Chapter XXII: Milling Machinery and Milling Tools (1)

THE MILLING MACHINE.--The advantages of the milling machine lie first in its capacity to produce work as true and uniform as the wear of cutting edges will permit (which is of especial value in work having other than one continuous plane surface); second, in the number of cutting edges its tools will utilize in one tool or cutter; and third, in its adaptability to a very wide range of work, and in the fact that when the work and the cutters are once set the operator may turn out the best quality of work without requiring to be a skilled machinist.

The extended use of the milling machine, which is an especial feature of modern machine shop practice, is due, in a very large degree, to the solid emery wheel, which provides a simple method of sharpening the cutters without requiring them to be annealed and rehardened, it being found that annealing and rehardening reduces the cutting qualifications of the steel, and also impairs the truth of the cutting edges by reason of the warping or distortion that accompanies the hardening process. Rotary cutters are somewhat costly to make, but this is more than compensated for in the uniformity of their action, since in the case of the cutter the expense is merely that involved in forming the cutting edges with exactitude to shape; once shaped the cutter will produce a great quantity of work uniform in shape, whereas in the absence of such cutters each piece of work would require, to bring it to precise form, as much precision and skill as is required in shaping the cutter.

If a piece of work is shaped in a planing machine, the different steps, curves, or members must be cut or acted upon by the tool separately, and the dimensions must be measured individually, giving increased liability to error of measurement, and requiring a fine adjustment of the cutting tool for each step or member. Furthermore, neither a planing machine or any other machine tool can have in simultaneous cutting operation so great a length of cutting edge as is possible with a rotary cutter.

Again, in the planing machine each cut requires to be set individually, and cannot be so accurately gauged for its depth, whereas with a rotary cutter an error in this respect is impossible, because the diameters of the various steps on the cutter determine the depth of the respective cuts or steps in the work.

In a milling machine the cut is carried continuously from its commencement to its end, whereas in a shaping or planing machine the tool does not usually cut during the back or return stroke. In either of these machines, therefore, the operator's skill is required as much in measuring the work, setting the tools feeds, &c., as in shaping the tools, whereas in the milling machine all the skill required lies in the chucking and adjustment of the work to the cutter, rather than in operating the machine, which may therefore be operated by comparatively unskilled labor.

The multiplicity of cutting edges on a rotary cutter so increases its durability, and the intervals at which it must be sharpened are so prolonged, that, with the aid of the present improved cutter grinding machines, one tool maker can make and keep in order the cutters for many machines.

The speed at which milling cutters are run varies very widely in the practice in different workshops. Thus upon cast iron, cutting speeds of 15 circumferential feet per minute will be employed upon the same class of work that in another shop would be done at a cutting speed of as high as fifty feet per minute. With the quick speeds, however, lighter feeds are employed. As the teeth of milling cutters are in cutting action throughout but a small portion of a revolution, they have ample time to cool, and may be freely supplied with oil, which enables them to be used at a higher rate of cutting speed than would otherwise be the case. Yet another element of importance in this connection is that when the cut is once started on a plain cutter, the cutting edges do not meet the surface skin of the metal, this skin always being hard and destructive to the cutting edges.

The simplest form in which the milling machine appears is termed the hand milling machine, and an example of this is shown in Fig. 1878. This machine consists of a head carrying a live spindle which drives the cutting tools, which latter are called cutters or mills. The front of the head is provided with a vertical slideway for the knee or bracket that carries an upper compound slide upon which the work-holding devices or chucks are held. The work is fed to the revolving cutter by the two levers shown, the end one of which is for the vertical and the other for the horizontal motion, which is in a direction at a right angle to the live spindle axis.

In other forms of the hand milling machine the live spindle is capable of end motion by a lever.

In Fig. 1878_a_ is shown Messrs. Brown and Sharpe's _plain_ milling machine, or in other words a milling machine having but one feed motion, and therefore suitable for such work only as may be performed by feeding the work in a straight line under the cutter, the line of feed motion being at a right angle to the axis of the cutter spindle.

Machines of this class are capable of taking heavy cuts because the construction admits of great rigidity of the parts, there being but one slideway, and therefore but one place in the machine in which the rigidity is impaired by the necessity for a sliding surface.

The construction of this machine is as follows: The head A which carries the cutter spindle is pivoted at C to a stiff and solid projection on the frame F, and means are provided to solidly clamp the two together.

A bracket B supports the outer end of the head; at its upper end B is split so that by means of a bolt it may firmly clamp the cylindrical end of A, which carries the dead centre piece D. The two lower ends of B are bolted to the frame F.

The work table T is gibbed to slideways in F, and is provided with suitable automatic feed and stop motion, and of course with a hand feed also.

To adjust the height of the cutter, the lower ends of B are released from F and the head A is swung on its centre C.

It is obvious that a machine of this class is suitable for cases where a large quantity of work of one kind is to be done and frequent changes of the adjustments are not required, and that for such work the solidity of the construction and the convenience of having all the handles employed in operating the machine accessible from one position are desirable elements obtained by a very simple construction.

