=HARDENING AND TEMPERING.=
=Purposes= 460
To resist wear 460
To increase elasticity 460
To provide a cutting edge 460
=Manufacturer's Temper= 460
=Blacksmith's Temper= 460
=Color Tempering= 460
=Practical Processes= 461 to 464
The muffle 461
Warping 461
Rapidity of reduction of temper 461
Brown and Sharpe's practice 461
Waltham Watch Co.'s practice 461
Pratt and Whitney Co.'s practice 461
Morse Twist Drill Co.'s practice 461
Outside hardening 462
Heating in fluxes 462
Monitor Sewing Machine Co.'s practice 462
Hardening saws 462
Drawing the temper 462
1. Lying in an open furnace 462
2. Stretched in a frame 462
3. Between dies 462
Stiffening saws 463
Tomlinson Carriage Spring Co.'s practice 463
Columbia Car Spring Co.'s practice 463
New Haven Clock Co.'s practice 464
APPENDIX.
=Part I.--Test Questions for Engineers= 467
=Part II.--Dictionary of Workshop Terms= 473
FULL-PAGE PLATES.
VOLUME II.
_Facing_
_Frontispiece._ COMPOUND MARINE ENGINE. TITLE PAGE
PLATE I. EXAMPLE OF MILLING MACHINE. 10
" II. EXAMPLES OF MILLING MACHINES. 12
" III. EXAMPLES OF MILLING MACHINES. 16
" IV. EMERY GRINDING MACHINERY. 45
" V. GRINDSTONE GRINDING. 54
" VI. FULL AUTOMATIC GEAR CUTTER. 55
" VII. GEAR CUTTING MACHINES. 56
" VIII. THE HAMMER AND ITS USES. 71
" IX. SCRAPERS AND SCRAPING. 97
" X. OIL-TESTING MACHINES. 153
" XI. TESTING PLANER BEDS AND TABLES. 180
" XII. EXAMPLES OF PULLEYS. 200
" XIII. THE ACTION OF SAW TEETH. 273
" XIV. EXAMPLE IN PATTERN WORK. 276
" XV. EXAMPLES IN STEAM HAMMER WORK. 232
" XVI. EXAMPLES IN HAND FORGING. 239
" XVII. FORGING UNDER THE HAMMER. 249
" XIX. DIMENSION SAWING MACHINE. 292
" XIX. RACK-FEED SAW BENCH. 302
" XX. PLANTATION SAW MILL. 305
" XXI. GAINING OR GROOVING MACHINE. 306
" XXII. BAND SAW WITH ADJUSTABLE FRAME. 311
" XXIII. BAND SAW MILL. 311
" XXIV. LOG CROSS-CUTTING MACHINE. 312
" XXV. HORIZONTAL SAW FRAME. 314
" XXVI. TRYING-UP MACHINE. 333
" XXVII. SANDING MACHINES. 348
" XXVIII. BOILER FOR STATIONARY ENGINES. 360
" XXIX. AMERICAN FREIGHT LOCOMOTIVE. 388
" XXX. AMERICAN PASSENGER LOCOMOTIVE. 390
" XXXI. LOCOMOTIVE LINK MOTION. 392
" XXXII. INJECTOR AS APPLIED TO A LOCOMOTIVE. 395
" XXXIII. LOCOMOTIVE AIR BRAKES. 396
" XXXIV. THE CORLISS VALVE GEAR. 425
" XXXV. STEAM FIRE ENGINE. 430
" XXXVI. COMPOUND MARINE ENGINE. 436
" XXXVII. TRIPLE EXPANSION MARINE ENGINE. 440
MODERN
MACHINE SHOP PRACTICE.
CHAPTER XXII.--MILLING MACHINERY AND MILLING TOOLS.
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.
[Illustration: Fig. 1878.]
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.
[Illustration: Fig. 1878_a_.]
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_.
[Illustration: Fig. 1879.]
[Illustration: Fig. 1880.]
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.
[Illustration: Fig. 1881.]
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.
[Illustration: Fig. 1882.]
[Illustration: Fig. 1883.]
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.
[Illustration: Fig. 1884.]
[Illustration: Fig. 1885.]
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.
[Illustration: Fig. 1886.]
[Illustration: Fig. 1887.]
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.
[Illustration: Fig. 1888.]
[Illustration: Fig. 1888_a_.]
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
------+-------+------------++------+-------+------------
[Illustration: Fig. 1889.]
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.
[Illustration: Fig. 1890.]
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.
[Illustration: Fig. 1891.]
[Illustration: Fig. 1892.]
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.
[Illustration: _VOL. II._ =EXAMPLE OF MILLING MACHINE.= _PLATE I._
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.
[Illustration: Fig. 1895.]
[Illustration: Fig. 1896.]
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.
[Illustration: Fig. 1897.]
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.
[Illustration: Fig. 1899.]
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.
[Illustration: _VOL. II._ =EXAMPLES OF MILLING MACHINES.= _PLATE II._
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.
[Illustration: Fig. 1901.]
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.
[Illustration: Fig. 1902.]
[Illustration: Fig. 1903.]
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.
Fig. 1904 represents a machine in which the base column and the head are
constructed upon the same design as that in Fig. 1900, but the circular
top and cap are replaced with a larger and heavier knee of rectangular
form, and the table is longer. A cross sectional view of the head is
shown in Fig. 1905. The bearings for the live spindle are solid bushes
slightly tapered, and are driven into the head from each end up to and
against the flanges.
The spindle is of tool steel 3-1/2 inches in diameter at the front
bearing, tapering uniformly 3/4 inch per foot to the back end. This
simple construction allows the spindle to be perfectly ground, and
accurately fitted to the boxes by scraping. After this is done the
spindle is withdrawn about the 1/100 part of an inch, and a flat babbitt
metal washer fitted to exactly the space between the shoulder on the
spindle and the front box. A check nut and sliding collar on the back
end holds the spindle in place. A perfectly uniform space for oil is
thus formed between the spindle and bearings. The worm-gear is forced
tightly on the taper spindle with a nut, and keyed to prevent turning.
The spindle has a hole 1-9/16 inches through its centre, tapering in
front to receive the arbor to 1-7/8 inches. The taper is made 1/2 inch
per foot, and for ordinary work is sufficient to prevent the arbor
turning, but for driving gangs or large mills an arbor is used having a
hexagon enlargement just outside the spindle. A cap to screw over the
end of the spindle, having a hexagon opening in it to fit the arbor,
completes a positive driver that has none of the objections to cutting a
mortise or keyway in the spindle or otherwise disfiguring it. This cap
protects the thread on the spindle, and may be readily removed for a
face plate or large facing mills.
[Illustration: Fig. 1904.]
[Illustration: Fig. 1905.]
The cone shaft and its bearings are made independent of the head. A long
sleeve, which is provided with a large flange, projects through cored
openings in the side of the head. The bosses around these openings are
faced off square and parallel, and a large flat ring threaded on the
end of the sleeve draws the flange against the opposite face. The large
end of the sleeve is counterbored to receive the worm, and is cut away
on the under side to allow the worm to drop into mesh with the gear. The
worm is feathered on the shaft, the thrust of the worm being taken in
one direction against the shoulder in the sleeve, and in the opposite
direction (the machine can be driven either right or left-handed)
against the end of a bush, which is screwed in the sleeve and forms one
bearing for the cone shaft. Friction washers are placed to form the
step, and all wear or lost motion can be removed by screwing in the
bearing, which, when adjusted, is prevented from turning by a small
set-screw. The cone-shaft bearings are babbitt lined, but the spindle
bearings are made of cast iron, in which steel scrap has been melted.
The worm-gear has 40 teeth, and the worm is triple threaded, thus making
a back gear equivalent to 40-3, or 13-1/3 to 1. As the sleeve does not
fit the openings in the head, the worm and gear may be readily adjusted
to each other at all times, and held firmly and squarely in place by
drawing the flange tight against the side of the head. Set-screws
through the head prevent accidental displacement of the sleeve after
being adjusted.
[Illustration: Fig. 1906.]
Fig. 1906 represents a double spindle milling machine. The second
spindle is for driving the finishing cutters, so that as the two
spindles are capable of independent adjustment, the work may be finished
at one feed traverse, thus avoiding the necessity of removing the work
or making special adjustments.
Fig. 1907 represents a milling machine for globe valves and other
similar work. Here there are two cutter-driving spindles, one on each
end of the bed, and the work is held vertically. It is provided with an
index wheel for milling squares, hexagons, or octagons, and the pen for
the index wheel is operated by treadle. The work is fed across the bed,
the chucking devices being carried on a slide rest. In the figure a
globe valve is shown chucked between two plugs or arbors fitting its
bore, but it is obvious that centres or other work-holding appliances
may be used to suit the kind of work.
