As far as possible, chucks should be used for holding cylindrical parts, owing to their convenience. The jaws should be set against an interior cylindrical surface whenever this is feasible. To ill.u.s.trate, the flywheel in Fig. 3 is gripped by the inside of the rim which permits the outside to be turned at this setting of the work. It is also advisable to set a flywheel casting in the chuck so that a spoke rests against one of the jaws as at _d_, if this is possible. This jaw will then act as a driver and prevent the casting from slipping or turning in the chuck jaws, owing to the tangential pressure of the turning tool. When a cut is being taken, the table and work rotate as shown by arrow _a_, and the thrust of the cut (taken by tool _t_) tends to move the wheel backward against the direction of rotation, as shown by arrow _b_. If one of the chuck jaws bears against one of the spokes, this movement is prevented.

It is not always feasible to use a chuck jaw as a driver and then a special driver having the form of a small angle-plate or block is sometimes bolted directly to the table. Another method of driving is to set a brace between a spoke or projection on the work and a chuck jaw or strip attached to the table. Drivers are not only used when turning flywheels, but in connection with any large casting, especially when heavy cuts have to be taken. Of course, some castings are so shaped that drivers cannot be employed.

=Turning in a Boring Mill.=--The vertical type of boring mill is used more for turning cylindrical surfaces than for actual boring, although a large part of the work requires both turning and boring. We shall first consider, in a general way, how surfaces are turned and then refer to some boring operations. The diagram _A_, Fig. 4, ill.u.s.trates how a horizontal surface would be turned. The tool _t_ is clamped in tool-block _t_{1}_, in a vertical position, and it is fed horizontally as the table and work rotate. The tool is first adjusted by hand for the proper depth of cut and the automatic horizontal feed is then engaged.

When a cylindrical surface is to be turned, the tool (provided a straight tool is used) is clamped in a horizontal position and is fed downward as indicated at _B_. The amount that the tool should feed per revolution of the work, depends upon the kind of material being turned, the diameter of the turned part and the depth of the cut.

[Ill.u.s.tration: Fig. 4. (A) Turning a Flat Surface. (B) Turning a Cylindrical Surface]

Most of the parts machined in a vertical boring mill are made of cast iron and, ordinarily, at least one roughing and one finishing cut is taken. The number of roughing cuts required in any case depends, of course, upon the amount of metal to be removed. An ordinary roughing cut in soft cast iron might vary in depth from 1/8 or 3/16 inch to 3/8 or 1/2 inch and the tool would probably have a feed per revolution of from 1/16 to 1/8 inch, although deeper cuts and coa.r.s.er feeds are sometimes taken. These figures are merely given to show, in a general way, what cuts and feeds are practicable. The tool used for roughing usually has a rounded end which leaves a ridged or rough surface. To obtain a smooth finish, broad flat tools are used. The flat cutting edge is set parallel to the tool's travel and a coa.r.s.e feed is used in order to reduce the time required for taking the cut. The finishing feeds for cast iron vary from 1/4 to 3/4 inch on ordinary work. The different tools used on the vertical mill will be referred to more in detail later.

All medium and large sized vertical boring mills are equipped with two tool-heads and two tools are frequently used at the same time, especially on large work. Fig. 9 ill.u.s.trates the use of two tools simultaneously. The casting shown is a flywheel, and the tool on the right side turns the upper side of the rim, while the tool on the left side turns the outside or cylindrical surface. As a boring mill table rotates in a counter-clockwise direction, the left-hand tool is reversed to bring the cutting edge at the rear. By turning two surfaces at once, the total time for machining the casting is, of course, greatly reduced.

The turning of flywheels is a common vertical boring mill operation, and this work will be referred to in detail later on.