Fig. 1879 represents Pratt & Whitney's _power_ milling machine. The cone and live spindle are here carried in boxes carried in vertical slideways in the headstock, so as to be adjustable in height from the work table, and is provided with a footstock for supporting the outer end of the live spindle, which is necessary in all heavy milling. The carriage is adjustable along the bed, being operated by a screw whose operating hand wheel is shown at the left-hand end of the bed.

The automatic feed is obtained as follows: The large gear on the right of the main driving cone operates a pinion driving a small four-step cone connected by belt to the cone below, which, through the medium of a pair of spur-gears, drives the feed rod, on which is seen a long worm engaging a worm-wheel which drives the feed screw. A suitable stop motion is provided.

What is termed a universal milling machine is one possessing the capacity to cut spiral grooves on either taper or parallel work, and is capable of cutting the teeth of spur and bevel-gears or similar work other than that which can be held in an ordinary vice. These features may be given to a machine by devices forming virtually an integral part of the machine, or by providing the machine with separate devices which are attachable to the work table.

In Fig. 1880 is represented a small size universal milling machine, in which A is the frame that affords journal bearing to the live spindle, in the coned mouth _a_ of which the mandrel carrying the rotary cutter is fitted, means being afforded for taking up the wear of the live spindle journal and bearings. B is the cone pulley for driving _a_. Upon the front face of A is a vertical slide upon which may be traversed the knee or table C, which by being raised, regulates the depth to which the cutters enter the work. To operate C the vertical screw _b_ is provided, it being operated (by bevel-gears) from a horizontal shaft whose handle end is shown at _c_.

The nut for elevating screw _b_ is formed by a projecting lug from or on the main frame A. To enable C to be raised to a definite height so that the cutters shall enter successive pieces of work to an equal depth, a stop motion is provided in the rod _d_, which passes through a plain hole in the lug on A that forms a nut for _b_. Rod _d_ is threaded and is provided with a nut and chuck nut whose location on the length of the rod determines the height to which C can be raised, which ceases when the faces of the nuts meet the face of the projecting lug.

The upper surface of C is provided with a slide on which is a slider D, which, by means of a feed screw whose handle end is shown at _e_, may be traversed in a line parallel to the axial line of the live spindle or arbor, as it is more often termed, this motion being employed to set the width of the work in the necessary position with relation to the rotary cutters. To D is attached E, which is pivoted at its centre so as to be capable of swinging horizontally, means being provided to fasten it to D in its adjusted position. This is necessary to enable the line of traverse of the work to be at other than a right angle to the axial line of the cutter spindle when such is desired, as in the case of cutting spirals; E serves as a guide to the carriage F, the latter being operated endwise by means of a screw whose handle is shown at _e´´_, the nut being attached to E, handle _e´´_ being to traverse E by hand. To feed F automatically gear-wheel _f_ is attached to the other end of the same screw, this automatic feed being actuated as follows:--

At the rear end of the live spindle is a three-stepped cone pulley attached by belt to cone pulley G, which connects by rod to and drives gear _f_. The construction of the rod is so designed as to transmit the rotary motion from G to F without requiring any adjustment of parts when C is raised or lowered or _f_ traversed back or forth, which is accomplished as follows:--

At _g_ _g_ are two universal joints attached respectively to G and F, and to two shafts which are telescoped one within the other. The inner rod is splined to receive a feather in the outer. The rotary motion is communicated from G to the universal joint, through that joint to the outer or enveloping shaft which drives the inner shaft, the latter driving a universal joint which drives _f_, the inner shaft passing freely within the outer or sliding out from it (while the rotary motion is continuing) to suit the varying distance from and position of _f_ with relation to G. This automatic feed motion may be adjusted to cease at any point in the traverse of E by a stop and lever provided for the purpose, so that if an attendant operates more than one machine, or if the feed require to be carried a definite distance, it will stop automatically when that point has been reached.

The carriage F may carry various chucks or attachments to suit the nature of the work. As shown in the cut it carries a tailblock I and head J, both fitting into a way provided in F so that they will be in line one with the other at whatever part in the length of F they may be set or fixed. Both I and J carry centres between which the work may be held, as in the case of lathe work. Part _j_ is pivoted to J so that it may be set at an angle if required, thus setting the centre, which fits in the hole at _h_, above the level of that in I, as may be necessary in milling taper work, the raising of _j_ answering to the setting over of the tailstock of a lathe for taper turning.

To enable the accurate milling of a polygon, the spindle _h_ may be rotated through any given portion of a circle by means of the index wheel at _i_, it being obvious that if a piece of work be traversed beneath the cutter, and _h_ be rotated a certain portion of a circle after each traverse, the work will be cut to a polygon having a number of sides answering to the portion of a circle through which _h_ is rotated after each traverse. Means are also provided to rotate _h_ while F is traversing beneath the cutter; hence when these two feed motions act simultaneously the path of the work beneath the cutter is a spiral, and the action of the cutter in the work is therefore spiral; hence spiral grooves may be cut or spiral projections left on the work, as may be determined by the shape of the cutters. K is a chuck that may be connected to _h_ to drive the work, and H a work-holding vice, that may be used instead upon F in place of heads I J.

