Fig. 1528Fig. 1528.
Fig. 1528.
It is obvious that it is the capability ofgto rotate in their sockets that enablesfto be set at an angle and still have the teeth ofgengage properly with those on the base plate.
Fig. 1529Fig. 1529.
Fig. 1529.
Fig. 1530Fig. 1530.
Fig. 1530.
The mechanism for swivelling the upper part or body upon the base and for locking it in its adjusted position is shown inFigs. 1529and1530. The bodydis provided with an annular ring fitting into the bore of the base, which is coned atq. The half-circular disksrfit this cone and are held to the body of the chuck by four boltsn, which are adjusted to admit disksrto move without undue friction.kis a key having on it the nutv, which receives a screw whose squared end is shown ats. By operatingsin one direction keykexpands disksr, causing them to firmly grip the base at the bevelq, hence the base and the body are locked together. By operatingsto unscrew in the nutv,kis moved in the opposite direction andr,rrelease their grip atqand the bodydmay be swung round in any position, carrying with it all the mechanism except basep.
To enable the body to be readily moved a quarter revolution, or in other words, moved to a right angle, there is provided a taper pin, the base having holes so situated that the body will have been moved a quarter revolution when the pin having been removed from one hole in the base is seated firmly home in the other.
Referring again toFig. 1526, there are shown one pair of parallel pieces marked respectivelya, having bevelled edges, and another pair marked respectivelyb. Both pairs are provided with a small rib fitting into a groove in the jaws of the chuck, as shown in the figure.
These ribs and grooves are so arranged that the upper pair (a,a) may be used in the place of the lower ones, and the uses of these pieces are asfollows:—
Fig. 1531Fig. 1531.
Fig. 1531.
Suppose a very thin piece of work is to be planed, and in order to plane it parallel, which is ordinarily a difficult matter, it must bed fair down upon the face of the vice, which it is caused to do when chucked as inFig. 1531, in which the work is shown laid flat upon the face of the vice, and gripped at its edges by the piecesa,a.
These pieces, it may be noted, do not bed fair against the gripping faces of the jaws, but are a trifle open at the bottom as ate,e, hence when they are pressed against the work they cant over slightly and press the work down upon the chuck face causing it to bed fair. Furthermore, the work is supported beneath its whole surface, and has, therefore, less tendency to spring or bend from the holding pressure; and as a result of these two elements much thinner work can be planed true and parallel than is possible when the work is lifted up and supported upon separate parallel pieces, because in the latter case the work, being unsupported between the parallel pieces, has more liberty to bend from the pressure due to the tool cut, as well as from the holding pressure.
Fig. 1532Fig. 1532.
Fig. 1532.
Fig. 1532shows the chuck holding a bracket, having a projection or eye. The work rests on piecesb,b, and is gripped by piecesa,a. It will be observed thata,abeing beveled enables the cut to be carried clear across the work.
Fig. 1533Fig. 1533.
Fig. 1533.
Fig. 1533represents the chuck in use for holding a piece of shaftingsto cut a keyway or spline in it. In this case a bevelled piecejis employed, its bevelled face holding the work down upon the chuck face.
Fig. 1534Fig. 1534.
Fig. 1534.
Fig. 1534represents a chuck termed shaper centres, because the work is held between centres as in the case of lathe work. The live spindle is carried in and is capable of motion in a sleeve, the latter having upon it a worm-wheel, operated by a worm, so that it can be moved through any given part of a circle, and has index holes upon its face to determine when the wheel has been moved to the required amount.
For work that is too large to be operated upon in the class of shaping machine shown inFig. 1506, and yet can be more conveniently shaped than planed, a class of machine is employed in which the tool-carrying slide is fed to the work, which is chucked to a fixed table or to two tables.
Fig. 1535Fig. 1535.
Fig. 1535.