Fig. 1908 represents an eighty-inch milling machine, the table of which
has longitudinal motion; and provision for vertical and crosswise
movements are made in the head which carries the driving mechanism.
The machine table sets low on a bed supported by four box legs, and is
actuated by a steel screw driven by a worm and worm-gear connected with
a pair of spur-gears. The gearing is outside the bed, and therefore
accessible, and is protected by a shield, as shown in cut. The
arrangement for belting to feed works is also shown too plainly to need
description. The head upon which the spindle carrier is mounted travels
in ways upon the bed, and is adjusted crosswise on it by means of a
screw connected with a hand wheel, partially shown at the left of
engraving. For convenience and ease in fine adjustment this wheel, and
also the wheel at top of machine, connected with the elevating screw,
are worked by a hand lever, the wheels having sockets in their periphery
for this purpose.
The carrier, upon which is mounted the driving spindle, is gibbed to the
head, and has a vertical range sufficient to allow work 18 inches high
to pass under centres. From this carrier projects a large arm for
outside centre support of mill spindle, intended for use on work where a
back stand is not admissible. There is, however, as may be seen, a back
stand or tailstock of a very solid character. The arm is readily
removable, when desired, or the tailstock can be slid off its seat if
required. In most cases, however, the arm need not be removed, the yoke
on it being swung up out of the way, leaving the centre of mill arbor
free to engage with that on the back stand. This combination provides
for operating on a wide range of work.
As shown in the engraving, the space between head and tailstock is about
24 inches, but if required the tailstock can be made to travel in line
with the head, and its support be extended to any distance desired.
The method of driving the spindle is simple and strong, and allows of
free adjustment of the spindle without disarrangement of the driving and
feed belts.
The cone, which is made for 3-1/2 inch belt, is mounted in a stirrup
which is pivoted to the bed, and the pinion which engages with the
driving gear on the spindle is held at correct distance by a connecting
yoke, and is driven by a feather.
The machine has longitudinal feed only, but where it is desired an
automatic feed motion can be applied to the elevating screw in the head,
giving feed in a vertical direction.
The table is arranged to be run back rapidly by power, by a device which
is not seen in the engraving. As the table weighs one ton, the relief to
the operator by this improvement is obvious.
All the operations of the machine are intended to be conducted from the
front side, without any change in the position of the operator. The feed
can be thrown out by hand at any moment by means of a rod which connects
with the latch shown in the front of the cut, and the power quick-return
applied; or the table can be run back by hand, and the feed thrown in by
a foot lever, which lifts the drop box shown in front of cut. Adjustable
dogs automatically drop the feed motion at any point.
The machine is massive in all its parts, and is intended for heavy
milling of any description, but more particularly for shafting,
railroad, or engineering shops, being specially adapted for key-seating
long and heavy shafting, finishing guide bars, connecting rods, &c.
Its weight is 7,500 pounds. The work table is 7 feet long by 20 inches
wide; length of longitudinal feed, 84 inches; distance between uprights,
24 inches. The cast-steel spindle is 4 inches in diameter, and the mill
arbor 2-1/2 inches diameter. Arm for outer centre support 5 inches
diameter at its smallest part.
[Illustration: Fig. 1909.]
[Illustration: _VOL. II._ =EXAMPLES OF MILLING MACHINES.= _PLATE III._
Fig. 1907.
Fig. 1908.]
MILLING CUTTERS OR MILLS.--The simplest form of milling cutter is that
shown in Fig. 1909, the teeth being equidistantly arranged upon the
circumference only. Its size is usually designated by its length, which
is termed the face. Thus a cutter having its teeth parallel to its axis
and an inch long would be said to have 1 inch face. Cutters of more than
about half an inch face usually, however, have their teeth cut spirally,
as in Fig. 1910; the degree of spiral is one turn in a length of 3 feet
for cutters between 2-1/4 and 4 inches in diameter. For cutters of less
than 2-1/4 the degree in the spiral is increased; thus for an inch
cutter, the degree is one turn in 15 inches, while for 6 inches one turn
in about 60 inches is used.
[Illustration: Fig. 1910.]
In the following table is given the sizes of cutters as made by one
company, the bores being 1 inch.
+---------+-----------------------++---------+-----------------------+
| Width of| || Width of| |
| face. | Diameter of cutter. || face. | Diameter of cutter. |
+---------+-------+-------+-------++---------+-------+-------+-------+
| inch. | inch. | inch. | inch. || inch. | inch. | inch. | inch. |
| 1/8 | 2-1/2 | 3 | 4 || 15/16 | 2-1/2 | 3 | 4 |
| 3/16 | 2-1/2 | 3 | 4 || 1 | 2-1/2 | 3 | 4 |
| 1/4 | 2-1/2 | 3 | 4 || 1-1/8 | 2-1/2 | 3 | 4 |
| 5/16 | 2-1/2 | 3 | 4 || 1-1/4 | 2-1/2 | 3 | 4 |
| 3/8 | 2-1/2 | 3 | 4 || 1-1/2 | 2-1/2 | 3 | 4 |
| 7/16 | 2-1/2 | 3 | 4 || 1-3/4 | 2-1/2 | 3 | 4 |
| 1/2 | 2-1/2 | 3 | 4 || 2 | 2-1/2 | 3 | 4 |
| 9/16 | 2-1/2 | 3 | 4 || 2-1/4 | 2-1/2 | 3 | 4 |
| 5/8 | 2-1/2 | 3 | 4 || 2-1/2 | 2-1/2 | 3 | 4 |
| 11/16 | 2-1/2 | 3 | 4 || 3 | 2-1/2 | 3 | 4 |
| 3/4 | 2-1/2 | 3 | 4 || 3-1/2 | 2-1/2 | 3 | 4 |
| 13/16 | 2-1/2 | 3 | 4 || 4 | 2-1/2 | 3 | 4 |
| 7/8 | 2-1/2 | 3 | 4 || | | | |
+---------+-------+-------+-------++---------+-------+-------+-------+
The keyways are semicircular, the key being composed of a piece of No.
25 Stubbs steel wire.
The following is a table of the sizes of milling cutters made by another
company.
+----------+------------+---------++----------+------------+---------+
| | | || | | |
| Width of | Diameter | Size of || Width of | Diameter | Size of |
| face. | of cutter. | hole. || face. | of cutter. | hole. |
+----------+------------+---------++----------+------------+---------+
| inch. | inch. | inch. || inch. | inch. | inch. |
| 1/8 | 2-1/4 | 1 || 3/4 | 2-7/8 | 1 |
| 3/16 | 2-1/4 | 1 || 7/8 | 2-7/8 | 1 |
| 1/4 | 2-1/2 | 1 || 1 | 2-1/2 | 1 |
| 5/16 | 2-1/2 | 1 || 1-1/4 | 2-1/2 | 1 |
| 3/8 | 2-5/8 | 1 || 1-1/2 | 2-1/2 | 1 |
| 7/16 | 2-5/8 | 1 || 1-3/4 | 2-1/2 | 1 |
| 1/2 | 2-3/4 | 1 || 2 | 2-1/2 | 1 |
| 9/16 | 2-3/4 | 1 || 2-1/2 | 2-1/2 | 1 |
| 5/8 | 2-3/4 | 1 || 3 | 2-1/2 | 1 |
| 11/16 | 2-7/8 | 1 || | | |
+----------+------------+---------++----------+------------+---------+
Cutters of 1 inch face and over have teeth of a spiral form.
The object of providing spiral teeth is to maintain a uniformity of
cutting duty at each instant of time.
Suppose, for example, that the teeth are parallel to the cutter axis,
when the cutter first meets the work the tooth will take its cut along
its full length at the same instant, causing in wide cuts a jump to the
work because of the spring of the various parts of the work-holding
devices, and of the cutter driving spindle; furthermore as the cutter
revolves the number of teeth in action upon the work varies. Thus in
Fig. 1912 it is seen that one tooth only is in action, but when the
cutter has revolved a little more there will be two teeth in action, as
shown in Fig. 1913. This variation causes a corresponding variation of
spring or give to the machine, producing a surface very slightly marked
by undulations. But if the teeth are cut spiral the cut begins at one
end of the tooth and proceeds gradually along it, thus avoiding violent
shock, and after the cut is fairly started across the work the length of
cutting edge in action is maintained uniform, producing smoother work,
especially in the case of wide surfaces and deep cuts.
[Illustration: Fig. 1911.]
[Illustration: Fig. 1912.]
[Illustration: Fig. 1913.]
When the cutter is required to cut on the sides of the work as well as
on its upper face it is termed a face cutter, and its side faces are
provided with teeth, as shown in Fig. 1914; and when these cutters are
arranged in pairs as in Fig. 1915, so as to cut in the side faces only
of the work D, they are termed twin or straddle mills, both being of the
same diameter.
