Machinist Course - Milling Machine Operations
Machinist Course - Milling Machine Operations
Machinist Course - Milling Machine Operations
OD1644 8
EDITION 8
US Army Correspondence
Course Program
6 Credit Hours
NEW: 1988
GENERAL
Six credit hours are awarded for successful completion of this subcourse.
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MILLING MACHINE OPERATIONS - OD1644
TABLE OF CONTENTS
Section Page
TITLE................................................................. i
TABLE OF CONTENTS..................................................... ii
REFERENCES............................................................ 74
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MILLING MACHINE OPERATIONS - OD1644
When used in this publication "he," "him," "his," and "men" represent both
the masculine and feminine genders, unless otherwise stated.
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MILLING MACHINE OPERATIONS - OD1644
STUDENT NOTES
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
LESSON 1
CONDITIONS
STANDARDS
REFERENCES
1. Introduction
Milling machines were first invented and developed by Eli Whitney to mass
produce interchangeable musket parts. Although crude, these machines
assisted man in maintaining accuracy and uniformity while duplicating parts
that could not be manufactured with the use of a file.
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2. Milling Machines
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of the worktable. The worktable traverses to the right or left upon the
saddle, feeding the workpiece past the milling cutter. The table may be
manually controlled or power fed.
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generally not power fed on this size machine. The saddle slides on a
dovetail on the knee providing crossfeed adjustment. The knee moves
vertically up or down the column to position the worktable in relation to
the spindle.
c. Major Components. The machinist must know the name and purpose of
each of the main parts of a milling machine to understand the operations
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discussed in this text. Keep in mind that although we are discussing a knee
and a column milling machine, this information can be applied to other
types. Use figure 1 on page 3 (which illustrates a plain knee and column
milling machine) to help become familiar with the location of the various
parts of these machines.
(1) Column. The column, including the base, is the main casting which
supports all other parts of the machine. An oil reservoir and a pump in the
column keeps the spindle lubricated. The column rests on a base that
contains a coolant reservoir and a pump that can be used when performing any
machining operation that requires a coolant.
(2) Knee. The knee is the casting that supports the table and the
saddle. The feed change gearing is enclosed within the knee. It is
supported and can be adjusted by the elevating screw. The knee is fastened
to the column by dovetail ways. The lever can be raised or lowered either
by hand or power feed. The hand feed is usually used to take the depth of
cut or to position the work, and the power feed to move the work during the
machining operation.
(3) Saddle and Swivel Table. The saddle slides on a horizontal dovetail,
parallel to the axis of the spindle, on the knee. The swivel table (on
universal machines only) is attached to the saddle and can be swiveled
approximately 45° in either direction.
(4) Power Feed Mechanism. The power feed mechanism is contained in the
knee and controls the longitudinal, transverse (in and out) and vertical
feeds. The desired rate of feed can be obtained on the machine by
positioning the feed selection levers as indicated on the feed selection
plates. On some universal knee and column milling machines the feed is
obtained by turning the speed selection handle until the desired rate of
feed is indicated on the feed dial. Most milling machines have a rapid
traverse lever that can be engaged when a temporary increase in speed of the
longitudinal, transverse, or vertical feeds is required. For example, this
lever would be engaged when positioning or aligning the work.
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NOTE
(5) Table. The table is the rectangular casting located on top of the
saddle. It contains several T-slots for fastening the work or workholding
devices. The table can be moved by hand or by power. To move the table by
hand, engage and turn the longitudinal hand crank. To move it by power,
engage the longitudinal directional feed control lever. The longitudinal
directional control lever can be positioned to the left, to the right, or in
the center. Place the end of the directional feed control lever to the left
to feed the table to the left. Place it to the right to feed the table to
the right. Place it in the center position to disengage the power feed, or
to feed the table by hand.
(6) Spindle. The spindle holds and drives the various cutting tools. It
is a shaft, mounted on bearings supported by the column. The spindle is
driven by an electric motor through a train of gears, all mounted within the
column. The front end of the spindle, which is near the table, has an
internal taper machined on it. The internal taper (3 1/2 inches per foot)
permits mounting tapered-shank cutter holders and cutter arbors. Two keys,
located on the face of the spindle, provide a positive drive for the cutter
holder, or arbor. The holder or arbor is secured in the spindle by a
drawbolt and jamnut, as shown in figure 3 on the following page. Large face
mills are sometimes mounted directly to the spindle nose.
(7) Overarm. The overarm is the horizontal beam to which the arbor
support is fastened. The overarm, may be a single casting that slides in
the dovetail ways on the top of the column. It may consist of one or two
cylindrical bars that slide through the holes in the column. On some
machines to position the overarm, first unclamp the locknuts and then extend
the overarm by turning a crank. On others, the overarm is moved by merely
pushing on it. The overarm should only be extended far enough to so
position the arbor support as to make the setup as rigid as possible. To
place the arbor supports on an overarm, extend one of the bars approximately
1-inch farther than the other bar.
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NOTE
(9) Size Designation. All milling machines are identified by four basic
factors: size, horsepower, model, and type. The size of a milling machine
is based on the longitudinal (from left to right) table travel, in inches.
Vertical, cross, and longitudinal travel are all closely related as far as
the overall capacity. However, for size designation, only the longitudinal
travel is used. There are six sizes of knee-type milling machines, with
each number representing the number of inches of travel.
No. 1 22 inches
No. 2 28 inches
No. 3 34 inches
No. 4 42 inches
No. 5 50 inches
No. 6 60 inches
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If the milling machine in the shop is labeled No. 2HL, it has a table
travel of 28 inches; if it is labeled No. 5LD, it has a travel of 50 inches.
