Chapter II, in which this subject is treated.

=Turning a Flywheel on a Vertical Mill.=--The turning of a flywheel is a good example of the kind of work for which a vertical boring mill is adapted. A flywheel should preferably be machined on a double-head mill so that one side and the periphery of the rim can be turned at the same time. A common method of holding a flywheel is shown in Fig. 9. The rim is gripped by four chuck jaws _D_ which, if practicable, should be on the inside where they will not interfere with the movement of the tool. Two of the jaws, in this case, are set against the spokes on opposite sides of the wheel, to act as drivers and prevent any backward shifting of work when a heavy cut is being taken. The illustration shows the tool to the right rough turning the side of the rim, while the left-hand tool turns the periphery. Finishing cuts are also taken over the rim, at this setting, and the hub is turned on the outside, faced on top, and the hole bored.

The three tools _A_, _B_ and _C_, for finishing the hole, are mounted in the turret. Bar _A_, which carries a cutter at its end, first rough bores the hole. The sizing cutter _B_ is then used to straighten it before inserting the finishing reamer _C_. Fig. 10 shows the turret moved over to a central position and the sizing cutter _B_ set for boring. The head is centrally located (on this particular machine) by a positive center-stop. The turret is indexed for bringing the different tools into the working position, by loosening the clamping lever _L_ and pulling down lever _I_ which disengages the turret lock-pin. When all the flywheels in a lot have been machined as described, the opposite side is finished.

In order to show more clearly the method of handling work of this class, the machining of a flywheel will be explained more in detail in connection with Fig. 11, which illustrates practically the same equipment as is shown in Figs. 9 and 10. The successive order in which the various operations are performed is as follows: Tool _a_ (see sketch _A_) rough turns the side of the rim, while tool _b_, which is set with its cutting edge toward the rear, rough turns the outside. The direction of the feeding movement for each tool is indicated by the arrows. When tool _a_ has crossed the rim, it is moved over for facing the hub, as shown by the dotted lines. The side and periphery of the rim are next finished by the broad-nose finishing tools _c_ and _d_ (see sketch _B_). The feed should be increased for finishing, so that each tool will have a movement of say 1/4 or 3/8 inch per revolution of the work, and the cuts should, at least, be deep enough to remove the marks made by the roughing tools. Tool _c_ is also used for finishing the hub as indicated by the dotted lines. After these cuts are taken, the outside of the hub and inner surface of the rim are usually turned down as far as the spokes, by using offset tools similar to the ones shown at _C_ and _D_ in Fig. 7. The corners of the rim and hub are also rounded to give the work a more finished appearance, by using a tool _L_.

The next operation is that of finishing the hole through the hub. The hard scale is first removed by a roughing cutter _r_ (sketch _C_), which is followed by a "sizing" cutter _s_. The hole is then finished smooth and to the right diameter by reamer _f_. The bars carrying cutters _r_ and _s_ have extensions or "pilots" which enter a close-fitting bushing in the table, in order to steady the bar and hold it in alignment.

When the hole is finished, the wheel is turned over, so that the lower side of the rim and hub can be faced. The method of holding the casting for the final operation is shown at _D_. The chuck jaws are removed, and the finished side of the rim is clamped against parallels _p_ resting on the table. The wheel is centrally located for turning this side by a plug _e_ which is inserted in a hole in the table and fits the bore of the hub. The wheel is held by clamps which bear against the spokes. Roughing and finishing cuts are next taken over the top surface of the rim and hub and the corners are rounded, which completes the machining operations. If the rim needs to be a certain width, about the same amount of metal should be removed from each side, unless sandy spots or "blow-holes" in the casting make it necessary to take more from one side than from the other. That side of the rim which was up in the mold when the casting was made should be turned first, because the porous, spongy spots usually form on the "cope" or top side of a casting.