The countershaft shown at the foot of the machine has two loose pulleys and a tight one between them, this being necessary because, in cutting spiral work, the work must rotate while on the back traverse as well as on the forward one, hence a crossed as well as an open belt is necessary.

Fig. 1881 represents a large Brown & Sharp universal milling machine, in which the cone spindle is provided with back gear, and a supporting arm is also provided for the outer end of the cutter arbor. The feed motions for this machine correspond to those already described for the smaller one, Fig. 1880, the construction of the important parts being shown in the following figures.

The construction of the bearings for the cutter driving spindle of the machine is as in Figs. 1882 and 1883. A is the spindle having a double cone to fit corresponding cones in the sleeve B, the fit of one to the other being adjusted by means of the nut C, which is threaded upon A. The mouth of A is coned to receive the arbors or mandrels for driving the mills or cutters. At the back bearing, Fig. 1883, the journal A´, and bore of the sleeve B´, is parallel, this sleeve being split at the top so that when it is (by means of nut D) drawn within the head E its coned exterior will cause it to close to a proper fit upon A´, by which means the wear of the parts may be taken up as they become perceptible.

The head J, Fig. 1880, is used (in connection with the foot block I) to suspend or hold work by or between centres, its centre fitting into the spindle at _h_, which is capable of being revolved continuously (to enable the cutting of spirals), by means of change gears, and intermittently through a given part of a circle by means of the index wheel _i_. The block _j_ carrying the spindle is also capable of elevation for conical or taper work, two examples of such uses being shown in Figs. 1884 and 1885, in which C is the cutter and W the work.

Fig. 1886 is a sectional view in a vertical plane through the centre of the head, and showing the construction of the spindle and the means of elevating the block _j_; _h_ is the spindle having journal bearing in _j_, and secured from end motion by the cone at _a_ and the nut _b_; its bore is coned at the front end to receive the arbor C carrying the centre D, upon which is the piece E for driving the work dog, which is secured within E by the set-screw _f_. Fast upon spindle _h_ is a worm-wheel F made in two halves, which are secured together by the screws _g_. At G is the worm-wheel (for driving F) fast upon the shaft H´.

It is obvious that the block _j_ may be raised at its centre end upon H as a centre of motion, the worm F simply moving around upon G. At V is a bolt to lock _j_ to J, and thus secure it in its adjusted position. W W are lugs or blocks fitting into the slot in the work table, and serving to secure the head, being in line with the foot block (shown at 1 in Fig. 1880). A sleeve Z is used to cover the thread and protect it when a chuck is not used.

Fig. 1887 is an end view partly in section to show the construction of the worm shaft and the index plate. H is a sleeve upon which _j_ pivots, and H´ the worm shaft, which may be revolved by hand by the lever L, or automatically by means of the bevel-gear K, which connects with the train of change gears; these change gears being thrown out of operation when gear K (and therefore _h_) is not required to revolve automatically nor continuously. L is an arm for carrying the index pin _l_ for the index plate _i_. The pin _l_ is adjustable for radius from the centre of H (so as to come opposite to the necessary circle of holes on the plate _i_), the arm L being slotted to permit of this adjustment, and being secured in its adjusted position by the nut on the end of H´. Pin _l_ is pushed into the index holes by means of the spiral spring coiled around _l_ at _m_, which permits _l_ to be withdrawn from _i_ under an end pressure, but pushes it into _i_ when that pressure is released. To indicate the amount of rotation of _i_, without counting the number of holes, a sector N N´ is employed, it having two arms adjustable for their widths apart so as to embrace any given number of holes on the required circle. At R´ is a pin which is pulled forward and into holes provided in the plate _i_ to prevent its turning when using the lever L. N and N´ are held to the face of _i_ by the friction of the spring Q. A face view of index plate _i_ is shown in Fig. 1888, the lever L, Fig. 1887, being removed to expose N and N´.

The surface of the plate is provided with rings of holes marked respectively 20, 19, 18, &c., the holes in each ring or circle being equidistantly spaced.

The sector arms N and N´ may be opened apart or closed together so as to embrace any required number of holes in either of the circles. As shown in the cut they embrace one quarter of the circle of 20, there being five divisions between the holes S and _t_. The screw W secures them in their adjustment apart. Suppose that pin _l_ (Fig. 1887), is in S, and arm N´ is moved up against it, the arm N leaves _t_ open, and indicates that _t_ is the next hole for pin _l_, which is withdrawn from S, and lever L (Fig. 1887) is moved around until the pin will enter _t_, and the sector is then moved into the position shown in Fig. 1888A, indicating that hole _u_ is the next one for the pin. This obviates the necessity of counting the holes, and prevents liability to error in the counting. Three of these index plates are provided, each having different numbers of holes in the circles, and in the following tables are given those specially prepared for use in cutting the teeth of gear-wheels:

