A facing tool, shown in the working position in Fig. 36, is placed at this station of the turret, being held in the turret hole. This tool has a pilot bar and a holder which contains a facing blade. Feeding by hand, as before, the tool is adjusted lengthwise so as to rough-face the work to the dimension desired. In a similar way the finish-turning and facing tools for the second position of the turret are set, the cam-shaft being revolved by hand to bring this second face and second cam into the working position. (The finish-facing tool is not shown in place in Fig. 36.)

[Ill.u.s.tration: Fig. 38. Diagram of Cross-slide Cams and Feeding Mechanism]

=Setting the Cross-slide Cam.=--As previously mentioned, the third turret face has no tool, the cutting off of the collar being done during this part of the cycle of operations. It has been taken for granted that in setting the turret slide, room has been left between it and the chuck for the cross-slide. The cross-slide is clamped in a longitudinal position on the bed, convenient for the cutting-off operation, which is done with a tool _D_ (Fig. 36) in the rear toolpost, thus leaving the front un.o.bstructed for the operator. When both forming and cutting off are to be done, the forming tool is generally held at the front and the cutting-off tool at the back because heavier and more accurate forming can be done with the work revolving downward toward a tool in the front toolpost, than with the tool at the rear where it is subjected to a lifting action.

The arrangement of the cross-slide cams is shown in Fig. 38, which is an end view of the large drum _E_, Fig. 32. The rear feed cam is the one to be used, and since this cutting-off operation is a short one, it may be done during the return of the turret for position No. 3. The cam drum is, therefore, rotated by hand until the turret face No. 3 has begun to return. The cross-slide cams are then loosened and the rear feed cam is swung around to just touch the roller _R_ which operates arm _A_, the cross-slide having been adjusted out to nearly the limit of its forward travel, leaving approximately enough movement for cutting off the collar. The rear feed cam is then clamped in this position.

A cutting-off tool is next placed in the rear toolpost at the proper height. The rear toolpost slide is then adjusted to bring the point of the cutting-off tool up to the work, and the cam drum is revolved by hand until the piece is cut off. The cross-slide tool is, of course, set in the proper position to make a collar of the required thickness.

Feeding by hand is discontinued when the roll is on the point of the cam; the cutting-off tool slide is then permanently set on the cross-slide so that the point of the cutting-off tool enters the bore just far enough to completely sever the collar from the bushing. The motion of the cam drum is continued, by hand, until the roll is over the point of the feed cam. The cross-slide is then pushed back, by hand, until the cam and roll are again in contact, when the return cam is brought up and clamped in position, so that there is just room for the roll between the feed cam and the return cam. The rear return cam (as the hand feed of the cam drum is continued) brings the cross-slide back to its central position. Since there is no front tool used for this series of operations (although a tool is shown in the front toolpost, Fig. 36), the first feed and return cams are allowed to remain wherever they happen to be. These cam adjustments can all be made from the front of the machine.

=Setting the Boring Tool for Recessing.=--The feeding of the turret slide is now continued to make sure that the cutting-off tool is returned to its normal position before the facing tool in the next face of the turret begins to work. The facing of the bushing, so far as the setting of the tool is concerned, is merely a repet.i.tion of the facing operation at the first position of the turret. The recessing tool is next set. This tool, which is shown diagrammatically in Fig. 39, is very simple as compared with the somewhat complex operation it has to perform. This recess is for clearance only, and accurate dimensions and fine finish are not necessary. The recessing tool consists simply of a slender boring-bar held in the turret and carrying a cutter suitably located about midway the bar. The forward end of the bar is small enough to enter a bell-mouthed bushing held in the chuck. The boring-bar is bent to one side far enough so that the cutter clears the hole as the bar enters, but is forced into the work as the rounded hole of the bushing engages the end of the bar and deflects it into the working position. The upper diagram shows the position of the bar as it enters the hole, and the lower one the position after it has entered the bushing and is engaged in turning the recess. This bar is set in the turret so that at the extreme forward travel of the turret slide, the recess will be bored to the required length. The cutter must also be adjusted to bore to the desired diameter. This completes the setting of the cutting tools.

