Modern Machine-Shop Practice Part 115

Another excellent method is to balance the bed on three points, two at one end and one at the other, and to then pack it up equally at all four corners.

To test if the surface of a piece of such work has been planed straight, the following plan may be pursued:--

[Ill.u.s.tration: Fig. 1632.]

Suppose that surface E, Fig. 1632, is to be tested, it having been planed in the position it occupies in the figure, and the casting may be turned over so that face E stands vertical, as in Fig. 1632, and a tool may be put in the tool post of the planer, the bed being adjusted on the planer table so that the tool point will just touch the surface at each end of the bed. The planer table is then run so that the tool point may be tried with the middle of the bed length, when, if the face E is true, it will just meet the tool point at the middle of its length as well as at the ends.

In the planing of the [V]-guides and guideways of a bed for a machine tool, such as, for example, a planer bed and table, the greatest of care is necessary, the process being as follows:--

Beginning with the bed it has been shown in Fig. 1601 that the sides of the guideways must all be of the same height as well as at the same angle, and an excellent method of testing this point is as follows:--

[Ill.u.s.tration: Fig. 1633.]

In Fig. 1633 is shown at A a male gauge for testing the [V]-guideways in the bed, and at B a female gauge for testing those on the table. These two gauges are accurately made to the correct angle and width, and fitted together as true as they can be made, being corrected as long as any error can be found, either by testing one with the other or by the application of a surface plate to each separate face of the guides and guideways. The surfaces C and D of the respective gauges are made parallel with the [V]-surfaces, a point that is of importance, as will be seen hereafter. It is obvious that the female gauge B is turned upside down when tried upon the table.

[Ill.u.s.tration: Fig. 1634.]

Suppose it is required to test the sides _e_, _f_, of the bed guideways in Fig. 1634, and the gauge must be pulled over in the direction of the arrow so that it touches those two sides only; a spirit-level laid upon the top of the gauge will then show whether the two faces _e_, _f_, are of equal height. It is obvious that to test the other two faces the gauge must be pulled over in the opposite direction.

This test must be applied while fitting the [V]s to the gauge. Suppose, for example, that when the gauge is applied and allowed to seat itself in the ways, the two outside angles _e_, _g_, are found to bear while the two inside ones do not touch the gauge at all, then by this test it can be found whether the correction should be made by taking a cut off _e_ or off _g_, for if the spirit-level stood level when the gauge was pulled in either direction, then both faces would require to be operated upon equally, but suppose that the gauge and spirit-level applied as shown proved end _e_ to be high, then it would be the one to be operated on, or if when the gauge was pulled over in the opposite direction end _g_ was shown (by the spirit-level) to be high, then it would be the one to be operated upon.

By careful operation the table and bed may thus be made to fit more perfectly than is possible by any other method. To test the fit of the gauge to the [V]s it is a good plan to make a light chalk mark down each [V] and to then apply the gauge, letting it seat itself and moving it back and forth endways, when if it is a proper fit it will rub the chalk mark entirely out. It may be noted, however, that a light touch of red marking is probably better than chalk for this purpose.

It is of importance that the [V]s be planed as smooth as possible, and to enable this a stiff tool holder holding a short tool, as in Fig. 1635 should be used, the holder being held close up to the tool box as shown.

It will be obvious that when the head is set over to an angle it should be moved along the cross slide to plane the corresponding angle on the other side of the bed.

Fig. 1636 represents a planer chuck by Mr. Hugh Thomas. The angle piece A is made to stand at an angle, as shown, for cylindrical work, such as shafts, so that the work will be held firmly down upon the table. The base plate B has ratchet teeth at each end C, into which mesh the pawls D, and has slotted holes for the bolts which hold it down to the table, so that it has a certain range of movement to or from the angle piece A, and may therefore be adjusted to suit the diameter or width of the work.

The movable jaw E is set up by the set-screw F and is held down by the bolts shown. The pawls D are constructed as shown in Fig. 1637, the pin or stem S fitting the holes in the planer table and the tongue P being pivoted to the body R of the pawl. As the pawls can be moved into any of the holes in the table, the base plate B may be set at an angle, enabling the chuck to be used for taper as well as for parallel work, while the chuck has a wide range of capacity.

In Fig. 1614 is shown a supplementary table for increasing the capacity of planer tables, and which has already been referred to, and Fig. 1638 represents an application of the table as a chucking device. A, A, &c., are frames whose upper surfaces are to be planed. An angle plate is bolted to the planer table and the supplementary table is bolted to the angle plate. The first frame is set against the vertical face of the supplementary table, and the remaining ones set as near as possible, B, B, &c., being small blocks placed between the frames which are bolted to the planer table as at C.

[Ill.u.s.tration: Fig. 1635.]

In many cases this method of chucking possesses great advantages. Thus in the figure there are six frames to be planed, and as they would be too long to be set down upon the planer table, only three or four could be done at a time, and a good deal of measuring and trying would be necessary in order to get the second lot like the first. This can all be avoided by chucking the whole six at once, as in figure.

Another application of the same tables as useful chucking devices is shown in Fig. 1639, where two frames E, F, are shown bolted to the machine table and supported by the supplementary tables T, which are bolted to the main table and supported by angle-pieces _b_, _b_. Work that stands high up from the planer table may be very effectively steadied in this way, enabling heavier cuts and coa.r.s.er feeds while producing smoother work.

[Ill.u.s.tration: Fig. 1640.]