[Illustration: Fig. 1914.]
In mills or cutters used in this way the cutting duty is excessive on
the outer corners of the teeth, which, therefore, rapidly dull; hence it
is usual to provide teeth on both sides of the cutter, as in Fig. 1916,
so that after having been used in the position shown in the engraving
until the teeth are dull the positions of cutters may be changed,
bringing the unused cutting edges into use.
[Illustration: Fig. 1915.]
Twin or heading cutters are right and left hand, a right-hand one being
that in which the teeth at the top of the wheel revolves towards the
right, while a left-hand one revolves (at the top) towards the left.
[Illustration: Fig. 1916.]
[Illustration: Fig. 1917.]
If the machine is belted so that it can be revolved in either direction,
both sides of the cutter may be utilised by taking the cutters off the
arbor, turning them around and then replacing them in their original
positions on the same. Thus in Fig. 1917 we have at A a left-hand cutter
that if reversed upon its arbor would be a right-hand one as at B, and
it is obvious that the direction of revolution must be in each case as
denoted by the arrows F G, which are in opposite directions. In this
case the direction of work feed must be reversed, the work for A feeding
in the direction of C, and that for B in the direction of D. It is to be
observed, however, that the cutter could not be reversed if it was
driven by an arbor that screwed upon the driving spindle of the milling
machine. For if the machine has a right-hand thread then the cutter must
revolve in the direction of G, and the work feed must be in that of C;
whereas if the machine spindle drives its chucks, arbors, &c., by a
left-hand thread, then the direction of cutter revolution must be as at
F, and that of work feed as at D. But if the cutters are upon an arbor
that is driven by a conical seat in the machine spindle, or by any other
means enabling the arbor to revolve in either direction without becoming
released from that spindle, then the cutter may be simply turned around
and the feed direction reversed, as already explained. The reason for
reversing the direction of feed when the direction of cutter revolution
is reversed is as follows:--
[Illustration: Fig. 1918.]
In Fig. 1918 A and B represent two pieces of work of which B is to be
fed in the direction of arrow C, so that the pressure of the cut tends
to force the work back from under the cutter, whereas in the case of the
work A, feeding in the direction of D, the teeth act to pull the work
beneath the cutter, which causes tooth breakage.
Suppose, for example, that in Fig. 1919 P is a piece of work fastened to
the table T, feeding in the direction of A, the cutter W revolving in
the direction of arrow B, N representing the feed nut operated by the
feed screw S. Now while the table is being pulled in the direction of A,
the sides C of the feed screw thread will bear against the sides of the
thread in the nut, and whatever amount of looseness there may be between
the threads of the screw and nut will in this case be on the sides D of
the threads. So soon, therefore, as the wheel meets the work P, it will
suddenly pull the work forward to the amount of the play or looseness on
the sides D of the threads, and this in addition to the feed given by
the rotating screw S, would cause the wheel to lock upon the work
surface.
[Illustration: Fig. 1919.]
In all milling operations, therefore, the work is fed against the cutter
as at B, in Fig. 1918, unless, in the case of twin mills, it is fed (as
at E and F in the same figure) in the middle of the cutters, in which
case it is preferable to present it as at F, so that the pressure of the
cut will tend to hold the work down to the table, and the table down
upon its guideways. This position of the work presents some advantages
for small work which will be explained hereafter.
[Illustration: Fig. 1920.]
Fig. 1920 represents angular cutters, the teeth being at an angle to the
cutter axis. These cutters are made right and left as at A and B in Fig.
1921, the teeth of A being cut in the opposite direction to those at B,
so as to be able to cut equal angles on the work when these angles lie
in opposite directions, as C and D in the figure. Furthermore these
cutters are sometimes screwed to their arbors, and can therefore be
revolved in one direction only, which prevents their being turned around
end for end, even though the machine be so belted as to be capable of
revolving its spindle in either direction.
[Illustration: Fig. 1921.]
The angular cutters shown in Fig. 1921 have their teeth arranged for a
Brainard milling machine, in which the live spindle has a right-hand
thread for driving the chucks, arbors, &c.; hence the direction of
cutter revolution, and the arrangement of the teeth are as in the
figure.
[Illustration: Fig. 1922.]
[Illustration: Fig. 1923.]
In Fig. 1922 are segments of two wheels, A and B (corresponding to A and
B in Fig. 1921), but with their teeth arranged for a Brown and Sharpe
milling machine, in which the machine spindle has a left-hand thread;
hence the direction of cutter revolution is reversed, as denoted by the
arrows in the two figures.
[Illustration: Fig. 1924.]
Fig. 1923 represents a round edge cutter; and it is obvious that the
curvature or roundness of the cutting edges may be made to suit the
nature of the work, whether the same be of regular or irregular form. In
cutters of this description it would be a difficult matter to resharpen
the teeth by grinding their backs, hence they are ground on the front
faces; and to maintain the form or profile of the cutting edges,
notwithstanding the grinding, we have a patent form of cutter, an
example of which is shown in the gear tooth cutter in Fig. 1924. The
backs of the teeth are of the same form throughout their entire length,
so that grinding away the front face to sharpen the cutting edge does
not alter the contour or shape of the cutting edge. This is of especial
advantage in cutters for gear teeth, and those for irregular forms,
Figs. 1925, 1926, and 1927 forming prominent examples.
[Illustration: Fig. 1925.]
End mills or shank cutters are formed as in Fig. 1928, the shank
sometimes being made parallel with a flat place at A, to receive the
set-screw pressure, and at others taper, the degree of taper being 1/2
inch per foot. The hole at the end facilitates both the cutting of the
tooth in the making and also the grinding. Shank cutters may be used to
cut their way into the work, with the teeth on the end face, and then
carry it along, bringing the circumferential teeth into operation; or
the end teeth may be used to carry the cut after the manner of a face
cutter.
[Illustration: Fig. 1926.]
[Illustration: Fig. 1927.]
Shank cutters are rarely made above an inch in diameter, and are largely
used for cutting grooves or recesses, and sometimes to dress out slots
or grooves that have been cast in the work, as in the case of the steam
and exhaust ports of steam engine cylinders. In work of this kind the
direction of the feed is of great importance and must be varied
according to the depth of cut taken on the respective sides of the
cutter. Suppose, for example, that the conditions are such as
illustrated in Fig. 1929, the cut being deepest on the side A of the
slot, and the cutter must be entered at the end of the slot and fed in
the direction of D, so that the pressure of the cut may tend to push the
cutter back, it being obvious that on the side B the cutter has a
tendency to walk or move forward too rapidly to its cut, and if the cut
was heaviest on that side it would do, this increasing the cut rapidly
and causing tooth breakage.
[Illustration: Fig. 1928.]
[Illustration: Fig. 1929.]
This tendency, however, is resisted by the pressure on the side A of the
slot, which acts, as already stated, to push the cutter back. In
starting the cutter therefore, it is necessary to do so at that end of
the slot that will cause the deepest cut to act in the direction to
retard the feed. Suppose, for example, that the heaviest or deepest cut,
instead of being on the side A of the slot, as in Fig. 1929, was on the
side B, and in that case it would be necessary to start the cut from the
other end of the slot as in Fig. 1930, the arrow C denoting the
direction of feed.
[Illustration: Fig. 1930.]
[Illustration: Fig. 1931.]
Similarly when a groove has been roughed out from the solid, and it is
determined to take a finishing cut, the direction of the feed for the
latter is of importance. Suppose, for example, a [T]-groove is to be
cut, and that a slot is first cut with a shank cutter as in Fig. 1931,
leaving a light finishing cut of, say, 3/64 inch to finish the neck to
the dotted lines A B, and entering to within 1/16 inch of the full depth
as denoted by line C. The enlarged part of the groove may then be cut
out, leaving about 3/64 inch at the top and bottom, D and E, the cutter
having a plain shank (as in Fig. 1933), whose diameter should just clear
the narrow part of the groove already roughed out. The work will then be
ready for the finishing cutter, formed as in Fig. 1932, whose teeth (on
both the shank and the enlarged end) should have a diameter of 3/32 less
than that of the finished slot. In taking the finishing cut this cutter
must be set first to cut the sides B E to finished size, the direction
of the feed being such that the pressure of the cut acts to push the
cutter back as already explained, and when the cut is finished on this
side the finishing cut may be put on the side A D, without traversing
the cutter back, or in other words the feed must be carried in the
opposite direction, so that the cutter will run under the cut and be
pushed back by it, so as to prevent it from running forward as explained
with reference to figure.
[Illustration: Fig. 1932.]
