Modern Machine-Shop Practice Part 209

If a saw is to be sharpened by filing, it should be made as hard as it can be to file properly, even at the expense of rapidly wearing out the file, because the difference in the amount of work the saw will do without getting dull enough to require resharpening is far more than enough to pay the extra cost of files.

Circular saws with inserted teeth are made of thicker plate than solid saws of corresponding diameters, which is necessary in order that they may securely hold the teeth. The princ.i.p.al difference in the various forms of inserted teeth lies in the method of locking or securing the teeth in the saw.

Figs. 3084 and 3085 represent the chisel tooth saws of R. Hoe and Company. The No. 2 tooth is that used on gang edging machines and for bench work. No. 3 tooth is that used in miscellaneous sawing, for hard woods and for frozen lumber. No. 4 is the shape used in the soft and pitchy woods of southern and tropical countries.

The method of inserting the teeth is shown in Fig. 3084 on the left, the pin wrench being shown in position to move the socket whose projection at C carries the tooth D home to its seat and locks it there.

The sockets for the numbers 3 and 4 tooth are, it is seen, provided with a split, which gives to them a certain amount of elasticity that prevents the sockets from getting loose.

Swing-frame saws are made in various forms, generally for cross-cutting purposes or cutting pieces to length.

[Ill.u.s.tration: Fig. 3084.]

[Ill.u.s.tration: Fig. 3085.]

[Ill.u.s.tration: Fig. 3086.]

Fig. 3086 represents a swing-frame saw that is mounted over a work bench, and can therefore be used without necessitating carrying the work from the bench. It consists essentially of a frame pivoted at the upper end to the pulley shaft and carrying below a circular saw driven by belt over pulleys on the upper shaft and the saw arbor. In this machine the iron hubs carrying the frame have sockets fitting over the outer diameter of the hanger hubs, so that the frame hangs upon those hubs and not upon the pulley shaft. The advantage of this plan is that the frame joint is relieved of the wear which would ensue were it hung upon the revolving spindle, while at the same time the movement of the joint is so small as to induce a minimum of abrasion. To counterbalance the frame while it is placed out of the perpendicular, there is provided a compensating weight as shown in the engraving.

[Ill.u.s.tration: Fig. 3087.]

Fig. 3087 represents an example of that cla.s.s of cutting-off saw bench in which the length of the work is determined by the width apart of the saws.

This machine is constructed by Trevor and Company, and is designed for cutting barrel staves to exact and uniform lengths.

[Ill.u.s.tration: Fig. 3088.]

The stave is laid upon the bars of the upright swing-frame (which is pivoted at its lower end), and the latter is vibrated by hand, which may obviously be done both easily and quickly on account of the lightness of the swing-frame and its vertical position. A dimension sawing machine, by G. Richards and Company, is shown in Fig. 3088. This machine is designed for general fine work, such as pattern making, and its general features are as follows:

It carries two saws (a cross-cut and a rip-saw), mounted on a frame that can be quickly revolved by a worm and worm wheel to bring either saw into position as may be required.

There is a fixed table and adjustable fence on one side of the saw, and a movable table and fence on the other.

The saws are ground thin at the centre, as shown in Fig. 3089, so that but little or no set need be given to the saw teeth; hence the cutting edges of the teeth are more substantial and true, and as a result the work is cut very smoothly, and if the machine is kept in thoroughly good order, the sandpaper may follow the saw.

In Fig. 3088, A is a substantial box frame, to which is bolted the fixed table T. T' is the movable table which runs on rollers, and is guided by the [/] slideway at _e_. This table the workman pushes to and fro by hand, the work being adjusted upon the table or to the fence, as the case may be. At W is the wheel for swinging the frame to bring the required saw into position.

[Ill.u.s.tration: _VOL. II._ =DIMENSION SAWING MACHINE.= _PLATE XVIII._

Fig. 3089.]

In Fig. 3089 the worm gear for swinging the saws into position is shown, and also a sectional view of one saw arbor and of the movable table. A is the main frame, and _f_ the disc frame carrying the two saw arbors.

The disc _d_ is turned to fit a seating formed in the base, while the other end of the disc frame fits through a substantial bearing B; W' is the worm wheel, and W" the worm for swinging the disc frame. The worm teeth fit closely to the worm wheel teeth, and backlash or play is prevented by means of the spring bearing shown at D, the spiral springs forcing the worm teeth into the worm wheel teeth. Thus _a_ is the bearing for the worm carried in the box _c_, upon which is the spiral spring whose tension is regulated by the screw _g_.

The end of the worm is therefore held in a swivel joint that causes it to operate very easily.

[Ill.u.s.tration: Fig. 3090.]

