Modern Machine-Shop Practice Part 108

[Ill.u.s.tration: Fig. 1522.]

The base A is bolted to the work table, and is in one piece with the fixed jaw B. The movable jaw C is set up to meet the work by hand, and being free to move upon A may be used for either taper or parallel work.

To fasten C upon the work, three screws threaded through F abut against the end of C; F being secured to the upper surface of A by a key or slip, which fits into a groove in F, and projects down into such of the grooves in the upper surface of A as may best suit the width of work to be held in the vice; C is held down by the bolts and nuts at G.

The operation of securing work in such a chuck is as follows:--The screws both at F and at G being loosened, and jaw C moved up to meet the work and hold it against the fixed jaw B, then nuts G should be set up lightly so that the sliding jaw will be set up under a slight pressure, screws F may then be set up and finally nuts G tightened.

[Ill.u.s.tration: Fig. 1523.]

This is necessary for the following reasons:--The work must, in most cases, project above the level of the jaws so that the tool may travel clear across it; hence, the strain due to holding the work is above the level of the three screws, and the tendency, therefore, is to turn the jaw C upwards, and this tendency the screws G resist. A similar chuck mounted upon a circular base so that it may be swivelled without moving the base on the work table is shown in Fig. 1523. The capacity to swivel the upper part of the chuck without requiring the base of the chuck to be moved upon the table is a great convenience in many cases.

[Ill.u.s.tration: Fig. 1524.]

Fig. 1524 represents an English chuck in which the fixed jaw is composed of two parts, A which is solid with the base G, and D which is pivoted to A at F. The movable jaw also consists of two parts, B which carries the nut for the screw that operates B, and C which is pivoted to B at E.

The two pivots E, F being above the surface of the gripping jaws C, D, causes them to force down upon the surface of G as the screw is tightened, the work, if thin, being rested, as in the case of the chuck shown in Fig. 1523, upon parallel pieces.

[Ill.u.s.tration: Fig. 1525.]

Fig. 1525 represents a chuck made by W. A. Harris, of Providence. The jaws in this case carry two pivoted wings A, B, between the ends of which the work C is held, and the pivots being above the level of the work the tendency is here again to force the work down into the chuck, the strain being in the direction denoted by the arrows.

Here the work rests on four pins which are threaded in the collars H, so that by rotating the pins they will stand at different heights to suit different thicknesses of work, or they may be set to plane tapers by adjusting their height to suit the amount of taper required. The spiral springs simply support the pins, but as the jaws close the pins lower until the washer nuts H meet the surface of recess I.

[Ill.u.s.tration: Fig. 1526.]

[Ill.u.s.tration: Fig. 1527.]

Figs. 1526 and 1527 represent Thomas's patent vice, which possesses some excellent conveniences and features.

In Fig. 1526 it is shown without, and in Fig. 1527 with a swivel motion.

The arrangement of the jaws upon the base in Fig. 1526 is similar to that of the chuck shown in Fig. 1522, but instead of there being a key to secure the piece F to the base, there is provided on each side of the base a row of ratchet teeth, and there is within F a circular piece G (in Fig. 1528) which is serrated to engage the ratchet teeth. This piece may be lifted clear of the ratchet teeth by means of the pin at H, and then the piece F may be moved freely by hand backwards or forwards upon the base and swung at any required angle, as in Fig. 1528, or set parallel as in Fig. 1527; F becoming locked, so far as its backward motion is concerned, so soon as H is released and G engages with the ratchet teeth on the base. But F may be pushed forward toward the fixed jaw without lifting H, hence the adjustment of the sliding jaw to the work may be made instantaneously without requiring any moving or setting of locking keys or other devices.

[Ill.u.s.tration: Fig. 1528.]

It is obvious that it is the capability of G to rotate in their sockets that enables F to be set at an angle and still have the teeth of G engage properly with those on the base plate.

[Ill.u.s.tration: Fig. 1529.]

[Ill.u.s.tration: Fig. 1530.]