The horsepower designation refers to the rating of the motor which is used
to power the machine. The model designation is determined by the
manufacturer and features vary with different brands. The type of milling
machine is designated as plain or universal, horizontal or vertical, and
knee and column, or bed. In addition, machines may have other special type
designations and, therefore, may not fit any standard classification.
(1) Description.
(a) Milling machine arbors are made in various lengths and in standard
diameters of 7/8, 1, 1 1/4, and 1 1/2 inch. The shank is made to fit the
tapered hole in the spindle, the other end is threaded.
NOTE
(b) Arbors are supplied with one of three tapers to fit the milling
machine spindle (figure 4 on the following page), the milling machines
Standard taper, the Brown and Sharpe taper, and the Brown and Sharpe taper
with tang.
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(d) The Brown and Sharpe taper is found mostly on older machines.
Adapters or collets are used to adapt these tapers to fit the machines whose
spindles have milling machine Standard tapers.
(e) The Brown and Sharpe taper with tang also is used on some of the
older machines. The tang engages a slot in the spindle to assist in driving
the arbor.
(2) Standard Milling Machine Arbor (figure 4 below, and figure 5 on page
13).
(b) The end of the arbor opposite the taper is supported by the arbor
supports of the milling machine. One or more supports are used, depending
on the length of the arbor and the degree of rigidity required. The end may
be supported by a
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lathe center, bearing against the arbor nut (figure 4 on the previous page)
or by a bearing surface of the arbor fitting inside a bushing of the arbor
support. Journal bearings are placed over the arbor in place of sleeves
where an intermediate arbor support is positioned.
(c) The most common means of fastening the arbor in the milling machine
spindle is by use of a draw-in bolt (figure 4). The bolt threads into the
taper shank of the arbor to draw the taper into the spindle and hold it in
place. Arbors secured in this manner are removed by backing out the draw-in
bolt and tapping the end of the bolt to loosen the taper.
(3) Screw Arbor (figure 5 on the following page). Screw arbors are used
to hold small cutters that have threaded holes. These arbors have a taper
next to the threaded portion to provide alignment and support for tools that
require a nut to hold them against a tapered surface. A right-hand threaded
arbor must be used for right-hand cutters; a left-hand threaded arbor is
used to mount left-hand cutters.
(4) Slitting Saw Milling Cutter Arbor (figure 5). The slitting saw
milling cutter arbor is a short arbor having two flanges between which the
milling cutter is secured by tightening a clamping nut. This arbor is used
to hold the metal slitting saw milling cutters that are used for slotting,
slitting, and sawing operations.
(5) End Milling Cutter Arbor. The end milling cutter arbor has a bore in
the end in which the straight shank end milling cutters fit. The end
milling cutters are locked in place by means of a setscrew.
(6) Shell End Milling Cutter Arbor (figure 5). Shell end milling arbors
are used to hold and drive shell end milling cutters. The shell end milling
cutter is fitted over the short boss on the arbor shaft and is held against
the face of the arbor by a bolt, or a retaining screw. The two lugs on the
arbor fit slots in the cutter to prevent the cutter from rotating on the
arbor during the machining operation. A special wrench is used to tighten
and loosen a retaining screw/bolt in the end of the arbor.
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(7) Fly Cutter Arbor (figure 5). The fly cutter arbor is used to support
a single-edge lathe, shaper, or planer cutter bit, for boring and gear
cutting operations on the milling machine. These cutters, which can be
ground to any desired shape, are held in the arbor by a locknut. Fly cutter
arbor shanks may have a Standard milling machine spindle taper, a Brown and
Sharpe taper, or a Morse taper.
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(3) Spindle Adapters. Spindle adapters are used to adapt arbors and
milling cutters to the standard tapers used for milling machine spindles.
With the proper spindle adapters, any tapered or straight shank cutter or
arbor can be fitted to any milling machine, if the sizes and tapers are
standard.
(2) The index fixture consists of an index head, also called a dividing
head, and a footstock, similar to the tailstock of a lathe. The index head
and the footstock are attached to the worktable of the milling machine by T-
slot bolts. An index plate containing graduations is used to control the
rotation of the index head spindle. The plate is fixed to the index head,
and an index crank, connected to the index head spindle by a worm gear and
shaft, is moved about the index plate. Workpieces are held between centers
by the index head spindle and footstock. Workpieces may also be held in a
chuck mounted to the index head
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spindle, or may be fitted directly into the taper spindle recess of some
indexing fixtures.
(3) There are many variations of the indexing fixture. The name
universal index head is applied to an index head designed to permit power
drive of the spindle so that helixes may be cut on the milling machine.
"Gear cutting attachment" is another name for an indexing fixture; in this
case, one primarily intended for cutting gears on the milling machine.
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operations are more easily accomplished with this attachment, due to the
fact that the cutter and the surface being cut are in plain view.
h. Offset Boring Head. The offset boring head is an attachment that fits
to the milling machine spindle and permits a single-edge cutting tool, such
as a lathe cutter bit, to be mounted off-center on the milling machine.
Workpieces can be mounted in a vise attached to the worktable and can be
bored with this attachment.
a. General.
(2) Milling machine worktables are provided with several T-slots, used
either for clamping and locating the workpiece itself or for mounting
various holding devices and attachments. These T-slots extend the length of
the table and are parallel to its line of travel. Most milling machine
attachments, such as vises and index
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fixtures, have keys or tongues on the underside of their bases so that they
may be located correctly in relation to the T-slots.
