Automatic Chucking and Turning Machine.—The chucking and turning machine shown inFig. 32is automatic in its operation, the feeding of the tools, indexing of the turret, etc., being done automatically after the machine is properly arranged, and the work is placed in the chuck. This machine is adapted to turning and boring a great variety of castings, forgings or parts from bar stock, and it is often used in preference to the hand-operated turret lathe, especially when a great many duplicate parts are required. It is provided with mechanism for operating the cross-slide, feeding the turret slide forward, returning it rapidly, rotating the turret to a new position, and feeding it forward quickly for taking a new cut. The cross-slideand turret-slide movements are effected by cams mounted on the large drumEseen beneath the turret, while the various speed and feed changes are effected by dogs and pins carried on diskDwhich is keyed to the same shaft that the cam drum is mounted upon. This shaft with the cam drum and governing diskD, makes one revolution for each piece of work completed. The cams for operating the turret slide are mounted upon the periphery of drumE. The roll which engages the angular faces of these cams and imparts movement to the turret is carried by an intermediate slide which has rack teeth engaging a pinion on the square shaftC. By turning this shaft with a crank, the position of the turret-slide, with relation to the cam, may be adjusted for long or short work and long or short tools, as may be required.
Rear View of Machine showing the Cross-slide Mechanism, Driving Gearing, etc.Fig. 33. Rear View of Machine showing the Cross-slide Mechanism, Driving Gearing, etc.
Fig. 33. Rear View of Machine showing the Cross-slide Mechanism, Driving Gearing, etc.
The cams which operate the cross-slide are mounted on the right-hand end of drumEand actuate the yokeA(seeFig. 33) which extends diagonally upward. The rear end of this yoke has rack teeth meshing with the teeth of a segmental pinion,which is fastened to rock-shaftB. At the headstock end, this rock-shaft carries another segmental pinion meshing with rack teeth formed on the cross-slide. The movement imparted to the yoke by the cams is thus transmitted through the pinions and rock-shaft to the cross-slide.
The Automatic Controlling Mechanism for Feeds and SpeedsFig. 34. The Automatic Controlling Mechanism for Feeds and Speeds
Fig. 34. The Automatic Controlling Mechanism for Feeds and Speeds
The cam drumEis driven by a pinion meshing with a gear attached to its front side. This pinion is driven through a train of gearing from pulleyL(seeFig. 34) which is belted to the spindle. The feeds are thus always dependent on the spindle speed. By means of epicyclic gearing and suitable clutches, the motion thus derived from the spindle may be made rapid for returning the turret to be indexed and then advancing it to the cutting position again, or very slow for the forward feed when the tools are at work. These changes from slow to fast orvice versaare controlled by diskD. This disk carries pins which strike a star wheel located back of the disk at the top, and as this star wheel is turned, the speeds are changed by operation of the gearing and clutches referred to. The first pinMthatstrikes the star wheel advances it one-sixth of a rotation, changing the feed from fast to slow; the next pin that strikes it advances it another sixth of a rotation, changing the feed from slow to fast and so on. By adjusting the pins for each piece of work, the feed changes are made to take place at the proper time. HandwheelEis geared with the cam-shaft on which the star wheel is mounted, so that the feeds may be changed by hand if desired.
In addition to these feed-changing pins, diskDhas a dog which operates a lever by which the feed movement is stopped when the work has been completed. Four rates of feed are provided by quick change gearing of the sliding gear type, operated by handleK. With this handle set in the central position, the feed is disengaged. On the periphery of diskDare also clamped dogs or camsN, which operate a horizontal swinging leverPconnected by a link with vertical leverJ, which controls the two spindle speeds with which the machine is provided. Either one of these speeds can be automatically engaged at any time, by adjusting the camsNon diskD.
LeverHconnects or disconnects the driving pulley from the shaft on which it is mounted, thus starting or stopping the machine. The square shaftGserves to operate the drums by hand and is turned with a crank. The rotation of the turret, which takes place at the rear of its travel, is, of course, effected automatically. A dog, which may be seen inFig. 32at the side of the bed, is set to trip the turret revolving mechanism at the proper point in the travel, to avoid interference between the tools and the work. The turret is provided with an automatic clamping device. The mechanism first withdraws the locking pin, unclamps the turret, revolves it, then throws in the locking pin and clamps the turret again.
