=Examples of Vertical Turret Lathe Work.=--In order to ill.u.s.trate 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 cla.s.s 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 ill.u.s.tration 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.
[Ill.u.s.tration: Fig. 19. Turning Gasoline Engine Flywheel--Second Position]
[Ill.u.s.tration: Fig. 20. Diagrams showing How Successive Operations are Performed by Different Tools in the Turret]
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 sh.e.l.l-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 circ.u.mference 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 ill.u.s.trate 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 coa.r.s.e 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.
[Ill.u.s.tration: Fig. 21. Two Types of Floating Reamer Holders]
There are many different designs of floating holders but the general principle upon which they are based is ill.u.s.trated 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 pa.s.ses. The lower end of the reamer shank is also spherical-shaped at _D_, and screw-pin _E_ secures the sh.e.l.l 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 sh.e.l.l; hence the reamer has a free floating action in any direction. This holder has given very satisfactory results.
[Ill.u.s.tration: Fig. 22. Multiple-spindle Cylinder Boring Machine]
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 ill.u.s.trated 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.
CHAPTER VII
HORIZONTAL BORING MACHINES
A boring machine of the horizontal type is shown in Fig. 1. The construction and operation of this machine is very different from that of a vertical boring mill and it is also used for an entirely different cla.s.s of work. The horizontal machine is employed princ.i.p.ally for boring, drilling or milling, whereas the vertical design is especially adapted to turning and boring. The horizontal type is also used for turning or facing f.l.a.n.g.es or similar surfaces when such an operation can be performed to advantage in connection with other machine work on the same part.
The type of machine ill.u.s.trated in Fig. 1 has a heavy base or bed to which is bolted the column _C_ having vertical ways on which the spindle-head _H_ is mounted. This head contains a sleeve or quill in which the spindle _S_ slides longitudinally. The spindle carries cutters for boring, whereas milling cutters or the auxiliary facing arm are bolted to the end _A_ of the spindle sleeve. The work itself is attached either directly or indirectly to the table or platen _P_. When the machine is in operation, the cutter or tool revolves with the spindle sleeve or spindle and either the cutter or the part being machined is given a feeding movement, depending on the character of the work. The spindle can be moved in or out by hand for adjustment, or by power for feeding the cutter, as when boring or drilling.
[Ill.u.s.tration: Fig. 1. Lucas Horizontal Boring, Drilling and Milling Machine]
The entire spindle-head _H_ can also be moved vertically on the face of the column _C_, by hand, for setting the spindle to the proper height, or by power for feeding a milling cutter in a vertical direction. When the vertical position of the spindle-head is changed, the outboard bearing block _B_ also moves up or down a corresponding amount, the two parts being connected by shafts and gearing. Block _B_ steadies the outer end of the boring-bar and the back-rest in which this block is mounted can be shifted along the bed to suit the length of the work, by turning the squared end of shaft _D_ with a crank. The platen _P_ has a cross-feed, and the saddle _E_ on which it is mounted can be traversed lengthwise on the bed; both of these movements can also be effected by hand or power. There is a series of power feeding movements for the cutters and, in addition, rapid power movements _in a reverse direction from the feed_ for returning a cutter quickly to its starting position, when this is desirable.
This machine is driven by a belt connecting pulley _G_ with an overhead shaft. When the machine is in operation, this pulley is engaged with the main driving shaft by a friction clutch _F_ controlled by lever _L_.
This main shaft drives through gearing a vertical shaft _I_, which by means of other gears in the spindle-head imparts a rotary movement to the spindle. As a machine of this type is used for boring holes of various diameters and for a variety of other work, it is necessary to have a number of speed changes for the spindle. Nine speeds are obtained by changing the position of the sliding gears controlled by levers _R_ and this number is doubled by back-gears in the spindle-head and controlled by lever _J_.