------+-------+------------++------+-------+------------
No. of| Index |No. of turns||No. of| Index |No. of turns
teeth.|circle.| of index. ||teeth.|circle.| of index.
------+-------+------------++------+-------+------------
2 | ANY | 20 || 35 | 49 | 1-7/49
3 | 39 | 13-13/39 || 36 | 27 | 1-3/27
4 | ANY | 10 || 37 | 37 | 1-3/37
5 | " | 8 || 38 | 19 | 1-1/19
6 | 39 | 6-26/39 || 39 | 39 | 1-1/39
7 | 49 | 5-35/49 || 40 | ANY | 1
8 | ANY | 5 || 41 | 41 | 40/41
9 | 27 | 4-12/27 || 42 | 21 | 20/21
10 | ANY | 4 || 43 | 43 | 40/43
11 | 33 | 3-21/33 || 44 | 33 | 30/33
12 | 39 | 3-13/39 || 45 | 27 | 24/27
13 | 39 | 3-3/39 || 46 | 23 | 20/23
14 | 49 | 2-42/49 || 47 | 47 | 04/47
15 | 39 | 2-26/39 || 48 | 18 | 15/18
16 | 20 | 2-10/20 || 49 | 49 | 20/49
17 | 17 | 2-6/17 || 50 | 20 | 16/20
18 | 27 | 2-6/27 || 52 | 39 | 30/39
19 | 19 | 2-2/19 || 54 | 27 | 20/27
20 | ANY | 2 || 55 | 33 | 24/33
21 | 21 | 1-19/21 || 56 | 49 | 35/49
22 | 33 | 1-27/37 || 58 | 29 | 20/29
23 | 23 | 1-17/23 || 60 | 39 | 26/39
24 | 39 | 1-26/39 || 62 | 31 | 20/31
25 | 20 | 1-12/20 || 64 | 16 | 10/16
26 | 39 | 1-21/39 || 65 | 39 | 24/39
27 | 27 | 1-13/27 || 66 | 33 | 20/33
28 | 49 | 1-21/49 || 68 | 17 | 10/17
29 | 29 | 1-11/29 || 70 | 49 | 28/49
30 | 39 | 1-13/39 || 72 | 27 | 15/27
31 | 31 | 1-9/31 || 74 | 37 | 20/37
32 | 20 | 1-5/20 || 75 | 15 | 8/15
33 | 33 | 1-7/33 || 76 | 19 | 10/19
34 | 17 | 1-3/17 || 78 | 39 | 20/39
------+-------+------------++------+-------+------------

------+-------+------------++------+-------+------------
No. of| Index |No. of turns||No. of| Index |No. of turns
teeth.|circle.| of index. ||teeth.|circle.| of index.
------+-------+------------++------+-------+------------
80 | 20 | 10/20 || 164 | 41 | 10/41
82 | 41 | 20/41 || 165 | 33 | 8/33
84 | 21 | 10/21 || 168 | 21 | 5/21
85 | 17 | 8/17 || 170 | 17 | 4/17
86 | 43 | 20/43 || 172 | 43 | 10/43
88 | 33 | 15/33 || 180 | 27 | 6/27
90 | 27 | 12/27 || 184 | 23 | 5/23
92 | 23 | 10/23 || 185 | 37 | 8/37
94 | 47 | 20/47 || 188 | 47 | 10/47
95 | 19 | 8/19 || 190 | 19 | 4/19
98 | 49 | 20/49 || 195 | 39 | 8/39
100 | 20 | 8/20 || 196 | 49 | 10/49
104 | 39 | 15/39 || 200 | 20 | 4/20
108 | 27 | 10/27 || 205 | 41 | 8/41
110 | 33 | 12/33 || 210 | 21 | 4/21
115 | 23 | 8/23 || 215 | 43 | 8/43
116 | 29 | 10/29 || 216 | 27 | 6/27
120 | 39 | 13/39 || 220 | 33 | 6/33
124 | 31 | 10/31 || 230 | 23 | 4/23
128 | 16 | 6/16 || 232 | 29 | 5/29
130 | 39 | 12/39 || 235 | 47 | 8/47
132 | 33 | 10/33 || 240 | 18 | 3/18
135 | 27 | 8/27 || 245 | 49 | 8/49
136 | 17 | 5/17 || 248 | 31 | 5/31
140 | 49 | 14/49 || 260 | 39 | 6/39
144 | 18 | 5/18 || 264 | 33 | 5/33
145 | 29 | 8/29 || 270 | 27 | 4/27
148 | 37 | 10/37 || 280 | 49 | 7/49
150 | 15 | 4/15 || 290 | 29 | 4/29
152 | 19 | 5/19 || 296 | 37 | 5/37
155 | 31 | 8/31 || 300 | 15 | 2/15
156 | 39 | 10/39 || 310 | 31 | 4/31
160 | 20 | 5/20 || 312 | 39 | 5/39
------+-------+------------++------+-------+------------

A plan view of one-half of the head is shown in Fig. 1889, the edge of J being graduated for a guide in elevating the head at an angle, at V is the bevel-gear for driving K, and at S is a pinion receiving motion from the change gears.

