Modern Machine-Shop Practice Part 54

[Ill.u.s.tration: Fig. 705.]

Fig. 705 is a sectional and end view of the core A of the chuck, and Fig. 706 a sectional and end view of the sh.e.l.l D.

[Ill.u.s.tration: Fig. 706.]

Fig. 707 represents a sectional side view and an end view of the cross slide, or cutting-off slide, which carries two tool posts, and therefore two cutting tools, one of which is at the back of the rest. In place of a feed screw and nut, or of a hand lever and link, it is provided with a segment of a gear-wheel P operating in a rack R, which avoids the tendency to twist the cross slides in its guides which exists when a hand lever and link is used.

[Ill.u.s.tration: Fig. 707.]

The cross slide is adjusted to fit in its guideway by a jaw S^{1}, Fig.

707, which is firmly screwed to and recessed into R. To take up the wear, the face of S^{1} is simply reduced. This possesses a valuable advantage, because it is rigid and solid, does not admit of improper adjustment, nor can the adjustment become impaired at the hands of the operator.

To adjust the position of the cross slide upon the shears a screw pa.s.ses between the shears and is threaded into the stud Q. This screw is operated by a hand wheel shown in the general view, Fig. 703, beneath the rear bearing of the headstock.

A special and excellent feature of the machine is the stop device for the motion of the cross slide which is shown in Fig. 707.

The screw S has one collar C, solid on it, and the screwed end is tapped into the sliding sleeve T, which is held from turning by the stud A.

Between the solid collar C and the loose collar B there is a short, stiff spiral spring, as shown; by means of the fast and loose collars, the spring and the screwed thimble D, a strong friction is had on the collar B, which is ample to keep the screw from turning while in use as a stop, although it permits the screw to turn easily enough when a wrench is applied to the square end. Precisely the same device is used at the other end of the slide to stop it in the opposite direction.

[Ill.u.s.tration: Fig. 708.]

Details of the mechanism of the turret and turret slide are shown in Figs. 708, 709, and 710. Fig. 708 is an end sectional view of the turret slide, which is traversed on its base by a segment D of a gear operating in a rack R (in the same manner as the cutting-off slide), the segment being connected by stud N to handle M. O represents the body of the slide, which is grooved at the sides to receive the gibs X, which secure it to the base P on which it slides. P is clamped to its adjusted position on the shears or bed by means of the gib, shown in dotted lines, which is pulled laterally forward by the screw S, which is tapped into the stem of the gib. The method of rotating the slide and of locking it in position is shown in Fig. 709, which is a top view of the turret head, and Fig. 710, which shows O removed from P and turned upside down. Pivoted to segment D is a rod E having at K a pin that as motion proceeds falls into S and rotates T, which is fast to the bottom of the turret. Upon the handle M being moved backward the segment begins its motion forward, as indicated by the arrow in Fig. 710, thereby moving the slide backward upon the gibs by the working of its cogs into the rack R, Fig. 708, which is attached to the base P. When the segment D has accomplished about one-half its motion the pin H, which is on the upper side of the segment D, comes in contact with the projection or lug on the side of the cam F, as shown by the arrow head in Fig. 710, bringing the opposite side of the cam against the pin G, Fig. 709, thereby moving it backward, compressing the spring U, and drawing the bolt L from its seat in the disc V. This operation is completed before the motion of the segment brings the pin K in contact with the ratchet-wheel T. The segment D in continuing its motion after the pin K is brought into the notch S, begins the revolution of the turret on its axis. As will be seen by the inspection of Fig. 710, the pin H works upon a much longer radius than the projection upon the cam with which it comes in contact, and therefore, after a given part of its motion is complete, gets beyond the reach of the cam, thereby releasing its hold and allowing the bolt L, Fig. 709, to be forced against the disc V by the expansion of the spring U, which occurs soon after the turret has commenced its revolution by the contact of pin K with the wheel T. The completion of the movement of the handle M (and the segment D) completes the revolution of the turret one-sixth of its circ.u.mference, thereby allowing the bolt L, by the further expansion of the spring U, to be forced into its next opening or seat in the disc V. The forward motion of the handle M brings the turret forward to its position at the work and restores the parts to their former positions, as shown in the ill.u.s.trations.

