Modern Machine-Shop Practice Part 211

The mechanism for traversing saws 2 and 3 corresponds in design, and may be described as follows:

The arbor A has a spline S to drive the sleeves D, D', which hold the saws and are carried by arms E, E', which operate in slideways and have racks F, F', into which gear pinions whose shafts G, G', are operated by the hand wheels H, J.

It is obvious that by means of the hand wheels H, J, saws 2 and 3 may be regulated both in their distances apart or in their distances from saw 1, while the machine is in full motion, the bushes or sleeves D and D'

being carried by and revolving in the slide pieces or sliding bearings E and E' respectively. Now suppose that E' be moved to the left by hand wheel J, until it abuts against the end of D, at the slide end, and a further movement of D' will also move D, causing it to operate its pinion and revolve the hand wheel H, hence D and D' may be simultaneously moved without disturbing their distances apart by operating hand wheel J. On the yoke above the saws is a coa.r.s.e-figured register plate to enable the setting of the saws to accurate widths apart.

RACK FEED SAW BENCH.

This machine is employed for the purpose of reducing balks or logs into planks of any thickness required. The machine is fixed on the floor of the saw mill, all the gearing being underneath the floor, so that the table may be set level with the floor, which is a great convenience when heavy logs are to be operated upon. The machine consists of a substantial bed plate or frame A, Fig. 3112, carrying the saw and the feed works. The carriage runs on rollers, some of which are fixed to the frame A, and others to the framing timbers B, which are long enough to support the carriage throughout its full length, when the carriage is at either end of its traverse.

[Ill.u.s.tration: Fig. 3110.]

[Ill.u.s.tration: Fig. 3111.]

The driving pulley for the saw arbor is shown at C, Fig. 3112, in dotted lines and in Fig. 3113 in full lines. Upon the saw arbor is a cone pulley D, Fig. 3113, for operating the carriage to the feed, the construction being as follows:

Referring to Figs. 3112 and 3113, cone pulley D connects by a crossed belt to cone pulley E, on whose shaft is a pulley _e_ which drives the pulley F, on whose shaft is the pinion _f_, which drives the gear G. On the same shaft as G is a pinion _g_, which drives the gear wheel H, which engages the rack J, on the carriage, and feeds the carriage to the cut. The diameters of pulleys E, F, and of _f_, G, and _g_, are proportioned so as to reduce the speed of the cone pulley D, down to that desirable for the carriage feed. But, as there are four steps on the cones D, E, therefore there are four rates of cutting feed or forward carriage traverse, which varies from 15 to 30 feet per minute.

The speed of the saw varies in practice, some running it as slow as 9,000 feet per minute at the periphery of the saw, and others running it as high as 16,000 feet per minute. The latter speed however, is usually obtained when the saws are packed with fibrous packing, which will be explained presently.

The quick return motion for the carriage is obtained as follows:

Referring to Figs. 3113, and 3114, K is a fast and K' a loose pulley on the shaft _k_, and receiving motion by belt from a countershaft.

[Ill.u.s.tration: _VOL. II._ =RACK-FEED SAW BENCH.= _PLATE XIX._

Fig. 3112.]

The speed of the fast pulley K is such as to give a return motion to the carriage of about 50 or 60 feet per minute, being about twice as fast as the carriage feed motion.

We have now to explain the methods of putting the respective carriage feed motions into and out of operation, and insuring that both shall not be in gear at the same time.

[Ill.u.s.tration: Fig. 3113.]

Referring therefore to Figs. 3113 and 3114, suppose the carriage to have completed a feed or cutting traverse, and the operator pushes with his knee the lever or handle _h_, Fig. 3114, which revolves shaft _m_, on which is an arm that moves the belt-shifting rod _n_, thus moving the belt from fast pulley F to loose pulley F', thus throwing the feed gear out of engagement and causing the carriage to stop. He then presses down the foot lever L, Fig. 3113, which operates the belt-shifting rod _p_, Fig. 3114, and moves the belt from loose pulley K', to fast pulley K, which having a crossed belt, operates the pulley F in the reverse direction and traverses the carriage backwards, or on the return motion.

Upon releasing the foot from the lever L, the weight W operates the foot lever L, and the belt is re-shifted from fast pulley K to loose pulley K', and the carriage stops.

The carriage is formed of iron plates with an open s.p.a.ce of about 1/2 inch between them, as shown in Fig. 3114, this s.p.a.ce forming a race to permit the carriage to travel past the saw. The only connection between the two sections or parts of the table, is a wide plate at the rear end which secures them together, and causes the lighter portion of the table, which is merely driven by the friction of the rollers C, to always travel with the lower or under portion, which is driven by the rack J. In larger machines for the heaviest work, both sections are driven by a rack motion.

The guide motion for the carriage is constructed as follows:

_a_, _a_, are brackets placed at intervals along the whole frame work.

These brackets support rollers _c_, which have f.l.a.n.g.es on them to prevent any side motion of the carriage, the construction being most clearly seen in Fig. 3113; _b_ being a bearing for the shaft _v_ of the rollers. Each section of the carriage, it will be seen, has two ribs or ways which rest on the rollers, which are arranged four on each shaft _v_ (_i.e._ two for each section of the carriage).