Example of Work done in Automatic Chucking and Turning MachineFig. 35. Simple Example of Work done in Automatic Chucking and Turning Machine
Example of Work done in Automatic Chucking and Turning Machine
Fig. 35. Simple Example of Work done in Automatic Chucking and Turning Machine
Example of Work on Automatic Turning Machine.—The piece selected for illustrating the “setting up” and operation of the automatic chucking and turning machine is shown inFig. 35. This is a second operation, and a very simple one which will clearly illustrate the principles involved. In the first operation, the hole was drilled, bored and reamed, the small endof the bushing faced, and the outside diameter finished, as indicated by the sketch to the left. (The enlarged diameter at the end was used for holding the work in the chuck.) In the second operation (illustrated to the right), the enlarged chucking end is cut off and, in order to prevent wasting this piece, it is made into a collar for another part of the machine for which the bushing is intended; hence, the outside diameter is turned and the outside end faced, before cutting off the collar. In addition, the bushing is recessed in the second operation, and the outer end faced. In order to have the surfaces finished in the second operation, concentric with those machined in the first operation, the chuck is equipped with a set of soft “false jaws” which have been carefully bored to exactly the diameter of the work to be held.
The first thing to determine when setting up a machine of this type is the order of operations. In this particular case, the order is as follows: At the first position of the turret, the outside collar is rough-turned and the outer end rough-faced. At the second position, the collar is turned to the required diameter and the outer face is finished. The third face of the turret is not equipped with tools, this part of the cycle being taken up in cutting off the collar with a cut-off tool on the rear cross-slide. The fourth operation is that of recessing the bushing, and the fifth operation, facing the end to remove the rough surface left by the cutting-off tool.
Front View of Machine set up for the Finishing Operation on the Recessed Bushing and Collar shown in the Foreground and in Fig. 35Fig. 36. Front View of Machine set up for the Finishing Operation on the Recessed Bushing and Collar shown in the Foreground and inFig. 35
Fig. 36. Front View of Machine set up for the Finishing Operation on the Recessed Bushing and Collar shown in the Foreground and inFig. 35
The toolsAandB,Fig. 36, used for turning the outside of the flange, are held in bracketsCbolted to the face of the turret.These brackets are each provided with three holes for carrying turning tool-holders. This arrangement provides for turning a number of diameters at different positions, simultaneously, but for this particular operation, a single cutting tool for each tool-holder is all that is necessary. A special device is used for recessing and will be described later.
Plate on the Headstock of Machine Illustrated in Fig. 32Fig. 37. Plate on the Headstock of Machine Illustrated inFig. 32giving the Speeds and Feeds
Fig. 37. Plate on the Headstock of Machine Illustrated inFig. 32giving the Speeds and Feeds
Determining Speed and Feed Changes.—As previously mentioned, the particular machine illustrated inFig. 32can be arranged for two automatic changes of speed to suit different diameters on the work. The change gears that will give the required spindle speeds should first be selected. These change gears for different speeds are listed on a speed and feed plate attached to the headstock of the machine (seeFig. 37). It is possible to use one speed from the list given for the fast train of gears, and one from the list for the slow train, so long as the same gears are not used in each case. The diameter of the collar on the work shown inFig. 35is 21/2inches, and the diameter of the body is 2 inches. Assuming that the surface speed for this job should be about 40 feet per minute, a little calculationshows that the 66 revolutions per minute, given by the fast train of gears, is equivalent to a surface speed of 43 feet per minute on a diameter of 21/2inches. Moreover, the 78 revolutions per minute obtained from the slow train of gearing, gives about 41 feet per minute on a diameter of 2 inches. The spindle gearing indicated for these speeds is, therefore, placed in position on the proper studs at the back of the machine.