[Ill.u.s.tration: Fig. 39. Flexible Boring Tool used for Recessing a Bushing in Automatic Chucking and Turning Machine]

=Adjustments for Automatic Feed and Speed Changes.=--The machine must now be set to perform automatically the desired changes of spindle speed and the fast and slow cam movements for the tools. After placing a new piece of work in the machine (the first one having been completed in the setting-up operation), the cam-shaft is revolved by hand until the turning tool in turret face No. 1 is just about to begin its cut. The control wheel _D_, Fig. 34, is rotated in its normal direction until the next graduation marked "slow" is in line with an index mark on the base of the machine. Then the nearest pin _M_ is moved up until it bears against a tooth of the star wheel (previously referred to) and is clamped in this position. The pin should now be in the proper location, but to test its position, rotate the cam shaft backward by hand and throw in the automatic feed; then watch the cut to see if the drum slows down just before the tool begins to work. If it does not, the pin should be adjusted a little, one way or the other, as may be required. (In going over a piece of work for the first time, it is best to have the feed set to the smallest rate, feed change handle _K_ being in position No. 1.)

After the cut has been completed and the turret feed cam-roll is on the high part of the cam, the power feed should again be stopped and the handwheel revolved until the next graduation marked "fast" is opposite the index mark. The next stop pin is then moved up until it just touches the star wheel, where it is clamped in position. The feed being again thrown in, the turret will be returned rapidly, indexed, and moved forward for the second operation. After stopping the automatic movement, the pins are set for this face, and so on for all the operations, including that in which the cross-slide is used for cutting off the finished collar.

As the first, second, and third operations are on comparatively large diameters, they should be done at the slow speed, handle _J_, Fig. 34, being set to give that speed. While the turret slide is being returned between operations 3 and 4, one of the spindle speed-changing dogs _N_ should be clamped to the rim of disk _D_ so as to change the spindle speed to the fast movement. This speed is continued until the last operation is completed, when a second dog is clamped in place to again throw in the slow movement. The feed knock-off dog should also be clamped in place on the disk to stop the machine at the completion of the fifth operation, when the turret is in its rear position. This completes the setting up of the machine. If the feed is finer than is necessary, the feed change handle _K_ may now be moved to a position which will give the maximum feed that can be used.

It has taken considerable time to describe the setting up of the machine for this simple operation, but in the hands of a competent man it can be done quite rapidly. While a simple operation has been referred to in the foregoing, it will be understood that a great variety of work can be done on a machine of this type. It is not unusual to see as many as ten cutting tools operating simultaneously on a piece of work, the tools being carried by the turret, cross-slide and back facing attachment. The latter is operated from a separate cam applied to the cam-shaft and acting through levers on a back facing bar which pa.s.ses through a hole in the spindle. In this back facing bar may be mounted drills, cutters, facing tools, etc. for machining the rear face of a casting held in the chuck jaws. Where extreme accuracy is required, a double back facing attachment may be used, arranged with cutters for taking both roughing and finishing cuts. The use of this attachment often saves a second operation. This automatic chucking and turning machine is also adapted for bar work, especially in diameters varying from 3 to 6 inches.

=Turning Flywheel in Automatic Chucking and Turning Machine.=--A typical operation on the Potter & Johnston automatic chucking and turning machine is ill.u.s.trated in Fig. 40, which shows the machine arranged for turning the cast-iron flywheel for the engine of a motor truck. The rim is turned and faced on both sides and the hub is bored, reamed and faced on both sides. The flywheel casting is held in a chuck by three special jaws which grip the inside of the rim. The order of the operations is as follows:

The rear end of the hub is faced by the back facing bar; the cored hole is started by a four-lipped drill in the turret and the front end of the hub is rough-faced. (These tools are on the rear side of the turret when the latter is in the position shown in the ill.u.s.tration.) After the turret indexes, the hole is rough-bored by tool _A_ and while this is being done, the outside of the rim is rough-turned by tool _B_ held in a special bracket attached to the turret. Both sides of the rim are also rough-faced by tools _C_ and _D_ held at the front of the cross-slide, this operation taking place at the same time that the rim is turned and the hole is being bored.

[Ill.u.s.tration: Fig. 40. Machining Flywheels in Potter & Johnston Automatic Chucking and Turning Machine]

The turret again automatically recedes and indexes, thus locating bar _E_ and turning tool _G_ in the working position. The hole is then finish-bored by tool _E_ and the hub is finish-faced by blade _F_; at the same time the rim is finish-turned by tool _G_ and the sides are finish-faced to the proper width by two tools held at the rear of the cross-slide. The turret automatically recedes and indexes a third time, thus locating the flat-cutter reamer-bar _H_ in the working position and then the hole is reamed to the required diameter. This completes the cycle of operations. The total time for machining this flywheel is forty minutes.

