2. Machining
• Machining
– A subtractive process used to get desired shape, size, and
finish by removing surplus material in the form of chips
by a cutting tool and by providing suitable relative motion
between the workpiece and cutting tool
– Process of finishing by which jobs are produced to the
desired dimensions and surface finish by gradually
removing the excess material from the preformed blank in
the form of chips with the help of cutting tool (s) moved
past the work surface (s).
6. Machine tool
• A machine tool is a non-portable power operated and
reasonably valued device or system of devices in which energy
is expended to produce jobs of desired size, shape and surface
finish by removing excess material from the preformed blanks
in the form of chips with the help of cutting tools moved past
the work surface (s)
• Physical functions of a Machine Tool in machining are:
– firmly holding the blank and the tool
– transmit motions to the tool and the blank
– provide power to the tool-work pair for the machining
action
– control of the machining parameters, i.e., speed, feed and
depth of cut
9. Basic Machine Tools
Shaping machine
• Ram: it holds and imparts cutting motion to the tool through
reciprocation
• Bed: it holds and imparts feed motions to the job (blank)
• Housing with base: the basic structure and also accommodate the
drive mechanisms
10. Basic Machine Tools
Shaping machine
• Power drive with speed and feed change mechanisms
• Shaping machines are generally used for producing flat surfaces,
grooving, splitting etc.
11. Basic Machine Tools
Planing machine
• In planing the job reciprocates for cutting motion and the tool
moves slowly for the feed motions unlike in shaping machine.
• Planing machines are usually very large in size and used for
large jobs and heavy duty work.
12. Basic Machine Tools
Drilling machine
• Drilling (originating or enlarging cylindrical holes)
• Boring, counter boring, counter sinking etc.
• Cutting internal threads in parts like nuts using suitable
attachment
13. Basic Machine Tools
Drilling machine
• Column with base: it is the basic structure to hold the other
parts
• Drilling head: this box type structure accommodates the power
drive and the speed and feed gear boxes
• Spindle: holds the drill and transmits rotation and axial
translation to the tool for providing cutting motion and feed
motion
• Pillar drill, column drill, radial drill, micro-drill etc.
15. Classification of Machine Tools
1. Direction of major axis
– horizontal center lathe, horizontal boring machine etc.
– vertical – vertical lathe, vertical axis milling machine etc.
– inclined – special
2. Purpose of use
– general purpose – e.g. lathes, milling, drilling machines etc.
– single purpose – e.g. facing lathe, roll turning lathe etc.
– special purpose – for mass production
3. Number of spindles
– single spindle – center lathes, milling machines etc.
– multi-spindle – gang drilling machines etc.
16. Classification of Machine Tools
4. Degree of automation
– Manual – e.g. lathes, drilling machines etc.
– Semi-automatic – e.g. turret lathe
– Automatic – e.g., CNC Drill, CNC Mill, CNC lathe etc.
5. Type of automation
– fixed automation – e.g., single spindle and multispindle
lathes
– flexible automation – e.g., Machining Centers
6. Precision
– Ordinary
– High precision
17. Classification of Machine Tools
7. Size
– Heavy duty – e.g., heavy duty lathes (e.g. ≥ 55 kW), boring
mills, etc.
– Medium duty – e.g., lathes (e.g. – 3.7 ~ 11 kW), column
drilling machines etc.
– Small duty – e.g., table top lathes, drilling machines,
milling machines.
– Micro duty – e.g., micro-drilling machine etc.
8. Configuration
– Stand alone type – most of the conventional machine tools.
– Machining system – e.g., machining center, FMS etc.
18. Cutting Tool
• Removes excess material through direct mechanical contact
• Tool moves along the workpiece at a certain velocity (cutting speed – V)
and a depth of cut (to) to produce a chip just ahead of tool by shearing the
material continuously along the shear plane
Tool material Selection depends on:
• Work material (hardness, chemical and metallurgical state)
• Part features (geometry, accuracy, finish, surface-integrity)
• Machine tool characteristics (rigidity, horsepower, speed, feed , precision)
• Support system (Operator, sensors, controls, method of chip removal,
lubrication, maintenance)
27. Cutting Tool
Tool steels
• Carbon and low-/medium-alloy steels
• Steel is considered to be carbon steel:
– when no minimum content is specified or required for Cr,
Co, molybdenum, Ni, Ti, W, V or zirconium etc.