[Ill.u.s.tration: Fig. 5. Tools for Boring and Reaming Holes]

=Boring Operations.=--There are several methods of machining holes when using a vertical boring mill. Ordinarily, small holes are cored in castings and it is simply necessary to finish the rough surface to the required diameter. Some of the tools used for boring and finishing comparatively small holes are shown in Fig. 5. Sketch _A_ shows a boring tool consisting of a cutter _c_ inserted in a shank, which, in turn, is held in the tool slide, or in a turret attached to the tool slide. With a tool of this type, a hole is bored by taking one or more cuts down through it. The tool shown at _B_ is a four-lipped drill which is used for drilling cored holes preparatory to finishing by a cutter or reamer.

This drill would probably finish a hole to within about 1/32 inch of the finish diameter, thus leaving a small amount of metal for the reamer to remove. The tool ill.u.s.trated at _C_ has a double-ended flat cutter _c_, which cuts on both sides. These cutters are often made in sets for boring duplicate parts. Ordinarily, there are two cutters in a set, one being used for roughing and the other for finishing. The cutter pa.s.ses through a rectangular slot in the bar and this particular style is centrally located by shoulders _s_, and is held by a taper pin _p_. Some cutter bars have an extension end, or "pilot" as it is called, which pa.s.ses through a close-fitting bushing in the table to steady the bar.

Sketch _D_ shows a finishing reamer. This tool takes a very light cut and is intended to finish holes that have been previously bored close to the required size. Sometimes a flat cutter _C_ is used for roughing and a reamer for finishing. The reamer is especially desirable for interchangeable work, when all holes must have a smooth finish and be of the same diameter. When a reamer is held rigidly to a turret or toolslide, it is liable to produce a hole that is either tapering or larger than the reamer diameter. To prevent this, the reamer should be held in a "floating" holder which, by means of a slight adjustment, allows the reamer to align itself with the hole. There are several methods of securing this "floating" movement. (See "Floating Reamer Holders.")

[Ill.u.s.tration: Fig. 6. Boring with Regular Turning Tools]

Large holes or interior cylindrical surfaces are bored by tools held in the regular tool-head. The tool is sometimes clamped in a horizontal position as shown at _A_, Fig. 6, or a bent type is used as at _B_. Cast iron is usually finished by a broad flat tool as at _C_, the same as when turning exterior surfaces. Obviously a hole that is bored in this way must be large enough to admit the tool-block.

[Ill.u.s.tration: Fig. 7. Set of Boring Mill Tools]

=Turning Tools for the Vertical Boring Mill.=--A set of turning tools for the vertical boring mill is shown in Fig. 7. These tools can be used for a wide variety of ordinary turning operations. When a great many duplicate parts are to be machined, special tool equipment can often be used to advantage, but as the form of this equipment depends upon the character of the work, only standard tools have been shown in this ill.u.s.tration. The tool shown at _A_ is a right-hand, roughing tool, and a left-hand tool of the same type is shown at _B_. Tool _C_ is an offset or bent, left-hand round nose for roughing, and _D_ is a right-hand offset roughing tool. A straight round nose is shown at _E_. Tool _F_ has a flat, broad cutting edge and is used for finishing. Left-and right-hand finishing tools of the offset type are shown at _G_ and _H_, respectively. Tool _I_ has a square end and is used for cutting grooves.

Right-and left-hand parting tools are shown at _J_ and _K_, and tool _L_ is a form frequently used for rounding corners.

[Ill.u.s.tration: Fig. 8. Diagrams Ill.u.s.trating Use of Different Forms of Tools]

The diagrams in Fig. 8 show, in a general way, how each of the tools ill.u.s.trated in Fig. 7 are used, and corresponding tools are marked by the same reference letters in both of these ill.u.s.trations. The right-and left-hand roughing tools _A_ and _B_ are especially adapted for taking deep roughing cuts. One feeds away from the center of the table, or to the right (when held in the right-hand tool-block) and the other tool is ground to feed in the opposite direction. Ordinarily, when turning plain flat surfaces, the cut is started at the outside and the tool feeds toward the center, as at _B_, although it is sometimes more convenient to feed in the opposite direction, as at _A_, especially when there is a rim or other projecting part at the outside edge. The tool shown at _A_ could also be used for turning cylindrical surfaces, by clamping it in a horizontal position across the bottom of the tool-block. The feeding movement would then be downward or at right-angles to the work table.