Fence F, Fig. 3088 is for slitting, and is made to swing back for bevel cutting, while F' is for cross cutting, and is adjustable for angle cutting. Fence F is fitted to a plate P, Fig. 3090, which rests on the table top, and also rests on the long slide _g_. This slide fits in a beveled way _h_, and contains a [_|_] groove. A tongue likewise beveled fits in the top of this groove, the tongue being permanently fast to the fence plate. The [_|_] bolt pa.s.ses through the tongue and fence plate, having at its upper end a milled or knurled thumb wheel R, which when tightened up fastens the fence plate and the slide together.

Upon slacking the thumb wheel R, the fence plate and [_|_] bolt may be readily s.h.i.+fted, setting the fence as near to gauge as possible by hand, and the thumb wheel is then tightened, and the slide (which carries the fence bodily with it) is adjusted by means of the hand wheel H and its screw which threads into a lug from the table.

The fence F is pivoted to plate P at _p_, and the angling link which holds it in position is secured by a hand nut M.

The front journal of the saw arbor has a double cone, and by means of the nuts _n n'_, Fig. 3089, can be regulated for fit independently of the back bearing and journal, the latter being also coned and capable of independent adjustment by means of the adjustment nuts _m m'_.

The countershaft for driving the saw arbors is below the machine, so that the saw that is not in use remains stationary.

[Ill.u.s.tration: Fig. 3091.]

Examples of the work done on this machine are shown in Fig. 3091, the various sections shown being produced by the vertical movement of the saw through the table and the cross movement of the fence. For example, for cutting out a core box, such as shown at 6, small grooves are cut through to remove the bulk of the wood, and the saw marks at the bottom of each saw cut serve as gauge lines for the workman in finis.h.i.+ng the circular bore with the gouge, etc.

An example in which the table is fixed to the frame and the saw is adjusted for height above the table is shown in Fig. 3092. The saw arbor is here carried in a frame that is pivoted at one end to the main frame, while at the other end is a handle through which pa.s.ses a locking screw for securing that end of the saw arbor frame to the arc slot shown on the main frame.

[Ill.u.s.tration: Fig. 3092.]

In a more expensive form of this machine an adjusting screw is used for regulating the height of the saw, and an iron table is employed instead of a wooden one.

[Ill.u.s.tration: Fig. 3093.]

A double saw machine constructed by P. Pryibil is shown in Fig. 3093. In this machine each saw is carried in separate frames, that are pivoted at one end to the main frame and secured at the other to segments, so that either saw may be elevated to the required distance above the work table.

One saw is for ripping and the other for cross cutting, and the arbor of the latter is provided with an adjusting screw operated by the hand wheel shown on the right hand of the machine.

As the saws are on independent arbors, they can be speeded differently to suit different saw diameters, which is an advantage because, as machines of this cla.s.s are for the lighter cla.s.ses of work, the ripping saw will rarely be required for work of more than about 3 or 4 inches thick, and a rip saw of large diameter is not therefore necessary.

The cross cut saw however requires to be of larger diameter, as its work includes cross cutting up to 8 or 10 inches diameter, and the saw being larger does not require so high a speed of revolution.

Both saws are provided with ripping gauges and with right and left hand mitre fences, adapted to the application of either short or long work, and provided with length gauges.

[Ill.u.s.tration: Fig. 3094.]

Fig. 3094 ill.u.s.trates the various gauges in place upon the table of a machine. The table is provided with a slideway, or slot, on each side of the saw, and parallel with it, and also with a slideway at one side of the table. In the figure, the mitre gauge, or gauge for sawing at an angle, is shown in two positions.

The gauge A A A is for cutting work to length, and for cropping the ends at the same time, an extension frame being used, as shown for unusually long work.

[Ill.u.s.tration: Fig. 3095.]

[Ill.u.s.tration: Fig. 3096.]

Fig. 3095 ill.u.s.trates the method of employment of the mitre gauge. The pointer is set to the degree of angle the work is to be cut to, and is fastened to its adjusted position by the set screw H. The stop is set to the required length, and the work is held by hand against the face of the gauge, and at the same time endways against the stop, and the gauge is then moved along the slot, feeding the work to the saw. When the work is sawn and is to be withdrawn, care must be taken to keep the work fair, both against the gauge and against the stop.

[Ill.u.s.tration: Fig. 3097.]

Figs. 3096 and 3097 show the application of the gauges for cropping off the ends of work and cutting it to exact length. There are two stops, S and T, each of which is secured in position by a set screw, and has a tongue that may be thrown over, as occasion may require--thus, suppose it is desired to merely crop off the end of the work--and both stops may be set for the work to rest against as in Fig. 3096, and the end of the work may be cut off or cropped to square it or remove a defective part.

Stop S may then be thrown over as in Fig. 3097, and the squared or cropped end of the work rested against stop T, to gauge the length to which the work will be cut. This is a simple and convenient method of cropping and gauging.

[Ill.u.s.tration: Fig. 3098.]