The feed motions for the traversing table (F, Fig. 1880) is shown in Figs. 1889, 1890, and 1891, _g_ represents the universal joint rotating continuously the spindle _a_, which provides journal bearing to bevel pinion _b_ and the clutch _c_, these two being fixed together; _d_ is a clutch which rotates with _a_, but is capable of a certain amount of end motion on or along _a_ to enable it to engage or disengage with its mate _c_. When _d_ engages with _c_ the rotary motion of _a_ is transmitted through _d_, _c_, _b_, to _f_, which actuates the feed screw A, while when _d_ is disengaged from _c_, it rotates, leaving _c_ _b_ _f_ idle. _d_ is operated to engage with or disengage from _c_, its hub is enveloped by the fork _e_, which is attached to rod _h_, which is provided with a recess to receive one end of the bell crank _l_, the other end of which lies in a recess in the rod _m_, to the end of which is connected the lever handle _n_, which is pivoted at O; hence operating _n_ laterally as denoted by the arrows, throws _d_ in or out of gear with _c_, according to the direction of motion, direction _p_ being that to throw it out of, and _q_ to throw it into gear or engagement. At _r_ is a stop that can be fixed at any adjusted position or desired location along the bed upon which the feed table or carriage (F, Fig. 1880) slides, so that when that carriage is being self-actuated it will traverse until the inner end of _n_ meets the stop, whereupon the stop will move _n_ and thereby disengage _d_ from _c_, causing the automatic feed to cease. All that is necessary, therefore, is to set _r_ in such a position along the bed that it will operate _n_ when the milling cutter has operated to the required distance along or over the work; _s_ is the stud arm that carries wheel _t_ to engage with and drive the pinions shown in Fig. 1889, and _u_ is the stud for carrying the wheels for giving the required changes of rotation to K, Fig. 1889, the wheels on _u_ receiving motion from a gear placed at the seat V on the feed screw A. The stud arm _s_ being slotted, can be moved forward, transmitting motion from the change wheels on _u_ to wheel S, Fig. 1890, causing the automatic spiral feed to actuate; or by moving _s_ outwards, this feed is thrown out of action, and either the hand feed of handle W or the self-acting feed traverse may be employed.

Thus the hand, and all the automatic feed motions are driven from the feed screw A, and each of the automatic feed motions may be started or stopped by operating the lever _n_, while the stop _r_ causes each of them to cease when the work has traversed to the required distance beneath the milling cutter.

Fig. 1892 represents an attachment to this machine to facilitate cutting the teeth of gears, which it does because its index plate operates the work-holding mandrel direct, and may, therefore, be set quicker. The base bolts to the machine table and the index head and tailblock are traversed in the base by means of the four-levered handle shown.

Figs. from 1893 to 1899 represent a universal milling machine. This machine is so constructed that all the features essential to a universal milling machine are obtained by means of attachments (each complete in itself) which may be removed, leaving the work table clear, and, therefore, serviceable for large work, or work which may be more conveniently held without the use of attachments.

The [T]-slots in the table are furnished to standard size, and are at right angles, so that the attachments will be held exactly parallel with, or at a right angle, as the case may be, to the live spindle of the machine; hence the machine will accomplish all the varied results required in the tool room or for machine work generally.

Thus for the cutting of spirals, a fixture capable of originating any spiral right or left hand, from 2 inches to 6 feet pitch, is provided. Two bolts secure it to the machine table, and when the job is finished it is removed. Similarly for the cutting of cams, an attachment fastened to the work table by three bolts is used, which cuts either cylinder or face cams of considerable size, and as conveniently as a machine built solely for cam cutting. A gear-cutting device is also applied in the same manner, as well as plain or universal work-holding centres.

The essential features of the machine are a standard A, Fig. 1894, with spreading base, carrying upon its top a driving cone B, which is fully back-geared like an engine lathe. The driving cone operates also the feed mechanism. Above the driving cone is an arch C, in which is inserted an arm D for supporting the outer end of the mill arbor when used for heavy work. Upon the face or front of the standard slides a knee E, which in its turn supports a carriage F, which traverses crosswise upon it and carries above it the work table, which is provided with an automatic feed at right angles with the movement of the carriage. These three movements, vertical, cross, and longitudinal, cover all that is usually required in a universal milling machine.

Coming to details we start with the spindle or arbor, the front end of which runs in bearings of bronze. These are made in two parts, tapering upon the outside and straight upon the inside, a corresponding taper hole to receive the spindle bearings being bored in the solid iron of the standard. A check nut upon each end of the bushing or bearing abuts against the end faces of the standard bearing, and by drawing the bushing or bearing through the taper hole in the standard, produces the exact required closeness of fit between the spindle journal and its bearing bore, and thus compensates for the wear of either the spindle journal or its bearing or bushing bore, the front check nut also providing a dust cap.

The back journal of the spindle runs in a bushing of considerable length. Upon the back end of the spindle is secured a train of feed gears G, the lower of which is upon a shaft that on its other end carries the first feed cone H. The corresponding feed cone I is fixed to the longer shaft J, carrying a worm (or tangent screw) K, which engages with the worm-gear L connected directly with the feed screw, for the longitudinal motion of the work table.