Fig. 1535represents a machine of this class. The tool-carrying slidea, in this case, operates in guideways provided inb, the latter being fitted to a slideway running the full length of the top of the framem. The base sliderbis fed along the bed by means of a screw operating in a nut on the under side ofb, this screw being operated once during each stroke of the tool-carrying slidea, by means of a pawl feeding arrangement atf, which corresponds to the feeding device shown inFig. 1501.
Two vertical frame piecesd,dare bolted against the front face of the machine, being adjustable along any part of the bed or frame length, because their holding bolts have heads capable of being moved (with the frame piecesd) along the twoT-shaped grooves shown, theirT-shape being visible at the end of the frame or bed. To framesdare bolted the work-holding tablese,e, the bolts securing them passing into verticalT-grooves ind, so thatemay be adjusted at such height upondas may be found necessary to bring the work within proper range of the cutting tool. The work tablese,eare raised or lowered upondby means of a vertical screw, which is operated by the handleh, this part of the mechanism accomplishing the same end as the elevating mechanism shown inFig. 1496. The swivel headjis here provided at its top with a segment of a worm-wheel which may be actuated to swivel that head by the wormg.
The swivel head may thus be operated upon its pivot, causing the tool point to describe an arc of a circle of which the pivot is the centre. To steady the swivel head when thus actuated, there is behind the worm segment aV-slide that is an arc, whose centre is also the centre of the pivot.
The tool-carrying slideais operated as follows: The driving pulleyprotates a shaft lying horizontal at the back of the machine. Along this shaft there is cut a featherway or spline driving a pinion which operates a link mechanism such as described with reference toFig. 1550.
The means of adjusting the distance the head ofashall stand out fromb, are similar to that described forFig. 1496, a bolt passing througha, and in both cases attaching to a connecting rod or bar.
Atkis a cone mandrel such as has been described with reference to lathe work upon which is chucked a cross-headc. By means of suitable mechanism, this mandrel is rotated to feed the circular circumference of the cross-head jaws to the cut, the sliderbremaining in a fixed position upon the bedm.
To support the outer end of the cone mandrel a beamlis bolted to the two tablese,e. Onlis a slideway for the piecep. Atsis a lug uponethrough which threads a screwr, which adjusts the height of the piecep, whileqis a bolt for securingpin its adjusted position. This cone mandrel and support is merely an attachment to be put on the machine as occasion may require.
Fig. 1536represents a shaping machine by the Pratt and Whitney Company. In this machine a single sliding head is used and the work remains stationary as in the case of the machine shown inFig. 1535. The vice is here mounted on a slide which enables the work to be finely adjusted beneath the sliding bar independently of that bar, which is provided with a Whitworth quick-return motion.
As the tool-carrying slide of a shaping machine leaves its guideways during each stroke, the tool is less rigidly guided as the length of slide stroke is increased, and on this account its use is limited to work that does not require a greater tool stroke than about 18 inches, and in small machines not to exceed 12 inches. The capacity of the machine, however, is obviously greatest whenthe length of the work is parallel to the line of motion of the feed traverse. Work whose dimension is within the limit of capacity of the shaper can, however, be more expeditiously shaped than planed because the speed of the cutting tool can be varied to suit the nature of the work, by reason of the machine having a cone pulley, whereas in a planing machine the cutting speed of the tool is the same for all sizes of work, and all kinds of metal. In shaping machines such as shown inFig. 1537, or in similar machines in which the work table is capable of being traversed instead of the head, the efficiency of the work-holding table and of the chucking devices may be greatly increased by constructing the table so that it will swivel, as inFig. 1538, which may be done by means of the employment of Thomas’s swivelling device inFig. 1530. By this means the ends of the work may be operated upon without removing it from the chuck. Or the work may be shaped taper at one part and parallel at another without unchucking it.
Fig. 1539shows a circular table swivelled by the same device, sitting upon a work table also swivelled.
Fig. 1540Fig. 1540.
Fig. 1540.