[Ill.u.s.tration: Fig. 709.]

[Ill.u.s.tration: Fig. 710.]

The stop motion for the forward motion of M, and that therefore determines the length of turret traverse forward, and hence the distance each tool shall carry its cut along the work, is shown in Fig. 711. The end of the screw A abuts against the stop B in the usual manner; it is, however, threaded through the eye of a bolt C, as well as through the end of the turret slide, so that it may be locked by simply operating the nut D. Thus the use of a wrench is obviated, and the adjustment is more readily effected.

[Ill.u.s.tration: Fig. 711.]

Figs. 712 and 713 represent a screw machine by the Pratt and Whitney Company, of Hartford, Connecticut, and having Parkhurst's patent wire or rod feed for moving the work through the hollow spindle and into position to be operated upon by the tools. The reference letters correspond in both figures.

At A is the front and at B the back bearing, affording journal bearing to a hollow spindle C, which carries the sh.e.l.l D of the work-gripping chuck, the clutch ring H and a collar I, in which is pivoted, at J, the clutch levers G. This collar is threaded upon C and is locked in position by a ring lock nut J'. The clutch arm K slides upon a rod X, and has a feather projecting into a spline in X. The core E of the work-gripping chuck is fast upon the inner spindle F, which revolves with the outer one C. The left-hand end of F abuts against the short arms of the clutch levers G, and it is obvious that when K is operated back and forth upon X, it moves the clutch H endways upon C, and the cone upon H operates the levers G, causing them to move the inner spindle F endways and the inner cone E of the chuck to open or close.

Suppose, for example, that K (and hence H) is moved to the right, and the long ends of G will be released and may close moving their short ends away from the end of F, and therefore releasing E from its grip upon the work. In moving K to the right the sleeve L is also moved to the right, and its serrations at L' being engaged with the tongue P, the sleeve M is pulled forward. Now the bar or rod of which the work is made is held at one end by the chuck, it is supported by the bushing Z in the end of spindle C, and in the bushing S in the arm of sleeve M, while it has fast upon it a collar T. When therefore M is pulled forward or to the right, its arm meets T and pulls the rod or bar for the work through the chuck E.

[Ill.u.s.tration: Fig. 712.]

[Ill.u.s.tration: Fig. 713.]

On the other hand when K and therefore H, L, and M, are moved to the left, levers G are opened at their long ends by the cone of H. The short ends of G push the inner spindle F to the right, E pa.s.ses through D, and being split, closes upon the work and grips it, the parts occupying the positions shown in the figure. The same motion of K pa.s.ses L through the sleeve M (the teeth at N raise the catch P, allowing L' to pa.s.s through M) so that at the next movement of K to the right, M will be pulled a second step forward, again pa.s.sing the work through the chuck. Q is merely a pin wherewith to lift P and enable M to be moved back, when putting in a new rod for the work; K is operated by a link from U to V, the handle for moving this link being shown at W in the general view.

To prevent the sleeve M from moving back with L it is provided with a shoe O, pressed by the spring R against X, thus producing a friction between M and X that holds M while L slides through it. R' is to regulate the tension of the spring at R. _y_ is merely a sleeve to protect the clutch mechanism from dust, &c.

Box tools for screw machines are used for a great variety of special work. They are simply boxes or heads carrying tools and a work-steadying rest.

Fig. 714 represents a box tool for a screw machine. The cylindrical stem fits into the turret holes and contains a steadying piece or rest G to support the work and keep it to its cut. In the box tool shown in the figure, there are four cutting tools set in to the depth of cut by the screws A, B, C, and D respectively, and a fifth for rounding off the end of the work is shown at E.