This whole feed work is shown fully in outline in Fig. 1894. The arm M that supports the two lower feed gears pivots upon the outboard end of the back bushing, hence its centre coincides with that of the spindle. At its lower end a projection inwards forms a hub upon which a second lug or arm N is pivoted. The lower end of this arm is bored out to receive the threaded end of a lug O with the bearing of the second feed cone I. This threaded end carries a milled or hand nut P, so that to tighten or loosen the feed belt a turn of the nut is sufficient, the effect being to increase or diminish the distance between the feed cones H and I. The front end of the feed rod is supported in a drop box Q, and is splined to allow the worm K to travel upon it. It will be seen, therefore, that the feed mechanism is undisturbed either by the vertical movement of the knee, or the cross motion of the carriage, or the longitudinal feed of the table. The feed gears are covered with a shield R, a part of which is shown broken away. The knee with its appendages is actuated vertically by means of a crank connected with bevel gearing at S, which moves a perpendicular screw T under the centre of the knee. Rotating with this crank-shaft is a finger U held by friction. This finger is in close proximity to a dial V graduated to thousandths of an inch, and as one revolution of the finger indicates 1/8 of an inch of elevation to the knee E, the ordinary subdivisions of an inch are obtained either with or without an inner circle of graduations on the dial. A similar dial upon the cross feed motion (not shown in the engraving) is also put on, which likewise reads to thousandths of an inch.

The feed of the work table is accomplished by means of a screw whose thread is in shape a half [V] and does not bear upon the bottom of the thread in the feed nut, which is in halves, with provision for closing up to compensate for wear, while check nuts on one end of the feed screw take up all end play.

The automatic feed is self-stopping (so as to enable one attendant to operate several machines) by means of the following construction:--

In the general view, Fig. 1893, there is seen a stop that is secured in the required position in the [T]-groove shown at X in the outline view, Fig. 1894, and when this stop meets the bell crank Y it unlatches it from a lug which is on the drop box Q, Fig. 1893, hence this box falls and with it that end of the worm shaft J, throwing it out of gear with the worm-wheel L, and therefore stopping the feed.

The attachments giving to this machine its universal qualifications are as follows:--

The rotary vice is shown on the work table in the general view, Fig. 1893; and requires but little description. Upon the underside of the base is a circular projection having beneath it a projection fitting into the [T]-slots in the work table. Two segmental slots in the base admit of a rotary movement of the vice within a range of 90°, and it is held to the table by two bolts. The crank or handle of the vice is made more convenient by means of two square holes that fit the end of the screw that actuates the movable jaw. Using the central hole allows the handle to clear the work table, but when the vice jaws need to be closed with considerable force the handle is shifted to the end or outer hole, thus doubling the leverage.

Fig. 1893.

Fig. 1894.]

THE UNIVERSAL HEAD AND BACK CENTRE.--This tool is used for making milling cutters either straight or angular, cutting small gears either spur or bevel, fluting taps or reamers, finishing nuts or bolt-heads, and a multitude of other jobs too numerous to particularise. The head consists, as seen in Fig. 1895, of a swinging block mounted centrally between the two upright sides or jaws of a base, and is clamped in any position by a set-screw on either side. The face of one side or jaw is laid out in degrees, and a finger or pointer on the block indicates its angle of elevation. On the front end of the spindle is secured a worm-wheel divided longitudinally, each half being used as a corrector (in the making) for the other half till all errors are eliminated. A dial is fixed upon the bushing through which passes the shaft that actuates the worm, and consequently revolves the worm-gear and the spindle. A pointer arm carrying a handle with a pointer and appendages is secured to the end of this shaft. Under it are the usual spaces for laying off or indicating the proper number of index holes for the required fraction of a circle the spindle is to be moved through. The spindle is hollow and has a screw on the outer end for taking a chuck or face plate. It has a taper hole for receiving the proper centre, which carries a lug for holding the dog used when the work to be finished is held between centres. Three index dials, which are made interchangeable, provide for most divisions except a few prime numbers to 360.

To prevent or take up lost motion between the worm and the worm-gear the entire bracket carrying the worm and indexing mechanism is made adjustable as follows:--

Through the base of the bracket thread two sleeves whose ends abut against the top of the block, and therefore determine the engagement of the worm with the worm-wheel. Through these sleeves pass the bolts which thread into the block and lock the bracket in its adjusted position. A simple screw bolts the back end of the bracket. The degree of fit between the worm and the wheel may be very sensitively made by revolving the worm spindle by hand.

The block carrying the back centre has some peculiar features, which enable it to be set in line with the axis of the work, whether the latter be parallel or taper, so as to suit the elevation or depression of the head, and enable the centre to fill the countersink of work held on centres, keeping it central and avoiding wear to one side. It consists of a block held between two uprights or jaws, and clamped thereto by two screw bolts. The block is slotted entirely through from side to side, the front slot being only wide enough to receive the bolt and making a changeable centre for the block to partially rotate upon. The rear slot is wider and is a segment of a circle. The screw bolts being slackened the back centre is raised, lowered, or tilted to any required position to bring the centre in line with the work axis, and is then clamped in place. One bolt holds this part of the machine to the work table. The centre is adjusted to place in the end of the work in the ordinary way, with a hand nut, &c.