=Convex Turning Attachment for Boring Mills.=--Fig. 12 shows a vertical boring mill arranged for turning pulleys having convex rims; that is, the rim, instead of being cylindrical, is rounded somewhat so that it slopes from the center toward either side. (The reason for turning a pulley rim convex is to prevent the belt from running off at one side, as it sometimes tends to do when a cylindrical pulley is used.) The convex surface is produced by a special attachment which causes the turning tool to gradually move outward as it feeds down, until the center of the rim is reached, after which the movement is inward.

The particular attachment shown in Fig. 12 consists of a special box-shaped tool-head _F_ containing a sliding holder _G_, in which the tool is clamped by set-screws passing through elongated slots in the front of the tool-head. In addition, there is a radius link _L_ which swivels on a stud at the rear of the tool-head and is attached to vertical link _H_. Link _L_ is so connected to the sliding tool-block that any downward movement of the tool-bar _I_ causes the tool to move outward until the link is in a horizontal position, after which the movement is reversed. When the attachment is first set up, the turning tool is placed at the center of the rim and then link _L_ is clamped to the vertical link while in a horizontal position. The cut is started at the top edge of the rim, and the tool is fed downward by power, the same as when turning a cylindrical surface. The amount of curvature or convexity of a rim can be varied by inserting the clamp bolt _J_ in different holes in link _L_.

The tools for machining the hub and sides of the rim are held in a turret mounted on the left-hand head, as shown. The special tool-holder _A_ contains two bent tools for turning the upper and lower edges of the pulley rim at the same time as the tool-head is fed horizontally. Roughing and finishing tools _B_ are for facing the hub, and the tools _C_, _D_, and _E_ rough bore, finish bore, and ream the hole for the shaft.

=Turning Taper or Conical Surfaces.=--Conical or taper surfaces are turned in a vertical boring mill by swiveling the tool-bar to the proper angle as shown in Fig. 13. When the taper is given in degrees, the tool-bar can be set by graduations on the edge of the circular base _B_, which show the angle _a_ to which the bar is swiveled from a vertical position. The base turns on a central stud and is secured to the saddle _S_ by the bolts shown, which should be tightened after the tool-bar is set. The vertical power feed can be used for taper turning the same as for cylindrical work.

Occasionally it is necessary to machine a conical surface which has such a large included angle that the tool-bar cannot be swiveled far enough around to permit turning by the method illustrated in Fig. 13. Another method, which is sometimes resorted to for work of this class, is to use the combined vertical and horizontal feeds. Suppose we want to turn the conical casting _W_ (Fig. 14), to an angle of 30 degrees, as shown, and that the tool-head of the boring mill moves horizontally 1/4 inch per turn of the feed-screw and has a vertical movement of 3/16 inch per turn of the upper feed-shaft. If the two feeds are used simultaneously, the tool will move a distance _h_ of say 8 inches, while it moves downward a distance _v_ of 6 inches, thus turning the surface to an angle _y_. This angle is greater (as measured from a horizontal plane) than the angle required, but, if the tool-bar is swiveled to an angle _x_, the tool, as it moves downward, will also be advanced horizontally, in addition to the regular horizontal movement. The result is that the angle _y_ is diminished and if the tool-bar is set over the right amount, the conical surface can be turned to an angle _a_ of 30 degrees. The problem, then, is to determine what the angle _x_ should be for turning to a given angle _a_.

The way angle _x_ is calculated will be explained in connection with the enlarged diagram, Fig. 15, which shows one-half of the casting. The sine of the known angle _a_ is first found in a table of natural sines. Then the sine of angle _b_, between the taper surface and center-line of the tool-head, is determined as follows: sin_b_ = (sin_a_ x _h_) / _v_, in which _h_ represents the rate of horizontal feed and _v_ the rate of vertical feed. The angle corresponding to sine _b_ is next found in a table of sines. We now have angles _b_ and _a_, and by subtracting the sum of these angles from 90 degrees, the desired angle _x_ is obtained. To illustrate: The sine of 30 degrees is 0.5; then sin _b_ = (0.5 x 1/4) / 3/16 = 0.6666; hence angle _b_ = 41 degrees 49 minutes, and _x_ = 90 deg.-(30 deg. + 41 deg. 49') = 18 degrees 11 minutes. Hence to turn the casting to angle _a_ in a boring mill having the horizontal and vertical feeds given, the tool-head would be set over from the vertical 18 degrees and 11 minutes which is equivalent to about 18-1/6 degrees.

