Chapter XVI: Shaping and Planing Machines (2)

The mechanism for actuating the feed at the end of the return stroke only, is shown in Fig. 1547. The shaft V (which is also seen in a dotted circle in Fig. 1545) carries a flange _c_, on each side of which is a leather disk, so that the pressure of the bolts which secure _b_ to the sleeve _a_ causes _c_ to revolve under friction, unless sleeve _a_, slotted bar _b_, and flange _c_ all revolve together, or, in other words, _c_ revolves under friction when it revolves within _a_ _b_.

Fig. 1548 is an end view of Fig. 1547.

Fig. 1549 gives a cross-sectional view of the shaft sleeve, &c. The sleeve _a_ is provided with two pins _i_, _i_, and a pin _k_ is fast in the frame of the machine, and it is seen that _a_ and V may revolve together in either direction until such time as one of the pins _i_ meets the stationary pin _k_, whereupon the further revolving of _a_ will be arrested and V will revolve within _a_, and as flange _c_, Fig. 1547, revolves with V, it will do so under the friction of the leather washers. The pins _i_ and the pin _k_ are so located that _a_ can have motion only when the ram or sliding-bar is at the end of the return stroke, and the feed-rod _f_, being connected to _b_, 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.

The principle of action when a vibrating link is employed may be understood from Fig. 1550, in which P is a pinion driven by the cone pulley and imparting motion to D. At L is a link pivoted at C. At A is 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 in the wheel D. As D rotates the link block slides in the slot and the link is caused to travel as denoted by the dotted lines. R is a rod connecting the tool-carrying slide S to the upper end of link L, and therefore causing it to reciprocate with L. But S being guided by its slide in the guideway traverses in a straight line.

Since the rotation of P and D is uniform, the vibrations of the link L will 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 motion C of the link, and the upper end of C will 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 in A is above the horizontal centre of wheel D.

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 end K of S, then S will be pushed to its cut by the rod R at an angle which will tend to lift S in the slideways. But suppose the direction of rotation of wheel D instead of being as denoted by the arrow at D be as denoted by the arrow at E, then S will be on its back stroke, the front of the machine being at J. In this case rod R will pull S to the cut, and S will, from the angularity of R, 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 projecting V, 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 of S pin A is so attached to wheel D that it may be adjusted in its distance from the centre of D.

The Whitworth quick-return motion is represented in Fig. 1551. At P is the pinion receiving motion from the cone pulley or driving pulley of the machine and imparting motion to the gear-wheel G, whose bearing is denoted by the dotted circle B. Through B passes a shaft C, which is eccentric to B and carries at its end a piece A in which is a slot to receive the pin X, which drives rod R whose end Z is attached to the ram of the machine. At D is a pin fast in gear-wheel G and passing into a slot in A.

Taking the position the parts occupy in the figures, and it is seen that the axis of B is the centre of motion of G and is the fulcrum from which the pin D is driven, the power being delivered at X. The path of motion of the driving pin D is denoted by the dotted circle H´, and it is apparent that as it moves from the position shown in the figure it recedes from the axis of C, and as the motion of G is uniform in velocity therefore D will move A faster while moving below the line M than it will while moving above it, thus giving a quick return, because the cutting stroke of the ram occurs while D is above the line M and the return stroke occurs while D is below M.

In some constructions the pin X and pin D work in opposite ends of the piece A, as shown in Fig. 1552. This, however, is an undesirable construction because the shaft C becomes the fulcrum, and as the power and resistance are on opposite ends of the lever A, the wheel G is 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.

In Fig. 1553 is a diagram of the tool motion given when the slide is operated by a simple crank C, the thickened line R representing the rod actuating the slide and line on the line of motion of the cutting tool. The circle H denotes the path of revolution of the crank pin, and the black dots 1, 2, 3, 4, &c., equidistant positions of the crank pin.

Line _m_ represents the path of motion of the cutting tool.

If a pair of compasses be set to the full length of the thick line R, that is from the centre of the crank pin to end B of line R, and these compasses be then applied to the centre of crank pin position 1, and to the line _m_, they will meet _m_ at a point denoted by line _a_, which will, therefore, represent the position of the tool point when the crank pin was in position 1. To find how far the tool point is moved while the crank pin moves from position 1 to position 2, we place the compass point on the centre of crank pin position 2 and mark line _b_. For crank position 3 we have by the same process line _c_, and so on, the twelve lines from _a_ to _l_ representing crank positions from 1 to 12.