For gear cutting, the universal head is enlarged and somewhat modified in design, as is shown in Fig. 1896, the worm and worm-wheel being much larger in diameter and exceedingly accurate by the following method having been adopted to test them: Two cast-iron disks were placed side by side on an arbor or mandrel held between the centres, and lines of division were marked across the edges of both of them (the index plate, of course, being used for the division). The disks were then separated and one of them moved and the lines of division again compared with a microscope, and no sensible errors were apparent.

The provisions for taking up the wear of the worm and its bearings, and of the worm and its wheel, are as follows: The worm-shaft runs in compensating bearings of phosphor bronze, and the bracket carrying the worm-shaft is adjustable towards the worm-wheel by the means already described for the ordinary universal head, and this head is said to be capable of making divisions as fine as one minute of an arc, or dividing the circle into 21,600 parts.

The employment of a worm and a worm-wheel necessitates that the index pointer arm be given a certain number of revolutions, in order to move the spindle the requisite amount for all divisions except those equal in number to the number of teeth contained in the worm-wheel, and to avoid any mistake in counting the number of revolutions of this index pointer arm the following device is employed: On the worm shaft is a pin, and to the right of the index plate is a dial plate which is clearly shown in the engraving. The circumference of the latter is cut with ratchet teeth, and the length of the pin on the worm-shaft is such that at each revolution it moves one tooth of the dial plate. In front of the dial plate is a fixed pointer, and as the face of the ratchet wheel is graduated and marked 1, 2, 3, &c., it is obvious that the pointer shows how many revolutions the dial plate, and therefore the worm shaft, has made. After the requisite number has been made and the index pin has been set in the index wheel, the small lever, shown on the right of the dial plate, is moved and a spring brings the dial plate back so that its zero number comes back to the pointer ready to count the number of revolutions when the worm-shaft is revolved for the next division or movement of the worm and wheel. For this head there are three index plates drilled with 23 circles of holes, making, in combination with the worm and wheel, all divisions up to 90, all even divisions up to 180, with most of the other divisions between 90 and 180, or 135 divisions and multiples of these divisions up to 16,200. The index plates are interchangeable, and additional ones for other divisions may obviously be added.

The device for cutting spirals as arranged for hand feeding is shown in Fig. 1897, while in Fig. 1898 it is shown arranged for automatic feeding, and is shown in position on the machine.

Referring to Fig. 1897 the hand wheel operates a worm engaging with a worm-wheel on the shaft of the largest gear shown in the engraving. From this gear motion is conveyed through intermediate wheels to the pinion on the same shaft as the first bevel-gear, which obviously drives the bevel-gear shown on the end of the head. The back face of this latter gear is provided with index holes, and the usual index arm and pin are provided.

The change gears provided for this device are sufficient to cut twelve different pitches, ranging from one turn in 2 inches to one turn in 6 feet. Obviously right or left-hand spirals are produced according to the direction of revolution of the hand wheel.

In the general view, Fig. 1898, the device is placed upon a box bolted to the work table, and obtains its automatic feed through the medium of the worm for the table feed.

The cam-cutting attachment, Fig. 1899, consists of a base bolted to the machine table and adjustable to any required position thereon. This base has a slide way in which a gibbed slide carrying a head is free to travel longitudinally. The pattern or former cam and the work are carried on the live spindle of the head, and the former cam is supported by circumferential contact with a roll carried on the vertical bracket shown on the right of the engraving. As shown, the device is arranged for cutting face cams, the cam-holding spindle being placed in line with the machine spindle. All that is necessary for cutting _cylinder_ cams is to set the device with its spindle at a right angle to the machine spindle and move the supporting bracket so that its roller will meet the perimeter of the former cam. In either case the slide carrying the head is pulled forward by weights suspended over the wheel shown on the end of the base, and the feed is put on by revolving the spindle by means of the worm and worm-wheel shown in the engraving, the ordinary crank handle of the machine fitting the worm shaft.

A hand feed for cam cutters is preferable to the automatic feed, because in turning corners or curves the rate of the feed requires to be reduced in order to obtain smooth work.

Fig. 1900 represents a universal milling machine. The live spindle head is fitted to a horizontal slide on the top of the main frame, and may therefore be moved on that slideway to adjust the cutters to the work, the motion being effected by a pinion operating a rack on the underside of the head, as shown in Fig. 1901, which is a sectional view of the machine.

Fig. 1898.

Fig. 1900.]

At the handle end of the pinion shaft there is provided a dial (which is seen in the general view of the machine) having an outer circle graduated to sixty-fourths of an inch, and an inner one graduated to fortieths of an inch. The driving shaft is at a right angle to the live spindle, and drives it by means of a hardened steel worm operating a bronze worm-wheel fast on the live spindle, and which runs in a trough of oil to provide ample lubrication.