Next we have to determine on which faces of the turret to place the different tools. Each turret face is numbered to agree with the corresponding feed cam on the drum. The speed and feed plate (Fig. 37) gives the various feeds obtainable per revolution of the spindle. As will be seen, the different cams give different feeds. Cam No. 1 has a coarse feed suitable for roughing; cam No. 2 a finer feed adapted to finishing, and so on. Since the first operation consists in rough-turning, cam No. 1 is used. Cam No. 2, which gives a finer feed, is used for the finish-turning operation. Cam No. 4, which is ordinarily usedfor reaming, could, in this case, be used for recessing, as this recess is for clearance only and may be bored with a coarse feed.
The final operation, which is that of facing, can be done with any cam and cam No. 5 may be used. It will be understood that for facing operations, the feeds given do not apply. As the roll passes over the point of the feed cam at the extreme end of the movement, the feed of the turret slide is gradually slowed down to zero; since the facing takes place in the last eighth or sixteenth inch of this movement, it is done at a feed which is gradually reduced to zero. This is, of course, as it should be, and it is not necessary to pay any attention to the tabulated feeds in facing operations.
Setting the Turret Slide.—The next adjustment is that of setting the turret slide. In making this adjustment the turret is set in such relation to the work that the tools will have but a small amount of overhang, the cam-shaft being revolved by hand until the cam-roll is at the extreme top of the forward feeding cam, so that the turret slide is at the extreme of its forward movement. When this adjustment has been made by the means provided, set the turret index tripping dog so as to revolve the turret at the proper point. After a turning tool-holder and tool is attached to the face of the turret, cam No. 1 is placed in its operating position and is revolved by hand until the roll is on the point of the cam and the turret at the forward extreme of its motion. At this point the tool-holder is set so that the cutter will be far enough forward to complete its turning operation. The feed cam is then turned backward, thus returning the turret slide, and the cutter is set to turn the flange to the proper diameter for the roughing cut. The turret slide is fed forward and back while the cutter is adjusted, and when it is properly set, the flange is turned, the cam-drum being fed by hand. This is the first trial cut on the piece.
A facing tool, shown in the working position inFig. 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 similarway 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 inFig. 36.)
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 toolD(Fig. 36) in the rear toolpost, thus leaving the front unobstructed 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.
Diagram of Cross-slide Cams and Feeding MechanismFig. 38. Diagram of Cross-slide Cams and Feeding Mechanism
Diagram of Cross-slide Cams and Feeding Mechanism
Fig. 38. Diagram of Cross-slide Cams and Feeding Mechanism
The arrangement of the cross-slide cams is shown inFig. 38, which is an end view of the large drumE,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 rollerRwhich operates armA, 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.
Flexible Boring Tool used for Recessing a Bushing in Automatic Chucking and Turning MachineFig. 39. Flexible Boring Tool used for Recessinga Bushing in Automatic Chucking and Turning Machine
Flexible Boring Tool used for Recessing a Bushing in Automatic Chucking and Turning Machine
Fig. 39. Flexible Boring Tool used for Recessinga Bushing in Automatic Chucking and Turning 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 thebushing, so far as the setting of the tool is concerned, is merely a repetition of the facing operation at the first position of the turret. The recessing tool is next set. This tool, which is shown diagrammatically inFig. 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.
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 wheelD,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 pinMis 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 handleKbeing 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, handleJ,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 dogsNshould be clamped to the rim of diskDso as to change the spindle speed to the fast movement. This speed is continued until the last operation is completed, when asecond 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 handleKmay 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 passes 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.
Machining Flywheels in Potter & Johnston Automatic Chucking and Turning MachineFig. 40. Machining Flywheels in Potter & Johnston AutomaticChucking and Turning Machine
Fig. 40. Machining Flywheels in Potter & Johnston AutomaticChucking and Turning Machine
Turning Flywheel in Automatic Chucking and Turning Machine.—A typical operation on the Potter & Johnston automatic chucking and turning machine is illustrated inFig. 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 therear side of the turret when the latter is in the position shown in the illustration.) After the turret indexes, the hole is rough-bored by toolAand while this is being done, the outside of the rim is rough-turned by toolBheld in a special bracket attached to the turret. Both sides of the rim are also rough-faced by toolsCandDheld 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.