Fig. 1540represents a general view of a shaping machine having the motion corresponding in effect to a planing machine, the object being to give a uniform rate of speed to the tool throughout, both on its cutting and return stroke. The feed always takes place at the end of the return stroke, so as to preserve the edge of the tool, and the length of the stroke may be varied, without stopping the machine, by simply adjusting the tappets or dogs, the range of stroke being variable from1⁄4inch to 20 inches, while the return stroke is 40 per cent. quicker than the cutting one. There are two different rates of cutting speed, one for steel and the other for the softer metals.
Fig. 1541Fig. 1541.
Fig. 1541.
The ram or bar is provided with a rack (z,Fig. 1545) which engages with a pinions,Fig. 1541,hbeing the driving shaft driven by the belt conesaandb. These two cones are driven by separate belts, but from the same counter-shaft, one being an open and the other a crossed belt. The open belt drives either the largest step of pulleyb, giving a cutting speed suitable for steel, or the smaller step, giving a cutting speed for softer metals, as cast iron, &c. The crossed belt drives, in either case, the pulleyafor the quick-return stroke, and this pulley revolve upon a sleeve or hubc, which revolves upon the shafth. The sleeve or hubcis in one piece with a pulleyc, whose diameter is such as to leave an annular opening between its face and the bore of the largest step of cone pulleyb, and pulleyais fast to the hub or sleevec. It will be seen that as the driving belts from the counter-shaft are one open and one crossed, therefore pulleyaruns constantly in one direction, while pulleybruns constantly in the other, so that the direction of motion of the driving shafthdepends upon whether it is locked to pulleyaor to pulleyb.
Fig. 1542Fig. 1542.
Fig. 1542.
Fig. 1543Fig. 1543.
Fig. 1543.
In the annular space left between the face of pulleycand the conebis a steel bandg,Fig. 1542, forming within a fraction a complete circle, and lined inside and out with leather, and this band is brought, by alternately expanding and contracting it, into contact with either the bore of the largest cone step ofbor with the outside face of pulleyc. The ends of this band are pivoted upon two pinsf, which are fast in two armseandd, inFig. 1542. Armeis fastened to the driving shafth, and its hub has two roller studsk,Fig. 1541, these being diametrically opposite on the said hub. The hub of armdis a working fit upon the hubofe, and has two slots to admit the above rollers. Hubdis also provided with two studs and rollers placed midway between the studsk. These latter rollers project into the spiral slotsk′of the ring inFig. 1543, this ring enveloping the hub ofdand being enveloped by the sleevem, which contains two spiral grooves diametrically opposite, and lying in an opposite direction to groovesk′,Fig. 1543. Sleevemis prevented from revolving by rollers on the studso, which are screwed into the bearing bushr, and carry rollers projecting into the slots inm.
It is evident that if the ringl,Fig. 1543, is moved endways withm, then the armse,d, together with the bandg, will be expanded or contracted according to the direction of motion of the ring, because the motion ofm, by means of its spiral grooves, gives a certain amount of rotary motion to the ringl, and the spiral grooves in the ring give a certain amount of rotary motion to the armsdande,Fig. 1542. When this rotary motion is in one direction the band is expanded; while when it is reversed it is contracted, and the direction of motion of shafthis reversed.
Fig. 1544Fig. 1544.
Fig. 1544.
Fig. 1545Fig. 1545.
Fig. 1545.
Fig. 1546Fig. 1546.
Fig. 1546.
The outer sleevemcarries the rodt,Figs. 1544and1545, which is connected to the leveru, the upper arm of which is operated by the tappets or dogsxon the ram or sliding bar, and it is obvious that whenuis vibrated sleevemis operated in a corresponding direction, and the ringlalso is moved endwise in a corresponding direction, actuating the band as before described, the direction of motion being governed, therefore, by the direction in whichuis moved by the tappets or dogs. A certain degree of friction is opposed to the motion of leveruin order to keep it steady, the construction being shown inFig. 1546, where it is seen that there is on each side of its nut a leather washer, giving a certain amount of elasticity to the pressure of the nut holding it in place on the shaftu.