For ordinary work not requiring great truth, however, the first cutter,
Fig. 1931, may be made of the finished diameter, and be followed by a
cutter such as in Fig. 1933, also of the finished diameter.
[Illustration: Fig. 1933.[31]]
[31] Figs. 1928, 1931, 1932, 1933, are from an article by John J.
Grant, in _The American Machinist_.
When a shank-cutter is required to enter solid metal endways, as in the
case of cutting grooves around the circumferential surface of a
cylinder, it is necessary to drill a hole to admit the cutter, leaving a
light finishing cut for the diameter of the cutter, and sufficient in
the depth to let the end face of the cutter remove or square up the cone
seat left by the drill. Shank cutters may obviously be made taper, or
to any other required angle or curvature, Figs. 1934 and 1935 being
examples which can be used in situations where other cutters could not,
as for example on the arms or spokes of wheels.
[Illustration: Fig. 1934.[32]]
[32] Figs. 1934, 1935, 1936, are from articles by John J. Grant, in
_The American Machinist_.
Fig. 1936, from _The American Machinist_, represents an example of the
employment of shank cutters, the work being a handle for a lathe
cross-feed screw, and it is obvious that the double cornering cutter may
be used upon both edges, and the cut being carried around the hub by the
parallel part of the cutter; the whole of the work on the handle
including the boring, if the hole is cast in, may be done by the shank
cutter, the handle end being finished and the boring done first, the hub
being finished on an arbor.
[Illustration: Fig. 1935.]
Shank mills may obviously be made of various shapes; thus in Fig. 1937
is shown two applications of an end or shank mill, one for cutting a
dovetailed groove and the other an angular one. In the case of the
dovetail groove the cutter will work equally well, whether it be used on
straight or spiral grooves; but this is not the case with angular
grooves for reasons which are explained with reference to angular
cutters and spiral groove cutting.
[Illustration: Fig. 1936.]
Shank cutters are provided with finer teeth than ordinary cutters, the
following being the numbers of teeth commonly employed for the
respective diameters:--
Diameter of cutter 1/8 or 3/16 inch, number of teeth 6
" " 1/4 " " " 7
" " 3/8 " " " 8
" " 1/2 " " " 8
" " 5/8 " " " 10
" " 3/4 " " " 10
" " 7/8 " " " 12
" " 1 " " " 14
The front faces of the teeth are radial as in other cutters, the angle
of the back of the tooth being 40° for the smaller, 50° for the medium,
and 60° for an inch cutter.
[Illustration: Fig. 1937.]
Fly cutters are single-toothed cutters, or rather tools, that are
largely used by watchmakers for cutting their fine pitches of gear
wheels.
Fig. 1938 represents a fly cutter in place in its holder or arbor, its
front face D being in line with the axis C of the arbor.
[Illustration: Fig. 1938.]
Let it be required to make a fly cutter for a very fine pitch of gear
tooth, such as used for watches, and a template, shown greatly magnified
at T in Fig. 1939, is made to fill a space and one half of each of the
neighboring teeth. From this template a cutting tool is made, being
carefully brought to shape with an oil-stone slip and a magnifying
glass. This tool is used for the production of fly cutters, and may be
employed by either of the following methods:--
[Illustration: Fig. 1939.]
The piece of steel to form the cutter is fastened in an arbor back from
the centre, as at D in Fig. 1940, and is then cut to shape by the tool
before referred to. It is then set for use in the milling machine, or in
such other machine as it may be used in, in the position shown in Fig.
1938, its front face D being in line with the axis C of the arbor. The
change of position has the effect of giving the tool clearance, thus
enabling it to cut while being of the same shape throughout its whole
thickness; face D may be ground to resharpen the cutter without altering
the shape it will produce. It is this capacity to preserve its shape
that makes the fly cutter so useful as a milling machine tool, since it
obviates the necessity of making the more expensive milling cutters,
which, unless made on the principle of the Brown and Sharpe cutters, do
not preserve their shapes.
[Illustration: Fig. 1940.]
It is to be observed, however, that a fly cutter made as above does not
produce work to exactly correspond to the template it was made from,
because moving it from the position it was made in (Fig. 1938) to the
position it is used in (Fig. 1940) causes it to cut slightly shallower,
but does not affect its width.
[Illustration: Fig. 1941.]
Another method of cutting up a fly cutter by the tool made to the
template is shown in Fig. 1941. The blank cutter is placed at an angle
to an arbor axis, and is cut to shape by the tool. For use it is placed
in line with the arbor axis as in Fig. 1942, the change of position here
again giving clearance as shown by the dotted arcs, the inside ones
showing the arc the cutter revolved on when it was in the arbor in Fig.
1938. Here again, however, the change of position causes the fly cutter
to produce a shape slightly different from the template to which the
first tool was made, hence the best method is as follows:--
[Illustration: Fig. 1942.]
The blank is let into an arbor of small diameter, as in Fig. 1943, its
face D being in line with the arbor axis. It is then cut up with the
tool made from the template. For use it is set in a larger arbor, as in
Fig. 1944, the difference in its path of revolution giving it the
necessary clearance. Thus, in the figure the inner dotted arcs show the
path of revolution of the cutter when it was in the small arbor, and the
outer arc of the path in the large arbor. The front face can be ground
without altering the shapes; the cutter will produce this front face,
being kept in line with the arbor axis by grinding the body of the steel
as much as the front face is ground when it is resharpened. Curves or
irregular shapes may be readily produced and preserved by fly cutters.
[Illustration: Fig. 1943.]
[Illustration: Fig. 1944.]
It is obvious, however, that when the tool made to the original template
is worn out, another must be made, and to avoid this trouble and
preserve the original shape beyond possible error, we have recourse to
the following additional method:--
[Illustration: Fig. 1945.]
With the tool made from the template we may cut up a wheel, such as in
Fig. 1945, and this wheel we may use as a turning tool to cut up fly
cutters, the principle of the wheel cutter having been shown in
connection with lathe tools. It may here be pointed out, however, that
if a wheel or circular cutter, as it is termed, is to be used, we may
make the template, and the master tool we make from it, for one side of
a tooth only, and use the master tool to cut up one side only of the
corner of the circular cutter, as shown in Fig. 1945.
[Illustration: Fig. 1946.]
[Illustration: Fig. 1947.]
The method of using the circular cutter is illustrated in Fig. 1946, in
which H is a holder, whose end face P is level with the axis of the
cutter, which is held to the holder by a screw. The side face of the
holder is out of the vertical so as to give the cutter side clearance. A
second holder has its side face inclined in the opposite direction, thus
enabling the one edge of the circular cutter to be used as a right or as
a left-hand tool and insuring uniformity, because the same edge of the
circular cutter is used in both cases, so that if used for say a tool
for a gear tooth, both sides of the tool will be cut from the same side
of the circular cutter.
It is obvious that instead of having one continuous cutter, the
necessary breadth of cutter face may be obtained by means of two or more
cutters placed side by side. Thus to mill a piece of work two inches
wide we may use two cutters of an inch face each (both of course being
of equal diameter), or we may use one cutter, of 1-1/4 inch and another
of 3/4 inch face. It is preferable, however, to use two cutters of an
inch face each, and to set one beam left-hand and the other right-hand
spiral teeth, because spiral teeth have considerable tendency to draw
the machine spindle endways in its bearings, because the teeth
correspond to a certain extent to a screw, and the work to a nut. A
cutter with a left-hand spiral exerts end pressure tending to draw the
driving spindle out from its bearings, while a right-hand one tends to
push it within them; hence by making the two cutters of equal length and
of the same degree of spiral, the effect of one cutter offsets that of
the other. Furthermore, it is found that the tendency to chatter which
increases with an increase in the width of the work, is diminished by
using right and left spiral cutters side by side.
[Illustration: Fig. 1948.]
In order that the cutting edges of cutters placed side by side in this
way may be practically continuous so as not to leave a line on the
finished work, the teeth may be made to overlap in two ways as in Fig.
1948, both representing magnified portions of cutters. In the method
shown on the left of the figure the usefulness of either cutter to be
used singly is not impaired, all that is necessary to insure the
overlapping being to cut the keyways in different positions with
relation to the teeth; whereas on the left of the figure neither cutter
would be efficient if used singly, except upon work as narrow as the
narrowest part of the cutter. On the other hand, however, it affords
excellent facilities for grinding, since the two cutters may be ground
together, thus ensuring that they be of equal diameters except in so far
as may be influenced by the wear of the emery wheel, which is, however,
almost inappreciable even in cutters of considerable width of face. In
the method shown on the left there is the further advantage that as the
teeth are not in line the cutting action is more continuous and less
intermittent, the arrangement having in a modified degree the same
advantage as the spiral cutter.