=Automatic Multiple-spindle Chucking Machine.=--An example of the specialized machines now used for producing duplicate parts, is shown in Fig. 41. This is a "New Britain" automatic multiple-spindle chucking machine of the single-head type and it is especially adapted for boring, reaming and facing operations on castings or forgings which can readily be held in chuck jaws. This particular machine has five spindles, which carry and revolve the tools. The work being machined is held stationary in the multiple chuck turret _A_ which holds each part in line with one of the spindles and automatically indexes, so that the work pa.s.ses from one spindle to another until it is finished. The turret then indexes the finished piece to a sixth or "loading position" which is not opposite a spindle, where the part is removed and replaced with a rough casting.

Each pair of chuck jaws is operated independently of the others by the use of a chuck wrench. These jaws are made to suit the shape of the work.

[Ill.u.s.tration: Fig. 41. New Britain Multiple-spindle Automatic Chucking Machine of Single-head Type]

When a single-head machine is in operation, the turret advances and feeds the work against the revolving tools so that a number of pieces are operated upon at the same time. The turret is fed by a cam drum _B_.

Cam strips are bolted to the outside of this drum and act directly against a roller attached to the yoke _C_ which can be clamped in different positions on the spindle _D_, the position depending upon the length of the work. On the opposite end of the turret spindle is the indexing mechanism _E_. An automatically spring-operated latch _F_ engages notches in the rim of the dividing wheel, thus accurately locating the turret. The turret is locked by a steadyrest _G_, which, for each working position, automatically slides into engagement with one of the notches in the turret. This relieves the indexing mechanism of all strain.

[Ill.u.s.tration: Fig. 42. Detail View of New Britain Double-head Eight-spindle Machine, Boring, Reaming and Facing Castings]

This type of machine is also built with two spindle heads, the double-head design being used for work requiring operations on both ends. When the double-head machine is in operation, the revolving spindles and tools advance on both sides of the chuck turret, the latter remaining stationary except when indexing. The feed drums on the double-head machine are located directly beneath each group of spindles.

Fig. 42 shows an example of work on a machine of the double-head design.

This is an eight-spindle machine, there being two groups of four spindles on each side of the turret. The castings _E_ are for the wheel hubs of automobiles. The order of the operations on one of the castings, as it indexes around, is as follows: The hole in the hub is first rough-reamed by taper reamer _A_ and the opposite end of the hub is rough-faced and counterbored by a tool in spindle _A_{1}_. When the turret indexes, this same casting is reamed close to the finished size by reamer _B_ and the left end of the hub is rough-faced by cutter _F_, while a tool in the opposite spindle _B_{1}_ finishes the counterboring and facing operation. At the third position, reamer _C_ finishes the hole accurately to size, and when the work is indexed to the fourth position, the hub on the left side is finish-faced by a tool in spindle _D_. (The third and fourth spindles of the right-hand group are not used for this particular operation.) When the turret again indexes, the finished casting is removed and replaced with a rough one. While the successive operations on a single casting have just been described, it will be understood that all of the tools operate simultaneously and that a finished casting arrives at the unloading and loading position each time the turret indexes. Three hundred of these malleable castings are machined in nine hours.

=Selecting Type of Turning Machine.=--The variety of machine tools now in use is very extensive, and as different types can often be employed for the same kind of work, the selection of the best and most efficient machine is often a rather difficult problem. To ill.u.s.trate, there are many different types and designs of turning machines, such as the ordinary engine lathe, the hand-operated turret lathe, the semi-automatic turning machine, and the fully automatic type, which, after it is "set up" and started, is entirely independent. Hence, when a certain part must be turned, the question is, what kind of machine should be used, a.s.suming that it would be possible to employ several different machines? The answer to this question usually depends princ.i.p.ally upon the number of parts that must be turned.

For example, a certain casting or forging might be turned in a lathe, which could be finished in some form of automatic or semi-automatic turning machine much more quickly. It does not necessarily follow, however, that the automatic is the best machine to use, because the lathe is designed for general work and the part referred to could doubtless be turned with the regular lathe equipment, whereas the automatic machine would require special tools and it would also need to be carefully adjusted. Therefore, if only a few parts were needed, the lathe might be the best tool to use, but if a large number were required, the automatic or semi-automatic machine would doubtless be preferable, because the saving in time effected by the latter type would more than offset the extra expense for tool equipment and setting the machine. It is also necessary, in connection with some work, to consider the degree of accuracy required, as well as the rate of production, and it is because of these varying conditions that work of the same general cla.s.s is often done in machines of different types, in order to secure the most efficient results.