Fig. 1547Fig. 1547.
Fig. 1547.
The mechanism for actuating the feed at the end of the return stroke only, is shown inFig. 1547. The shaftv(which is also seen in a dotted circle inFig. 1545) carries a flangec, on each side of which is a leather disk, so that the pressure of the bolts which securebto the sleeveacausescto revolve under friction, unless sleevea, slotted barb, and flangecall revolve together, or, in other words,crevolves under friction when it revolves withina b.
Fig. 1548Fig. 1548.
Fig. 1548.
Fig. 1548is an end view ofFig. 1547.
Fig. 1549Fig. 1549.
Fig. 1549.
Fig. 1549gives a cross-sectional view of the shaft sleeve, &c. The sleeveais provided with two pinsi,i, and a pinkis fast in the frame of the machine, and it is seen thataandvmay revolve together in either direction until such time as one of the pinsimeets the stationary pink, whereupon the further revolving ofawill be arrested andvwill revolve withina, and as flangec,Fig. 1547, revolves withv, it will do so under the friction of the leather washers. The pinsiand the pinkare so located thatacan have motion only when the ram or sliding-bar is at the end of the return stroke, and the feed-rodf, being connected tob, is therefore actuated at the same time.
Among the various mechanisms employed to give a quick return to the tool-carrying slide of shaping machines, those most frequently employed are a simple crank, a vibrating link, and the Whitworth quick-return motion, the latter being the most general one.
Fig. 1550Fig. 1550.
Fig. 1550.
The principle of action when a vibrating link is employed may be understood fromFig. 1550, in whichpis a pinion driven by the cone pulley and imparting motion tod. Atlis a link pivoted atc. Atais a link block or die capable of sliding in the slot or opening in the link and a working fit upon a pin which is fast inthe wheeld. Asdrotates the link block slides in the slot and the link is caused to travel as denoted by the dotted lines.ris a rod connecting the tool-carrying slidesto the upper end of linkl, and therefore causing it to reciprocate withl. Butsbeing guided by its slide in the guideway traverses in a straight line.
Since the rotation ofpanddis uniform, the vibrations of the linklwill vary in velocity, because while the link block is working in the lower half of the link slot it will be nearer to the centre of motioncof the link, and the upper end ofcwill move proportionately faster. The arrangement is such that during this time the tool-carrying slide is moved on its return stroke, the cutting stroke being made while the link block is traversing the upper half of the slot, or in other words, during the period in which the crank pin inais above the horizontal centre of wheeld.
Now suppose the arrangement of the parts is such that the front of the machine or the cutting tool end of the slide is at the endkofs, thenswill be pushed to its cut by the rodrat an angle which will tend to liftsin the slideways. But suppose the direction of rotation of wheeldinstead of being as denoted by the arrow atdbe as denoted by the arrow ate, thenswill be on its back stroke, the front of the machine being atj. In this case rodrwill pullsto the cut, andswill, from the angularity ofr, be pulled down upon the bed of the slideway guiding it, and will therefore be more rigidly held and less subject to spring, because the tendency to lift is resisted on one side by the adjustable gib only, and on the other by the projectingv, whereas the tendency to be pulled downwards is resisted by the strength of the frame of the machine.
Furthermore, as the pressure on the cutting tool is below the level of the tool-carrying slide it tends to force that slide down upon the slideway, and it will therefore be more rigidly and steadily guided when the force moving the slide and the tool pressure both act in the same direction.
To vary the length of stroke ofspinais so attached to wheeldthat it may be adjusted in its distance from the centre ofd.
Fig. 1551Fig. 1551.
Fig. 1551.