[Illustration: Fig. 1949.]
In both methods some latitude is given to adjust the total width of face
by placing paper washers between the cutters. If the plan on the right
is employed the projections may occupy one-fourth of the circumference,
there being two projections and two depressions on one end of the
cutter. When cutters of different diameters and shapes are put together
side by side on the same arbor the operation is termed gang milling.
[Illustration: Fig. 1950.]
Thus, in Fig. 1949 is shown a sectional view of a gang of three mills or
cutters, A, B, and C, of which A and C are recessed to admit of the ends
of B passing within them. The heavy black line representing a paper
washer inserted to adjust the distance apart of A and C, it being
obvious that this gives a means of letting them together after their
side teeth at D and E have been ground. As shown in the figure, A has
teeth on one only of its sides, while C has them on both sides as well
as in its circumference, while all three are of different widths of
face. This would capacitate A only for the inside cutter, as in the
figure, while B would be serviceable only when there was a cutter on
each side of it; or if used singly, only when its face overlapped the
width of the work on each side. But C, being cut on each side, could be
used singly for grooving or recessing, or for plain milling, or in the
position of B or A in the figure; hence it is preferable in gang milling
for general purposes to provide teeth on both sides as well as on the
circumference of the mill or cutter. But if a gang of mills are to be
made for some special purpose, and used for no other, the teeth may be
provided on the sides or not, as the circumstances may require.
[Illustration: Fig. 1951.]
Suppose, for example, that steps, such as shown in Fig. 1950, were
required to be cut in a piece of brass work, and that, the work
requiring to be very true, a set of roughing and one of finishing
cutters be used, then the latter may be put together as in Fig. 1951,
there being eight separate cutters, and their ends being slightly
recessed but without teeth. Such cutters would wear a long time and may
be readily sharpened, and there being no side teeth, the widths of the
cutters, individually and collectively, would not be altered by the
grinding; hence no readjustment with washers would be necessary. The
tooth corners must, however, be kept sharp, for in proportion as they
get dull or blunt, the sides of the cutter wedge in the work, causing
friction and extra power to drive them as well as producing inferior
work.
[Illustration: Fig. 1952.]
Fig. 1952, which is from an article by John J. Grant, represents a gang
of cutters arranged to mill out the jaws and the top faces of a head for
a lathe; and it is obvious that a number of such heads may be set in
line and all milled exactly alike.
THE NUMBER OF TEETH IN MILLS OR CUTTERS.--The teeth of cutters must
obviously be spaced wide enough apart to admit of the emery wheel
grinding one tooth without touching the next one, and the front faces of
the teeth are always made in the plane of a line radiating from the axis
of the cutter.
In cutters up to 3 inches in diameter, it is good practice to provide 8
teeth per inch of diameter, while in cutters above that diameter the
spacing may be coarser, as follows:--
Diameter of cutter 6 inches, number of teeth in cutter 40
" " 7 " " " 45
" " 8 " " " 50
[Illustration: Fig. 1953.]
MILLING CUTTERS WITH INSERTED TEETH.--When it is required to use milling
cutters of a greater diameter than about 8 inches, it is preferable to
insert the teeth in a disk or head, so as to avoid the expense of making
solid cutters and the difficulty of hardening them, not merely because
of the risk of breakage in hardening them, but also on account of the
difficulty in obtaining the uniform degree of hardness or temper. The
requirements for the heads for inserted teeth are, that the teeth shall
be locked firmly in position without lost motion, and be easily set to
gauge, ease of insertion and of removal being of secondary
consideration, as such teeth should be ground in their places in the
head, and are therefore rarely removed. The manner in which these
requirements are attained in the Brainard heads are, as shown in Fig.
1953. A disk of wrought iron of suitable thickness and diameter is
turned and squared, then a circle of index holes corresponding to the
number of teeth required is drilled in its face; this circle of holes is
used to insure the accurate spacing of the dovetail seats for the teeth,
and to attain accuracy in grinding the teeth. All the teeth are a
driving fit, and being milled are, of course, interchangeable. In order
to obtain a larger number of teeth in a given size of head than could be
got into the face, only one-half of the teeth are dovetailed into the
periphery of the head and the other half into its face, but yet all the
teeth are effective for face cutting, the construction being as
follows:--
Between each pair of face teeth is a slit sleeve, which meets them and
has a taper base, through which passes a taper bolt having a nut on the
back face of the head. Tightening this nut expands the sleeve, thus
locking the pair of teeth in their dovetail grooves. The circumferential
teeth are each counter-based to receive a screw tapped in the head, and
are firmly locked thereby. This affords a simple and reliable means of
inserting and adjusting other teeth with the certainty that they will be
true with those already in use.
The large size of some of these heads makes it convenient and desirable
to grind them in their places on the machine, and for this purpose a
special grinder is made by the same company. This grinder sets upon the
machine table and has a point or pin for the index holes or the cutter
head; by this means the grinding may be made as accurate as in small
milling cutters.
The head shown in figure represents one that has been in use ten years,
its cutters having been renewed but once; it is 28 inches in diameter,
contains 84 teeth, and weighs 400 lbs.
Arbors for milling cutters may be driven in two ways. In the first the
shank is made taper to fit the taper bore of the live spindle. The
standard taper is 1/2 inch per foot of length. The keyway is
semicircular, as shown at G in Fig. 1954, the key consisting of a piece
of No. 25 Stubbs steel wire, which being of uniform diameter enables a
number of keys of different lengths to be easily obtained or made, and
the nut is usually cylindrical, having two flat sides, A.
Fig. 1955 (from _The American Machinist_) represents an arbor, having a
cone at A, so that the cutter bore being coned to correspond, the cutter
will run true, notwithstanding that it may not fit the stem B. It is
obvious, however, that the nut and washer must be made quite true or the
cutter will be thrown out of line with the arbor axis and therefore out
of true, and also that such an arbor is not suitable for cutters of a
less width of face than the length of the cone A.
[Illustration: Fig. 1954.]
[Illustration: Fig. 1955.]
[Illustration: Fig. 1956.]
Shank cutters that have parallel shanks as in Fig. 1928 should have
their sockets eased away on the upper half of the bore as denoted by the
dotted arc D in Fig. 1956, which will enable the cutter shanks to be
made the full size of the socket bore proper, and thus run true while
enabling their easy insertion and extraction from the socket. Or the
same thing may be accomplished by leaving the socket bore a true circle
fitting the cutter shanks in tight, and then easing away that half of
the circumference that is above the centre line C in the figure. It is
preferable, however, to ease away the bore of the socket, which entails
less work than easing away the shanks of all the cutters that fit to the
one socket. When the cutter is held in a socket of this kind it allows
it to be set further in or out, to suit the convenience of the work in
hand, which cannot be done when the cutter has a taper shank fitting
into the coned bore of the machine spindles.
[Illustration: Fig. 1957.]
It is obvious that when the cutter requires to pass within the work, or
cut its way, as in the case of milling out grooves, a nut cannot be
used; hence, inch cutters are driven by a key as usual, but secured by a
screw, as in Fig. 1957, which is from the pen of John J. Grant, in _The
American Machinist_.
[Illustration: Fig. 1958.]
[Illustration: Fig. 1959.]
In many cases it becomes a question whether it is better to do a piece
of work with plain mills, with an end mill, or with face mills, a common
hexagon nut forming an example. Thus, in Fig. 1958, we have a nut being
operated upon by a plain mill; in Fig. 1959 by an end mill, and in Fig.
1960 by a pair of twin face mills.
In the case of the plain mill, it is obvious that only one side of the
nut is operated upon at a time, and as the whole of the pressure of the
cut falls on one side of the work it acts to spring or bend the mandrel
or arbor used to hold the nut, and this spring is sufficient, if several
nuts are milled at once on the same arbor, to make the arbor bend and
cause the nuts in the middle to be thicker than those at the ends of the
arbor. In the case of hand-forged nuts in which there may be more metal
to take off some nuts or some sides of nuts than off others, the extra
spring due to an increased depth of cut will make a sensible difference
to the size the work is milled to. In the case of the end mill the
pressure of the cut falls in line with the arbor axis and downwards;
hence the arbor spring is less and does not affect the depth of the cut.
In the case of the face mills the pressure of the cut falls on both
sides of the work, and the spring is mainly endways of the nut arbor;
hence, it does not affect the depth of the cut nor the truth of the
work. Furthermore, in both the end and the face mills, the work will be
true notwithstanding that the cutter may not be quite true, because each
point of the work surface is passed over by every tooth in the cutter,
so that the work will be true whether the cutter runs true or not;
whereas in the plain mill or cutter each tooth does its individual and
independent proportion of finishing. This is shown in Figs. 1961 and
1962. In Fig. 1961 we have the plain mill, and it is obvious that the
tooth does the finishing on the vertical line B, that being the lowest
point in its revolution. After a tooth has passed that point the work in
feeding moves forward a certain distance before the next tooth comes
into action; hence to whatever amount a tooth is too high it leaves its
mark on the work in the form of a depression, or _vice versâ_, a low
tooth will leave a projection.