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(a) There are two types of mandrels that may be used for mounting
workpieces between centers. The solid mandrel is satisfactory for many
operations, while the mandrel having a tapered shank is preferred when
fitting the workpiece into the indexing head of the spindle.
(c) Workpieces mounted between centers are fixed to the index head
spindle by means of a lathe dog. The bent tail of the dog should be
fastened between the setscrews provided in the driving center clamp in such
a manner as to avoid backlash and prevent springing the mandrel. When
milling certain types of workpieces a milling machine dog may be used to
advantage. The tail of the dog is held in a flexible ball joint which
eliminates springing or shaking of the workpiece and/or the dog. The
flexible ball joint allows the tail of the dog to move in a radius along the
axis of the workpiece, making it particularly useful in the rapid milling of
tapers.
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(a) The plain vise, similar to the machine table vise, is used for
milling straight workpieces; it is bolted to the milling machine table at
right angles or parallel to the machine arbor.
(b) The swivel vise (figure 7 on the following page) can be rotated and
contains a scale graduated in degrees at its base to facilitate milling
workpieces at any angle on a horizontal plane. This vise is fitted into a
graduated circular base fastened to the milling machine table and located by
means of keys placed in the T-slots. By loosening the bolts, which clamp
the vise to its graduated base, the vise may be moved to hold the workpiece
at any angle in a horizontal plane. To set a swivel vise accurately with
the machine spindle, a test indicator should be clamped to the machine arbor
and a check made to determine the setting by moving either the transverse or
the longitudinal feeds, depending upon the position of the vise jaws. Any
deviation as shown by the test indicator should be corrected by swiveling
the vise on its base.
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(2) Index Head. The bead of the indexing fixture contains an indexing
mechanism, used to control the rotation of the index head spindle in order
to space or divide a workpiece accurately. A simple indexing mechanism is
illustrated in figure 10 on the following page. It consists of a 40-tooth
worm wheel fastened to the index head spindle, a single-cut worm, a crank
for turning the wormshaft, and an index plate and sector. Since there are
40 teeth in the worm wheel, one turn of the index crank causes the worm
wheel, and consequently the index head spindle to, make one-fortieth of a
turn; so 40 turns of the index crank revolves the spindle one full turn.
(b) The same principle applies whether or not the divisions required
divide evenly into 40. For example, if it is desired to index for 6
divisions, 6 divided into 40 equals 6 2/3 turns; similarly, to index for 14
spaces, 14 divided into 40 equals 2 6/7 turns. Therefore, the following
rule can be derived: to determine the number of turns of the index crank
needed to obtain one division of any number of equal divisions on the
workpiece, divide
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40 by the number of equal divisions desired (provided the worm wheel has 40
teeth, which is standard practice).
(4) Index Plate. The index plate (figure 11 on the following page) is a
round metal plate with a series of six or more circles of equally spaced
holes; the index pin on the crank can be inserted in any hole in any circle.
With the interchangeable plates regularly furnished with most index heads,
the spacings necessary for most gears, boltheads, milling cutters, splines,
and so forth, can be obtained. The following sets of plates are standard
equipment:
(b) Cincinnati type, one plate drilled on both sides with circles
divided as follows:
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First side- 24, 25, 28, 30, 34, 37, 38, 39, 41, 42, 43 holes.
Second side- 46, 47, 49, 51,53, 54, 57, 58, 59, 62, 66 holes.
(5) Indexing Operation. The two following examples show how the index
plate is used to obtain any desired part of a whole spindle turn by plain
indexing.
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circle. When counting holes, start with the first hole ahead of the index
pin.
(6) Sector. The sector (figure 11 on the previous page) indicates the
next hole in which the pin is to be inserted and makes it unnecessary to
count the holes when moving the index crank after each cut. It consists of
two radial, beveled arms which can be set at any angle to each other and
then moved together around the center of the index plate. Assume that it is
desired to make a series of cuts, moving the index crank 1 1/4 turns after
each cut. Since the circle has 20 turns, the crank must be turned one full
turn plus 5 spaces after each cut. Set the sector arms to include the
desired fractional part of a turn, or 5 spaces, between the beveled edges of
its arms. If the first cut is taken with the index pin against the left-
hand arm, to take the next cut, move the pin once around the circle and into
the hole against the right-hand arm of the sector. Before taking the second
cut, move the arms so that the left-hand arm is again against the pin; this
moves the right-hand arm another five spaces ahead of the pin. Then take
the second cut; repeat the operation until all the cuts have been completed.
NOTE
(7) Direct Indexing. The construction of some index heads permits the
worm to be disengaged from the worm wheel, making possible a quicker method
of indexing, called direct indexing. The index head is provided with a knob
which, when turned through part of a revolution, operates an eccentric and
disengages the worm. Direct indexing is accomplished by an additional index
plate fastened to the index head spindle. A stationary plunger in the index
head fits the holes in the index plate. By moving the plate by hand to
index directly, the spindle and the workpiece rotate an equal distance.
Direct index plates usually have 24 holes and offer a quick means of milling
squares, hexagons, taps, etc. Any number of divisions which is a factor of
24 can be indexed quickly and conveniently by the direct indexing method.