– when the specified minimum for copper does not exceed
0.40 percent;
– when the maximum content specified is less than Mn - 1.65,
Si - 0.60, Copper - 0.60.
– steel which is not stainless steel
• 0.9 to 1.3% carbon
• With increase in carbon content, steel become harder and
stronger
28. Cutting Tool
Tool steels
• With increase in carbon content, steel become lesser ductile
and melting point decrease
• Hardness loss at 200 0C
• Mo and Cr increases hardenability
• Mo and W improves wear resistance
• Applications
– Drills, Taps, Dies etc.
– Low speeds
29. Cutting Tool
HSS
• Good wear resistance, hardenability and hot hardness
• Good toughness and resistance to fracture
• Good cutting at 400 0C
• Easy fabrication
• Types
– Molybdenum (M series)
• 10% Mo with Cr, V, W, Cr and Co
• High abrasion resistance than t series
• Less Distortion than T series
• Cheaper than T series
– Tungsten (T series)
• 12-18% W, Cr, V and Co (18-4-1 W-Cr-V)
• Used for complex tool geometries
30. Cutting Tool
TiN coated HSS
• Film thickness 0.00254 - 0.00508 mm
• 10-20% higher cutting speeds than HSS
• Gear cutters, drills, bandsaw, circular saw blades, form tools,
inserts etc.
• Reduced tool wear
• High hardness
• PVD
31. Cutting Tool
Cast Cobalt Alloys
• Cobalt rich, chromium-tungsten-carbon cast alloys
• Stellite tools (Deloro Stellite Company)
• Non-magnetic and corrosion-resistant cobalt alloy
• W or Mo and a small amount of carbon
• Retain hardness to much greater temperatures
• 25 % higher cutting speeds than HSS
• Cast to shape
• Used only for single point tools or saw blades
32. Cutting Tool
Carbide or Sintered Carbides
• Types:
– Tungsten carbide (WC bonded together in a cobalt matrix)
• 1-5 µm WC particles are combined with cobalt in a mixer, then presses and
sintered into the desired insert shapes.
• Cemented carbides Sintered Carbides
• With increase of Co – toughness increases but there is decrease in strength,
hardness and wear resistance
• Machining steels, CI, nonferrous and nonmetals
– Titanium Carbide (TiC in Ni-Mo alloy matrix)
• Higher wear resistance than WC
• Lesser toughness than WC
• Machining hard materials like steels, CI
• Higher speeds than WC
• Finishing and semifinishing ferrous alloys
• Auto industry using Ni-Mo binder
34. Cutting Tool
Inserts are clamped on tool shank with various locking
mechanisms
• (a) Clamping
• (b) Wing lock pins
• (c) Thread-less lock pins - secured with side
• (d) Brazed on a tool shank
35. Cutting Tool
Chip Breaker
• Continuous chips are undesirable as they are a potential safety hazard
• Cutting at low speed may lead to welding of chips to tool face
• Ideal chip – Shape of letter “C” or number “9” and fits within 25 mm
square block
• Procedure used for breaking chips intermittently is with use of chip breaker
36. Cutting Tool
Chip Breaker
(a) tightly curled chip
(b) chip hits workpiece and breaks
(c) continuous chip moving away from workpiece
(d) chip hits tool shank and breaks off
38. Cutting Tool
Chip Breaker
• Chip breaking in softer materials like Al include machining at
small increments and then pausing.
• In shaping, milling or other such intermittent operations chip
breakers are not required
39. Cutting Tool
• American National Standards Institute (ANSI) – C-1 to C-8
• ISO Standards – P, M and K
Classification of Tungsten Carbides
41. Cutting Tool
Coated Carbide tools
• Coating increase tool life by 200-300 times
• Coating increase 50-100% in speed of the same tool life
• 80-90 % of carbide tools are coated
• Bulk tool material can be tough, shock resistant carbide that can withstand
high temperature plastic deformation and resist breakage
• Thin chemically stable, hard refractory coating of TiC, TiN, TiCN or
Al2O3, Diamond, TiAlN, CrC, ZrN etc.