As horizontal surfaces can be planed very much quicker than vertical ones, it frequently occurs that it will pay to take extra trouble in order to chuck the work so as to plane it horizontally, an excellent example being the planing of the faces of the two halves of a large pulley, the chucking of which is ill.u.s.trated in Fig. 1640.

Four pieces, as at A, are made to engage the rims of the two halves of the pulley and hold them true, one with the other. The two plates T' and T" are set under the pulley halves to level the upper faces, and wooden clamps C, C, are bolted up to hold the pulleys together at the top, W representing wedges between the hubs. S represents supports to block up the pulley near its upper face, and at P are clamps to hold the two halves to the table. It is found that by this method of chucking more than half the time is saved, and the work is made truer than it is possible to get it by planing each half separately and laying them down on the table.

Supplemental tables may also be made in two parts, the upper one being capable of swiveling as in Fig. 1641, the swiveling device corresponding to that shown for the Thomas shaper chuck in Fig. 1530. This enables the work to be operated upon on several different faces without being released from the chuck. Thus in figure the segment could be planed on one edge and the upper table swiveled to bring the other edge in true with the table, which would be a great advantage, especially if the face it is chucked by has not been trued.

Figs. 1642 and 1643 show other applications of the same swiveling device.

It is obvious that the chuck shown in Fig. 1636 can be mounted on a supplemental and swiveling table as shown in Fig. 1644, thus greatly facilitating the chucking of the work and facilitating the means of presenting different surfaces or parts of the work to the tool without requiring to unchuck it. The pawls, also, may in heavy work have two pins to enter the work-table holes and be connected by a strap as in Fig. 1645.

In the exigencies of the general machine shop it sometimes happens that it is required to plane a piece that is too wide to pa.s.s between the uprights of the planing machine, in which case one standard or upright may be taken down and the cross slide bolted to the other, as in Fig.

1646, the blocks _a_, _a_, being necessary on account of the arched form of the back of the cross slide. In the example given the plates to be planed were nearly twice as wide as the planer table and were chucked as shown, the beam D resting on blocks E, F, and forming a pathway for the piece C, which was provided with rollers at each end so as to move easily upon D. The outer end of the plate was clamped between B and C, and the work was found to be easily and rapidly done. In this chucking, however, it is of importance that beam D be carefully levelled to stand parallel with the planer table face, while its height must be so adjusted that it does not act to cant or tilt the table sideways as that would cause one [V] of the planer ways to carry all or most of the weight, and be liable to cause it to cut and abrade the slide surfaces.

[Ill.u.s.tration: _VOL. I._ =EXAMPLES IN PLANING WORK.= _PLATE XVIII._

Fig. 1636.

Fig. 1637.

Fig. 1638.

Fig. 1639.]

[Ill.u.s.tration: Fig. 1641.]

[Ill.u.s.tration: Fig. 1642.]

[Ill.u.s.tration: Fig. 1643.]

[Ill.u.s.tration: Fig. 1644.]

[Ill.u.s.tration: Fig. 1645.]

[Ill.u.s.tration: Fig. 1646.]

CUTTING TOOLS FOR SHAPING AND PLANING MACHINES.--All the cutting tools forged to finished shape from rectangular bar steel, and described in connection with lathe work, are used in the planer and in the shaper, and the principles governing the rake of the top face remain the same.

But in the matter of the clearance there is the difference that in a planing tool it may be made constant, because the tool feeds to its cut after having left the work surface at the end of the back stroke, hence the clearance remains the same whatever the amount or rate of feed may be.

[Ill.u.s.tration: Fig. 1647.]

On this account it is desirable to use a gauge as a guide to grind the tool by, the application of such a gauge being shown in Fig. 1647. It consists of a disk turned to the requisite taper and laid upon a plate, whereon the tool also may be laid to test it. The tool should not be given more than 10 of clearance, unless in the case of broad flat-nosed tools for finis.h.i.+ng, for which 5 are sufficient.

[Ill.u.s.tration: Fig. 1648.]

[Ill.u.s.tration: Fig. 1649.]

The principle of pulling rather than pus.h.i.+ng the tool to its cut, can, however, be more readily and advantageously carried out in planer than in lathe tools, because the spring of the tool and of the head carrying it only need be considered, the position of the tool with relation to the work being otherwise immaterial. As a consequence it is not unusual to forge the tools to the end of pulling, rather than of pus.h.i.+ng the cutting edge.

[Ill.u.s.tration: Fig. 1650.]

In Figs. 1648 and 1649, for example, are two tools, W representing the work, and A the points off which the respective tools will spring in consequence of the pressure; hence the respective arrows denote the direction of the tool spring. As a result of this spring it is obvious the tool in Fig. 1648 will dip deeper into the work when the pressure of the cut increases, as it will from any increase of the depth of the cut in roughing out the work, or from any seams or hard places in the metal during the finis.h.i.+ng cut. On the other hand, however, this deflection or spring will have the effect of releasing the cutting edge of the tool from contact with the work surface during the back stroke, thus rendering it unnecessary to lift the tool to prevent the abrasion, on its back stroke, from dulling its cutting edge.

[Ill.u.s.tration: Fig. 1651.]

[Ill.u.s.tration: Fig. 1652.]

It will be noted that the radius from the point of support A is less for the tool in Fig. 1649 than for that in Fig. 1648, although both tools are at an equal height from the work, which enables that in Fig. 1649 to operate more firmly. In these two figures the extremes of the two systems are shown, but a compromise between the two is shown in Fig.

1650, the cutting edge coming even with the centre of the body of the steel, which makes the tool easier to forge and grind, and keeps the cutting edge in plainer view when at work, while avoiding the evils attending the shape shown in Fig. 1648.