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 position 7 the tool point will be at point _g_ on the forward stroke, and when the crank pin is in position 17 the tool will be at point _g_ on the backward stroke, as will be found by trial with the compasses; and it follows that the lines _a_, _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 line _m_, and the remaining five on the other side of _m_, as has been done in the figure.

Obviously the distances apart of the lines _a_, _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 position 1 to position 2 in the same time as it moves from position 2 to position 3, 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.

We may now plot out the motion of the link quick return that was shown in Fig. 1550, the dotted circle H´, in Fig. 1554, representing the path of the pin A, and the arc H representing the line of motion of the upper end of link L, and lines N, O, its centre line at the extreme ends of its vibrating motion. In Fig. 1554 the letters of reference refer to the same parts as those in Fig. 1550. We divide the circle H´ of pin motion into twenty-four equidistant parts marked by dots, and through these we draw lines radiating from centre C and cutting arc H, obtaining on the arc H the various positions for end Z of rod R, these positions being marked respectively 1, 2, 3, 4, &c., up to 24. With a pair of compasses set to the length of rod R from 1 on H, as a centre, we mark on the line of motion of the slide line _a_, which shows where the other end of the rod R will be (or, in other words, it shows the position of bolt B in Fig. 1550), when the centre of A, Fig. 1550, is in position 1, Fig. 1554.

From 2 on arc H, we mark with the compasses line _b_ on line M, showing that while the pin moved from 1 to 2, the rod R would move slide S, Fig. 1550, from _a_ to _b_, in Fig. 1554. From 3 we mark _c_, and so on, all these marks being above the horizontal line M, representing the line of motion, and being for the forward stroke. For the backward stroke we draw the dotted line from position 17 up to arc H, and with the compasses at 17 mark a line beneath the line M of motion, pursuing the same course for all the other pin positions, as 18, 19, &c., until the pin arrives again at position 24, and the link at O, 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.

In Fig. 1555 we have the motion of the Whitworth quick return described in Fig. 1551, H´ representing the path of motion of the driving-pin D about the centre of B, and H´ the path of motion of X about the centre C, these two centres corresponding to the centres of B and C respectively in Fig. 1551. Let the line M correspond to the line of motion M in Fig. 1551. Now, since pin D, Fig. 1551, drives, and since its speed of revolution is uniform, we divide its circle of motion H´ into twenty-four equal divisions, and by drawing lines radiating from centre B, and passing through the lines of division on H´, we get on circle H twenty-four positions for the pin X in Fig. 1551. Then setting the compasses to the length of the rod (R, Fig. 1551), we mark from position 1 on circle H as a centre, line _a_; from position 2 on H we mark line _b_, and so on for the whole twenty-four positions on circle H, obtaining from _a_ to _n_ for the forward, and from _n_ to _y_ for the motion during the backward stroke. Suppose, now, that the mechanism remaining precisely the same as before, the line M of motion be in a line with the centres C, B, instead of at a right angle to it, as it is in Fig. 1551, and the motion under this new condition will be as in Fig. 1556, the process for finding the amount of motion along M from the motion around H being precisely as before.

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 bed A, Fig. 1557, provided on its upper surface with guideways, on which a work carrying table T may be moved by suitable mechanism back and forth in a straight line.

This frame or bed carries two upright frames or stanchions B, which support a cross-bar or slide C, 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 slide C may be raised higher upon the uprights B by means of the bevel gears F, G, H, and T, the latter being on a shaft at the top of the machine, and operating the former, which are on vertical screws N, which pass down through nuts that are fast upon the cross slide C.

To secure C at its adjusted height, the uprights are provided with [T]-shaped slots H H, and bolts pass through C, their heads being in the [T]-grooves, and their nuts exposed so that a wrench may be applied to them.

The faces of the cross slide C are parallel one to the other, and stand at a right angle to the [V]-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 of C equally.

The construction of the head D corresponds to that of the head shown in Figs. 1497 and 1498 for a shaper, except that in this case the swivel head is secured to a saddle that slides along C, being provided with a nut operated by a feed screw J, which moves D along C.