• Fine grained coatings
• Free form binders and porosity
• Low coeff. of friction for coating – non adherence of chips on rake face
42. Cutting Tool
Coated Carbide tools
• Single or multiple
• Multiple coating provide stronger metallurgical bond between
coating and substrate
• For multiple coating:
– Innermost layer should bond
with substrate
– Outermost layer should resist
wear
– Intermediate layer should
bond well and be compatible
with both layers
44. Cutting Tool
Ceramics (White or cold-presses ceramics)
• 1950
• Pure Aluminium oxide, Al2O3, or SiC
• Pressed into insert shapes
under high pressure
• TiC and ZrO may be
added to improve
toughness and
resistance to thermal
shock
45. Cutting Tool
Ceramics
• Particulates or whiskers
• 2 to 3 times cutting speed than WC
• High hardness and chemical inertness
• Hard and brittle – require rigid tool holders and machine tools
• Less tendency to adhere to metals during machining – good SF
• Used for high speed cutting/finishing of super-alloys and high
strength steels
• Not suitable for Al, Ti as they react with alumina based
ceramics
46. Cutting Tool
Cermets (Ceramics + Metal)
• Black or hot-pressed ceramics
• Mix of 70% aluminium oxide and 30% TiC
• Intermediate performance between ceramics and carbides
47. Cutting Tool
Polycrystalline CBN
• High hardness (Knoop 4700 at 20 oC 4000 at 1000 oC)
• Low chemical reactivity
• 0.5-1 mm layer of PCBN is bonded to a carbide substrate by
sintering under pressure.
• Carbide provides toughness – CBN provides high wear
resistance and cutting edge strength
• Used for automotive industry
Difficult-to-machine materials
• Used for aerospace materials
• Higher cost than ceramics tools or cemented carbides but tool
life is 5-7 times that of a ceramic tool
49. Cutting Tool
Diamond
• High Wear resistance, low tool-chip friction, sharp cutting edges
• Used for fine surface finish and dimensional accuracy
• Brittle - Light and uninterrupted finishing cuts
• High speed machining and fine feeds
• Single-crystal diamond tool – machining optical mirrors
• Polishing is not required after machining
• Polycrystalline diamond tools (compacts or industrial diamonds) – small
synthetic crystals, fused by high pressure and temperature to a thickness of
.5-1 mm and bonded to a carbide substrate
51. Tool Geometry
• One or more sharp cutting edges
• Connected to cutting edge – two surfaces
– Rake face – directs the flow of newly formed chip and is
oriented at an angle α (rake angle – measured relative to
plane perpendicular to work surface)
• Positive rake angle – reduces cutting force
– Flank – provides a clearence between tool and newly
generated work surface, thus protecting the surface from
abrasion (relief angle)
52. Tool Geometry
• Tool point (nose radius) – The point (rounded to a certain
radius) on tool penetrates below the original work surface
53. Cutting Condition
• Cutting speed ‘v’
• Tool movement (lateral across the work) – feed ‘f’
• Penetration of cutting tool below the original work surface –
‘DOC’
RMR = vfd
where, RMR = material removal rate (mm3/min), v = cutting
speed (mm/s), d = DOC (mm)
54. Types of Chips
• Chip has two surfaces
Shiny – in contact with rake face (rubbing of chip as it moves
up the tool face)
Rough or jagged – no contact with any solid body
• Primary shear Zone – along the shear plane
• Secondary Zone – shearing action after chip has been formed
(results from friction between chip and tool along the rake
face)
• Continuous
• Continuous with BUE
• Serrated
• Discontinuous
55. Types of Chips
• Continuous
– Good surface
– Steady cutting force
– Undesirable in automated machining
– Formed in ductile materials at high cutting speeds and high rake angles
56. Tool Geometry
Continuous with BUE
• Ductile materials at low-to-medium cutting speeds, friction
between tool and chip tends to cause portions of work material
to adhere to rake face of tool near the cutting edge
• BUE forms and grow, then becomes unstable and breaks off
• Detached BUE sometimes takes away portions of tool rake
face (may lower tool life)
• Detached BUE that are not carried off may imbed in newly
created work surface causing roughness
• Thin stable edge protects tools
57. Types of Chips
Serrated (segmented, non-homogeneous)
• Difficult-to machine- materials like Ti, Ni-base super alloys at
higher cutting speeds.