The Whitworth quick-return motion is represented inFig. 1551. Atpis the pinion receiving motion from the cone pulley or driving pulley of the machine and imparting motion to the gear-wheelg, whose bearing is denoted by the dotted circleb. Throughbpasses a shaftc, which is eccentric toband carries at its end a pieceain which is a slot to receive the pinx, which drives rodrwhose endzis attached to the ram of the machine. Atdis a pin fast in gear-wheelgand passing into a slot ina.
Taking the position the parts occupy in the figures, and it is seen that the axis ofbis the centre of motion ofgand is the fulcrum from which the pindis driven, the power being delivered atx. The path of motion of the driving pindis denoted by the dotted circleh′, and it is apparent that as it moves from the position shown in the figure it recedes from the axis ofc, and as the motion ofgis uniform in velocity thereforedwill moveafaster while moving below the linemthan it will while moving above it, thus giving a quick return, because the cutting stroke of the ram occurs whiledis above the linemand the return stroke occurs whiledis belowm.
Fig. 1552Fig. 1552.
Fig. 1552.
In some constructions the pinxand pindwork in opposite ends of the piecea, as shown inFig. 1552. This, however, is an undesirable construction because the shaftcbecomes the fulcrum, and as the power and resistance are on opposite ends of the levera, the wheelgis therefore forced against its bearing, and this induces unnecessary friction and wear.
We may now consider the tool motion given by other kinds of slide operating mechanism.
Fig. 1553Fig. 1553.
Fig. 1553.
InFig. 1553is a diagram of the tool motion given when the slide is operated by a simple crankc, the thickened linerrepresenting the rod actuating the slide and line on the line of motion of the cutting tool. The circlehdenotes the path of revolution of the crank pin, and the black dots1,2,3,4, &c., equidistant positions of the crank pin.
Linemrepresents the path of motion of the cutting tool.
If a pair of compasses be set to the full length of the thick liner, that is from the centre of the crank pin to endbof liner, and these compasses be then applied to the centre of crank pin position1, and to the linem, they will meetmat a point denoted by linea, which will, therefore, represent the position of the tool point when the crank pin was in position1. To find how far the tool point is moved while the crank pin moves from position1to position2, we place the compass point on the centre of crank pin position2and mark lineb. For crank position3we have by the same process linec, and so on, the twelve lines fromatolrepresenting crank positions from1to12.
Now let it be noted that since the path of the crank pin is a circle, the tool point will on the backward stroke occupy the same position when the crank pin is at corresponding positions on the forward and backward strokes. For example, when the crank pin is in position7the tool point will be at pointgon the forward stroke, and when the crank pin is in position17the tool will be at pointgon the backward stroke, as will be found by trial with the compasses; and it follows that the linesa,b,c, &c., for the forward stroke will also serve for the backward one, which enables us to keep the engraving clear, by marking the first seven positions on one side of linem, and the remaining five on the other side ofm, as has been done in the figure.
Obviously the distances apart of the linesa,b,c,d, &c., represent the amount of tool motion during equal periods of time, because the motion of the crank pin being uniform it will move from position1to position2in the same time as it moves from position2to position3, and it follows that the cutting speed of the tool varies at every instant in its path across the work, and also that since the crank pin operates during a full one-half of its revolution to push the tool forward, and during a full one-half to pull it backward, therefore the speed of the two strokes are equal.
Fig. 1554Fig. 1554.
Fig. 1554.
We may now plot out the motion of the link quick return that was shown inFig. 1550, the dotted circleh′, inFig. 1554, representing the path of the pina, and the archrepresenting the line of motion of the upper end of linkl, and linesn,o, its centre line at the extreme ends of its vibrating motion. InFig. 1554the letters of reference refer to the same parts as those inFig. 1550. We divide the circleh′of pin motion into twenty-four equidistant parts marked by dots, and through these we draw lines radiating from centrecand cutting arch, obtaining on the archthe various positions for endzof rodr, these positions being marked respectively1,2,3,4, &c., up to24. With a pair of compasses set to the length of rodrfrom1onh, as a centre, we mark on the line of motion of the slide linea, which shows where the other end of the rodrwill be (or, in other words, it shows the position of boltbinFig. 1550), when the centre ofa,Fig. 1550, is in position1,Fig. 1554.