The amount of feed for the spindle, spindle-head, platen or saddle is varied by two levers _K_ and _K_{1}_ which control the position of sliding gears through which the feeding movements are transmitted. The direction of the feed can be reversed by shifting lever _O_. With this particular machine, nine feed changes are available for each position of the spindle back-gears, making a total of eighteen changes. The feeding movement is transmitted to the spindle-head, spindle, platen or saddle, as required, by the three distributing levers _T_, _U_ and _V_, which control clutches connecting with the transmission shafts or feed screws.
When lever _T_ is turned to the left, the longitudinal power feed for the spindle is engaged, whereas turning it to the right throws in the vertical feed for the spindle-head. Lever _U_ engages the cross-feed for platen _P_ and lever _V_, the longitudinal feed for saddle _E_. These levers have a simple but ingenious interlocking device which makes it impossible to engage more than one feed at a time. For example, if lever _T_ is set for feeding the spindle, levers _U_ and _V_ are locked against movement.
The feeds are started and stopped by lever _M_ which also engages the rapid power traverse when thrown in the opposite direction. This rapid traverse operates for whatever feed is engaged by the distributing levers and, as before stated, in a reverse direction. For example, if the reverse lever _O_ is set for feeding the spindle to the right, the rapid traverse would be to the left, and _vice versa_. The cross-feed for the platen can be automatically tripped at any point by setting an adjustable stop in the proper position and the feed can also be tripped by a hand lever at the side of the platen.
All the different feeding movements can be effected by hand as well as by power. By means of handwheel _N_, the spindle can be moved in or out slowly, for feeding a cutter by hand. When the friction clamp _Q_ is loosened, the turnstile _W_ can be used for traversing the spindle, in case a hand adjustment is desirable. The spindle-head can be adjusted vertically by turning squared shaft _X_ with a crank, and the saddle can be shifted along the bed by turning shaft _Y_. The hand adjustment of the platen is effected by shaft _Z_. The spindle-head, platen and saddle can also be adjusted from the end of the machine, when this is more convenient. Shafts _X_, _Y_ and _Z_ are equipped with micrometer dials which are graduated to show movements of one-thousandth inch. These dials are used for accurately adjusting the spindle or work and for boring holes or milling surfaces that must be an exact distance apart.
=Horizontal Boring Machine with Vertical Table Adjustment.=--Another horizontal boring machine is partly shown in Fig. 2. This machine is of the same type as that ill.u.s.trated in Fig. 1, but its construction is quite different, as will be seen. The spindle cannot be adjusted vertically as with the first design described, but it is mounted and driven very much like the spindle of a lathe, and adjustment for height is obtained by raising or lowering the work table. The design is just the reverse, in this respect, of the machine shown in Fig. 1, which has a vertical adjustment for the spindle, and a work table that remains in the same horizontal plane. The raising or lowering of the table is effected by shaft _E_, which rotates large nuts engaging the screws _S_.
Shaft _E_ is turned either by hand or power.
[Ill.u.s.tration: Fig. 2. Horizontal Boring and Drilling Machine with Vertical Table Adjustment]
The main spindle is driven by a cone pulley _P_, either directly, or indirectly through the back-gears shown. This arrangement gives six spindle speeds, and double this number is obtained by using a two-speed countershaft overhead. The motion for feeding the spindle longitudinally is transmitted through a cone of gears, which gives the required changes, to a pinion meshing with a rack which traverses the spindle.
The large handwheel _H_ and a corresponding wheel on the opposite side are used for adjusting the spindle rapidly by hand. The yoke or outboard bearing _B_ for the boring-bars can be clamped in any position along the bed for supporting the bar as close to the work as possible.
Horizontal boring machines are built in many other designs, but they all have the same general arrangement as the machines ill.u.s.trated and operate on the same principle, with the exception of special types intended for handling certain cla.s.ses of work exclusively. The horizontal boring, drilling and milling machine is very efficient for certain cla.s.ses of work because it enables all the machining operations on some parts to be completed at one setting. To ill.u.s.trate, a casting which requires drilling, boring and milling at different places, can often be finished without disturbing its position on the platen after it is clamped in place. Frequently a comparatively small surface needs to be milled after a part has been bored. If this milling operation can be performed while the work is set up for boring, accurate results will be obtained (provided the machine is in good condition) and the time saved that would otherwise be required for re-setting the part on another machine. Some examples of work on which different operations are performed at the same setting will be referred to later. The horizontal boring machine also makes it possible to machine duplicate parts without the use of jigs, which is important, especially on large work, owing to the cost of jigs.