[Illustration: Fig. 1960.]
[Illustration: Fig. 1961.]
[Illustration: Fig. 1962.]
In Fig. 1962 we have a piece of work being operated on by a face mill,
and it is obvious that while the teeth perform cutting duty throughout
the distance A, yet after the work has fed past the line A it is met by
the cutter teeth during the whole time that the work is feeding a
distance equal to A on the other side; hence the prolonged action of the
teeth insures truth in the work. On the other hand, however, it is clear
that the work requires to feed this extra distance before it is
finished.
[Illustration: Fig. 1963.]
Suppose, however, that the cutter being dead true the cutting action
ceases on the centre line, and therefore exists through the distance A
only, and if we take a plain cutter of the same diameter as in Fig. 1963
we see that its period of feed only extends through the length B, and it
becomes apparent that to perform an equal amount of work the face cutter
is longer under feed, and therefore does less work in a given time than
the plain cutter, the difference equalling twice that between A and B in
the two figures, because it occurs at the beginning and at the end of
the cut.
There is, however, another question to be considered, inasmuch as that
the face cutter must necessarily be of larger diameter than the plain
one, because the work must necessarily pass beneath the washer (C, Fig.
1915), that is between the two cutters; hence the cutter is more
expensive to make.
[Illustration: Fig. 1964.]
We may in very short work overcome this objection by feeding the work,
as at K in Fig. 1964, the face L to be milled requiring to feed the
length of the teeth instead of the distance H in the figure. In the end
mill the amount of feed also is greater for a given length of finished
surface than it is in the plain cutter, as will be readily understood
from what has already been said with reference to face mills.
Face milling possesses the following points of advantage and
disadvantage, in addition to those already enumerated: If the work is
sprung by the pressure of the holding devices it is in a line with the
plane of motion of the teeth, hence the truth of the work is not
impaired. On the other hand, the teeth meet the scale or skin of the
work at each cut, whereas in a cylindrical cutter this only occurs when
the cutter first meets the work surface.
The strain of the cut has more tendency to lift the work table than in
the case of a cylindrical cutter. The work must be held by end pressure;
hence the chuck or holding jaws must be narrower than the work,
rendering necessary more work-holding devices. Since, however, both
sides of the work are simultaneously operated on, there is no liability
of error in parallelism from errors in the second chucking, as is the
case with plain cutters.
[Illustration: Fig. 1965.]
[Illustration: Fig. 1966.]
To cut [V]-shaped grooves in cylindrical work, when it is required that
one face or side of the groove shall be a radial line from the centre of
the work, two methods may be employed. First we may form the cutter, as
in Fig. 1965, the side B of the cutter being straight and the point of
the cutter being set over the centre of the work. The objection to this
is that the finished groove will have a projection or burr on the radial
side of the groove, as shown at D in the figure, entailing the extra
labor of filing or grinding, to remove it; furthermore, that face will
have fine scored marks upon it, as denoted by the arcs at C, these
scores showing very plainly if the cutter has any high teeth upon it,
and more especially in the case of cutting spirals, as will appear
presently. The reason of this is that the side B of the cutter being
straight or flat the whole of the teeth that are within the groove have
contact with the side C of the groove, that is to say, all the teeth
included in the angle E in the figure, because the teeth on the side A
tend, from the pressure of the cut to force the cutter over towards the
side C of the groove. The second method referred to, which is that
commonly adopted for cutting the flutes of tapes, reamers, milling
cutters, &c., is to form the cutter on the general principle illustrated
in Fig. 1966, and set it to one side of the centre of the work so that
one of its faces forms a radial line, as shown in the figure, the
distance to which it is set to one side depending upon the angle of its
cutting edge to the face of the cutter.
[Illustration: Fig. 1967.]
Fig. 1967 represents a common form of cutter of this class that is used
for cutting spiral grooves on milling cutters up to 3 inches in
diameter, which contain eight teeth per inch of diameter. The angle of
the teeth on B is 12° to the side face A of the cutter, and the angle of
the teeth at C is 40° to the face D.
The effect produced by making face B at an angle instead of leaving it
straight, or in other words, instead of cutting the teeth on the face A,
may be shown as follows:--
[Illustration: Fig. 1968.]
Suppose that in Fig. 1968 we have a sectional view taken through the
middle of the thickness of a cutter for a rectangular groove, the
circumferential surface being at a right angle to the side faces, and it
is evident that the teeth, at every point in their length across the
cutter, except at the extreme corner that meets the side faces as C,
will have contact with the seat of the groove while passing through the
angle F only (which is only one half of the angle E in Fig. 1965); or in
other words, each tooth will have contact with the seat of the groove as
soon as it passes the line G, which passes through the axis of the
cutter; whereas, when the teeth are parallel with the side of the
cutter, as was shown in Fig. 1965, the teeth continue to have contact
with the side walls of the groove after passing the line G.
By forming the cutter as in Fig. 1967, therefore, we confine the action
to the angle F, Fig. 1968, the teeth having contact with the walls of
the groove as soon as they pass the line G.
[Illustration: Fig. 1969.]
In cutting spiral grooves this is of increased importance, for the
following reasons: In Fig. 1969 we have a cutter shown in section, and
lying in a spiral groove. Now suppose a tooth to be in action at the
bottom of the groove, and therefore on the line G G, and during the time
that it moves from that line until it has moved above the level of the
top of the groove, the work will have performed some part of a
revolution in the direction of the arrow, and has therefore moved over
towards that side of the cutter; hence, if that side of the cutter had
teeth lying parallel, as shown at B in Fig. 1965, the walls of the
groove would be scored as at C in that figure, whereas by placing the
teeth at an angle to the side face, they recede from the walls after
passing line G, and therefore produce smoother work.
A cutter of this kind must, for cutting the teeth of cutters, be
accurately set to the work, and the depth of cut must be accurate in
order to cut the grooves so that one face shall stand on a radial line,
and the top of the teeth shall not be cut to a feather edge. If the
teeth were brought up to a sharp edge the width of the groove at the top
would be obtained with sufficient accuracy by dividing the circumference
of the work by the number of flutes or teeth the work is to contain, but
it is usual to enter the cutter sufficiently deep into the work to bring
the teeth tops up to not quite a sharp edge. The method of setting the
cutter is to mark on the end of the work a central line R, Fig. 1970,
and make the distance E in same figure equal to about one tenth the
diameter of the work.
[Illustration: Fig. 1970.]
[Illustration: Fig. 1971.]
Obviously the cutter is set on opposite sides of the work centre,
according to which side of the groove is to have the radial face. Thus
for example, in Fig. 1970, the cutter is set to the left of line R, the
radial face of the groove being on the left, while in Fig. 1971 the
cutter is set on the right of line R, because the radial face is on the
right hand side of it, the work consisting (in these examples) in
cutting up a right and a left-hand mill or cutter.
The acting cutter J may in both cases be used to cut either a right or a
left-hand flute, according to the direction in which the work W is
revolved, as it is fed beneath the cutter J.
[Illustration: Fig. 1972.]
In Fig. 1972 we have an example of cutting straight grooves or teeth,
with an angular cutter having one side straight, and it is seen that we
may use the operating or producing cutter in two ways: first, so that
the feed is horizontal, as at A, or vertical, as at B; the first
produces a right-hand, and the second a left-hand cutter, as is clearly
seen in the plan, or top view. The feeds must, however, be as denoted by
the respective arrows being carried upwards for B, so that the cutter
may run under the cut and avoid cutter breakage.
[Illustration: Fig. 1973.]
The number of grooves or flutes producible by an angular cutter depends
upon the depth of the groove and the width of land or tooth between the
grooves. Thus Fig. 1973 represents a cutter producing in one case four
and in the other eight flutes with the same form of cutter, the left
being for taps, and the right for reamers.
For cutting the teeth of cutters or mills above 3 inches in diameter,
the angles of the acting or producing cutter are changed from the 12°
and 40° shown in Fig. 1967, to 12° as before on one side, and a greater
number on the other; thus in the practice of one company it is changed
to 12° and 48°, the 12° giving the radial face as before, and the 48°
giving a stronger and less deep tooth, the deep tooth in the small
cutters being necessary to facilitate the grinding of the teeth to
sharpen them.
