Modern Machine-Shop Practice Part 110

[Ill.u.s.tration: Fig. 1555.]

[Ill.u.s.tration: Fig. 1556.]

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 pa.s.s 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 pa.s.s 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 pa.s.s 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 pa.s.ses. 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 pa.s.ses.

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 s.h.i.+fted 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 pa.s.sed 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:--

[Ill.u.s.tration: Fig. 1557.]

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.

[Ill.u.s.tration: Fig. 1558.]

Fig. 1558 represents a planer by David W. Pond, of Worcester, Ma.s.sachusetts, in which the rod _x_ is connected direct from S to a pivoted piece _y_ in which is a cam-shaped slot through which pa.s.s 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 pa.s.s 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 pa.s.sed 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 s.h.i.+fted 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 pa.s.ses 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.

[Ill.u.s.tration: Fig. 1559.]

[Ill.u.s.tration: Fig. 1560.]

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.

[Ill.u.s.tration: Fig. 1561.]

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.

[Ill.u.s.tration: Fig. 1562.]

As the sizes of planing machines increase, they are given increased tool-carrying heads; thus, Fig. 1562 represents a cla.s.s 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 finis.h.i.+ng 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 pa.s.sing 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.

[Ill.u.s.tration: _VOL. I._ =EXAMPLES OF PLANING MACHINES.= _PLATE XVII._

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.

[Ill.u.s.tration: Fig. 1564.]

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 s.p.a.ce 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 s.p.a.ce 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 pa.s.sage 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.

CHAPTER XVII.--PLANING MACHINERY.