The offset round-nose tools _C_ and _D_ are for turning exterior or interior cylinder surfaces. The shank of this tool is clamped in the tool-block in a vertical position and as the bent end extends below the tool-block, it can be fed down close to a shoulder. The straight type shown at _E_ is commonly used for turning steel or iron, and when the point is drawn out narrower, it is also used for bra.s.s, although the front is then ground without slope. Tool _F_ is for light finishing cuts and broad feeds. The amount of feed per revolution of the work should always be less than the width of the cutting edge as otherwise ridges will be left on the turned surface. The offset tools _G_ and _H_ are for finishing exterior and interior cylindrical surfaces. These tools also have both vertical and horizontal cutting edges and are sometimes used for first finishing a cylindrical and then a horizontal surface, or _vice versa_. Tool _I_ is adapted to such work as cutting packing-ring grooves in engine pistons, forming square or rectangular grooves, and similar work. The parting tools _J_ and _K_ can also be used for forming narrow grooves or for cutting off rings, etc. The sketch _K_ (Fig. 8) indicates how a tool of this kind might be used for squaring a corner under a shoulder. Tool _L_ is frequently used on boring mills for rounding the corners of flywheel rims, in order to give them a more finished appearance. It has two cutting edges so that either side can be used as when rounding the inner and outer corners of a rim.

The turning tools of a vertical boring mill are similar, in many respects, to those used in a lathe, although the shanks of the former are shorter and more stocky than those of lathe tools. The cutting edges of some of the tools also differ somewhat in form, but the principles which govern the grinding of lathe and boring mill tools are identical, and those who are not familiar with tool grinding are referred to 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 ill.u.s.tration 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.

[Ill.u.s.tration: Fig. 9. Turning the Rim of a Flywheel]

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.

[Ill.u.s.tration: Fig. 10. Tool B set for Boring the Hub]

[Ill.u.s.tration: Fig. 11. Diagrams showing Method of Turning and Boring a Flywheel on a Double-head Mill having one Turret Head]

In order to show more clearly the method of handling work of this cla.s.s, the machining of a flywheel will be explained more in detail in connection with Fig. 11, which ill.u.s.trates 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.

[Ill.u.s.tration: Fig. 12. Gisholt Mill equipped with Convex Turning Attachment]

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 pa.s.sing 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_.

[Ill.u.s.tration: Fig. 13. Turning a Taper or Conical Surface]

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.

[Ill.u.s.tration: Fig. 14. Turning a Conical Surface by using the Combined Vertical and Horizontal Feeds]

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 ill.u.s.trated in Fig. 13. Another method, which is sometimes resorted to for work of this cla.s.s, 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_.

[Ill.u.s.tration: Fig. 15. Diagram showing Method of Obtaining Angular Position of Tool-head when Turning Conical Surfaces by using Vertical and Horizontal Feeding Movements]

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_ _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 ill.u.s.trate: The sine of 30 degrees is 0.5; then sin _b_ = (0.5 1/4) 3/16 = 0.6666; hence angle _b_ = 41 degrees 49 minutes, and _x_ = 90-(30 + 41 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 ill.u.s.trated 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 ill.u.s.trated) 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.

[Ill.u.s.tration: Fig. 16. Bullard Vertical Turret Lathe]

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 ill.u.s.trate, 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.

[Ill.u.s.tration: Fig. 17. Turning a Gear Blank on a Vertical Turret Lathe]

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 ill.u.s.trated, 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.

[Ill.u.s.tration: Fig. 18. Turning Gasoline Engine Flywheel on Vertical Turret Lathe--First Position]