In cutting angular grooves in which the angle is greater on one side
than on the other of the groove, the direction of cutter revolution and
the end of the work at which the groove is started; or in other words,
the direction of the feed, is of importance, and it can be shown that
the feed should preferably be so arranged that the side of the groove
having the least angle to the side of the cutter should be the one to
move away from the cutter after passing the lowest point of cutter
revolution.
[Illustration: Fig. 1974.]
In Fig. 1974, for example, we have at R a cylinder with a right-hand
groove in it, whose side C, representing the face of a tooth, is
supposed to be a radial line from the cylinder axis, the side B
representing the back of a cutter tooth, being at an angle of 40°.
Now if the work revolves in the direction of arrow A, and the cut be
started at end G (as it must to cut a right-hand groove with the work
revolving as at A), then the side C of the groove will move over towards
and upon the side of the cutter for the reasons explained with reference
to Fig. 1969, and the teeth on this side being at the least angle to the
side of the cutter, do not clear the cut so well, the teeth doing some
cutting after passing their lowest point of revolution--or in other
words, after passing the line G in Fig. 1968. The effect of this is to
cause the cutter to drag, as it is termed, producing a less smooth
surface on that side (C) of the groove or tooth.
We may, however, for a right-hand groove revolve cylinder R, as denoted
by arrow E, and start the cut at end D. The result of this is that the
side C of the groove, as the roller revolves, moves away from the side
of the cutter, whose teeth therefore do no cutting after passing their
lowest point of revolution (G, Fig. 1968), and the dragging action is
therefore avoided, and the cut smoother on this which is the most
important side of the tooth, since it is the one possessing the cutting
edge. When "dragging" takes place the burr that was shown in Fig. 1965
at D, is formed, and must, as stated with reference to that figure, be
removed either by filing or grinding.
Obviously if the direction of cutter revolution and of feed is arranged
to cause side C to move away from the side of the cutter, then side B
will move over towards the other side of the cutter; but on account of
the cutter teeth on this side being at a greater angle to the side of
the cutter, they clear better, as was explained with reference to Fig.
1968, and the dragging effect caused by the revolving of the work is
therefore reduced.
[Illustration: Fig. 1975.]
We have now to examine the case of a left-hand groove, and in Fig. 1975
we have such a groove in a cylinder L. Let it be supposed that the
direction of its revolution is as denoted by arrow F, and if the cutter
is started at H (as it must be to cut a left-hand groove if the work
revolves as at F), then the side C moves over towards the cutter, and
the dragging or crowding action occurs on that side; whereas if the
direction of revolution is as at K, and the cutter starts at N and feeds
to H, then side B of the groove moves towards the cutter; hence face C
of the groove is cut the smoothest. Obviously then the direction of
cutter and work revolution and of feed, in cutting angular grooves in
which one angle of the cutter is at a greater degree of angle than the
other to the side of the cutter, should be so arranged that the work
revolves towards that side of the cutter on which its teeth have the
greater angle, whether the spiral be a right-hand or a left-hand one. In
cutting grooves not truly circular the same principle should be
observed.
[Illustration: Fig. 1976.]
In Fig. 1976, for example, it is better if the side B is the one that
moves towards the cutter, the direction of revolution being as denoted
by the arrow, whether the groove be a right-hand or left-hand
(supposing, of course, that the cutter starts from end E of the work).
Obviously, also, the greater the degree of spiral the more important
this is, because the work revolves faster in proportion to the rate of
feed, and therefore moves over towards the outer faster.
In cutting spirals it is necessary first to put on such change gears as
are required to revolve the work at the required speed for the given
spiral, and to then set the work at such an angle that the cutter will
be parallel to the groove it cuts, for if this latter is not the case
the groove will not be of the same shape as the cutter that produces it.
[Illustration: Fig. 1977.]
In Fig. 1977 we have a spiral so set, the centre of the cutter and of
the groove being in the line O O, and the work axis (which is also the
line in which the work feeds beneath the cutter) being on the line C C.
The degrees of angle between the centre of the cutter, or line O O, and
the axis of the work, or line C C, are the number of degrees it is
necessary to set the work over to bring the cutter and the groove
parallel, this number being shown to be 20 in the example.
[Illustration: Fig. 1978.]
To find this angle for any given case we have two elements: first, the
pitch of the spiral, or in other words, the length or distance in which
it makes one complete turn or revolution; and second, the circumference
of the work; for in a spiral of a given pitch the angle is greater in
proportion as the diameter is increased as may be seen in Fig. 1978, in
which the pitch of the spirals is that in Fig. 1977, while the angle is
obviously different.
To find the required angle for any given case we may adopt either of two
plans, of which the first is to divide the circumference of the work in
inches by the number of inches which the spiral takes to make one turn.
This gives us the tangent of angle of the spiral.
The second method of setting the work to cut a given spiral is to chuck
the work and put on the necessary change gears. The cutter is then set
to just touch the work and the machine is started, letting the work
traverse beneath the cutter just as though the work was set at the
required angle to the cutter:
When the cutter has arrived at the end of the work it will have marked
on it a line, as in Fig. 1979, this line representing the spiral it will
cut with those change gears, and all that remains to do is to swing the
work over so that this line is parallel with the face of the cutter, as
shown in Fig. 1980. If the diameter of the cutter is small we may
obviously secure greater accuracy by placing a straight-edge upon the
side of the cutter so as to have a greater length to sight by the eye in
bringing the line fair with the cutter. This being done it remains to
merely set the cutter in its required position with reference to the
work diameter.
If an error be made in setting the angle of the work to the cutter the
form of groove cut will not correspond to that of the cutter. This is
shown in Fig. 1981, in which the cutter being at an angle to the groove
the latter is wider than the cutter thickness, and it is obvious that by
this means different shapes of grooves may be produced by the same
cutter. In proportion, however, as the cutter is placed out of true the
cutting duty falls on the cutting edges on one side only of the cutter,
which is the leading side C in the figure, while the duty on the other
side, B, is correspondingly diminished.
[Illustration: Fig. 1979.]
[Illustration: Fig. 1980.]
[Illustration: Fig. 1981.]
The simplest method of holding work to be operated upon in the milling
machine is either between the centres or in the vice that is provided
with the machine. The principles involved in holding work in the vise so
as to keep it true and avoid springing it for milling machine work, are
the same as those already described with reference to shaping machine
vises.
In milling tapers the work, if held in centres, should be so held that
its axial line is in line with the axes of both centres, for the
following reasons:--
[Illustration: Fig. 1982.]
[Illustration: Fig. 1983.]
[Illustration: Fig. 1984.]
In Figs. 1982 and 1983 we have a piece of work in which the axes of the
centres and of the work are not in line, and it is clear that the horn
_d_ of the dog D will, in passing from the highest to the lowest point
in its revolution, move nearer to the axis of the work. Suppose, then,
that the driver E is moved a certain portion of a revolution with tail
_d_ at its highest point, and is then moved through the same portion of
a revolution with _d_ at its lowest point in its path of revolution, and
being at a greater distance or leverage when at the top than when at the
bottom it will revolve the work less. Or if the tail _d_ of the dog is
taper in thickness, then in moving endways in the driver E (as it does
when the work is revolved) it will revolve the work upon the centres.
Suppose, then, that the piece of work in the figures required to be
milled square in cross-section, and the sides would not be milled to a
right angle one to another. This is avoided by the construction of the
Brainard back centre, shown in Fig. 1984, in which T represents the
surface of the work table and H the back centre. The block B is fitted
within head H, and has two slots A A, through which the bolts S S pass,
these bolts securing B in its adjusted position in H. The centre slide C
operates in B; hence B, and therefore C, may be set in line with the
work axis.
[Illustration: Fig. 1985.]
For heads in which the back centre cannot thus be set in line, the form
of dog shown in Fig. 1985 (which is from _The American Machinist_) may
be employed to accommodate the movement of the tail or horns through the
driver. Its horn or tail B is made parallel so as to lie flat against
the face of the slot in the driver. The other end of tail B is pivoted
into a stud whose other end is cylindrical, and passes into a hub
provided in one jaw of the dog, the set-screw A being loosened to permit
this sliding motion. This locks the horn in the clamp and permits the
dog to adjust itself to accommodate the motion endwise that occurs when
it is revolved. The amount of this motion obviously depends upon the
degree of taper, it being obvious (referring to Fig. 1982) that horn _d_
would pass through the chuck, as denoted by the dotted lines, when at
the bottom of its path of revolution.
[Illustration: Fig. 1986.]
It is obvious that when the head or universal head of the machine is
elevated so that it stands vertical, it may have a chuck screwed on and
thus possess the capacity of the swiveled vise. It is preferable,
however, to have a separate swiveled chuck, such as in Fig. 1986 (from
_The American Machinist_), which will not stand so high up from the
machine bed, and will therefore be more solid and suitable for heavy
work.