• Saw-tooth appearance (semi-continuous)
• Produced by cyclical chip formation of alternating high shear
strain followed by low shear strain
58. Types of Chips
Discontinuous
• Brittle materials (like CI) at low cutting speeds
• Chips forms as separate segments
• Fluctuating cutting forces
• Irregular texture to machined surface
• Desirable for ease of chip disposal
60. Orthogonal Cutting
• Cutting edge is perpendicular to direction of cutting speed
• Force by tool forms chip in material by shear deformation
along shear plane (angle Ø with work plane)
• Cutting edge is positioned at a certain distance below original
work piece (to - chip thickness prior to chip formation
• When chip forms along shear plane its thickness increases (tc)
• Chip thickness ratio ‘r’
– r = to/tc
61. Lathe
Lathe
• Oldest Machine Tool invented
• Principal form of surface produces – cylindrical
• Turning - Workpiece is rotated, while single-point cutting tool
removes material by traversing in direction parallel
(cylindrical jobs) to the axis of rotation
62. Lathe
Types:
– Engine lathe
– Tool room lathe
– Speed lathe
– Turret lathe
– Automatic lathe
– Numerical control lathe
Centre Lathe
• Generally workpiece is clamped by centres in lathe
• Also called as Engine lathe (driven by steam engines)
• Heavy duty machine tools with all the components have power
drive for all tool movements except on compound rest
• Most engine lathes are equipped with chip pans and a built-in
coolant circulating system
63. Lathe
Tool room lathe
• Tool making / smaller parts
• Greater accuracy and usually a wider range of speeds and
feeds than engine lathes.
• Designed to have greater versatility to meet the requirements
of tool and die work
• Generally used for machining smaller parts
• High range of sizes
64. Lathe
Speed Lathe
• Speed lathes usually have only a headstock, a tailstock, and a
simple tool post
• Usually three or four speeds
• Mainly used for wood turning, polishing, or metal spinning
• Spindle speeds up to 4000 rpm.
65. Lathe
Turret Lathe
• Hexagon turret replaces the tailstock
• Turret used for mounting tools and feed into the work piece
• Turret lathes Use the 11 station tooling and so as to increase
production rate by reducing tool changing time .
• Six tools can be mounted on the hexagon turret
• Turret can be rotated about the vertical axis to bring each tool
into the operating position
69. Lathe
Work Holding Devices
• Suitable locations
• Effective clamping
• Support
• Face plate: for holding irregular shape w/p
• Lathe centers: for holding long jobs
• Chuck:
– 3 jaw chuck for circular or hexagonal section
– 4 jaw chuck for irregular shapes
– Magnetic chuck for holding soft metal
72. Lathe
Mandrel
– for holding hollow disc shape w/p for machining
of side faces
73. Lathe
Collet
– for holing small diameter tool and work pieces
74. Lathe Tool Geometry
• Tool cross-section – square or rectangular
• Shank (supported in tool post of lathe) – part of tool, on one
end of which cutting point is formed
α=0 -α
+α
Positive Rake Zero Rake Negative Rake
Positive rake – helps reduce cutting force and thus cutting power requirement
Negative rake – to increase edge-strength and life of the tool
Zero rake – to simplify design and manufacture of the form tools.