[Ill.u.s.tration: Fig. 714.]

Fig. 715 represents a top view, Fig. 715_a_ a front view, and Fig.

715_b_ an end view, of a box tool for shaping the handles for the wheels of the feeding mechanism of machines. The work is first turned true and to its required diameter, and the rest is set to just bear against the work to steady it and hold it against the pressure of the cut. The cutter is cylindrical with a gap cut in it at G, so as to give a cutting edge. By grinding the face of this gap the tool is sharpened without altering its shape, as is explained with reference to circular or disc tools for lathe work. The cutter is provided with a stem by which it is held in the slide, through the medium of the clamp. The slide is operated by an eccentric on the spindle or rod R, which is operated by the handle H. The stop obviously arrests the motion of the slide when it meets the box B, and this determines the diameter of the work, which is represented by W in the end view figure.

[Ill.u.s.tration: Fig. 715.]

[Ill.u.s.tration: Fig. 715_a_.]

[Ill.u.s.tration: Fig. 715_b_.]

Fig. 716 represents the die holder and die for the Pratt and Whitney Co.'s screw machine. The die is cut through on four sides, and is enveloped by a split ring having a screw through its two lugs, so that by operating the screw the die may be closed to take up the wear and adjust it for diameter. It is secured in a collar by the set-screw shown, and this collar is clutch shaped on its back face, engaging a similar clutch face on the shoulder of the arbor, the object of this arrangement being as follows. Suppose it is required to cut a thread a certain distance, as say, 3/4 inch, along a stud, and that the depth of the clutch is 1/4 inch. Suppose that when the turret is fed forward sufficiently the thread is cut half an inch along the work at the moment that the turret meets its stop and comes to rest, then the die will continue to feed forward one-quarter of an inch, moving along the body or stem of the holder until its clutch face disengages, when the die will revolve with the work.

[Ill.u.s.tration: Fig. 716.]

[Ill.u.s.tration: Fig. 717.]

Fig. 717 represents a cutting-off tool and holder for a screw machine.

The tool fits into a dovetail groove in the split end of the holder, and is ground taper in thickness to give the necessary clearance on the sides. It is held by the screw shown, which closes the split and grips the dovetail; obviously the top face only is ground to resharpen it.

[Ill.u.s.tration: Fig. 718.]

Fig. 718 represents a special lathe for wood work designed and constructed by Charles W. Wilder, of Fitchburg, Ma.s.sachusetts. It is intended to produce small articles in large quant.i.ties, cutting them to duplicate form and size without any further measurements than those necessary to set the tools in their proper respective positions. It is employed mainly for such work as druggists' boxes, tool handles, straight spokes for toy vehicles, piano pins, b.a.l.l.s, rings, and similar work.

Its movements are such that the tools are guided by stops determining the length and the diameter of the work so as to make it exactly uniform, while the form of the cutting tools determines the form of the work, which must therefore be uniform.

The lathe may be described as one having a carriage rest spanning the bed of the lathe, which rest holds the work axially true with the lathe centres without the aid of the dead centre, while it at the same time trues the end of the work and leaves it free to be operated upon by other tools, which, after once being set and adjusted, shape any number of pieces of work to exact and uniform diameter and shape.

[Ill.u.s.tration: Fig. 719.]