The mechanism for swivelling the upper part or body upon the base and for locking it in its adjusted position is shown in Figs. 1529 and 1530.

The body D is provided with an annular ring fitting into the bore of the base, which is coned at Q. The half-circular disks R fit this cone and are held to the body of the chuck by four bolts N, which are adjusted to admit disks R to move without undue friction. K is a key having on it the nut V, which receives a screw whose squared end is shown at S. By operating S in one direction key K expands disks R, causing them to firmly grip the base at the bevel Q, hence the base and the body are locked together. By operating S to unscrew in the nut V, K is moved in the opposite direction and R, R release their grip at Q and the body D may be swung round in any position, carrying with it all the mechanism except base P.

To enable the body to be readily moved a quarter revolution, or in other words, moved to a right angle, there is provided a taper pin, the base having holes so situated that the body will have been moved a quarter revolution when the pin having been removed from one hole in the base is seated firmly home in the other.

Referring again to Fig. 1526, there are shown one pair of parallel pieces marked respectively A, having bevelled edges, and another pair marked respectively B. Both pairs are provided with a small rib fitting into a groove in the jaws of the chuck, as shown in the figure.

[Ill.u.s.tration: Fig. 1531.]

These ribs and grooves are so arranged that the upper pair (A, A) may be used in the place of the lower ones, and the uses of these pieces are as follows:--

Suppose a very thin piece of work is to be planed, and in order to plane it parallel, which is ordinarily a difficult matter, it must bed fair down upon the face of the vice, which it is caused to do when chucked as in Fig. 1531, in which the work is shown laid flat upon the face of the vice, and gripped at its edges by the pieces A, A.

[Ill.u.s.tration: Fig. 1532.]

These pieces, it may be noted, do not bed fair against the gripping faces of the jaws, but are a trifle open at the bottom as at _e_, _e_, hence when they are pressed against the work they cant over slightly and press the work down upon the chuck face causing it to bed fair.

Furthermore, the work is supported beneath its whole surface, and has, therefore, less tendency to spring or bend from the holding pressure; and as a result of these two elements much thinner work can be planed true and parallel than is possible when the work is lifted up and supported upon separate parallel pieces, because in the latter case the work, being unsupported between the parallel pieces, has more liberty to bend from the pressure due to the tool cut, as well as from the holding pressure.

[Ill.u.s.tration: Fig. 1533.]

Fig. 1532 shows the chuck holding a bracket, having a projection or eye.

The work rests on pieces B, B, and is gripped by pieces A, A. It will be observed that A, A being beveled enables the cut to be carried clear across the work.

Fig. 1533 represents the chuck in use for holding a piece of shafting S to cut a keyway or spline in it. In this case a bevelled piece J is employed, its bevelled face holding the work down upon the chuck face.

[Ill.u.s.tration: Fig. 1534.]

Fig. 1534 represents a chuck termed shaper centres, because the work is held between centres as in the case of lathe work. The live spindle is carried in and is capable of motion in a sleeve, the latter having upon it a worm-wheel, operated by a worm, so that it can be moved through any given part of a circle, and has index holes upon its face to determine when the wheel has been moved to the required amount.

For work that is too large to be operated upon in the cla.s.s of shaping machine shown in Fig. 1506, and yet can be more conveniently shaped than planed, a cla.s.s of machine is employed in which the tool-carrying slide is fed to the work, which is chucked to a fixed table or to two tables.

[Ill.u.s.tration: Fig. 1535.]

Fig. 1535 represents a machine of this cla.s.s. The tool-carrying slide A, in this case, operates in guideways provided in B, the latter being fitted to a slideway running the full length of the top of the frame M.

The base slider B is fed along the bed by means of a screw operating in a nut on the under side of B, this screw being operated once during each stroke of the tool-carrying slide A, by means of a pawl feeding arrangement at F, which corresponds to the feeding device shown in Fig.

1501.