The spindle is hollow and has tapered journals. The arm for supporting the outer end of the cutter arbor is cylindrical, and fits to a bore provided in the top of the frame of the head, which is split and has two binding screws. When these screws are loosened the arm may be readily adjusted for position, while when they are screwed up they lock the arm in its adjusted position. By this means the arm only projects out as far as the particular work in hand requires.

The knee for carrying the work table and chucking devices terminates at its top in a circular box cast open on top. This box is covered with a circular cap, in the upper face of which are the slideways or guides for the work table. The cap is recessed into the box so as to be kept central, and is fastened therein by an expanding ring operated by a single stud which projects through the walls of the box. This ring has a [V]-shaped groove on its periphery, which in expanding closes over corresponding bevelled ledges on the inside of both the cap and the box. The edge of the cap is graduated for cutting spirals.

By this arrangement the table can be set to move at any required angle with the live spindle and quickly clamped in position, while the ring being of larger diameter and bearing evenly around the entire circle, the cap is rigidly held. In this box, securely protected from the cuttings or dirt, is a large worm-gear secured to a short vertical shaft, on the upper end of which is a pinion projecting through the cap and engaging with a rack upon the underneath side or face of the work table. This shaft also carries a bevel-pinion which meshes with a pinion on the end of the short shaft seen projecting through the front of the box and provided with a hand crank, the hand lever shown behind this crank being for securing or releasing the cap to or from the box. The gearing is so arranged that one revolution of the hand crank traverses the work table a distance of 2 inches, thus providing for the rapid motion of the table to expedite putting in and taking out the work.

The knee is operated vertically by a pair of bevel-gears, the shaft for operating which is shown on the left-hand side of the knee. On this shaft is a pointer for an indexed dial, which has two graduated circles, the outer of which is divided so that each division corresponds to a knee motion of 1/32 of an inch, while the inner one denotes a knee motion of 1/1000 inch.

Automatic feed motion for the work table is provided as follows: The cone shaft projects through the live head and carries a leather-covered friction disk which drives a vertical shaft carried by a bracket hinged to the head. A small pulley splined on this shaft, and held at any point by a spring-pressed catch, bears against the leather-covered face of the disk, and it is obvious that the nearer to the centre of the disk the pulley is set the slower the latter will be revolved, and therefore the finer the feed will be, while the direction of revolution of the small pulley will be reversed if it be set on the upper half or above the centre of the disk, thus providing for reversing the direction of feed. By this arrangement both the rate and direction of the feed can be set without stopping the machine.

This vertical feed shaft carries a splined worm driving a worm-gear splined on a horizontal shaft which is carried by the knee, which has a projecting arm or bracket for carrying the back end of the shaft, so that the latter rises or falls with the knee. A worm on this horizontal shaft engages a large worm-wheel within the box and fast upon the short upright shaft, whose pinion engages the table rack and thus completes the feed motion.

It will be seen in the sectional view that the worm-wheel for the automatic feed is in one piece, with a smaller bevel-wheel engaging with a bevel-pinion for the hand feed.

A clutch joint near the centre of the horizontal shaft affords the means for putting the automatic feed either into or out of action.

The table can be fed its full length in either direction, and when placed so that one end will pass the main frame or column may be swung around parallel to the spindle, thus enabling the machine to be used as a boring mill for short holes, or by turning the table a half revolution work may be done on both sides of a piece at one chucking, thus insuring perfect parallelism.

The construction of the index head of this machine is as follows: Fig. 1902 represents it on a plate with a back centre and a centre rest, and Fig. 1903 represents the head elevated. The head is a hollow box, the outline of which is about two-thirds of a circle. The opening, in front or chord side, is surrounded by a flange, and bored out as large as permissible. This forms the front bearing of the spindle and face plate, which is cast in one piece. A rear and smaller bearing is provided on the circular part of the case. The end of the spindle projects through the case, and is held from coming out by a recessed nut and washer. The spindle also carries an accurately-divided steel gear of sixty teeth. This gear is made as large as will go through the opening in front, or about 6 inches in diameter. Directly under this gear the box is pierced from the side. In this opening is inserted a long bush, through which a steel worm engages with the gear. An index plate secured to the outer end of the bush, and an adjustable arm and index pin attached to the projecting end of the worm, complete the dividing mechanism. Substantial but delicate adjustments are provided for eliminating lost motion.

On the periphery of the case is turned a dovetail shoulder, which slides around in a corresponding groove in the quadrant-shaped base. The case is graduated on its edge, and may be clamped at any angle of elevation from 15 degrees below a horizontal line to a vertical position, being equally stable in all positions. The face plate is no farther from the bed in one position than another, and being seated to the case, and adapted to hold work directly on its face, forms a stiff and substantial device for cutting bevel-gears and other work requiring angular motion. The tail centre is also of a strong and substantial design.

An adjustable centre rest of novel design also accompanies the outfit, and an extra bed or table, with straps for securing it to the table of the machine. With the centres arranged on this bed the line of centres may be set at any angle with the sliding table, A sufficient number of index plates are provided to divide all numbers up to 100 and all even numbers to 200.