The manner in which this is accomplished is as follows: Fig. 718 is a general external view of the lathe; Fig. 719 is an end elevation view of the rest from the cone spindle end, and Fig. 720 is an end view of the rest viewed from the tailstock end of the lathe. A is a ring fastened in the rest R by the set-screw B. The mouth C of the ring which first meets the work is coned, or beveled, as shown, and an opening on one side of the ring admits a cutting tool T. Now the work is placed one end in the cone driving chuck on the lathe spindle, and the other end in the cone or mouth C, Fig. 719, being kept up to the driving chuck by the end pressure of C. As the work rotates, the tool T cuts it to the diameter D of the ring bore, the carriage or rest R traversing along the lathe bed as fast as tool cuts; hence the bore D serves as a guide to hold the work and make it run true, this bore being axially true with the lathe centres. The cone surface of C thus operates the same as the sole of an ordinary carpenter's plane, the tool T cutting more or less rapidly according as its cutting edge is set to project more or less in advance of the surface of the cone or recess C. This admits of the tool cutting at a rate of feed that may best suit the diameter of the work and the nature of the wood. The tool T, is operated laterally to increase or diminish the rate of feed by the screw E, which also serves as a pivot, so that by operating the thumb-screw F, the tool point may be adjusted for distance from the centre of the bore D, or in other words the diameter to which the tool T will turn the work is adjusted by the thumb-screw F. G is the head of the pivot screw that the swing tool holder H works upon, and this swing motion carries the forming tool or cutter X, which shapes the work to the required form. I is a shaft upon which a lever, carrying the tool holder J, works, the latter carrying the severing tool K, which severs the finished work from the stick of wood from which the work is made.

The tool holders H and J are connected by means of the arms L and M to the stud O, fast in wheel P, operated by a knee lever Q, which is pivoted at S to _u_, which is fast to one of the gibs that hold the carriage to the lathe [V]s. The knee lever Q is connected to the wheel P by a raw-hide strap, or belt V, so that the operator, by pressing his knee upon the end of the lever Q, causes the wheel P, to partly rotate, carrying O with it (O being fast in P), and gives a forward radial motion to tool holder H and cutter X, causing the latter to enter the work until such time as the stud O and the screw stud W are in line, horizontally with the centre of the wheel P, after which tool holder H will move back, while the severing tool K (which has a continuous upward or vertical movement) is cutting off the finished work, which has been formed to shape, and reduced to the required diameter by the forward movement of the tool or cutter X. The object of the backward or retiring motion of H is to relieve the shaping tool X from contact with the work, while K cuts it off, or otherwise the work might meet X when cut off, and receive damage from contact with it. The stud W, connecting tool holder H with the wheel P, is threaded with a right and left-hand screw, by operating which the tool X may be operated to reduce the work to any required diameter.

The rest or carriage R traverses along the lathe shears or bed Z, carrying with it all the levers and tools, so far described.

[Ill.u.s.tration: Fig. 720.]

The tailstock, or back head, carries a tool holder in the rear of the spindle, in which fits also a drill bit or other cutting tool. The method of traversing and operating the carriage R and the back head is as follows:

At the back of the bed or shears is a table, shown at T, in Fig. 718.

Upon this table is a stand to which is pivoted the end of a lever, as is shown at 1 in figure. This lever has a joint at 2, and is connected to the tailstock spindle at a joint marked 3. It is obvious that by operating the lever laterally, joint 2 will double, and the tail spindle will be moved along the bed. If the tail spindle is not locked it will simply feed through the tailstock and the tool in the spindle will operate, but if it is locked (by the ordinary screw shown), then the handle will slide the whole tailstock and the tool in the holder at the back of the tail spindle may operate.

[Ill.u.s.tration: Fig. 721.]

At 4 is an adjusting screw, which, by coming into contact with the carriage R causes it also to traverse, which it will do until it meets against a screw on the other side, marked 5, in Fig. 718, which, standing farther out than the chuck prevents the cutting tool from meeting the chuck.

The movement of the carriage continues until the stop-gauge 6 meets the end of the work, hence the length of the work is from the cutting-off tool to the face of stop 6. The adjustment for the length of the work is made by means of screw 4, which will slide the carriage R, as soon as it meets it, independent of what distance the stop 6 may be from the work end. The tailstock carries two tool holders, similar to those on an ordinary lathe. When the cutting tools are used to cut completely over the end of the work, as in ball turning or a round ended handle, the stop 6 is not used, the tool which rounds the end acting as a stop of itself.

When bits are used they are held in the tail spindle and are made of a proper length to give the required depth of hole, or sometimes the face of the bit-holder may be used as a stop.