[Illustration: Fig. 1987.]
Another very handy form of chuck for general work is the angle chuck
shown in Fig. 1987, which is from an article by John J. Grant, in _The
American Machinist_. The work-holding plate has [T]-grooves to chuck the
work on and is pivoted at one end, while at the other is a segment and
bolt to secure it in its adjusted angle. Two applications of the chuck
are shown in the figure.
[Illustration: Fig. 1988.]
[Illustration: Fig. 1989.]
Fig. 1988 represents a top, and Fig. 1989 an end view of a chuck to hold
rectangular bars that are to be cut into pieces by a gang of mills. A,
A, A, are grooves through the chuck jaws through which the cutters pass,
severing the bar through the dotted lines. Each piece of the bar is held
by a single screw on one side and by two screws on the other, which is
necessary in order to obtain equal pressure on all the screws and
prevent the pieces from moving when cut through, and by moving, gripping
the cutters and causing them to break.
In chucking the bar the two end screws D D must be the first to be set
up to just meet the bar: next the screws B C on the other side must be
set up, holding the bar firmly. The two screws between D D are then set
up to just bind the bar, and then the middle four on the other side are
screwed up firmly. By this method all the screws will hold firmly and
the pieces cannot move.
VERTICAL MILLING, DIE SINKING, OR ROUTING MACHINE.--Fig. 1990 represents
Warner & Swazey's die sinking machine. The cutter driving spindle is
here driven by belt direct, imparting a smooth motion. The knee is
adjustable for height on the vertical slideway on the face of the
column, which is provided with a stop adjustable to determine how high
the knee and work-holding devices can be raised, and, therefore, the
depth to which the cutter can enter the work, and a _former_ pin is
placed 6 inches behind the cutter to act as a stop against which a
pattern may be moved when work is to be copied from a _former_ or
pattern piece. The work-holding device consists of a compound rest and a
vise capable of being swiveled to any angle or of being revolved to feed
the work to the cutter, hence the work may be moved in any required
direction, in either a straight line, in a circle, or in any irregular
manner to suit the shape of the work.
PROFILING MACHINE.--The profiling machine is employed mainly to cut the
edges of work, and to sink recesses or grooves in the upper surface of
the same to correspond to a pattern. A provisional template of the form
of the work is fastened on the bed of the machine, and from this is cut
in the machine a thicker one termed the "former," which is then used to
copy the work from.
Fig. 1991 represents Pratt & Whitney's profiling machine. On the cross
slide are two separate sliding heads, each of which carries a live
spindle for the cutting tool, and beside it a spindle to receive a pin,
which by being kept against the pattern or _former_ causes the work to
be cut to the same shape as the former.
The work is fastened to the table, which is operated upon the raised
[V]s shown by the handle on the left, which operates a pinion geared to
a rack on the underneath side of the table. The handle on the right
operates the heads along the cross slide also by a rack and pinion
motion. The gearing and racks in both cases are double, so that by two
independent adjusting screws the wear of the teeth may be taken up and
lost motion prevented. By means of these two handles the work may be
moved about the cutter with a motion governed by the form or shape of
the _former_, of which the work is thus made a perfect pattern both in
size and shape. The tool used is a shank or end mill, such as was shown
in Fig. 1928. In some profiling machines the spindle carrying the guide
or former pin is stationary, in which case the provisional template is
put beneath it and the _former_ is cut by the live spindle, and for use
must be moved from the position in which it was cut and reset beneath
the _former_ spindle. This machine, however, is provided with
Parkhurst's improvement, in which the _former_ spindle is provided with
a gear-wheel, by which it may be revolved from the live spindle, hence
the provisional template may be set beneath the live spindle in which
the guide pin is then placed. The cutter is then placed in the _former_
spindle, and the _former_ cut to shape from the provisional template
while in the actual position it will occupy when used.
[Illustration: Fig. 1990.]
[Illustration: Fig. 1991.]
[Illustration: Fig. 1992.]
Fig. 1992 represents Brainard's machine for grinding milling cutters. It
consists of a threaded column A to which is fitted the knee B, which as
it fits the top of the threads on the column may be swung or revolved
about the column without being altered in its height upon the same
except by means of the threaded ring C. At D is a lever for clamping the
knee B to the column after adjustment; W represents the emery wheel
mounted on the end of the horizontal spindle having journal bearing at
the top of the column. The face of the knee B has a slideway _d_ for the
fixtures, &c., which hold the cutters to be ground, and at E is a lug
pierced to receive an arbor whereon to place cutters to be ground, the
lug being split and having a binding screw to lock the arbor firmly in
place. F is a slide for receiving the grinding attachments, one of which
is shown at K carrying a milling cutter in position to be ground on the
face.
Fig. 1993 shows the fixture employed to grind parallel cutters, S
representing a stand upon slide F (which corresponds to slide F in the
general view of the machine in Fig. 1992) in which is fixed the arbor H.
The cutter C is slid by hand along arbor H and beneath the emery wheel,
the method of guiding the cutter to the wheel being shown in Fig. 1994,
which represents a front view of the machine. At E is the lug (shown
also at E in the general view) which has a hole to receive a rod P, and
is split through at S, so that operating binding screw L locks rod P in
E. At R is a rod secured to the rod P, and G is a gauge capable of
swivelling in the end of R and of being secured in its adjusted
position. The end of this gauge is adjusted to touch the front face of
the tooth to be ground on the cutter C, which must be held close against
the end of the gauge in order to grind the cutting edge to a straight
line parallel to its axis.
A not uncommon error is to place the gauge G against the tooth in front
of that which is being ground, as in Fig. 1995, the gauge being against
tooth C while tooth B is the one being ground. In this case the truth of
the grinding depends upon the accuracy of the tooth spacing. Suppose,
for example, that teeth B and C are too widely spaced, tooth C being
too far ahead, and this error of spacing would cause tooth B to be too
near the centre of the emery wheel and its cutting edge to be ground too
low.
[Illustration: Fig. 1993.]
[Illustration: Fig. 1994.]
[Illustration: Fig. 1995.]
The object of feeding the cutter by hand along the arbor H is twofold:
first, the amount of cut must be very light and the feed very delicate,
for if the grinding proceeds too fast the cutting edge will be what is
termed burned, that is to say, enough heat will be generated to soften
the extreme cutting edge, which may be discovered by holding the front
face of the tooth to the light, when a fine blue tint will be found
along the cutting edge, showing that it has been softened in the
grinding, and this will cause it to dull very rapidly.
[Illustration: Fig. 1996.]
The second object is to insure parallelism in the cutter. Suppose, for
example, that the cutter C was fast upon arbor H and was fed to the
wheel by moving slide F, and if the arbor H stood at an angle, as in
Fig. 1996, to the slide upon which F moved, the cutter would be ground
taper, whereas if the cutter is fed along the arbor it will be ground
parallel whether the arbor is true or not with the slideway of F, the
only essential being that the arbor H be parallel and straight, which is
much easier to test and to maintain than it is in the slideway (D, Fig.
1992). Here it may be noted that oil should not be applied either to
arbor H or to the cutter bore or slideway D, as lubrication only
increases the wear of the parts, causing the fine emery particles that
inevitably fall upon them to cut more freely.
As thin cutters would not have sufficient length of bore to steady them
upon the arbor and insure parallelism, the cutter sleeve shown in Fig.
1997, which is from _The American Machinist_, is employed to hold them.
It is provided with a collar, is threaded at T for the nut N to hold the
cutter against collar C, and is bored to fit the cutter arbor H, which
corresponds to H in Fig. 1993.
This device also affords an excellent means of holding two or more thin
cutters requiring to be ground of exactly equal diameters.
It follows from what has been said that taper tools, such as taper
reamers, must be held with their upper face parallel to the line of
their motion in being fed to the wheel, as in Fig. 1998, in which line M
represents this line of motion, line N the axis of the reamer, and line
O the line on which the fixture that holds the reamer must move, O being
parallel to M.
Fig. 1999 represents Slate's fixture for this class of work. A is a
stand that bolts upon the slideway _d_ in Fig. 1992. Upon A is fixed a
rectangular bar B, upon which (a sliding fit) is the shoe C. Upon C fits
the piece D, which is pivoted to shoe C by the pin at E. At the other
end of D is a lug, against which abuts the end of screw G, which is
threaded through the end of C, so that by operating the screw G, D may
be set to any required angle upon C, and at F is a set-screw threaded
through D and abutting against C, so as to lock D in its adjusted
position. At P is a pointer for the graduations on C, which are marked
to correspond with the graduations upon the taper turning attachment of
a lathe.
[Illustration: Fig. 1997.]
[Illustration: Fig. 1998.]
[Illustration: Fig. 1999.]