The turret again automatically recedes and indexes, thus locating barEand turning toolGin the working position. The hole is then finish-bored by toolEand the hub is finish-faced by bladeF; at the same time the rim is finish-turned by toolGand 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-barHin 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.
New Britain Multiple-spindle Automatic Chucking Machine of Single-head TypeFig. 41. New Britain Multiple-spindle AutomaticChucking Machine of Single-head Type
Fig. 41. New Britain Multiple-spindle AutomaticChucking Machine of Single-head Type
Automatic Multiple-spindle Chucking Machine.—An example of the specialized machines now used for producing duplicate parts, is shown inFig. 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 turretAwhich holds each part in line with one of the spindles and automatically indexes, so that the work passes 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.
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 drumB. Cam strips are bolted to the outside of thisdrum and act directly against a roller attached to the yokeCwhich can be clamped in different positions on the spindleD, the position depending upon the length of the work. On the opposite end of the turret spindle is the indexing mechanismE. An automatically spring-operated latchFengages notches in the rim of the dividing wheel, thus accurately locating the turret. The turret is locked by a steadyrestG, 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.
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.
Detail View of New Britain Double-head Eight-spindle Machine, Boring, Reaming and Facing CastingsFig. 42. Detail View of New Britain Double-head Eight-spindleMachine, Boring, Reaming and Facing Castings
Fig. 42. Detail View of New Britain Double-head Eight-spindleMachine, Boring, Reaming and Facing Castings
Fig. 42shows 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 castingsEare 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 reamerAand the opposite end of the hub is rough-faced and counterbored by a tool in spindleA1. When the turret indexes, this same casting is reamed close to the finished size by reamerBand the left end of the hub is rough-faced by cutterF, while a tool in the opposite spindleB1finishes the counterboring and facing operation. At the third position, reamerCfinishes 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 spindleD. (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 illustrate, 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, assuming that it would be possible to employ several different machines? The answer to this question usually depends principally 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 doesnot 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 class is often done in machines of different types, in order to secure the most efficient results.
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 classes of work to the best advantage. The machine illustrated inFig. 1belongs 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 tableBeither 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-blocksT) 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-blocksTare inserted in tool-barsT1carried by saddlesSwhich are mounted on cross-railC. Each tool-head (consisting of a saddle and tool-bar) can be moved horizontally along cross-railC, and the tool-barsT1have a vertical movement. These movements can be effected either by hand or power.
Gisholt Vertical Boring and Turning MillFig. 1. Gisholt Vertical Boring and Turning Mill
Fig. 1. Gisholt Vertical Boring and Turning Mill
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 screwsHandH1, and the vertical feed for the tool-bars is obtained from the splined shaftsVandV1, 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 shaftsAandA1on 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 shaftsVor screwH, by a movable gear, which is placed on whichever shaft will give the desired direction of feed. The particular machine illustrated is so arranged that either the right or left screw or feed shaft can be engaged by simply shifting leversD1orD.
The amount of feed per revolution of the table is varied for each tool-head by feed-changing mechanismsFon 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 machineby shifting leverE, and this number is doubled by shifting leverG. 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 leverR, which is also used for engaging or disengaging the feeds. This machine is equipped with the dialsIandI1which 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 tableBis 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 leversJandKand the table can be started, stopped or rotated part of a revolution by leverLwhich 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-cranksN, and the tool slides can be moved vertically by turning shaftsVwith 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 leversM. 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 leverRand leverD. 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-railChas 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.
Small Boring and Turning Mill with Single Turret-headFig. 2. Small Boring and Turning Millwith Single Turret-head
Fig. 2. Small Boring and Turning Millwith Single Turret-head
All modern vertical boring mills of medium and large sizes are equipped with two tool-heads, as shown inFig. 1, because a great deal of work done on a machine of this type can have two surfaces machined simultaneously. On the other hand, smallmills of the type illustrated inFig. 2have a single head. The toolslide of this machine, instead of having a single tool-block, carries a five-sided turretTin which different tools can be mounted. These tools are shifted to the working position as they are needed, by loosening binder leverLand turning or “indexing” the turret. The turret is located and locked in any of its five positions by leverI, 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 principally 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 illustrated inFig. 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 quantities 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.