Modern Machine-Shop Practice Part 214

On the same shaft as the friction wheel O, is a pinion driving the gear X, which is on the same shaft as the pinion Y, which drives the two gears Y' and Y".

Referring now to Fig. 3142, gear Y' drives the pair of bevel gears Z and Z', for the feed roll _e_, and the pair of bevel gears shown at Z", the feed roll _f_. The gear Y" drives similar gearing for the feed rolls _e'_ and _f'_, seen in the plan Fig. 3140.

Referring now to the plan Fig. 3140, and the side elevation, Fig. 3142, the feed roll _f_ is carried in a frame _g_, which is fitted on the slideway _d_, _d_, and receives a screw _i_, upon which is a hand wheel _h_; at the back of this wheel is the lever _j_, which is weighted as shown, so that the force with which feed roll _f_ grips the work is determined by the weighted lever _j_, and may be varied to suit the nature of the work by moving the weight along _j_.

The construction of the gear for feed roll _f'_ is similar, as may be seen in the plan Fig. 3140, _f'_ being in a slide _g'_, which has a screw _i'_, and hand wheel _h'_, a weighted lever corresponding to _j_ acting against wheel _h'_. In proportion as _f_ and _f'_ are opened out to admit thick stuff or work, the hand wheels _h_ and _h'_, respectively are used to screw the screws _i_ and _i'_ into their respective slides _g_ and _g'_, and thus maintain the weighted levers in their requisite horizontal positions. The feed rolls _e_ and _e'_ are carried in slides _c_ and _c'_, and are adjusted to suit the thickness of the stuff or work by a hand gearing, which consists of the hand wheel _a_, seen in the plan and in the front elevation, Fig. 3141, which drives the pinions _b_ and _b'_, which operate screws for the slides _c_ and _c'_, the latter being a left hand screw. The front rolls _e_ and _e'_ are therefore held in a fixed position, whereas the back ones _f_ and _f'_ may open out under the pressure of the weighted levers _j_, and thus accommodate any variation in the thickness of the work.

The rate of feed is varied to suit the nature of the work by the following construction: The friction wheel O and the hand wheel R are connected by a yoke _q_, Fig. 3142, at the ends of which are the joints P, Q, seen in the plan, Fig. 3140. Hand wheel R is threaded to receive the screw S, and it follows that by revolving R, the friction wheel O may be moved towards the centre of the friction disc N, which would reduce the velocity with which N would drive O, and therefore reduce the rate of feed. If the friction wheel O be moved from the position it occupies in the plan Fig. 3140, to any point on the other side of the centre of the friction disc N, the direction of feed motion would be reversed.

A band saw machine for the conversion of logs into timber, and constructed by Messrs. London, Berry & Orton, is shown in Fig. 3143. The logs are fixed to the carriage by dogs and the carriage traverses the log to the feed.

RECIPROCATING CROSS CUTTING SAW FOR LOGS.--The machine shown in Figs.

3144 and 3145 is designed for the purpose of cutting heavy and long logs into convenient lengths preparatory to cutting the logs up in other machines, and it is usually therefore placed at the entrance to the mill, where it is of immediate service as the lumber comes into the building.

The machine here shown is intended for logs up to 36 inches in diameter, is simple in construction, requires very little foundation, is easy to handle, and occupies but very little room.

The saw is here fed mechanically to its cut, whereas in some machines it is fed by its own weight, and therefore requires great care to be taken, when the saw is finishing its cut, in order to prevent it from falling after it has pa.s.sed through the log.

Fig. 3145 is a side elevation and Fig. 3144 a plan of the machine, in which A is the frame of the machine on which are the bearings for the shaft B carrying the fast pulley C, loose pulley D and fly-wheel E at one end, and at the other, a crank disc F, whose pin is shown at G. This drives the saw K through the medium of the connecting rod H.

