid, to enable a 3/4-in. bolt to be tapped in for the purpose of clamping the vice to the lathe bed. This end of the casting is half-round, as shown in section at Fig. 7, and continues so until it nears the vice jaws, when it merges into a flat top with vertical sides. The fixed jaw is solid, and is added to the pattern after the body is built up. On the flat top of this casting is a £ in. slot, which extends from the fixed jaw to within 3/4 in. of the extremity, this slot being either cast in or cut out afterwards, whichever method is more convenient. Beneath the flat top and on the edges of the 5/8- in. slot are two racks of teeth 1/4 in. deep, 3/8 in. apart, and 1/2 in. wide, into which fits the tail of the bolt that tightens the loose jaw on to the work. Fig. 8, which is a section on the line Z Z (Fig. 2), shows the method of tightening the work. The hole in the loose jaw of the vice, through which the 5/8 .in. bolt passes, should be elongated into a taper slot at the bottom. The counter-weight casting is merely a cylinder with a | in. clearing hole through the center of its length.
The saw frame itself is a forging from 1 1/2 in. x 1/2 in. iron, 11 1/8 in. between the legs, and 5 in. from the extremities to the top (inside measurement). The two pieces to which the saw blade is attached (shown sepr arately at Figs. 9 and 10) are made and fitted to the frame in such a position as to bring the cutting edge of the saw 4 1/2 in. below the lower surface of the frame. The forward piece (Fig. 10) is made of 1 in. x 3/8 in. iron, and is drilled in three places to accommodate 8-in., 9 in., and 10 in. saws, with a pin at the end on which the blade fits; this is recessed flush in the frame and secured with a 3/8 in. screw and nut. The tail piece (Fig. 9) is made of the same iron, and also has a pin at one end for the saw blade, the other end being fashioned into a | in. screw for pulling the blade up taut by means of a nut bearing on a 1/4 in, plate let into the frame for that purpose. Details of this fitting are given at Fig. 11, where K is the saw frame, L the steel plate, and M the tension screw; N is a 3/8-in. screw which locks the fitting together after the proper degree of tightness has been attained, the slot to accommodate this screw being shown in Fig. 9.
Attached centrally to the top of the frame at the back by means of three 3/8 in. screws is a 10 in. piece of 1 in. by 1/2 in. iron or steel, preferably steel, undercut to slide to and fro in the saw-frame guide (see Fig. 5). A 1/2 in. hole is also drilled and tapped centrally on the back leg of the frame, 2 1/4 in, below the under side of the top, and with a suitably screwed stud carries one end of the connecting liuk, the other end being attached to the driving plate. This link is made from
3/8-in. x l 1/2-in. iron, and is drilled with two 5/8 in. clearing holes, centers of which are 6| in. apart.
A 5/8-in. bolt should next be forged out to the shape and dimensions given at Fig. 12, and a nut made to suit it; this nut should be at least 1 in. in length, otherwise it will soon strip, and must be rounded at the bottom. A 3/4-in. iron rod is then cut 1 ft. 1 in. long, and screwed for 1 in., and is afterward tapped into the boss on the saw-frame guide, to carry the counterweight, which is secured with a set screw. The guide casting should next be taken in hand, and the circular part bored to a diameter of 2 1/4 in. This should be done on the face plate, but as it requires a large lathe, it will probably have to be bored with a cutter bar against the poppet head. After boring, clean down the sides until the coating is 3/4 in. thick. Great care must be taken to ensure that the bore is parallel and square with the casting. The casting should be planed in the sliding part to take the piece of steel on the back of the saw frame, and the slip piece 0 (Figs. 1 and 5), the dimensions of which are given in Fig. 13. The slip, which is 1 ft. 3 in. long, is held in position by three small screws P (Figs. 1, 2, and 5), and is used to adjust the saw for wear and tear. When planing out this slide, see that the 2 1/4-in. diameter hole is absolutely vertical; this will correct any slight error in the angle of the bore. A hole for lubricating purposes is made at Q (Fig. 2), and the boss drilled and tapped | in. to take the iron rod. The lower end of this casting is drilled and tapped 1/2 in. to take the set screw and nut R (Fig. 1), which can be adjusted to bear against the bed of the lathe and thus arrest the downward progress of the saw at any desired place. A 2 1/2-in, peg is tapped into this casting at the foremost part, to take additional weights when the saw becomes blunt.
The driving plate is screwed out to fit the mandrel, and, if possible, turned on the lathe it will eventually be used upon to the dimensions given at Fig. 4. Care must be taken to make this casting fit nicely in the bored part of the saw-frame guide; when the collar is tightened up against the shoulder, there should be no shake in either direction. While the plate is on the lathe, turn in a line 2 1/4 in. from the center, and on this line drill and tap a 1/2-in. hole to carry, with a suitably screwed stud, the connecting link, the other end of which is screwed to the saw frame.
The vice is now planed up to fit in the lathe bed, and a 3/4 in. bolt tapped into clamp it firmly in position, after which it can be cleaned up at the other end and the 5/8-in. shot filed out, if necessary, to allow the bolt (Fig. 12) to pass easily. This 1/2-in. hole in the vice (see Figs. 1 and 8) is drilled 1 1/2 in. below the flat top, and slightly forward of the fixed jaw, to allow the 1/2-in. iron gauge (Fig. 14) to slide through, this being fixed in position by the small thumbscrew S (Figs. 1 and 8). The loose jaw is then machined up, and the bearing for the 5/8-in. nut cleaned out with a circular cutter to correspond with the rounded end of the nut (see Fig. 8); thus when the nut is tightened up the bolt takes a position more approaching the perpendicular than it could do if the hole fitted the bolt all the way, while if the nut had a flat bottom it could only set down on the casting in the one position.
This completes the instruction, and everything is now ready for working. To give the best results, the lathe should make sixty revolutions per minute. -"Work," London.