The fence or gauge against which the face of the work runs is very simply arranged as is shown in Figs. 3113, and 3114, being secured to the shaft _q_, by a long bolt _t_, threaded into the top of the fence, and at its lower end ab.u.t.ting against a shoe fitting partly around the top of the shaft _q_. It is squared at the top to receive a wrench or handle _u_, and it is obvious that uns.c.r.e.w.i.n.g the handle releases the fence from shaft _q_, so that the fence may be moved rapidly by hand across the table to approximate the adjustment of the fence from the saw. The fence having been thus approximately adjusted, and locked to the shaft by means of the handle _u_, the final adjustment is made by means of the hexagon nut _w_, on the bed of the shaft nut _x_, serving as a lock nut, to hold _q_ in its adjusted position.

FIBROUS PACKING.--The fibrous packing before referred to is composed of hemp, plaited in a four strand plait and inserted in an open-top trough, along the sides of the saw for a distance about two inches less than the radius of the smallest saw the machine uses.

[Ill.u.s.tration: Fig. 3114.]

This packing steadies and stiffens the saw, and also affords a means of adjusting its tension, while the saw is running.

Suppose for example, that the saw is rim bound,[47] and the fibrous packing may be rammed tightly to the saw, as near to the saw rim as possible, and less tight as centre of the saw is approached.

[47] For the principles involved in hammering saws to equalize the tension see page 69 (Vol. II.) _et seq._

This warms the saw, but makes it warmer at the circ.u.mference than at the centre, expanding the circ.u.mference, and by equalizing the tension, enables the saw to run straight.

[Ill.u.s.tration: Fig. 3115.]

When the packing is to be adjusted, the carriage is run out of the way, and the packing operation is performed by hand, with a caulking tool.

The packing and its box, as applied to a rack saw bench is shown in Fig.

3115, by the dark rectangles. By thus packing the saw to guide it and keep it straight, thinner saws may be used, saws 52 inches in diameter, and having a thickness of but 7 or 8 gauge being commonly employed, and in some cases of 9 gauge.

Saws that are thus packed, produce much smoother work.

The packing, it may be observed, is kept well lubricated with oil, and the following is the method of adjusting it.

[Ill.u.s.tration: _VOL. II._ =PLANTATION SAW MILL.= _PLATE XX._

Fig. 3117.]

The side of the saw on which the operator stands is the last to be packed, the packing on the other side being inserted so as bed fairly but lightly against the saw, so as not to spring it, which may be tried with a straight-edge. The packing on the other side is then inserted to also bed fairly against the saw, without springing it, and the saw is run until it gets as warm as it may, from the friction of the packing.

If, then, the saw flops from side to side, the outside (circ.u.mference) is _loose_, and the packing is rammed together on both sides of the saw and near the saw arbor or mandrel, care being taken that in ramming the packing the saw is not unduly pressed on either side.

Expert sawyers generally change the packing when the saw is changed, and thus keep for each saw its own packing. The slot or pocket in which the packing lies is about 1-1/4 inches deep, and 1/2 inch wide.

[Ill.u.s.tration: Fig. 3116.]

In ordinary circular saw benches or machines the packing comes about up to the level of the table, as shown in Fig. 3116, in which A is a hand hole for putting in and lifting out the plate B, so as to put in or remove the wooden pieces C, D, upon which the packing rests.

Fig. 3117 represents a saw mill constructed by the Lane & Bodley Company. In this machine two circular saws are employed, the upper one being of small diameter and revolving in the same direction as the log feed. A is the driving pulley for the main saw arbor _a_, and B the driving pulley for the upper saw arbor _b_. The carriage feed is obtained by belt from cone pulley C to cone pulley D, on whose shaft is a friction pulley _e_, which, for the feed motion, is moved by lever E into driving contact with pulley F, whose shaft drives the pinion G, which gears with the rack of the carriage. The three steps on the cones C, D, give three rates of feed, and a quick return motion is given to the carriage by engaging the friction pulley with a wheel not shown in the engraving.

The log to be sawn rests upon the slideway S S', and is secured thereon by the dogs J, J, which are capable of sliding up or down upon the heads H, H'. When the handles K are raised the slides carrying dogs J are free to be moved up and down H, H', whereas when handles K are depressed the dogs J are locked and hold the log. The operation is to raise the dog slides to the top of H, H', set the log up to the faces of H, H', and then by raising handles K, let the dog slides fall, their weight forcing the dogs into the log, and the depression of K locks the dog slides upon H, H', respectively.

The log feed is obtained from the lever L, which operates the ratchet wheel T, which drives bevel gears V and W, which operate the screws that slide the heads H, and H', along the slideways S and S'.

Three rates of log feed are obtained by regulating the amount of motion that can be given to the lever L, the construction being as follows:

In the lever L is a slot in which a stop _r_ can be secured at different heights, and the piece M has four notches. The limit to which L can be moved to the left is until it comes against the stop _x_, but the limit to which it can be moved to the right is governed by the height of the stop _r_ in the slot in L. If stop _r_ is set at its highest position in the slot, L can be moved to the right until the stop _r_ meets the right hand step on the circ.u.mference of M, and a maximum of log feed is given.

TUBULAR SAW MACHINE.

[Ill.u.s.tration: Fig. 3118.]