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(a) When you must divide work into degrees or fractions of degrees by
plain indexing, remember that one turn of the index crank will rotate a
point on the circumference of the work 1/40 of a revolution. Since there
are 360° in a circle, one turn of the index crank will revolve the
circumference of the work 1/40 of 360°, or 9°. Hence, in using the index
plate and fractional parts of a turn, 2 holes in a 18-hole circle equals 10,
1 hole in a 27-hole circle equals 2/3°, 3 holes in a 54-hole circle equals
1/3°. To determine the number of turns, and parts of a turn of the index
crank for a desired number of degrees, divide the number of degrees by 9.
The quotient will represent the number of complete turns and fractions of a
turn that you should rotate the index crank. For example, the calculation
for determining 15° when an index plate with a 54-hole circle is available,
is as follows:
or one complete turn plus 36 holes on the 54-hole circle. The calculation
for determining 13 1/2° when an index plate with an 18-hole circle is
available, is as follows:
(b) When indexing angles are given in minutes and approximate divisions
are acceptable, movement of the index crank and the proper index plate may
be determined by the following calculations:
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You can determine the number of minutes represented by one turn of the index
crank by multiplying the number of degrees covered in one turn of the index
crank by 60:
9° x 60 = 540'
Therefore, one turn of the index crank will rotate the index head spindle
540 minutes.
(c) The number of minutes (540) divided by the number of minutes in the
division desired, indicates the total number of holes required in the index
plate used. (Moving the index crank one hole will rotate the index spindle
through the desired number of minutes of the angle.) This method of
indexing can be used only for approximate angles since ordinarily the
quotient will come out in mixed numbers, or in numbers for which no index
plate is available. However, when the quotient is nearly equal to the
number of holes in an available index plate, the nearest number of holes can
be used and the error will be very small. For example, the calculation for
24 minutes would be:
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(1) Before setting up a job, be sure that the workpiece, the table, the
taper in the spindle, and arbor or cutter shank, are all clean and free from
chips, nicks, or burrs.
(2) Set up every job as close to the milling machine spindle as the
circumstances permit.
(6) Always lower the table before backing the workpiece under a revolving
milling cutter.
(9) When using clamps to secure the workpieces, be sure that they are
tight and that the workpiece is held so that it will not spring or vibrate
while it is being cut.
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(11) Keep chips away from the workpiece; brush them out of the way by any
convenient means, but do not do so by hand or with waste.
(12) Use good judgment and common sense in planning every job, and profit
by previous mistakes.
(1) Face Milling - machining flat surfaces which are at right angles to
the axis of the cutter.
(2) Plain or Slab Milling - machining flat surfaces which are parallel to
the axis of the cutter.
(1) General. The speed of a milling cutter is the distance in feet per
minute that each tooth travels as it cuts its chips. The number of spindle
revolutions per minute necessary to give a desired peripheral speed on the
size of the milling cutter. The best speed is determined by the type of
material being cut and the size and type of cutter used. The smoothness of
the finish desired and the power available are other factors relating to the
cutter speed.
(a) The approximate values given in table 1 on the following page may be
used as a guide for selecting the proper cutting speed. If the operator
finds that the machine, the milling cutter, or the workpiece cannot be
handled suitably at these speeds, immediate readjustment should be made.
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the speed should be about one-half the speed recommended in the table. If
carbide-tipped cutters are used, the speed can be doubled.
(d) For roughing cuts, a moderate speed and coarse feed give best
results; for finishing cuts, the best practice is to reverse these
conditions, using a higher speed and a lighter cut.
(a) The formula for calculating spindle speed in revolutions per minute
is as follows:
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For example, the spindle speed for machining a piece of steel at a speed of
35 rpm with a cutter 2 inches in diameter is calculated as follows:
Therefore, the milling machine spindle would be set for as near 70 rpm as
possible. If the calculated rpm cannot be obtained, the next lower
selection should be made.
(1) General. The rate of feed, or the speed at which the workpiece
passes the cutter, determines the time required for cutting a job. In
selecting the feed, there are several factors which should be considered.
These factors are:
(a) Forces are exerted against the workpiece, the cutter, and their
holding devices during the cutting process. The force exerted varies
directly with the amount of metal removed and can be regulated by the feed
and the depth of cut.
Therefore, the correct amount of feed and depth of cut are interrelated, and
in turn are dependent upon the rigidity and power of the machine. Milling
machines are limited by the power that they can develop to turn the cutter
and the amount of vibration they can resist when using coarse feeds and deep
cuts.
(b) The feed and depth of cut also depend upon the type of milling
cutter being used. For example, deep cuts or coarse feeds should not be
attempted when using a small diameter end milling cutter, as such an attempt
would spring or break the
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cutter. Coarse cutters with strong cutting teeth can be fed at a faster
rate because the chips may be washed out more easily by the cutting oil.
(c) Coarse feeds and deep cuts should not be used on a frail workpiece,
or on a piece that is mounted in such a way that its holding device is not
able to prevent springing or bending.
(d) The degree of finish required often determines the amount of feed.
Using a coarse feed, the metal is removed more rapidly but the appearance
and accuracy of the surface produced may not reach the standard desired for
the finished product. Because of this, finer feeds and increased speeds are
used for finer, more accurate finishes. Most mistakes are made through
overspeeding, underspeeding, and overfeeding. Overspeeding may be detected
by the occurrence of a squeaking, scraping sound. If vibration (referred to
as "chattering") occurs in the milling machine during the cutting process,
the speed should be
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reduced and the feed increased. Too much cutter clearance, a poorly
supported workpiece, or a badly worn machine gear are common causes of
"chattering."
(a) Feed for milling cutters will generally run from 0.002 to 0.250 inch
per cutter revolution, depending upon the diameter of the cutter, the kind
of material, the width and depth of the cut, the size of the workpiece, and
the condition of the machine.