If the required angle _a_ were greater than angle _y_ obtained from the combined feeds with the tool-bar in a vertical position, it would then be necessary to swing the lower end of the bar to the left rather than to the right of a vertical plane. When the required angle _a_ exceeds angle _y_, the sum of angles _a_ and _b_ is greater than 90 degrees so that angle _x_ for the tool-head = (_a_ + _b_) - 90 degrees.

=Turret-lathe Type of Vertical Boring Mill.=--The machine illustrated in Fig. 16 was designed to combine the advantages of the horizontal turret lathe and the vertical boring mill. It is known as a "vertical turret lathe," but resembles, in many respects, a vertical boring mill. This machine has a turret on the cross-rail the same as many vertical boring mills, and, in addition, a side-head _S_. The side-head has a vertical feeding movement, and the tool-bar _T_ can be fed horizontally. The tool-bar is also equipped with a four-sided turret for holding turning tools. This arrangement of the tool-heads makes it possible to use two tools simultaneously upon comparatively small work. When both heads are mounted on the cross-rail, as with a double-head boring mill, it is often impossible to machine certain parts to advantage, because one head interferes with the other.

The drive to the table (for the particular machine illustrated) is from a belt pulley at the rear, and fifteen speed changes are available. Five changes are obtained by turning the pilot-wheel _A_ and this series of five speeds is compounded three times by turning lever _B_. Each spoke of pilot-wheel _A_ indicates a speed which is engaged only when the spoke is in a vertical position, and the three positions for _B_ are indicated, by slots in the disk shown. The number of table revolutions per minute for different positions of pilot-wheel _A_ and lever _B_ are shown by figures seen through whichever slot is at _C_. There are five rows of figures corresponding to the five spokes of the pilot-wheel and three figures in a row, and the speed is shown by arrows on the sides of the slots. The segment disk containing these figures also serves as an interlocking device which prevents moving more than one speed controlling lever at a time, in order to avoid damaging the driving mechanism.

The feeding movement for each head is independent. Lever _D_ controls the engagement or disengagement of the vertical or cross feeds for the head on the cross-rail. The feed for the side-head is controlled by lever _E_. When this lever is pushed inward, the entire head feeds vertically, but when it is pulled out, the tool-bar feeds horizontally. These two feeds can be disengaged by placing the lever in a neutral position. The direction of the feeding movement for either head can be reversed by lever _R_. The amount of feed is varied by feed-wheel _F_ and clutch-rod _G_. When lever _E_ is in the neutral position, the side-head or tool-bar can be adjusted by the hand-cranks _H_ and _I_, respectively. The cross-rail head and its turret slide have rapid power traverse movements for making quick adjustments. This rapid traverse is controlled by the key-handles _J_.

The feed-screws for the vertical head have micrometer dials _K_ for making accurate adjustments. There are also large dials at _L_ which indicate vertical movements of the side head and horizontal movements of the tool slide. All of these dials have small adjustable clips _c_ which are numbered to correspond to numbers on the faces of the respective turrets. These clips or "observation stops" are used in the production of duplicate parts. For example, suppose a tool in face No. 1 for the main turret is set for a given diameter and height of shoulder on a part which is to be duplicated. To obtain the same setting of the tools for the next piece, clips No. 1, on both the vertical feed rod and screw dials, are placed opposite the graduations which are intersected by stationary pointers secured to the cross-rail. The clips are set in this way after the first part has been machined to the required size and before disturbing the final position of the tools. For turning a duplicate part, the tools are simply brought to the same position by turning the feed screws until the clips and stationary pointers again coincide. For setting tools on other faces of either turret, this operation is repeated, except that clips are used bearing numbers corresponding to the turret face in use.