=Drilling and Boring--Cutters Used.=--Holes are drilled in a horizontal machine by simply inserting a drill of required size either directly in the spindle _S_ (see Fig. 1), or in a reducing socket, and then feeding the spindle outward either by hand or power. When a hole is to be bored, a boring-bar _B_{1}_ is inserted in the spindle and the cutter is attached to this bar. The latter is then fed through the hole as the cutter revolves. The distinction made by machinists between drilling and boring is as follows: A hole is said to be drilled when it is formed by sinking a drill into solid metal, whereas boring means the enlargement of a drilled or cored hole either by the use of a single boring tool, a double-ended cutter which operates on both sides of the hole, or a cutter-head having several tools.
There are various methods of attaching cutters to boring-bars and the cutters used vary for different cla.s.ses of work. A simple style of cutter which is used widely for boring small holes is shown at _A_ in Fig. 3. The cutter _c_ is made from flat stock and the cutting is done by the front edges _e_ and _e_{1}_, which are beveled in opposite directions. The cutter is held in the bar by a taper wedge _w_ and it is centered by shoulders at _s_, so that the diameter of the hole will equal the length across the cutter. The outer corners at the front should be slightly rounded, as a sharp corner would be dulled quickly.
These cutters are made in different sizes and also in sets for roughing and finishing. The roughing cutter bores holes to within about 1/32 inch of the finish size and it is then replaced by the finishing cutter. A cutter having rounded ends, as shown by the detail sketch _a_, is sometimes used for light finishing cuts. These rounded ends form the cutting edges and give a smooth finish.
[Ill.u.s.tration: Fig. 3. Boring-cutters of Different Types]
Another method of holding a flat cutter is shown at _B_. The conical end of a screw bears against a conical seat in, the cutter, thus binding the latter in its slot. The conical seat also centers the cutter. A very simple and inexpensive form of cutter is shown at _C_. This is made from a piece of round steel, and it is held in the bar by a taper pin which bears against a circular recess in the side of the cutter. This form has the advantage of only requiring a hole through the boring-bar, whereas it is necessary to cut a rectangular slot for the flat cutter.
[Ill.u.s.tration: Fig. 4. Boring with a Flat Double-ended Cutter]
Fig. 4 shows how a hole is bored by cutters of the type referred to. The bar rotates as indicated by the arrow _a_ and at the same time feeds longitudinally as shown by arrow _b_. The speed of rotation depends upon the diameter of the hole and the kind of material being bored, and the feed per revolution must also be varied to suit conditions. No definite rule can be given for speed or feed. On some cla.s.ses of work a long boring-bar is used, which pa.s.ses through the hole to be bored and is steadied at its outer end by the back-rest _B_, Figs, 1 and 2. On other work, a short bar is inserted in the spindle having a cutter at the outer end. An inexpensive method of holding a cutter at the end of a bar is shown at _D_, Fig. 3. The cutter pa.s.ses through a slot and is clamped by a bolt as shown. When it is necessary to bore holes that are "blind"
or closed at the bottom, a long boring-bar which pa.s.ses through the work cannot, of course, be used.
Sometimes it is necessary to have a cutter mounted at the extreme end of a bar in order to bore close to a shoulder or the bottom of a hole. One method of holding a cutter so that it projects beyond the end of a bar is indicated at _E_. A screw similar to the one shown at _B_ is used, and the conical end bears in a conical hole in the cutter. This hole should be slightly offset so that the cutter will be forced back against its seat. The tool shown at _F_ has adjustable cutters. The inner end of each cutter is tapering and bears against a conical-headed screw _b_ which gives the required outward adjustment. The cutters are held against the central bolt by fillister-head screws _f_ and they are clamped by the screws _c_. Boring tools are made in many different designs and the number and form of the cutters is varied somewhat for different kinds of work.