Two vertical frame pieces D, D are bolted against the front face of the machine, being adjustable along any part of the bed or frame length, because their holding bolts have heads capable of being moved (with the frame pieces D) along the two [T]-shaped grooves shown, their [T]-shape being visible at the end of the frame or bed. To frames D are bolted the work-holding tables E, E, the bolts securing them pa.s.sing into vertical [T]-grooves in D, so that E may be adjusted at such height upon D as may be found necessary to bring the work within proper range of the cutting tool. The work tables E, E are raised or lowered upon D by means of a vertical screw, which is operated by the handle H, this part of the mechanism accomplishing the same end as the elevating mechanism shown in Fig. 1496. The swivel head J is here provided at its top with a segment of a worm-wheel which may be actuated to swivel that head by the worm G.

The swivel head may thus be operated upon its pivot, causing the tool point to describe an arc of a circle of which the pivot is the centre.

To steady the swivel head when thus actuated, there is behind the worm segment a [V]-slide that is an arc, whose centre is also the centre of the pivot.

The tool-carrying slide A is operated as follows: The driving pulley P rotates a shaft lying horizontal at the back of the machine. Along this shaft there is cut a featherway or spline driving a pinion which operates a link mechanism such as described with reference to Fig. 1550.

The means of adjusting the distance the head of A shall stand out from B, are similar to that described for Fig. 1496, a bolt pa.s.sing through A, and in both cases attaching to a connecting rod or bar.

At K is a cone mandrel such as has been described with reference to lathe work upon which is chucked a cross-head C. By means of suitable mechanism, this mandrel is rotated to feed the circular circ.u.mference of the cross-head jaws to the cut, the slider B remaining in a fixed position upon the bed M.

To support the outer end of the cone mandrel a beam L is bolted to the two tables E, E. On L is a slideway for the piece P. At S is a lug upon E through which threads a screw R, which adjusts the height of the piece P, while Q is a bolt for securing P in its adjusted position. This cone mandrel and support is merely an attachment to be put on the machine as occasion may require.

Fig. 1536 represents a shaping machine by the Pratt and Whitney Company.

In this machine a single sliding head is used and the work remains stationary as in the case of the machine shown in Fig. 1535. The vice is here mounted on a slide which enables the work to be finely adjusted beneath the sliding bar independently of that bar, which is provided with a Whitworth quick-return motion.

As the tool-carrying slide of a shaping machine leaves its guideways during each stroke, the tool is less rigidly guided as the length of slide stroke is increased, and on this account its use is limited to work that does not require a greater tool stroke than about 18 inches, and in small machines not to exceed 12 inches. The capacity of the machine, however, is obviously greatest when the length of the work is parallel to the line of motion of the feed traverse. Work whose dimension is within the limit of capacity of the shaper can, however, be more expeditiously shaped than planed because the speed of the cutting tool can be varied to suit the nature of the work, by reason of the machine having a cone pulley, whereas in a planing machine the cutting speed of the tool is the same for all sizes of work, and all kinds of metal. In shaping machines such as shown in Fig. 1537, or in similar machines in which the work table is capable of being traversed instead of the head, the efficiency of the work-holding table and of the chucking devices may be greatly increased by constructing the table so that it will swivel, as in Fig. 1538, which may be done by means of the employment of Thomas's swivelling device in Fig. 1530. By this means the ends of the work may be operated upon without removing it from the chuck. Or the work may be shaped taper at one part and parallel at another without unchucking it.

Fig. 1539 shows a circular table swivelled by the same device, sitting upon a work table also swivelled.

[Ill.u.s.tration: Fig. 1540.]

Fig. 1540 represents a general view of a shaping machine having the motion corresponding in effect to a planing machine, the object being to give a uniform rate of speed to the tool throughout, both on its cutting and return stroke. The feed always takes place at the end of the return stroke, so as to preserve the edge of the tool, and the length of the stroke may be varied, without stopping the machine, by simply adjusting the tappets or dogs, the range of stroke being variable from 1/4 inch to 20 inches, while the return stroke is 40 per cent. quicker than the cutting one. There are two different rates of cutting speed, one for steel and the other for the softer metals.