Modern Machine-Shop Practice Part 114

[Ill.u.s.tration: Fig. 1616.]

The [T]-shaped slots _f_, _g_, _h_, are to receive the heads of bolts as shown in Fig. 1616. The bolt head is rounded at corners _a_, _b_, and the square under the head has the corresponding diagonal corners as _c_ also rounded, so that the width of the head being slightly less than that of the slot it may be pa.s.sed down in the slot and then given a quarter revolution in the direction of the arrow, causing the wings of the head to pa.s.s under the recess of the [T]-groove, as shown in Fig.

1617, which is a sectional end view of the groove with the bolt in place. The square corners at _e_ and at _f_ prevent the bolt from turning round more than the quarter revolution when s.c.r.e.w.i.n.g up the bolt nut, and when the nut is loosened a turn the bolt can be rotated a quarter revolution and lifted out of the groove.

Now it is obvious that these slots serve the same purpose as the longitudinal [T]-grooves, since they receive the bolt heads, and it might therefore appear that they could be dispensed with, but it is a great convenience to be able to adjust the position of the bolt across the table width, which cannot be done if longitudinal grooves only are employed. Indeed, it might easily occur that the longitudinal grooves be covered by the work when the short transverse ones would serve to advantage, and in the wide range of work that large planers generally perform, it is desirable to give every means for disposing the bolts about the table to suit the size and shape of the work.

[Ill.u.s.tration: Fig. 1617.]

It is obvious that the form of bolt head shown in Fig. 1616 is equally applicable to the longitudinal grooves as to the cross slots, enabling the bolt to be inserted, notwithstanding that the work may cover the ends of the longitudinal slots.

The round holes _a_, _b_, _c_, &c., in Fig. 1612, are preferable to the square ones, inasmuch as they weaken the table less and are equally effective. Being drilled and reamed parallel the plugs that fit them may be pa.s.sed through them to any desirable distance, whereas the square plugs being taper must be set down home in their holes, necessitating the use of plugs of varying length, so that when in their places they may stand at varying heights from the table, and thus suit different heights of work. Whatever kind of holes are used it is obvious that they must be arranged in line both lengthways of the table and across it, so that they will not come in the way of the ribs R, which are placed beneath it to strengthen it.

The longitudinal grooves are planed out to make them straight and true with the [V]-guides and guideways, so that chucking appliances fitting into the grooves may be known to be set true upon the table.

[Ill.u.s.tration: Fig. 1618.]

[Ill.u.s.tration: Fig. 1619.]

In Fig. 1618, for example, is shown an angle piece A having a projection fitting into a longitudinal groove, the screws whose heads are visible pa.s.sing through A into nuts that are in the widened part of the groove, so that operating the screws secures A to the table. The vertical face of A being planed true, a piece of work, as a shaft S, may be known to be set in line with the table when it is clamped against A by clamps as at P, or by other holding devices. Angle pieces such as A are made of varying lengths and heights to suit different forms and sizes of work.

In some planing machine tables a [V]-groove is cut along the centre for the purpose of holding spindles to have featherways or splines cut in them, the method of chucking being shown in Fig. 1619. This, however, is not a good plan, as the bolts and plates are apt to bend the shaft out of straight, so that the groove cut in the work will not be straight when the spindle is removed from the clamp pressure. The proper method of chucking such work will, however, be given in connection with examples on planer work.

For the round holes in planer tables several kinds of plugs or stops are employed, the simplest of them being a plain cylindrical plug or stop.

[Ill.u.s.tration: Fig. 1620.]

Fig. 1620 represents a stop provided with a screw B. The stem A fits into the round holes, and the screw is operated to press against the work. By placing the screw at an angle, as shown, its pressure tends to force the work down upon the planer table.

[Ill.u.s.tration: Fig. 1621.]

A similar stop, termed a bunter screw, S, Fig. 1621, may be used in the longitudinal slots, the shape of its hook enabling it to be readily inserted and removed from the slot. These screws may be applied direct to the work when the circ.u.mstances will permit, or a wedge W may be interposed between the screw and the work, as shown.

[Ill.u.s.tration: Fig. 1622.]