(b) Good finishes may be obtained using a 3-inch plain milling cutter at
a 40 feet per minute speed, with a feed of 0.040-inch per cutter revolution.
e. Cutting Oils.
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also serves to lubricate the cutter face and to flush away the chips,
consequently reducing the possibility of marring the finish.
(2) Cutting oil compounds for various metals are given in table 3 on the
following page. In general, a simple coolant is all that is required for
roughing. Finishing requires a cutting oil with a good lubricating
properties to help produce a good finish on the workpiece. Aluminum and
cast iron are almost always machined dry.
f. Plain Milling.
(1) General. Plain milling, also called surface milling and slab
milling, is milling flat surfaces with the milling cutter axis parallel to
the surface being milled. Generally, plain milling is accomplished with the
workpiece surface mounted to the milling machine table and the milling
cutter mounted on a standard milling machine arbor. The
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(a) For plain milling operations, a plain milling cutter should be used.
Deeper cuts may generally be taken when narrow cutters are used than with
wide cutters. The choice of milling cutters should be based on the size of
the workpiece. If a wide area is to be milled, fewer traverses will be
required using a wide cut.
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g. Angular Milling.
(2) Operation.
(a) When cutting dovetails on the milling machine, the workpiece may be
held in the vice, clamped to the table, or clamped to an angle plate.
Figure 15 on page 38 shows the workpiece mounted to a lathe faceplate for
angular milling with the milling and grinding lathe attachment. The tongue
or groove is first roughed-out using a side milling cutter, after which the
angular sides and base are finished with an angle cutter.
h. Face Milling.
(1) General. Face milling, also called end milling and side milling, is
machining surfaces perpendicular to the axis of the cutter.
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(c) When face milling, the workpiece may be clamped to the table or
angle plate, or supported in a vise, fixture, or jig.
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(f) Angular surfaces can also be face milled on a swivel cutter head
milling machine. In this case, the workpiece is mounted to the table and
the cutter head is swiveled to bring the end milling cutter perpendicular to
the surface to be produced.
(g) During face milling operations, the workpiece should be fed against
the milling cutter so that the pressure of the cut is downward, thereby
holding the work against the table.
(h) Whenever possible, the edge of the workpiece should be in line with
the center of the cutter. This position of the workpiece, in relation to
the cutter, will help eliminate slippage.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
(i) When setting the depth of the cut, the workpiece should be brought
up to just touch the revolving cutter. After a cut has been made from this
setting, a measurement of the workpiece is taken. The graduated dial on the
traverse feed is then locked and used as a guide in determining the depth of
the cut.
1 When starting the cut, the workpiece should be moved so that the
cutter is nearly in contact with its edge, after which the automatic feed
may be engaged.
i. Straddle Milling.
(1) General. When two or more parallel vertical surfaces are machined at
a single cut, the operation is called straddle milling. Straddle milling is
accomplished by mounting two side milling cutters on the same arbor, set
apart so that they straddle the workpiece.
j. Gang Milling.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
on one arbor when cutting horizontal surfaces. The usual method is to mount
two or more milling cutters of different diameters, shapes and/or widths on
an arbor as shown in figure 18 on the following page. The possible cutter
combinations are unlimited and are determined in each case by the nature of
the job.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
k. Form Milling.
(2) Operation. The more common form milling operations involve milling
half-round recesses and beads and quarter-round radii on the workpieces
(figure 19 on the following page). This operation is accomplished by using
convex, concave, and corner rounding milling cutters ground to the desired
circle diameter.
(3) Other jobs for formed milling cutters include milling intricate
patterns on workpieces and milling several complex surfaces in a single cut,
such as produced by gang milling.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
(1) General. Keyways are machined grooves of different shapes, cut along
the axis of the cylindrical surface of shafts, into which keys are fitted to
provide a positive method of locating and driving members mounted on the
shafts. A keyway is also machined on the mounted member to receive the key.
The type of key and corresponding keyway to be used depends on the class of
work for which it is intended. The most commonly used type of key is the
woodruff.
(2) Operation.
(b) Woodruff key sizes are designated by a code number in which the last
two digits indicate the diameter of the key in eighths of an inch. These
digits precede the last two digits and give the width of the key in thirty-
seconds of an inch. Thus, a number 204 woodruff key would be 4/8 or 1/2
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
inch in diameter and 2/32 or 1/16 inch wide; a number 1012 woodruff key
would be 12/8 or 1 1/2 inches in diameter and 10/32 or 5/16 inch wide.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
m. Gear Cutting.
(1) General. Gear teeth are cut on the milling machine using formed
milling cutters called involute gear cutters. These cutters are
manufactured in many pitch sizes and shapes for different numbers of teeth
per gear (table 4 on the following page).
(2) Operation. If involute gear cutters are not available and the teeth
must be restored on gears that cannot be replaced, a lathe cutter bit can be
ground to the shape of the gear tooth spaces and mounted in a flycutter for
the operation. The gear is milled in the following manner:
NOTE
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
(a) Fasten the indexing fixture to the milling machine table. Use a
mandrel to mount the gear between the index head and the footstock centers.
Adjust the indexing fixture on the milling machine table, or adjust the
position of the cutter, to make the gear axis perpendicular to the milling
machine spindle axis.
(b) Take the cutter bit that has been ground to the shape of the gear
tooth spaces and fasten it in the flycutter arbor. Adjust the cutter
centrally with the axis of the gear. Rotate the milling machine spindle to
position the cutter bit in the flycutter so that its cutting edge is
downward.