The saw is fast at the b.u.t.t end to along slide J, J, which works in a long guide formed on the face of the swinging frame L, which pivots at one end on the shaft B and at the other is carried by a slide P, on the vertical slideway M, and is fed down the same to give the saw its cut by the screw whose hand wheel is shown at N.

V is a second guide for the saw, and being connected to the slide feeds down with the saw until it meets the log.

A counterweight W balances the weight of the slides and saw, so that there being a pit beneath the balance weight the saw and its guides may be raised so that the saw stands out of the way when not in use. Y is a dog for holding the log, which is also blocked by the wedges Z Z'.

[Ill.u.s.tration: Fig. 3146.]

The construction of the main bearing is shown in Fig. 3146, in which it is seen that the hub or boss of the loose pulley is much longer than that of the fast one, thus providing a large amount of bearing surface, which is advantageous because the belt will remain longer at the loose pulley than it will on the tight one. The sleeves or bushes in which the shaft runs afford a simple means of renewal to restore the fit when the shaft has worn loose in its bearings.

It is obvious that as the guide frame L is pivoted to the shaft B, it carries the end of the saw (as it is fed down) in an arc of a circle of which the axis of B is the centre, whereas the slideway M is straight, and slide P therefore moves in a straight line instead of in the required arc. Provision however is made to accommodate these two motions as follows:

[Ill.u.s.tration: Fig. 3147.]

[Ill.u.s.tration: Fig. 3148.]

Fig. 3147 is a sectional view of the slides on the slideway M and Fig.

3148 a plan of the same. The hand wheel N corresponds to N in Fig. 3145.

Upon the vertical slideway (in Fig. 3145) of the standard fits the slide P, which has a horizontal slideway for the slide R, which is free to slide automatically, having no screw or other device to restrain it, save the guide frame L, and therefore as this frame is lowered to feed the saw the slide R moves automatically to accommodate the arc of a circle in which the guide moves on account of being pivoted at B.

HORIZONTAL SAW FRAME.--This machine is designed for the more expensive woods, such as mahogany, and is finding much favor because it will cut at a very high speed, the saw travelling about 150 feet per minute.

[Ill.u.s.tration: _VOL. II._ =LOG CROSS-CUTTING MACHINE.= _PLATE XXIV._

Fig. 3144.

Fig. 3145.]

[Ill.u.s.tration: Fig. 3143.]

The roughest shaped trunk may be easily fixed on the travelling table, and a thin saw may be used as it may be very tightly strained. This machine is used either for breaking down timber, or for converting it from the log to any desired thickness, the thickness of the boards being very readily and easily varied.

The machine consists essentially of a framework carrying either one or two very thin and tightly strained saws operating horizontally and cutting on both strokes, so that the feed is continuous, the construction being as follows:

[Ill.u.s.tration: Fig. 3150.]

Referring to Figs. 3149 and 3150, A is a base plate or bed carrying two uprights or standards B, B, having guideways C, C, for the cross-head D, which has slideways E, E', for carrying the frame F, F, which carries the saw G, which is guided on each side of the work by the guides H, H'.

The frame F, F is connected to the slides J, J', and has the rod K, to which the connecting rod pin L is attached, and the rod M, which acts as a stretcher. A connecting rod P, connects the pin L to the crank pin Q, on the crank Q', which is driven by belt from the pulley T, a fly-wheel being provided at S.

It is obvious that as the crank revolves the saw reciprocates, its line of motion being determined by the guideways E, E'.

The construction of the saw is shown in Fig. 3151, and it is seen that for half its length, the teeth are formed to cut when the saw moves in one direction, while for the other half the teeth slope in the opposite direction, and are therefore arranged to cut when the saw is on the opposite or return stroke, and the construction whereby the saw is enabled to cut on both strokes is obtained as follows:

[Ill.u.s.tration: _VOL. II._ =HORIZONTAL SAW FRAME.= _PLATE XXV._

Fig. 3149.]