The main turret of this machine has five holes in which are inserted the necessary boring and turning tools, drills or reamers, as may be required. By having all the tools mounted in the turret, they can be quickly and accurately set in the working position. When the turret is indexed from one face to the next, binder lever _N_ is first loosened. The turret then moves forward, away from its seat, thus disengaging the indexing and registering pins which accurately locate it in any one of the five positions. The turret is revolved by turning crank _M_, one turn of this handle moving the turret 1/5 revolution or from one hole to the next. The side-head turret is turned by loosening lever _O_. The turret slide can be locked rigidly in any position by lever _P_ and its saddle is clamped to the cross-rail by lever _Q_. The binder levers for the saddle and toolslide of the side-head are located at _U_ and _V_, respectively. A slide that does not require feeding movements is locked in order to obtain greater rigidity. To illustrate, if the main tool slide were to feed vertically and not horizontally, it might be advisable to lock the saddle to the cross-rail, while taking the vertical cut.

The vertical slide can be set at an angle for taper turning, and the turret is accurately located over the center of the table for boring or reaming, by a positive center stop. The machine is provided with a brake for stopping the work table quickly, which is operated by lifting the shaft of pilot-wheel _A_. The side-and cross-rails are a unit and are adjusted together to accommodate work of different heights. This adjustment is effected by power on the particular machine illustrated, and it is controlled by a lever near the left end of the cross-rail. Before making this adjustment, all binder bolts which normally hold the rails rigidly to the machine column must be released, and care should be taken to tighten them after the adjustment is made.

=Examples of Vertical Turret Lathe Work.=--In order to illustrate how a vertical turret lathe is used, one or two examples of work will be referred to in detail. These examples also indicate, in a general way, the class of work for which this type of machine is adapted. Fig. 17 shows how a cast-iron gear blank is machined. The work is gripped on the inside of the rim by three chuck jaws, and all of the tools required for the various operations are mounted in the main and side turrets. The illustration shows the first operation which is that of rough turning the hub, the top side of the blank and its periphery. The tools _A_ for facing the hub and upper surface are both held in one tool-block on the main turret, and tool _A_{1}_ for roughing the periphery is in the side turret. With this arrangement, the three surfaces can be turned simultaneously.

The main turret is next indexed one-sixth of a revolution which brings the broad finishing tools _B_ into position, and the side turret is also turned to locate finishing tool _B_{1}_ at the front. (The indexing of the main turret on this particular machine is effected by loosening binder lever n and raising the turret lock-pin by means of lever _p_.) The hub, side and periphery of the blank are then finished. When tools _B_ are clamped in the tool-blocks, they are, of course, set for turning the hub to the required height. The third operation is performed by the tools at _C_, one of which "breaks" or chamfers the corner of the cored hole in the hub, to provide a starting surface for drill _D_, and the other turns the outside of the hub, after the chamfering tool is removed. The four-lipped shell-drill _D_ is next used to drill the cored hole and then this hole is bored close to the finished size and concentric with the circumference of the blank by boring tool _E_, which is followed by the finishing reamer _F_. When the drill, boring tool and reamer are being used, the turret is set over the center or axis of the table, by means of a positive center stop on the left-side of the turret saddle. If it is necessary to move the turret beyond the central position, this stop can be swung out of the way.

Figs. 18 and 19 illustrate the turning of an automobile flywheel, which is another typical example of work for a machine of this type. The flywheel is finished in two settings. Its position for the first series of operations is shown in Fig. 18, and the successive order of the four operations for the first setting is shown by the diagrams, Fig. 20. The first operation requires four tools which act simultaneously. The three held in tool-block _A_ of the turret, face the hub, the web and the rim of the flywheel, while tool _a_ in the side-head rough turns the outside diameter. The outside diameter is also finished by broad-nosed tool _b_ which is given a coarse feed. In the second operation, the under face of the rim is finished by tool _c_, the outer corners are rounded by tool _d_ and the inner surface of the rim is rough turned by a bent tool _B_, which is moved into position by indexing the main turret. In the third operation, the side-head is moved out of the way and the inside of the rim is finished by another bent tool _B_{1}_. The final operation at this setting is the boring of the central hole, which is done with a bar _C_ having interchangeable cutters which make it possible to finish the hole at one setting of the turret.