(c) Align the tooth space to be cut with the flycutter arbor and cutter
bit by turning the index
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
crank on the index head. Proceed to mill the tooth or teeth in the same
manner as you would when milling a keyway.
n. Drilling.
(1) General. The milling machine may be used effectively for drilling,
since the accurate location of the hole may be secured by means of the feed
screw graduations. Spacing holes in a circular path, such as the holes in
an indexing plate, may be accomplished by indexing the workpiece with the
indexing head that is positioned vertically.
(2) Operation. Twist drills may be supported in drill chucks that are
fastened in the milling machine spindle or mounted directly in the milling
machine collets or adapters. The workpiece to be drilled is fastened to the
milling machine table by means of clamps, vises, or angle plates. Remember,
proper speeds and feeds are important functions to consider when performing
drilling operations on the milling machine.
(1) Adjustments.
(a) Proper gib adjustment procedures must be done after 40 hours on new
mills.
(b) Each 700 and 800 series of mills have three gibs. One at the front
dovetail of the table, one on the left dovetail of the saddle, and one on
the left dovetail of the knee. Each gib is supplied with two lock or
adjustment screws. The table gib has a
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
lock screw on the right front of the saddle and the adjusting screw on the
left front of the saddle.
(c) The saddle gib is at the rear of the saddle on the left side, while
the adjusting screw is at the front of the saddle on the left side. The
knee gib lock screw is on the bottom of the knee on the left side and the
adjusting screw is on the top on the left side.
(d) To adjust the table gib, loosen the table gib lock screw several
turns and tighten the adjusting screw on the opposite side of the table
until the gib is pressing against the table dovetail. Tighten the lock
screw. (Do not tighten the lock screw too tight as it distorts the gib.)
Run the table back and forth and check the table for drag. To adjust the
saddle and knee, use the same procedures as above.
(a) When checking the gibs with a dial indicator, the following checks
should be made: (Use figure 22 on the following page as reference.)
(b) With the dial indicator mounted, as in Position 3, the table can be
tested for looseness by pulling back and forth on the end of the table.
Anything over 0.0015-inch is too much and requires the gibs to be adjusted,
also the table should snap back to the "0" reading each time after the table
is released.
(d) The knee gib will be checked as shown, with the dial indicator in
Position 5, by grasping the table and lifting up and pushing down. The
reading of deflection here should not be more than 0.0003 of an inch.
(e) As a final check, set the dial indicator on Position 2 and run the
table to its extreme right and left positions. The indicator runout should
not be more than 0.0015 of an inch.
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MILLING MACHINE OPERATIONS - - OD1644 LESSON 1/TASK 1
(a) In the rear of the head, between the head and the adapter, is a hex
nut with a 10-24 x 1/2 inch socket head cap screw, used for a lock. Unscrew
this lock screw until you can rotate it freely with your fingers.
(c) It may also be desirable to adjust the travel of the clutch plunger:
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
(4) Troubleshooting.
NOTE
1 Cause - The gibs are out of adjustment, they are either too tight
or too loose. This causes the gib to "wedge."
1 Cause - Dirt in the spindle taper, causing a bad fit between the
tool holder shank and the spindle taper.
2 Remedy - Clean the spindle taper and the shank of the tool holder.
4 Remedy - Replace the shank or dress off the burrs, if they are due
to nicks.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
11 Cause - Hard spot at the splice of the drive or the worm belts.
(d) Failure To Hold The Center Distance When Locating For Boring.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
2 Remedy - Take the back-off tension off from the lead screw after
coming up to the indicator reading and lock the table in position.
(1) General. The spindle bearings used in the spindle head are the taper
roller type and have been properly adjusted for average conditions before
leaving the factory. They should not require readjustment before the
machine is to be used. If desired, the end play in the spindle bearings may
be checked after a few months of operation in the following manner: Using a
lead or composition hammer, gently tap the face of the spindle until all of
the play is taken up towards the rear of the machine. Place a dial
indicator against the face of the spindle, and then tap the spindle shaft
forward from the rear. If the play exceeds 0.001 inch, adjustment may be
made as follows:
CAUTION
(2) Adjustment.
(d) Tighten the set screw and reassemble the rear cap on the cutter
head.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
(b) The gibs are properly adjusted at the factory. When readjustment
becomes necessary, proceed as follows: The table gib is adjusted by means
of two shouldered screws located on each end of the saddle. By first
loosening one and then tightening the other, the taper gib may be adjusted
as needed. The saddle and knee gibs are adjusted in a similar manner.
(c) The ram gib is adjusted by two adjusting screws. The front and the
end screw are the adjusting screws. To adjust the gib, the ram stops must
first be removed. These stops are located on the bottom of the ram. To
remove the stops, loosen the set screws, which are located on the front and
back end of the column, and turn both screws on the gib an equal amount.
After proper adjustment has been accomplished, retighten the set screws in
the column to hold the adjustment and then replace the ram stops.
(4) Table Feed Screw. Backlash in the table feed screw is adjusted by an
adjustable bronze feed screw nut that is located at the left hand end of the
saddle. This nut is located in the saddle mechanism just above the saddle
binder. To make any desired adjustment, first loosen the check nut and
insert a pin in any of the many holes around the flange of the nut. Then
turn the screw in either direction until the backlash is from 0.002-inch to
0.005-inch. After you have completed this adjustment, tighten the check
nut.
(5) Saddle Feed Screw. The saddle feed screw is adjusted by means of a
bronze adjusting nut. This adjusting nut is located in the rear end of the
bracket which is used to carry the screw, located under the saddle. To
adjust the feed screw, remove the plate from the left side of the knee.