CHAPTER VI

VERTICAL BORING MILL PRACTICE

All the different types of turning machines now in use originated from the lathe. Many of these tools, however, do not resemble the lathe because, in the process of evolution, there have been many changes made in order to develop turning machines for handling certain cla.s.ses of work to the best advantage. The machine ill.u.s.trated in Fig. 1 belongs to the lathe family and is known as a vertical boring and turning mill.

This type, as the name implies, is used for boring and turning operations, and it is very efficient for work within its range. The part to be machined is held to the table _B_ either by clamps or in chuck jaws attached to the table. When the machine is in operation, the table revolves and the turning or boring tools (which are held in tool-blocks _T_) remain stationary, except for the feeding movement. Very often more than one tool is used at a time, as will be shown later by examples of vertical boring mill work. The tool-blocks _T_ are inserted in tool-bars _T_{1}_ carried by saddles _S_ which are mounted on cross-rail _C_. Each tool-head (consisting of a saddle and tool-bar) can be moved horizontally along cross-rail _C_, and the tool-bars _T_{1}_ have a vertical movement. These movements can be effected either by hand or power.

When a surface is being turned parallel to the work table, the entire tool-head moves horizontally along the cross-rail, but when a cylindrical surface is being turned, the tool-bar moves vertically. The tool-heads are moved horizontally by the screws _H_ and _H_{1}_, and the vertical feed for the tool-bars is obtained from the splined shafts _V_ and _V_{1}_, there being a separate screw and shaft for each head so that the feeding movements are independent. These feed shafts are rotated for the power feed by vertical shafts _A_ and _A_{1}_ on each side of the machine.

These vertical shafts connect with the feed shafts through bevel and spur gears located at the ends of the cross-rail. On most boring mills, connection is made with one of the splined shafts _V_ or screw _H_, by a movable gear, which is placed on whichever shaft will give the desired direction of feed. The particular machine ill.u.s.trated is so arranged that either the right or left screw or feed shaft can be engaged by simply shifting levers _D_{1}_ or _D_.

[Ill.u.s.tration: Fig. 1. Gisholt Vertical Boring and Turning Mill]

The amount of feed per revolution of the table is varied for each tool-head by feed-changing mechanisms _F_ on each side of the machine.

These feed boxes contain gears of different sizes, and by changing the combinations of these gears, the amount of feed is varied. Five feed changes are obtained on this machine by shifting lever _E_, and this number is doubled by shifting lever _G_. By having two feed boxes, the feeding movement of each head can be varied independently. The direction of either the horizontal or vertical feed can be reversed by lever _R_, which is also used for engaging or disengaging the feeds. This machine is equipped with the dials _I_ and _I_{1}_ which can be set to automatically disengage the feed at any predetermined point. There are also micrometer dials graduated to thousandths of an inch and used for adjusting the tools without the use of measuring instruments.

The work table _B_ is driven indirectly from a belt pulley at the rear, which transmits the power through gearing. The speed of the table can be varied for turning large or small parts, by levers _J_ and _K_ and the table can be started, stopped or rotated part of a revolution by lever _L_ which connects with a friction clutch. There are corresponding feed and speed levers on the opposite side, so that the machine can be controlled from either position.

The heads can be adjusted along the cross-rail for setting the tools by hand-cranks _N_, and the tool slides can be moved vertically by turning shafts _V_ with the same cranks. With this machine, however, these adjustments do not have to be made by hand, ordinarily, as there are rapid power movements controlled by levers _M_. These levers automatically disengage the feeds and enable the tool-heads to be rapidly shifted to the required position, the direction of the movement depending upon the position of the feed reverse lever _R_ and lever _D_.

This rapid traverse, which is a feature applied to modern boring mills of medium and large size, saves time and the labor connected with hand adjustments. The cross-rail _C_ has a vertical adjustment on the faces of the right and left housings which support it, in order to locate the tool-heads at the right height for the work. This adjustment is effected by power and is controlled by levers at the sides of the housings.

Normally, the cross-rail is bolted to the housings, and these bolts must be loosened before making the adjustment, and must always be tightened afterwards.

The function of these different levers has been explained to show, in a general way, how a vertical boring machine is operated. It should be understood, however, that the arrangement differs considerably on machines of other makes. The construction also varies considerably on machines of the same make but of different size.