The remaining operations are performed on the opposite side of the work which is held in "soft" jaws _J_ accurately bored to fit the finished outside diameter as indicated in Fig. 19. The tool in the main turret turns the inside of the rim, and the side-head is equipped with two tools for facing the web and hub simultaneously. As the tool in the main turret operates on the left side of the rim, it is set with the cutting edge toward the rear. In order to move the turret to this position, which is beyond the center of the table, the center stop previously referred to is swung out of the way.

=Floating Reamer Holders.=--If a reamer is held rigidly in the turret of a boring mill or turret lathe, it is liable to produce a hole which tapers slightly or is too large. When a hole is bored with a single-point boring tool, it is concentric with the axis of rotation, and if a reamer that is aligned exactly with the bored hole is fed into the work, the finished hole should be cylindrical and the correct size. It is very difficult, however, to locate a reamer exactly in line with a bored hole, because of slight variations in the indexing of the turret, or errors resulting from wear of the guiding ways or other important parts of the machine.

To prevent inaccuracies due to this cause, reamers are often held in what is known as a "floating" holder. This type of holder is so arranged that the reamer, instead of being held rigidly, is allowed a slight free or floating movement so that it can follow a hole which has been bored true, without restraint. In this way the hole is reamed straight and to practically the same size as the reamer.

There are many different designs of floating holders but the general principle upon which they are based is illustrated by the two types shown in Fig. 21. The reamer and holder shown to the left has a ball-shank _A_ which bears against a backing-up screw _B_ inserted in the end of holder _C_ through which the driving pin passes. The lower end of the reamer shank is also spherical-shaped at _D_, and screw-pin _E_ secures the shell reamer to this end. It will be noted that the hole in the shank for pin _E_ is "bell-mouthed" on each side of the center and that there is clearance at _F_ between the shank and reamer shell; hence the reamer has a free floating action in any direction. This holder has given very satisfactory results.

The holder shown to the right is attached to the face of the turret by four fillister-head screws. Sleeve _C_ is held in plate _A_ by means of two steel pins _B_ which are tight in plate _A_ and made to fit freely in bayonet grooves _D_. Reamer holder _E_ floats on sleeve _C_, the floating motion being obtained through the four steel pins _G_ extending into driving ring _F_. Two of the pins are tight in the holder _E_ and two in sleeve _C_. The faces of sleeve _C_, driving ring _F_, and reamer holder _E_ are held tightly against each other by means of spring _H_ which insures the reamer being held perfectly true. Spring _H_ is adjusted by means of nut _I_ which is turned with a spanner wrench furnished with each holder. The reamer is so held that its axis is always maintained parallel to the center of the hole, and, at the same time, it has a slight self-adjusting tendency radially, so that the hole and reamer will automatically keep in perfect alignment with each other.

=Multiple Cylinder Boring Machine.=--In automobile and other factories where a great many gasoline engine cylinders are required, multiple-spindle boring machines of the vertical type are commonly used. The machine shown in Fig. 22 is a special design for boring four cylinders which are cast _en bloc_ or in one solid casting. The work is held in a box jig which has a top plate equipped with guide bearings for holding the spindles rigidly while boring. The lower end of each spindle has attached to it a cutter-head and the boring is done by feeding the table and casting vertically. This feeding movement is effected by power and it is disengaged automatically when the cutters have bored to the required depth. The particular machine illustrated is used for rough boring only, the cylinders being finished by reaming in another similar machine. The cylinders are bored to a diameter of 3-5/8 inches, and about 3/8 inch of metal is removed by the roughing cut. The spindles have fixed center-to-center distances as the machine is intended for constant use on cylinders of one size, so that adjustment is not necessary. Of course, a special machine of this kind is only used in shops where large numbers of cylinders of one design are required continually. Some cylinder boring machines of the vertical type have spindles which can be adjusted for different center-to-center distances if this should be necessary in order to accommodate a cylinder of another size.