The mechanism for operating the work table or platen T is as follows:--P P´ are two loose pulleys and P´´ is a driving pulley fast on the same shaft. This shaft drives, within the casing at Q, a worm operating a worm-wheel, which actuates inside the frame A and 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 the [V]-guideways provided on top of the frame A, the direction of table motion being governed by the direction in which the wheel revolves.

This direction is periodically reversed as follows:--The pulley P is driven by a crossed belt, while pulley P´ is driven by an open or uncrossed one, hence the direction of revolution of the driving pulley P´´ will be in one direction if the belt is moved from P to P´´, and in the other if the belt is moved from P´ to P´´. Mechanism is provided whereby first one and then the other of these belts is moved so as to pass over upon P´´ and drive it, the construction being as follows:--

To the edge of the work table there is fixed a stop R, which as the table traverses to the right meets and moves a lever arm S, which through the medium of a second lever operates the rod X, which operates a lever _u_, which has a slot through which one of the driving belts passes. The lever _u_ operates a second lever _w_ on the other side of the pulleys, and this lever also has a slot through which the other driving belt passes.

When the stop R moves the lever arm S levers _u_ and _w_ therefore move their respective belts, one moving from the tight pulley P´´ to a loose one as P, and the other moving its belt from the loose pulley as P´ to the tight one P´´, and as the directions of belt motions are opposite the direction of revolution of P´´ is reversed by the change of belt operating it. There are two of the stops R, one on each side of the lever S, hence one of these stops moves the lever S from 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 pulley P´´ while the other belt will be on pulley P. Then as the stop R moves S and operates X the arm _u_ will move its belt from P´´ to P´, and arm _w_ will move its belt from P to P´´, reversing the direction of motion of P´´, and therefore causing the table T to move from left to right, which it will continue to do until the other stop corresponding to R meets S and 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 stops R, and these may be adjusted as follows:--

They are carried by bolts whose heads fit in a dovetail groove Z provided 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 pulley P´´ before the other moves on it the lever motions of _u_ and _w_ are so arranged that when the belt is moving from P´´ to P lever _u_ moves in advance of lever _w_, while when the other belt is being moved from P´´ to P´ lever _w_ moves in advance of lever _u_.

To enable the work table to remain at rest, one driving belt must be upon P and the other upon P´, which is the case when the lever arm S is in mid position, and to enable it to be moved to this position it is provided with a handle K forming part of lever S.

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 to Fig. 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 following mechanism:--

At _a_ is a rack that is operated simultaneously with S and by the same stop R. This rack operates a pinion _b_, which rotates the slotted piece _c_, in which is a block that operates the vertical rod _d_, which is attached to a segmental rack _e_, which in turn operates a pinion which may be placed either upon the cross-feed screw J, or upon the rod above it; the latter operates the vertical feed of the tool through mechanism within the head D and 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.

Fig. 1558 represents a planer by David W. Pond, of Worcester, Massachusetts, in which the rod _x_ is connected direct from S to a pivoted piece _y_ in which is a cam-shaped slot through which pass pins from the belt-moving arms _u_ and W. The shape of the slot in _y_ is such as to move the belt-moving arms one in advance of the other, as described with reference to Fig. 1566.

The feed motions are here operated by a disk C, which is actuated one-half a revolution when the work table is reversed. This disk is provided on its face with a slide-way in which is a sliding block that may be moved to or from the centre of C by the screw shown, thus varying at will the amount of stroke imparted to the rod which moves the rack by means of which the feed is actuated through the medium of the gear-wheels at _f_. The handle _g_ is for operating the feed screw when the self-acting feed is thrown out of operation, which is done by means of a catch corresponding in its action to the catch shown in Fig. 1501. S and S´ are in one piece, S´ being to move the two driving belts on to the loose pulleys so as to stop the work table from traversing.

The size of a planer is designated from the size of work it will plane, and this is determined by the greatest height the tool can be raised above the planer table, the width between the stanchions, and the length of table motion that can be utilized while the tool is cutting; which length is less than the full length of table stroke, because in the first place it is undesirable that the rack should pass so far over the driving wheel or pinion that any of the teeth disengage, and, furthermore, a certain amount of table motion is necessary to reverse after the work has passed the tool at the end of each stroke.

