Modern Machine-Shop Practice Part 112

[Ill.u.s.tration: Fig. 1577.]

[Ill.u.s.tration: Fig. 1578.]

[Ill.u.s.tration: Fig. 1579.]

Fig. 1579 is a front view, and Fig. 1580 a sectional top view, of a sunk vertical slide, corresponding to that shown in Figs. 1573 and 1578, but in this case the gib has a tongue _t_, closely fitted into a recess or channel in the vertical slider S, and to allow room for adjustment, the channel is made somewhat deeper than the tongue requires when newly fitted. The adjustment is effected by means of two sets of screws, _a_ and _b_, of which the former, being tapped into the gib, serve to tighten, and the latter, being tapped into the slide, serve to loosen the gib. By thus acting in opposite directions the screws serve to check each other, holding the gib rigidly in place. To insure a close contact of the gib against the vertical surface of the slide, the screws _b_ are placed in a line slightly outside of the line of the screws _a_.

Fig. 1581 represents a similar construction when the slideways on the swing frame project outwards, instead of being sunk within that frame.

Fig. 1582 represents the construction of the Pratt & Whitney Company's planer head, in which the swivel head instead of pivoting upon a central pin and being locked in position by bolts, whose nuts project outside and on the front face of the swing frame, is constructed as follows:--

A circular dovetail recess in the saddle receives a corresponding dovetail projection on the swivel head or swing frame, and the two are secured together at that point by a set-screw A. In addition to this the upper edge B of the saddle is an arc of a circle of which the centre is the centre of the dovetail groove, and a clamp is employed to fasten the swivel head to the saddle, being held to that head by a bolt, and therefore swinging with it. Thus the swivel head is secured to its saddle at its upper edge, as well as at its centre, which affords a better support.

The tool box is pivoted upon the vertical slider, and is secured in its adjusted position by the bolts _n_ in Fig. 1573, the object of swinging it being to enable the tool to be lifted on the back stroke and clear the cut, when cutting vertical faces, as was explained with reference to shaping machines.

The tool ap.r.o.n is in American practice pivoted between two jaws, which prevent its motion sideways, and to prevent any play or lost motion that might arise from the wear of the taper pivoting pin _b_, in Fig.

1583, the ap.r.o.n beds upon a bevel as at _a_, so that in falling to its seat it will be pulled down, taking up any lost motion upon _b_.

[Ill.u.s.tration: Fig. 1580.]

[Ill.u.s.tration: Fig. 1581.]

[Ill.u.s.tration: Fig. 1582.]

[Ill.u.s.tration: Fig. 1583.]

[Ill.u.s.tration: Fig. 1584.]

[Ill.u.s.tration: Fig. 1585.]

The bevel at _a_ would also prevent any side motion to the ap.r.o.n should wear occur between it and the jaws. In addition to this bevel, however, there may be employed two vertical bevels _c_ in the top view in Fig.

1584. In English practice, and especially upon large planing machines, the ap.r.o.n is sometimes made to embrace or fit the outsides of the tool box, as in Fig. 1585, the object being to spread the bearings as wide apart as possible, and thus diminish the effect of any lost motion or wear of the pivoting pin, and to enable the tool post or holder to be set to the extreme edge of the tool box as shown in the figure.

It is desirable that the tool ap.r.o.n bed as firmly as possible back against its seat in the tool box, and this end is much more effectively secured when it is pivoted as far back as possible, as in Fig. 1585, because in that case nearly all the weight of the ap.r.o.n, as well as that of the tool and its clamp, acts to seat the ap.r.o.n, whereas when the pivot is more in front, as _m_, in Fig. 1573, it is the weight of the tool post and tool only that acts to keep the ap.r.o.n seated.

In small planing machines it is a great advantage to provide an extra ap.r.o.n carrying two tool posts, as in Fig. 1586, so that in planing a number of pieces, that are to be of the same dimension, one tool may be used for roughing and one for finis.h.i.+ng the work. The tools should be wider apart than the width of the work, so that the finis.h.i.+ng tool will not come into operation until after the roughing tool has carried its cut across.