[Ill.u.s.tration: Fig. 2. Small Boring and Turning Mill with Single Turret-head]

All modern vertical boring mills of medium and large sizes are equipped with two tool-heads, as shown in Fig. 1, because a great deal of work done on a machine of this type can have two surfaces machined simultaneously. On the other hand, small mills of the type ill.u.s.trated in Fig. 2 have a single head. The toolslide of this machine, instead of having a single tool-block, carries a five-sided turret _T_ in which different tools can be mounted. These tools are shifted to the working position as they are needed, by loosening binder lever _L_ and turning or "indexing" the turret. The turret is located and locked in any of its five positions by lever _I_, which controls a plunger that engages notches at the rear. Frequently, all the tools for machining a part can be held in the turret, so that little time is required for changing from one tool to the next. Some large machines having two tool-heads are also equipped with a turret on one head.

=Boring and Turning in a Vertical Boring Mill.=--The vertical boring mill is, in many respects, like a lathe placed in a vertical position, the table of the mill corresponding to the faceplate or chuck of the lathe and the tool-head to the lathe carriage. Much of the work done by a vertical mill could also be machined in a lathe, but the former is much more efficient for work within its range. To begin with, it is more convenient to clamp work to a horizontal table than to the vertical surface of a lathe faceplate, or, as someone has aptly said, "It is easier to lay a piece down than to hang it up." This is especially true of the heavy parts for which the boring mill is princ.i.p.ally used. Very deep roughing cuts can also be taken with a vertical mill. This type of machine mill is designed for turning and boring work which, generally speaking, is quite large in diameter in proportion to the width or height. The work varies greatly, especially in regard to its diameter, so that boring mills are built in a large range of sizes. The small and medium sizes will swing work varying from about 30 inches to 6 or 7 feet in diameter, whereas large machines, such as are used for turning very large flywheels, sheaves, etc., have a swing of 16 or 20 feet, and larger sizes are used in some shops. The size of a vertical mill, like any other machine tool, should be somewhat in proportion to the size of the work for which it is intended, as a very large machine is unwieldy, and, therefore, inefficient for machining comparatively small parts.

=Holding and Setting Work on Boring Mill Table.=--There are three general methods of holding work to the table of a boring mill; namely, by the use of chucks, by ordinary bolts and clamps, or in special fixtures. Chucks which are built into the table (as ill.u.s.trated in Fig.

2) and have both universal and independent adjustments for the jaws can be used to advantage for holding castings that are either round or irregular in shape. The universal adjustment is used for cylindrical parts, such as disks, flywheels, gear blanks, etc., and the independent adjustment, for castings of irregular shape. Chucks which have either an independent or universal movement for the jaws are known as a "combination" type and usually have three jaws. There is also a four-jaw type which has the independent adjustment only. This style is preferable for work that is not cylindrical and which must be held very securely.

Chuck jaws that do not form a part of the machine table, but are bolted to it in the required position, are also employed extensively, especially on comparatively large machines.

Most of the work done in a vertical mill is held in a chuck.

Occasionally, however, it is preferable to clamp a part directly to the table. This may be desirable because of the shape and size of the work, or because it is necessary to hold a previously machined surface directly against the table in order to secure greater accuracy.

Sometimes a casting is held in the chuck for turning one side, and then the finished side is clamped against the table for turning the opposite side. Parts which are to be machined in large quant.i.ties are often held in special fixtures. This method is employed when it enables the work to be set up more quickly than would be possible if regular clamps or chuck jaws were used.

Work that is to be turned or bored should first be set so that the part to be machined is about central with the table. For example, the rim of a flywheel should be set to run true so that it can be finished by removing about the same amount of metal around the entire rim; in other words, the rim should be set concentric with the table, as shown in Fig.

3, and the sides of the rim should also be parallel to the table.

[Ill.u.s.tration: Fig. 3. Plan View showing Flywheel Casting Chucked for Turning]

A simple tool that is very useful for testing the position of any cylindrical casting consists of a wooden shank into which is inserted a piece of wire, having one end bent. This tool is clamped in the toolpost and as the work revolves the wire is adjusted close to the cylindrical surface being tested. The movement of the work with relation to the stationary wire point will, of course, show whether or not the part runs true. The advantage of using a piece of wire for testing, instead of a rigid tool, is that the wire, owing to its flexibility, will simply be bent backward if it is moved too close to a surface which is considerably out of true. The upper surface of a casting can be tested for parallelism with the table by using this same wire gage, or by comparing the surface, as the table is revolved slowly, with a tool held in the toolpost. An ordinary surface gage is also used for this purpose.

The proper surface to set true, in any case, depends upon the requirements. A plain cylindrical disk would be set so that the outside ran true and the top surface was parallel with the table. When setting a flywheel, if the inside of the rim is to remain rough, the casting should be set by this surface rather than by the outside, so that the rim, when finished, will be uniform in thickness.