Then loosen the two Allen screws that holds the bronze
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 1
nut. Insert a pin into one of the holes in the circumference of the nut and
turn it until the backlash is from 0.002-inch to 0.005-inch. After the
correct adjustment has been made, tighten the two Allen screws and replace
the cover plate.
7. Conclusion
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
LESSON 1
CONDITIONS
STANDARDS
REFERENCES
1. Introduction
2. Milling Cutters
a. General.
(1) There are different types of milling machine cutters. Some cutters
can be used for several operations, others can be used for only one
operation. Some cutters have straight teeth,
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
others have helical teeth. Some cutters have mounting shanks, others have
mounting holes. The machine operator must decide which cutter to use. To
make this decision, he must be familiar with various types of cutters and
their uses.
(2) Standard milling cutters are made in many shapes and sizes for
milling both regular and irregular shapes. Various cutters designed for
specific purposes also are available.
(3) Milling cutters generally take their names from the operation which
they perform. Those commonly recognized are: (1) plain milling cutters of
various widths and diameters, used principally for milling flat surfaces
which are parallel to the axis to the cutter; (2) angular milling cutters,
designed for milling V-grooves and the grooves in reamers, taps, and milling
cutters; (3) face milling cutters, used for milling flat surfaces at right
angles to the axis of the cutter; and (4) forming cutters, used for the
production of surfaces with some form of irregular outline.
(1) Pitch. The pitch refers to the angular distance between like parts
on the adjacent teeth. The pitch is determined by the number of teeth.
(2) Face of Tooth. The tooth face is the forward facing surface of the
tooth which forms the cutting edge.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
(3) Cutting Edge. The cutting edge is the angle on each tooth which
performs the cutting.
(4) Land. The land is the narrow surface behind the cutting edge of each
tooth.
(5) Rake Angle. The rake angle is the angle formed between the face of
the tooth and the centerline of the cutter. The rake angle defines the
cutting edge and provides a path for chips that are cut from the workpiece.
(6) Primary Clearance Angle. The primary clearance angle is the angle of
the land of each tooth, measured from a line tangent to the centerline of
the cutter at the cutting edge. This angle prevents each tooth from rubbing
against the workpiece after it makes its cut.
(7) Secondary Clearance Angle. The secondary clearance angle defines the
land of each tooth and provides additional clearance for the passage of
cutting oil and the chips.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
(8) Hole Diameter. The hole diameter determines the size of arbor that
is necessary to mount the milling cutter.
(a) Plain milling cutters that are more than 3/4 inch in width are
usually made with spiral or helical teeth.
(11) Types of Teeth. The teeth of milling cutters are either right-hand
or left-hand, viewed from the back of the machine. Right-hand milling
cutters cut when rotated clockwise; left-hand milling cutters cut when
rotated counterclockwise.
(a) Saw Teeth. Saw teeth similar to those shown in figure 23 on the
previous page are either straight or helical in the smaller sizes of plain
milling cutters, metal slitting saw milling cutters, and end milling
cutters. The cutting edge is usually given about 5° primary clearance
angle. Sometimes the teeth are provided with offset nicks which break up
the chips and make coarser feeds possible.
(b) Formed Teeth. Formed teeth are usually specially made for machining
irregular surfaces or profiles. The possible varieties of formed-tooth
milling cutters are almost unlimited. Convex, concave, and corner-rounding
milling cutters are of this type. Formed cutters are sharpened by grinding
the faces of the teeth radially. Repeated sharpenings are possible without
changing the contour of the cutting edge.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
blades in place. Inserted teeth are more economical and convenient for
large-size cutters because of their reasonable initial cost and because worn
or broken blades can be replaced more easily and at less cost.
(a) Plain Milling Cutter (figure 24 on the following page). The most
common type of milling cutter is known as a plain milling cutter. It is
merely a metal cylinder having teeth cut on its periphery for producing a
flat horizontal surface (or a flat vertical surface in the case of a
vertical spindle machine). When the cutter is over 3/4 inch wide, the teeth
are usually helical, which gives the tool a shearing action which requires
less power, reduces chatter, and produces a smoother finish. Cutters with
faces less than 3/4 inch wide are sometimes made with staggered or alternate
right-and left-hand helical teeth. The shearing action, alternately right
and left, eliminates side thrust on the cutter and arbor. When a plain
milling cutter is considerably wider than its diameter, it is often called a
slabbing cutter; slabbing cutters may have nicked teeth that prevent
formation of large chips.
(b) Metal Slitting Saw Milling Cutter (figure 25 on the following page).
The metal slitting saw milling cutter is essentially a very thin, plain
milling cutter. It is ground slightly thinner toward the center to provide
side clearance. It is used for metal sawing and for cutting narrow slots in
metal.
(c) Side Milling Cutters (figure 26 on page 61). Side milling cutters
are essentially plain milling cutters with the addition of teeth on one or
both sides.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
without changing the width of the slot that will be machined. After each
sharpening, a washer is placed between the two cutters to compensate for the
ground-off metal. The staggered tooth cutter is the most efficient type
used for milling slots where the depth exceeds the width.
1 End milling cutters, also called end mills, have teeth on the end
as well as the periphery (figure 27 on the following page). The smaller end
milling cutters have shanks for chuck mounting or direct spindle mounting.