Clearance angle must be positive (3o ~ 15o)
76. Lathe
• Right/Left tool
– Tools have primary cutting edge by means of which the
direction of the movement of tool for removing of metal is
indicated
– Tool is termed as right, right palm is placed on tool, the
direction of thumb indicates the direction of tool motion
(tool towards the headstock)
77. Lathe Tool Geometry
• Zero or negative rake are used for better heat conductivity on
carbide, ceramic PCD and PCBN tools
• Negative rake angle increase tool forces, it keeps tool in
compression and provides added support to cutting edge. This
help in making intermittent cuts and in absorbing impact
during initial engagement of tool
78. Lathe Tool Geometry
Systems of description of tool geometry
• Tool-in-Hand System
– where only the salient features of the cutting tool point are identified or
visualized (no quantitative information)
• Machine Reference System – ASA system
79. Lathe Tool Geometry
Machine Reference System
• American Standards Association (ASA) system
• Geometry of a cutting tool refers mainly to its several angles
or slope of its salient working surfaces and cutting edges.
Those angles are expressed w.r.t. some planes of reference.
• Machine Reference System (ASA) is based on three planes of
reference and three coordinates of reference. These references
are chosen based on the configuration and axes of the machine
tool concerned.
81. Lathe Tool Geometry
• Back-rake angle: Angle b/w face of tool and base of shank (measured in a
plane through the side cutting edge, and at right angle to base)
• Side-rake angle: Angle b/w face of the tool and the base of shank
(measured in a plane perpendicular to the base, to the side cutting edge)
The side rake and back rake angle combines to form effective rake
angle (true rake or resultant rake)
• End-relief angle: Angle between the portion of the end flank immediately
below the end cutting edge, and a line drawn through this cutting edge
perpendicular to the base (measured in plane perpendicular to the end
flank)
• Side-relief angle: Angle between portions of the end flank immediately
below the side-cutting edge and a line drawn through this cutting edge
perpendicular to the side flank
Relief angles affects tool life and surface quality of workpiece
82. Lathe
a. 3D views of tool
b. Oblique view of tool from cutting edge
83. Lathe Tool Geometry
• Side and end cutting-edge angles defines nose angle. Side
cutting Edge angle controls the width and thickness of chips
• Nose radius has a major influence on surface finish. High nose
radius decrease tool wear and improves surface finish.
84. Lathe
Turning is the process of machining external cylindrical and
conical surfaces.
– Straight turning: for producing cylindrical shapes
– Taper turning: for producing conical shapes
– Facing: making edges square and clear
– Chamfering: slightly tapering and rounding off of edges
– Threading: for producing threads
– Drilling: for creating /producing hole
– Boring: for enlarging hole and correcting shape
– Parting off or necking: separating or making square groove
– Knurling: making impression for firm gripping
– Reaming: finishing purpose
86. Lathe - Turning
Turning Cuts
Roughing
– As heavy as proper chip thickness, tool life, machine power
and work material properties permit
– Slow speeds for hard workpieces
Finishing
– Light, usually less than (0.015 in)
– Usually same tool is used for roughing and finishing
88. Lathe - Turning
Cutting speed – V (fps)
DOC d = (D1-D2)/2
Length of Cut = Distance travelled ‘L’ + Allowance ‘A’
Feed - f
Rpm value of machine tool - N = 12V/πD1
Cutting Time – T = (L+A)/fN
MRR = L(πD12- πD22)/4
(L+A)/fN
Neglecting A and substituting N
MRR = 12Vfd (d is very small as compared to D1(d = 1))
89. Lathe - Turning
Cutting speed – V (fps)
DOC d = (D1-D2)/2
Length of Cut = Distance travelled ‘L’ + Allowance ‘A’
Feed - f
Rpm value of machine tool - N = 12V/πD1
Cutting Time – T = (L+A)/fN
MRR = L(πD12- πD22)/4
(L+A)/fN
Neglecting A and substituting N
MRR = 12Vfd (d is very small as compared to D1(d = 1))
90. Lathe – Taper Turning
• Cutting tool is fed at an angle to the axis of rotation producing
an external/internal conical surface.