Referring to Fig. 3149, the two slides E, E', on which the saw-carrying frame F F slides, are not in line or parallel one with the other, but each slide is at an angle of about 85 degrees to the line of feed, so that as frame F is reciprocated at each stroke, one end of the saw advances towards the cut, and the other recedes from it, thus causing the saw to cut first on one half and then on the other of its length, one half cutting on the forward, and the other on the return stroke.

[Ill.u.s.tration: Fig. 3151.]

The studs or saw-buckles for attaching the saw to the frame are shown in Fig. 3151, in place on the ends of the saw, the part I, that fits in the frame F, Fig. 3149, being squared so that the saw cannot be twisted in tightening up the nuts of the saw-buckle.

The belt works for driving the saw are arranged as follows: at T are the fast and loose pulleys for driving pulley R, the belt pa.s.sing from T over two pulleys (shown dotted in, Fig. 3149), U, U', whence it stretches to the crank driving pulley R, whose bearing is provided on the cross-head, so that the two move together when the cross-head is altered in height from the work-table or carriage, to accommodate different thicknesses or diameters of logs.

It is obvious that in proportion as the cross-head is set nearer to the carriage, the belt from T to U, U' would become slack; provision is made however, to prevent this as follows:

Pulley U, is carried on a frame or swing lever X, to which is attached by rope V the weight W, which therefore regulates the tension of the belt.

The cross-head D may be raised or lowered by belt power or by hand, as occasion may require, the usual course being to move it to nearly the required position by belt power, and then complete the adjustment by hand, a graduated scale being provided as shown, whereby the rack can be set to cut the required thickness of plank without measuring the timber.

The belt motion for raising or lowering the cross-head is obtained by the pulleys at Y, the wheel for the hand adjustment being shown at Y'.

In either case the bevel gear wheels Z, Z' operate, respectively, a vertical screw engaging a nut on the cross-head.

The log feed is obtained by a motion separate from the return motion, there being three rates of feed and a quick return motion, the construction being as follows:

Referring to Figs. 3149 and 3150, a is a belt pulley fast on the crank shaft, and driving pulley _b_, which is also shown dotted in. Pulley _b_ drives the vertical shaft _c_, on which is the cone pulley _d_, having three steps, and which drives (by means of belt _d'_) cone pulley _e_, on which is a worm _f_, driving the worm wheel _g_, which runs idle on its shaft unless engaged therewith by means of the clutch _h_. The shaft of worm wheel _g_ is omitted in Fig. 3149, so as to leave the belt-shifting mechanism for pulleys _q_, _q'_ exposed to view. On this shaft however is a pinion driving the gear wheel _k_, on whose shaft is a pinion _l_, driving the gear _m_, which engages the rack _n_, on the under side of the carriage.

The clutch _h_ is engaged by the lever _i_, to the upper arm of which is attached the rod _j_, _j_, from the lever _p_, hence operating _p_ (which is done by hand), back and forth, throws clutch _h_ into and out of gear with the worm wheel _g_, and puts the carriage feed on or throws it out, according to the direction in which _p_ is moved.

The upper end of shaft _c_ is carried in a bearing on the cross-head, and is provided with a featherway or spline, so that as the cross-head is raised or lowered the upper end of _c_ pa.s.ses through its upper bearing, and the pulley _b_ travels with the cross-head. The three rates of carriage feed are obviously obtained by means of the three steps on the cone pulleys _d_ and _e_.

We have now to explain the construction of the mechanism for traversing the table back, and giving it a quick return motion, or in other words a quicker motion on the back than on the feed traverse, and this is arranged as follows:

_q_, is a fast and _q'_, _q"_, are loose pulleys, one driven by an open belt _r_, Fig. 3150, and the other by a crossed belt _r'_, from a countershaft. The belt-shifting forks are operated by lever _s_, whose upper end engages with the rod _t_, which is operated by the lever _u_.

The loose pulleys _q'_ and _q"_ are twice as wide as the fast pulley _q_.