From2on arch, we mark with the compasses linebon linem, showing that while the pin moved from1to2, the rodrwould move slides,Fig. 1550, fromatob, inFig. 1554. From3we markc, and so on, all these marks being above the horizontal linem, representing the line of motion, and being for the forward stroke. For the backward stroke we draw the dotted line from position17up to arch, and with the compasses at17mark a line beneath the linemof motion, pursuing the same course for all the other pin positions, as18,19, &c., until the pin arrives again at position24, and the link ato, and has made a full revolution, and we shall have the motion of the forward stroke above and that of the backward one below the line of motion of the slide.
On comparing this with the crank and with the Whitworth motion hereafter described, we find that the cutting speed is much more uniform than either of them, the irregularity of motion occurring mainly at the two ends of the stroke.
Fig. 1555Fig. 1555.
Fig. 1555.
Fig. 1556Fig. 1556.
Fig. 1556.
InFig. 1555we have the motion of the Whitworth quick return described inFig. 1551,h′representing the path of motion of the driving-pindabout the centre ofb, andh′the path of motion ofxabout the centrec, these two centres corresponding to the centres ofbandcrespectively inFig. 1551. Let the linemcorrespond to the line of motionminFig. 1551. Now, since pind,Fig. 1551, drives, and since its speed of revolution is uniform, we divide its circle of motionh′into twenty-four equal divisions, and by drawing lines radiating from centreb, and passing through the lines of division onh′, we get on circlehtwenty-four positions for the pinxinFig. 1551. Then setting the compasses to thelength of the rod (r,Fig. 1551), we mark from position1on circlehas a centre, linea; from position2onhwe mark lineb, and so on for the whole twenty-four positions on circleh, obtaining fromatonfor the forward, and fromntoyfor the motion during the backward stroke. Suppose, now, that the mechanism remaining precisely the same as before, the linemof motion be in a line with the centresc,b, instead of at a right angle to it, as it is inFig. 1551, and the motion under this new condition will be as inFig. 1556, the process for finding the amount of motion alongmfrom the motion aroundhbeing precisely as before.
Fig. 1557Fig. 1557.
Fig. 1557.
The iron planing machine, or iron planer as it is termed in the United States, is employed to plane such surfaces as may be operated upon by traversing a work table back and forth in a straight line beneath the cutting tool. It consists essentially of a frame or beda,Fig. 1557, provided on its upper surface with guideways, on which a work carrying tabletmay be moved by suitable mechanism back and forth in a straight line.
This frame or bed carries two upright frames or stanchionsb, which support a cross-bar or slidec, to which is fitted a head which carries the cutting tool.
To enable the setting of the tool at such a height from the table as the height of the work may require, the cross slidecmay be raised higher upon the uprightsbby means of the bevel gearsf,g,h, andt, the latter being on a shaft at the top of the machine, and operating the former, which are on vertical screwsn, which pass down through nuts that are fast upon the cross slidec.
To securecat its adjusted height, the uprights are provided withT-shaped slotsh h, and bolts pass throughc, their heads being in theT-grooves, and their nuts exposed so that a wrench may be applied to them.
The faces of the cross slidecare parallel one to the other, and stand at a right angle to theV-guideways on which the work table (or platen as it is sometimes termed) slides; hence the cross slide will, if the table is planed true or parallel with this cross slide, be parallel with the table at whatever height above the table it is set, providing that the elevating screws, when operated, lift each end ofcequally.
The construction of the headdcorresponds to that of the head shown inFigs. 1497and1498for a shaper, except that in this case the swivel head is secured to a saddle that slides alongc, being provided with a nut operated by a feed screwj, which movesdalongc.