• Tapers generally specified in degrees of included angle between
the sides (or rate of change in diameter along the length
mm/mm)
Taper tuning can be performed by using:
• Swiveling of compound rest (short and steep tapers)
• Form tools
• Offsetting tail stock
• Taper turning attachment (fine taper-ness)
• NC lathe with programmed movement of tool
91. Lathe – Taper Turning
Swiveling of compound rest (short and steep
tapers)
Tool is set
at half of taper angle w.r.t. lathe
axis and moved with compound rest
only
Manual Feed (non-uniform)
Short and steep tapers
Limited movement of comp. rest
Low productivity
Poor surface roughness
92. Lathe – Taper Turning
Swiveling of compound rest (short and steep
tapers)
93. Lathe – Taper Turning
Form Tools
Feed is given by plunging the tool directly into the work
Short tapers like chamfering
Tool may vibrate excessively on long tapers
Poor surface quality in long tapers
94. Lathe – Taper Turning
Offsetting tail stock
Offsetting results in inclination in job’s axis of rotation
by half angle of taper
The feed is given parallel to guide ways
98. Lathe – Taper Turning
Taper turning arrangement
Separate slide way is arrange at rear of cross-slide. This slide can
be rotated at angle
The cross-slide is made free by disconnecting it from lead screw
99. Taper turning
attachment
• Cross
slide is
made free
and tool
is moved
with help
of
attachme
nt at an
angle
100. Lathe-Boring
Boring
Enlarging of an existing hole
Correction of eccentricity
Holes may be bored straight, tapered or irregular threads
Similar to internal turning while feeding tool parallel to rotation
axis of workpiece
Higher clearance angle and lower length to diameter
Boring bar is used
102. Lathe-Facing
Facing
Producing flat surface
Tool is fed across the end of rotating workpiece
Tool feeds perpendicular to axis of rotating workpiece
Cutting speed is determined from largest diameter on workpiece
Tool point must be set exactly at height of center on workpiece
Length of cut - L = D1/2 (rod)
- L = (D1-D2)/2 (tube)
104. Lathe-Facing
Facing
Producing flat surface
Tool is fed across the end of rotating workpiece
Tool feeds perpendicular to axis of rotating workpiece
Cutting speed is determined from largest diameter on workpiece
Tool point must be set exactly at height of center on workpiece
Length of cut - L = D1/2 (rod)
- L = (D1-D2)/2 (tube)
105. Lathe-Facing
Cutting Time – T = (L+A)/fN = (D1/2 + A)/fN
Rpm value of machine tool - N = 12V/πD1
MRR = π D12dfN
substituting N, L=D1/2 MRR = 6Vfd
106. Lathe-Facing
End facing: facing by tool moving radially
outward from the center
Shoulder facing: facing the stepped
cylindrical work piece
108. Cut-off tool is used
Lathe - Parting
One section of workpiece is severed from remaining
Tool should be set exactly at height of axis of rotation
Tool is fed perpendicular to rotational axis
Length of cut - L = D1/2 (rod)
- L = (D1-D2)/2 (tube)
Cutting Time – T = (L+A)/fN = (D1/2 + A)/fN
Rpm value of machine tool - N = 12V/πD1
MRR = π D12dfN
substituting N, L=D1/2 MRR = 6Vfd
109. Lathe - Drilling
Drilling
Tool (Drill) can be mounted on the tailstock of engine lathes or
turrets of turret lathes
Fed by hand against a rotating work piece along the axis of lathe
Coolant can be used
Occasional withdrawal to clear chips and delivery of coolant to
cutting edge
110. Lathe - Reaming
Similar to drilling on lathe
It is semi-finishing operation that
enlarges an existing hole
Tool is rotated and fed along
rotational axis.
111. Lathe - Knurling
Knurling
Roughening the surface of work
piece for better gripping.
Generally a cold-forming process
Process involves pressing of two
hardened rolls against the rotating
work piece with sufficient force to
form impression (the knurl) like
raised diamond pattern.
113. Contour turning
The tool follows a contour creating a
contoured form on the turned part
instead of parallel to the axis.
Cross slide is made free to follow
the path of contour.
Form Turning
Cutting edge of Tool has a Specific Form or Shape and is
fed radially inward towards the axis of rotating work
piece.
114. Chamfering
The tool is fed radially inward
used to cut an angle on the
corner of the cylinder,
forming a chamfer to avoid
sharp edges.
115. Drilling
• Drilling is most common single machining
operation
• Drilling makes up 25% of machining
• Drilling occurs at the end of a tool
116. Drilling
1. A small hole is formed by the web—chips are not cut here in
the normal sense.