[Ill.u.s.tration: Fig. 5. Cutter-heads for Boring Large Holes]
=Cutter-heads for Boring Large Holes.=--When large holes are to be bored, the cutters are usually held in a cast-iron head which is mounted on the boring-bar. One type of cutter-head is shown in Fig. 5. This particular head is double-ended and carries two cutters _c_. The cutter-head is bored to fit the bar closely and it is prevented from turning by a key against which a set-screw is tightened. By referring to the end view, it will be seen that each cutter is offset with relation to the center of the bar, in order to locate the front of the tool on a radial line. The number of cutters used in a cutter-head varies. By having several cutters, the work of removing a given amount of metal in boring is distributed, and holes can be bored more quickly with a multiple cutter-head, although more power is required to drive the boring-bar. The boring-bar is also steadied by a multiple cutter-head, because the tendency of any one cutter to deflect the bar is counteracted by the cutters on the opposite side.
A disk-shaped head having four cutters is ill.u.s.trated in Fig. 6. The cutters are inserted in slots or grooves in the face of the disk and they are held by slotted clamping posts. The shape of these posts is shown by the sectional view. The tool pa.s.ses through an elongated slot and it is tightly clamped against the disk by tightening nut _n_. This head is also driven by a key which engages a keyway in the boring-bar.
[Ill.u.s.tration: Fig. 6. Cutter-head with Four Boring Tools]
Two other designs of cutter-heads are shown in Fig. 7. The one ill.u.s.trated at _A_ has three equally s.p.a.ced cutters which are held in an inclined position. The cutters are clamped by screws _c_ and they can be adjusted within certain limits by screws _s_. The cutters are placed at an angle so that they will extend beyond the front of the head, thus permitting the latter to be moved up close to a shoulder. The cutter-heads shown in Figs. 5 and 6 can also be moved up close to a shoulder if bent cutters are used as shown in the right-hand view, Fig.
5. The idea in bending the cutters is to bring the cutting edges in advance of the clamping posts so that they will reach a shoulder before the binding posts strike it. The arrangement of cutter-head _B_ (Fig. 7) is clearly shown by the ill.u.s.tration.
Cutter-heads are often provided with two sets of cutters, one set being used for roughing and the other for finishing. It is a good plan to make these cutters so that the ends _e_ (Fig. 6) will rest against the bar or bottom of the slot, when the cutting edge is set to the required radius.
The cutters can then be easily set for boring duplicate work. One method of making cutters in sets is to clamp the annealed stock in the cutter-head and then turn the ends to the required radius by placing the head in the lathe. After both sets of cutters have been turned in this way, they are ground to shape and then hardened.
[Ill.u.s.tration: Fig. 7. Cutter-heads equipped with Adjustable Tools]
Boring cutters intended for roughing and finishing cuts are shown in the detail view Fig. 8 at _A_ and _B_, respectively. The side of the roughing cutter _A_ is ground to a slight angle _c_ to provide clearance for the cutting edge, and the front has a backward slope _s_ to give the tool keenness. This tool is a good form to use for roughing cuts in cast iron. The finishing tool at _B_ has a broad flat edge _e_ and it is intended for coa.r.s.e feeds and light cuts in cast iron. If a round cutting edge is used for finishing, a comparatively fine feed is required in order to obtain a smooth surface. The corners of tool _B_ are rounded and they should be ground to slope inward as shown in the plan view. The top or ends _d_ of both of these tools are "backed off"
slightly to provide clearance. This clearance should be just enough to prevent the surface back of the cutting edge from dragging over the work. Excessive end clearance not only weakens the cutting edge, but tends to cause chattering. As a finishing tool cuts on the upper end instead of on the side, the front should slope backward as shown in the side view, rather than sidewise as with a roughing cutter. The angle of the slope should be somewhat greater for steel than cast iron, unless the steel is quite hard, thus requiring a strong blunt tool.
[Ill.u.s.tration: Fig. 8. Boring Tools for Roughing and Finishing Cuts]