When the roughing tool has become dulled it should, after being ground up, be set to the last roughing cut taken, so that it will leave the same amount of finis.h.i.+ng cut as before.

The advantage of this system is that the finis.h.i.+ng tool will last to finish a great many pieces without being disturbed, and as a result the trouble of setting its cut for each piece is avoided; on which account all the pieces are sure to be cut to the same dimension without any further measuring than is necessary for the first piece, whereas if one tool only is used it rapidly dulls from the roughing cut, and will not cut sufficiently smooth for the finis.h.i.+ng one, and must therefore be more frequently ground up to resharpen it, while it must be accurately set for each finis.h.i.+ng cut. A double tool ap.r.o.n of this kind is especially serviceable upon such work as planing large nuts, for it will save half the time and give more accurate work.

In some planing machines, and notably those made by Sir Joseph Whitworth, a swiveling tool holder is made so that at each end of the stroke the cutting tool makes half a revolution, and may therefore be used to cut during both strokes of the planer table. A device answering this purpose is shown in Fig. 1587. The tool-holding box is pivoted upon a pin A, and has attached to it a segment of a circular rack or worm-wheel, operated by a worm upon a shaft having at its upper end the pulley shown, so that by operating this pulley, part of a revolution at the end of each work-table stroke, one or the other of the two tools shown in the tool box, is brought into position to carry the cut along.

Thus two tools are placed back to back, and it is obvious that when the tool box is moved to the right, the front tool is brought into position, while when it is moved to the left, the back or right-hand tool is brought into position to cut, the other tool being raised clear of the work.

[Ill.u.s.tration: Fig. 1586.]

[Ill.u.s.tration: Fig. 1587.]

The objections to either revolving one tool or using two tools so as to cut on both strokes are twofold: first, the tools are difficult to set correctly; and, secondly, the device cannot be used upon vertical faces or those at an angle, or in other words, can only be used upon surfaces that are nearly parallel to the surface of the work table.

[Ill.u.s.tration: Fig. 1588.]

[Ill.u.s.tration: Fig. 1589.]

Figs. 1588 and 1589 represent the sliding head of the large planer at the Was.h.i.+ngton Navy Yard, the sectional view, Fig. 1589, being taken on the line X X in Fig. 1588. C is the cross bar and S the saddle, F being the swing frame or fiddle, as some term it, and S' the vertical slider; B is the tool box, and A the ap.r.o.n.

The wear of the cross slider is taken up by the set screws _a_, and that of the vertical slide by the screws _b_.

The graduations of the degrees of a circle for setting over the swing frame F, as is necessary when planing surfaces that are at an angle to the bed and to the cross slide, are marked on the face of the saddle, and the pointer (_f_, Fig. 1578) is fastened to the edge of the swing frame. When the swing frame is vertical the pointer is at 90 on the graduated arc, which accords with English practice generally. In American practice, however, it is customary to mark the graduations on the edge of the swing frame as in Fig. 1590, so that the pointer stands at the zero point _o_ when the swing frame is vertical, and the graduations are marked on the edge of the swing frame as shown, the zero line _o_ being marked on the edge of the saddle.

In the English practice the swing frame is supposed to stand in its neutral or zero position when it is vertical, and all angles are a.s.sumed to be measured from this vertical zero line, so that if the index point be set to such figure upon the graduated arc as the angle of the work is to be to a vertical line, correct results will be obtained.

Thus in Fig. 1591 (which is from _The American Machinist_) the pointer is set to 40 and the bevelled face is cut to an angle of 40 with the vertical face as marked. But if the head be graduated as in Fig. 1592, the face of the planer table being taken as the zero line _o_, then the swing frame would require to be set over to 30 out of its normal or neutral vertical position as is shown in figure, the bevelled face being at an angle of 50 from a vertical, and 40 from a horizontal line, hence the operator requires to consider whether the number of degrees of angle are marked on the drawing from a zero line that is vertical on one that is horizontal.