Fig. 1622 represents a form of planer chuck used on the smaller sizes of planers, and commonly called planer centres. A is the base or frame bolted to the planer table at the lugs L; at B is a fixed head carrying what may be termed the live centre D, and C is a head similar to the tailstock of a lathe carrying a dead centre; F is an index plate having worm-teeth on its edge and being operated by the worm G. At S is a spring carrying at its end the pin for the index holes. To bring this pin opposite to the requisite circle of holes, the bolt holding S to A is eased back and S moved as required. On the live centre D is a clamp for securing the work or mandrel holding dog. Head C is split as shown, and is held to the surface of A by the bolt H, which is tapped into the metal on one side of the split.

It is obvious that polygons may be planed by placing the work between the centres and rotating it by means of G after each successive side of the polygon has been planed or shaped, the number of sides being determined by the amount of rotation of the index plate.

[Ill.u.s.tration: Fig. 1623.]

Fig. 1623 shows a useful chuck for holding cylindrical work, such as rolls. The base is split at E, so that by means of the bolt and nut D the [V]-block a may be gripped firmly; B and C are screws for adjusting the height of the [V]-block A. At F is the bolt for clamping the chuck to the planer table, and G is a cap to clamp the work W in the block A.

It will be seen that this chuck can be set for taper as well as parallel work.

[Ill.u.s.tration: Fig. 1624.]

[Ill.u.s.tration: Fig. 1625.]

Fig. 1624 represents a chucking device useful for supporting or packing up work, or for adjusting it in position ready to fasten it to the work table, it being obvious that its hollow seat at A enables it to set steadily upon the table, and that its screw affords a simple means of adjusting its height. It may also be used between the jaws of a connecting rod strap or other similar piece of work to support it, as in Fig. 1625, and prevent the jaws from springing together under the pressure of the tool cut.

[Ill.u.s.tration: Fig. 1626.]

Another and very useful device for this purpose is shown in Fig. 1626, consisting of a pair of inverted wedges, of which one is dovetailed into the other and having a screw to operate them endwise, the purpose being to hold the two jaws the proper distance apart and prevent their closure under pressure of the planer vice jaws. It is obvious that the device in Fig. 1625 is most useful for work that has not been faced between the jaws, because the device in Fig. 1626 would, upon rough work that is not true, be apt to spring the work true with the inside faces, which may not be true with the outside ones, and when the wedges were removed the jaws would spring back again, and the work performed while the inverted wedges were in place would no longer be true when they were removed.

[Ill.u.s.tration: Fig. 1627.]

Fig. 1627 represents a centre chuck to enable the cutting of spirals.

The principle of the design is to rotate the work as it traverses, and this is accomplished as follows:--

Upon the bed of the machine alongside of the table is bolted the rack A A, into which gears the pinion B, which is fixed to the same shaft as the bevel-gear C, which meshes with the bevel-wheel D. Upon the same shaft as D is the face plate E, and in the spindle upon which D and E are fixed is a centre, so that the plate E answers to the face plate of a lathe. F is a bearing for the shaft carrying B and C, and G is a bearing carrying the spindle to which E and D are fixed. H is a standard carrying the screw and centre, shown at I, and hence answers to the tailstock of a lathe. K represents a frame or plate carrying the bearings F and G, and the standard H. L represents the table of the planing machine to which K is bolted. The reciprocating motion of the table L causes the pinion B to revolve upon the rack A A. The pinion B revolves C, which imparts its motion to D, and the work W being placed between the centres as shown, is revolved in unison with E, revolving in one direction when the table K is going one way, and in the other when the motion of the table is reversed; hence a tool in the tool post will cut a spiral groove in the work.

To enable the device to cut grooves of different spirals or twist, all that is necessary is to provide different sizes of wheels to take the places of C and D, so that the revolutions of E, and hence of the work W, may be increased or diminished with relation to the revolutions of B; or, what is the same thing, to a given amount of table movement, or a stud may be put in so as to enable the employment of change gears.

[Ill.u.s.tration: Fig. 1628.]

Figs. 1628 and 1629 represent a universal planer chuck, designed and patented by John H. Greenwood, of Columbus, Ohio, for planing concave or convex surfaces, as well as ordinary plane ones, with the cross feed of the common planer.

The base L of the chuck is bolted to the planer work table in the ordinary manner.