Fig. 1559 represents a method employed in some English planing machines to drive the work table and to give it a quick return motion. In this design but one belt is used, being shifted from pulley A, which operates the table for the cutting stroke, to pulley J, which actuates the table for the return stroke. The middle pulley K is loose upon shaft B, as is also pulley J, which is in one piece with pinion J´. Motion from A is conveyed through shaft B and through gear C, D, E to F, and is reduced by reason of the difference in diameter between D and E and between F and G. Motion for the quick return passes from J direct to F without being reduced by gears D, E, hence the difference between the cutting speed and the speed of the return stroke is proportionate to the relative diameters or numbers of teeth in D and E, and as E contains 12 and D 20 teeth, it follows that the return is 8/12 quicker than the cutting stroke.

In this design the belt is for each reversal of table motion moved across the loose pulley K from one driving pulley to the other, and therefore across two pulleys instead of across the width of one pulley only as in American machines.

In American practice the rack R, Fig. 1559, is driven by a large gear instead of by a pinion, so that the strain on the last driving shaft S, in Fig. 1560, shall be less, and also the wheel less liable to vibration than a pinion would be, because in the one case, as in Fig. 1559, the power is transmitted through the shaft, while in the other, as in Fig. 1560, it is transmitted through the wheel from the pinion P to the rack R.

Fig. 1561 represents a planer, designed for use in situations where a solid foundation cannot be obtained, hence the bed is made of unusual depth to give sufficient strength and make it firm and solid on unstable foundations, such as the floors in the upper stories of buildings. In all other respects the machine answers to the general features of improved planing machines.

As the sizes of planing machines increase, they are given increased tool-carrying heads; thus, Fig. 1562 represents a class in which two sliding heads are used, so that two cutting tools may operate simultaneously. Each head, however, is capable of independent operation; hence, one tool may be actuated automatically along the cross slide to plane the surfaces of the work, while the other may be used to carry a cut down the sides of the work, or one tool may take the roughing and the other follow with the finishing cut, thus doubling the capacity of the machine.

In other large planers the uprights are provided with separate heads as shown in the planer in Fig. 1563, in which each upright is provided with a head shown below the cross slide. Either or both these heads may be employed to operate upon the vertical side faces of work, while the upper surface of the work is being planed.

The automatic feed motion for these side heads is obtained in the Sellers machine from a rod actuated from the disk or plate in figure, this rod passing through the bed and operating each feed by a pawl and feed wheel, the latter being clearly seen in the figure.

To enable the amount of feed to be varied the feed rod is driven by a stud capable of adjustment in a slot in the disk.

Fig. 1561.

Fig. 1563.]

Fig. 1563 represents a planing machine designed by Francis Berry & Sons, of Lowerby Bridge, England. The bed of the machine is, it will be seen, [L]-shaped, the extension being to provide a slide to carry the right-hand standard, and permit of its adjustment at distances varying from the left-hand standard to suit the width of the work. This obviously increases the capacity of the machine, and is a desirable feature in the large planers used upon the large parts of marine engines.

ROTARY PLANING MACHINE.--Fig. 1564 is a rotary planing machine. The tools are here carried on a revolving disk or cutter head, whose spindle bearing is in an upper slide with 2 inches of motion to move the bearing endways, and thereby adjust the depth of cut by means of a screw. The carriage on which the spindle bearing is mounted is traversed back and forth (by a worm and worm-wheel at the back of the machine) along a horizontal slide, which, having a circular base, may be set either parallel to the fixed work table or at any required angle thereto.

By traversing the cutter head instead of the work, less floor space is occupied, because the head requires to travel the length of the work only, whereas when the work moves to the cut it is all on one side of the cutter at the beginning of the cut, and all on the other at the end, hence the amount of floor space required is equal to twice the length of the work.

The disk or cutter head is in one piece with the spindle, and carries twenty-four cutters arranged in a circle of 36 inches in diameter. These cutters are made from the square bar, and each cutting point should have the same form and position as referred to one face, side, or square of the bar, so that each cutter may take its proper share of the cutting duty; and it is obvious that all the cutting edges must project an equal distance from the face of the disk, in which case smooth work will be produced with a feed suitable for the whole twenty-four cutters, whereas if a tool cuts deeper than the others it will leave a groove at each passage across the work, unless the feed were sufficiently fine for that one tool, in which case the advantage of the number of tools is lost.

The cutters may be ground while in their places in the head by a suitable emery-wheel attachment, or if ground separately they must be very carefully set by a gauge applied to the face of the disk.