The mechanism for operating the work table or platentis as follows:—p p′are two loose pulleys andp′′is a driving pulley fast on the same shaft. This shaft drives, within the casing atq, a worm operating a worm-wheel, which actuates inside the frameaand beneath the work table a train of gears, the last of which gears with a rack, provided on the underneath side of the table.
The revolutions of this last wheel obviously cause the work table to slide back and forth while resting on theV-guideways provided on top of the framea, the direction of table motion being governed by the direction in which the wheel revolves.
This direction is periodically reversed as follows:—The pulleypis driven by a crossed belt, while pulleyp′is driven by an open or uncrossed one, hence the direction of revolution of the driving pulleyp′′will be in one direction if the belt is moved fromptop′′, and in the other if the belt is moved fromp′top′′. Mechanism is provided whereby first one and then the other of these belts is moved so as to pass over uponp′′and drive it, the construction being asfollows:—
To the edge of the work table there is fixed a stopr, which as the table traverses to the right meets and moves a lever arms, which through the medium of a second lever operates the rodx, which operates a leveru, which has a slot through which one of the driving belts passes. The leveruoperates a second leverwon the other side of the pulleys, and this lever also has a slot through which the other driving belt passes.
When the stoprmoves the lever armsleversuandwtherefore move their respective belts, one moving from the tight pulleyp′′to a loose one asp, and the other moving its belt from the loose pulley asp′to the tight onep′′, and as the directions of belt motions are opposite the direction of revolution ofp′′is reversed by the change of belt operating it. There are two of the stopsr, one on each side of the levers, hence one of these stops moves the leversfrom left to right and the other from right to left.
Suppose, then, that the table is moving from right to left, which is its cutting stroke, and the driving belt will be on the pulleyp′′while the other belt will be on pulleyp. Then as the stoprmovessand operatesxthe armuwill move its belt fromp′′top′, and armwwill move its belt fromptop′′, reversing the direction of motion ofp′′, and therefore causing the tabletto move from left to right, which it will continue to do until the other stop corresponding tormeetssand moves it from right to left, when the belts will be shifted back again. The stroke of the table, therefore, is determined by the distance apart of the stopsr, and these may be adjusted asfollows:—
They are carried by bolts whose heads fit in a dovetail groovezprovided along the edge of the table, and by loosening a set screw may therefore be moved to any required location along the bed.
To give the table a quick return so that less time may be occupied for the non-cutting stroke, all that is necessary is to make the countershaft pulley that operates during the back traverse of larger diameter than that which drives during the cutting traverse of the table.
In order that one belt may have passed completely off the driving pulleyp′′before the other moves on it the lever motions ofuandware so arranged that when the belt is moving fromp′′topleverumoves in advance of leverw, while when the other belt is being moved fromp′′top′leverwmoves in advance of leveru.
To enable the work table to remain at rest, one driving belt must be uponpand the other uponp′, which is the case when the lever armsis in mid position, and to enable it to be moved to this position it is provided with a handlekforming part of levers.
To cause the tool to be fed to its cut before it meets the cut and thus prevent it from rubbing against the side of the cut, as was described with reference toFig. 1503, the feed takes place when the table motion is reversed from the back or return stroke to the cutting or forward stroke by the followingmechanism:—
Atais a rack that is operated simultaneously withsand by the same stopr. This rack operates a pinionb, which rotates the slotted piecec, in which is a block that operates the vertical rodd, which is attached to a segmental racke, which in turn operates a pinion which may be placed either upon the cross-feed screwj, or upon the rod above it; the latter operates the vertical feed of the tool through mechanism within the headdand not therefore shown in the engraving. Thus the self-acting tool feed may take place vertically or across the work table at will by simply placing the pinion upon the cross-feed screw or upon the feed rod, as the case may be.