The work-holding frame or vice is supported, for circular surfaces, by being pivoted to the base at O, O, and by the gibbed head D, which has journal bearing at E. The work is held between the stationary jaw _b_ or _b'_ (at option) and the movable jaw C which may face either _b_ or _b'_ (by turning C round). Suppose then, that while the chuck is pa.s.sing the cutting tool, end I of the work-holding frame is raised, lifting that end of the work above the horizontal level (the work-holding frame swinging at the other end on the pivots O, O), then the tool will obviously cut a convex surface. Or if end I of the work-holding frame be lowered while the cut is proceeding, the tool will cut a concave surface.

[Ill.u.s.tration: Fig. 1629.]

Now end I is caused to rise or lower as follows:--The head D is adjusted by means of its gibs to be a sliding fit on the bar G in Fig. 1629, which bar is rigidly fixed at P to the planer bed; hence as the planer table and the chuck traverse, D slides along bar G. If this bar is fixed at an angle to the length of the planer head, D must travel at that same angle, causing end I of the work-holding frame to rise or lower (from O, O, as a centre of motion) as it traverses according to the direction of motion of the planer table.

Suppose that in Fig. 1629, the planer table is moving on the back or non-cutting stroke, then head D will be moving towards the point of suspension P of the bar G, and will therefore gradually lower as it proceeds, thus lowering end I of the work-holding frame and causing the curved link to pa.s.s beneath the tool with a curved motion or suppose the table to be on its cutting traverse, then head D will be raised as the table moves and the cut proceeds, and the surface cut by the tool will be concave.

Now, suppose that the bar G were fixed at an angle, with its end, that is towards the back end of the planer, inclined towards the table instead of away from it as in Fig. 1629, and then on the cutting traverse head D would cause end I (Fig. 1628) of the work-holding vice or frame to lower as the cut proceeded, and the tool would therefore plane a convex surface.

Thus the direction of the angle in which G is fixed governs whether the surface planed shall be a concave or a convex one, and it is plain that the amount of concavity or convexity will be governed and determined by the amount of angle to which G is set to the planer table.

When the chuck is not required to plane curved surfaces the bar G is altogether dispensed with, and the chuck becomes an ordinary one possessing extra facilities for planing taper work.

Thus for taper work the work-holding frame may be set out of parallel with the base of the chuck to an amount answering to the required amount of taper, being raised or lowered (as may be most convenient) at one end by means of the gears M, of which there is one on each side mes.h.i.+ng into the segmental rack shown, the work-holding frame being secured in its adjusted position by means of a set bolt.

To set the work-holding frame parallel for parallel planing, a steady pin is employed, the frame being parallel to the base when that pin is home in its place.

The construction of the chuck is solid, and the various adjustments may be quickly and readily made, giving to it a range of capacity and usefulness that are not possessed by the ordinary forms of planer chucks.

PLANING MACHINE BEDS.--In long castings such as lathe or planer beds, the greatest care is required in setting the work upon the planer table, because the work will twist and bend of its own weight, and may have considerable deflection and twist upon it notwithstanding that it appears to bed fair upon the table. To avoid this it is necessary to know that the casting is supported with equal pressure at each point of support. In all such work the surface that is to rest upon the foundation or legs should be planed first.

[Ill.u.s.tration: Fig. 1630.]

Thus supposing the casting in Fig. 1630 to represent a lathe shears, the surfaces _f_ whereon the lathe legs are to be bolted should be planed first, the method of chucking being as follows:--

[Ill.u.s.tration: Fig. 1631.]

The bed is balanced by two wedges A, in Fig. 1630, one being placed at each end of the bed, and the position of the wedges being adjusted so that it lies level. A line coincident with the face of the bed (as face _d_) is then drawn across the upper face of each wedge. Wedges (as B, C,) are then put in on each side of the bed until they each just meet the bed, and a line coincident with the bed surface is drawn across their upper surfaces. Wedge B is then driven in until it relieves A of the weight of the bed, and a second line is drawn across its upper face.

It is then withdrawn to the first line, and the wedge on the opposite side of the bed is driven in until A is relieved of the weight, when a second line is drawn on this wedge's face. The wedges at the other end (as C) are then similarly driven in and withdrawn, being also marked with two lines, and then the four wedges (B, C, and the two corresponding ones on the opposite side of the bed) are withdrawn, having upon their surfaces two lines each (as A, B, in Fig. 1631).

Midway between these two lines a third (as C) is drawn, and all four wedges are then driven in until line C is coincident with the bed surface, when it may be a.s.sumed that the bed is supported equally at all the four points. When the bed is turned over, surfaces _f_ may lie on the table surface without any packing whatever, as they will be true.