2. Chips are formed by the rotating lips.
3. Chips are removed from the hole by the screw action of the
helical flutes.
4. The drill is guided by lands or margins that rub against the
walls of the hole.
Twist Drill
119. Drilling
• Rake angle of a drill varies along the cutting edges (lips)
– Negative close to point
– Equal to helix angle out at lip
• Generally rake angle is 24o
• High speed drilling - rake angle is 30o
• Soft materials (plastics) – rake angle is 0o to 20o
• Cone angle – affects direction of flow of chip across the tool
face and into the flute
– Generally cone angle of 118°
– Brittle materials (gray CI, Mg alloys) 90° to 118°
– Ductile materials (Al alloys) 118° - 135°
120. Drilling
• The most common drills are twist drills
• Twist drills have three parts
– Body: consisting of spiral grooves called flutes, separated
by lands
– Point: a wide variety of geometry are used
– Shank: a straight or tapered section where the drill is
clamped.
121. Drilling
(a) straight shank with tang,
(b) tapered shank with tang,
(c) straight shank with whistle notch,
(d) straight shank with flat notch.
122. Drilling
Cutting Speed at drill center is low (approaching zero)
Cutting speed at outer tips is highest
Intersection of web and
cone produces a
straight line chisel end
123. Drilling
• Straight line chisel point causes drills to “walk” along the
surface
• This effect is counter by using centering techniques
– Center punches
– Pre-drilled guide holes for large holes
• Specialized tips are used to produce self centering holes where
hole position is critical.
– Helical tips
– Four-facet tips
– Racon
– Bickford
– Center core, or slot drills
128. Drilling
• Specialty Drills
– Hole cutters: used for holes in sheet stock
– Step drill – used for two or more diameters
– Subland drills: used for multi diameter holes
– Indexable drills: used for high speed shallow holes in solid
stock
– Centre drill bit with internal coolant
– Micro drills (pivot drills): used for holes 0.02 to 0.0001
inch diameter where grain boundaries and inclusion
produce non-uniform material properties
129. Drilling
Hole Cutters
• When cutting large
holes in sheet stock, a
hole cutter is used
• Hole cutters have a pilot
drill in the center used
to accurately locate the
center
• Also called a hole saw
130. Step Drill
Drilling
Single set of flutes and is ground to two or more diameters
Subland Drill
Separate set of flutes on a single body for each diameter.
133. Drilling
Drill Chucks
• Small Drill Press – Chuck is permanantly
attached
• Large Drill Press – Chuck has tapered shank
that fits into the taper on machine spindle
• Chucks use chuck keys/collet-type holders
135. Machine Tools for Drilling
• Drilling can be performed on:
– Lathes
– Vertical mills
– Horizontal mills
– Boring machines
– Machine centers
• Specialized machines designed specifically for
drilling called “drill presses”
136. DRILLING MACHINE
Drilling is Most Commonly Performed on a Drill Press.
DRILL PRESS Consists
of Following Parts
1. Base,
2. Column
3. Power-Head
4. Spindle
5. Worktable
These may be bench
or floor mounted
depending on the
size
Drill can be fed
manually or Upright Drill Press.
automatically
137. TYPES of DRILLING MACHINES
MAIN TYPE Applications
1. BENCH Holes up to 0.5 in. Diameter can
be Drilled. Very High Speed up to
30,000 rpm
2. UPRIGHT Speeds Ranges from 60 to 3500
RPM
3. RADIAL For Large Workpieces that
Cannot Easily be Handled
Manually.
138. TYPES of DRILLING MACHINES
MAIN Applications
TYPE
4. GANG Mass Production variety of
purposes such as Holes of
Different Sizes, Reaming,
Counterboring, on a Single Part.
139. TYPES of DRILLING MACHINES
MAIN Applications, Designation
TYPE
5. MULTI- Mass Production Machines with as many
SPINDLE as 50 Spindles Driven by a Single
Power head and Fed Simultaneously
into Work.
6. DEEP- For Drilling Long (Deep) Holes in
HOLE Rifle Barrels, Connecting Rods, and
Long Spindles.