[Ill.u.s.tration: Fig. 1590.]

[Ill.u.s.tration: Fig. 1591.]

[Ill.u.s.tration: Fig. 1592.]

[Ill.u.s.tration: Fig. 1593.]

[Ill.u.s.tration: Fig. 1594.]

Referring again to Fig. 1588 the slots for the tool post extend fully across the ap.r.o.n, so that the tool posts may be set at any required point in the tool-box width, and the tool or tool holder may be set nearer to the edge of the tool box than is the case when fixed bolts, as in Fig. 1590, are used, because these bolts come in the way.

This is mainly important when the tool is required to carry a deep vertical cut, in which case it is important to keep the tool point as close in to the holder as possible so that it may not bend and spring from the pressure of the cut.

The tool or holder may be held still closer to the edge of the head, and therefore brought still closer to the work, when the ap.r.o.n embraces the outside of the tool box, as was shown in Fig. 1585, and referred to in connection therewith.

[Ill.u.s.tration: Fig. 1595.]

[Ill.u.s.tration: Fig. 1596.]

A sectional side view and a top view of Fig. 1588 through the centre of the head is given in Figs. 1595 and 1596, exposing the mechanism for the self-acting feed traverse, and for the vertical feed. For the feed traverse the feed screw (_m_, Fig. 1588) pa.s.ses through the feed nut N.

For the vertical feed the feed rod (_n_, Fig. 1588) drives a pair of bevel-gears at P, which drives a second pair at Q, one of which is fast on a spindle which pa.s.ses through the vertical feed screw, and is secured thereto by the set screw _e_. The object of this arrangement is that if the self-acting vertical feed should be in action and the tool or swing frame S' should meet any undue obstruction, the set screw _e_ will slip and the feed would stop, thus preventing any breakage to the gears at P or Q. The feed screw is threaded into the top of S'. At E is the pin on which the tool box pivots to swing it at an angle.

The mechanism for actuating the cross-feed screw and the feed rod is shown in the top view, Fig. 1597, and the side view, Fig. 1598, in which A is a rod operated vertically and actuated from the stop (corresponding to stop R in Fig. 1558) that actuates the belt s.h.i.+fting gear. Upon A is the sleeve B, which actuates rod C, which operates the frame D. This frame is pivoted upon a stud which is secured to the cross bar C, and is secured by the nut at E. Frame D carries pawls F and G, the former of which engages gear-wheel H, which drives the pinion _n_, Fig. 1598, that is fast on the feed rod, while the latter drives the gear K, which in turn drives pinion P, which is fast upon the feed screw in Fig. 1588.

The feeds are put into or thrown out of action as follows:--On the same shaft or pin as the pawls G and F, is secured a tongue T, Fig. 1599, whose end is wedge shaped and has a correspondingly shaped seat in a plate V, whose cylindrical stem pa.s.ses into a recess provided in D, and is surrounded by a spiral spring which acts to force V outwards from the recess.

[Ill.u.s.tration: Fig. 1597.]

[Ill.u.s.tration: Fig. 1598.]

[Ill.u.s.tration: Fig. 1599.]

In the position shown in the figure the end of T is seated in the groove in V, and the pressure of the spring acts to hold T still and keep the pawl G from engaging with the teeth of gear-wheel H. But suppose the handle W (which is fast on the pawl G) is pulled upwards, and T will move downwards, disengaging from the groove in V, and the upper end of pawl G will engage with the teeth of H, actuating in the direction of the arrow during the upward motion of rod A, and thus actuating pinion _n_ and putting the vertical feed in motion in one direction. When the rod A makes its downward stroke the pawl G will slip over the teeth of H, because there is nothing but the spiral spring to prevent the end of the pawl from slipping over these teeth. To place the vertical feed in action in the other direction, handle W is pressed downwards, causing the bottom end X of the pawl to engage with the teeth of H.