Part 15 (1/2)
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 bus.h.i.+ng. 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 bus.h.i.+ng, 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 bus.h.i.+ng 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 bus.h.i.+ng 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 bus.h.i.+ng 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 Bus.h.i.+ng 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 finis.h.i.+ng 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