Larger end milling cutters (over 2 inches in diameter) are called shell end
milling cutters and are mounted on arbors like plain milling cutters. End
milling cutters are employed in the production of slots, keyways, recesses,
and tangs. They are also used for milling angles, shoulders, and the edges
of workpieces.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
(e) Face Milling Cutter. Face milling cutters are cutters of large
diameter having no shanks. They are fastened directly to the milling
machine spindle with adapters. Face milling machine cutters are generally
made with inserted teeth of
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
(f) T-Slot Milling Cutter (figure 28). The T-slot milling cutter is
used to machine T-slot grooves in worktables, fixtures, and other holding
devices. The cutter has a plain or side milling cutter mounted to the end
of a narrow shank. The throat of the T-slot is first milled with a side or
end milling cutter and the headspace is then milled with the T-slot milling
cutter.
(h) Angle Milling Cutters. The angle milling cutter has peripheral
teeth which are neither parallel nor perpendicular to the cutter axis.
Common operations performed with angle cutters are cutting teeth in ratchet
wheels, milling dovetails, and cutting V-grooves. Angle cutters may be
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
(i) Concave and Convex Milling Cutters. Concave and convex milling
cutters (figure 30 on the following page) are formed tooth cutters shaped to
produce concave and convex contours of one-half circle or less. The size of
the cutter is specified by the diameter of the circular form the cutter
produces.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
(k) Gear Hob. The gear hob (figure 31) is a formed-tooth milling cutter
with helical teeth arranged like the thread on a screw. These teeth are
fluted to produce the required cutting edges. Hobs are generally used for
such work as finishing spur gears, spiral gears, and worm wheels. They may
also be employed for cutting ratchets and spline shafts.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
(1) Special Shaped-formed Filing Cutter. Formed milling cutters have the
advantage of being adaptable to any specific shape for special operations.
The cutter is made for each specific job. In the field, a fly cutter is
made to machine a specific shape. The fly cutter (figure 32) is often
manufactured locally. It is a single-point cutting tool similar in shape to
a lathe or shaper tool. It is held and rotated by a fly cutter arbor. The
cutter can be ground to almost any shape, form, or contour that is desired.
The cutter can be sharpened many times without destroying the shape of the
cutter or the cut being made. There will be a very limited number of times
when a special formed cutter will be needed for cutting or boring
operations, this is why a fly cutter is the most practical cutter to use in
this type of situation.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
(2) Method of Folding The Workpiece. For example, 45° angular cuts may
either be made with a 45° single-angle milling cutter while the workpiece is
held in a swiveled vise, or with an end milling cutter while the workpiece
is set at the required angle in a universal vise.
(3) Hardness of The Material To Be Cut. The harder the material, the
greater will be the heat that is generated during the cutting process.
Cutters should be selected for their heat-resisting properties.
(6) Class of Work Being Done. Some operations can be accomplished with
more than one type of cutter, such as in milling the square end on a shaft
or reamer shank. In this case, one or two side milling cutters or an end
milling cutter may be used. However, for the majority of operations,
cutters are specially designed and named for the operation they are to
perform.
(7) Rigidity and Size of The Workpiece. The milling cutter used should
be small enough in diameter so that the pressure of the cut will not cause
the workpiece to be sprung or displaced while being milled.
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
(1) New cutters received from stock are usually wrapped in oilpaper which
should not be removed until the cutter is to be used.
(2) Care should be taken to operate the machine at the proper speed for
the cutter that is being used; excessive speed will cause the cutter to wear
rapidly from overheating.
(3) Whenever practicable, the proper cutting oil should be used on the
cutter and the workpiece during the operation, since lubrication helps
prevent overheating and consequent cutter wear.
(4) Cutters should be kept sharp, because dull cutters require more power
to drive them and this
68
MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/TASK 2
power, being transformed into heat, softens the cutting edges. Dull cutters
should be marked as such and set aside for grinding.
(6) Care should be taken to prevent the putter from striking the hard
jaws of the vise, chuck, clamping bolts, or nuts.
(7) A milling cutter should be thoroughly cleaned and lightly coated with
oil before storing.
3. Conclusion
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/PE 1
PRACTICAL EXERCISE
1. Instructions
2. Requirement
c. Which component holds and drives the various cutting tools on the
knee-type milling machine?
d. Which component on the ram-type milling machine aligns the outer end
of the arbor with the spindle?
f. What is the most common means of fastening the arbor in the milling
machine spindle?
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/PE 1
p. What is the required time allocated for proper gib adjustment on a new
milling machine?
q. When making knee gib adjustments with a dial indicator, the deflection
should not be more than how many thousandths of an inch?
r. When the gibs are adjusted too tightly, what is the end result?
s. Which type milling cutter requires less power to operate and produces
a smoother finish?
w. Which type cutters are used for cutting relatively wide slots with
accuracy?
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/PE 1
Requirement
c. The spindle
d. Arbor support
f. Draw-in bar
j. 40 turns of the index crank revolves the spindle one complete turn (40
to 1 ratio).
k. 24 holes
l. Right angles
m. The type of materials being cut and the size of the cutter being used
n. Angular milling is milling flat surfaces that are neither parallel nor
perpendicular to the axis of the milling cutter.
p. After 40 hours
q. 0.0003 inch
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MILLING MACHINE OPERATIONS - OD1644 - LESSON 1/PE 1
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MILLING MACHINE OPERATIONS - OD1644 - REFERENCES
REFERENCES
74
MILLING MACHINE OPERATIONS - OD1644 - REFERENCES
REFERENCES
DA Pam 738-750
TM 9-3417-213-10
TM 9-3417-213-14&P
FM 9-24
75