conventional lathe machine
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Conventional Lathe Machine
Mohd Zaid B. Akop15 January 2008
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CONTENTS
1. Introduction
2. Machine Function
3. Safety Precautions
4. Cutting Tools
5. Toolholders
6. Lathe Operations
7. Speeds & Feeds
8. Tools Geometry
FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA
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1. INTRODUCTION
Description: The purpose of a lathe is to rotate a part against a cutting
tool, thereby removing metal. It is used for fabricating parts and/or features that have a circular cross section. The spindle is the part of the lathe that rotates. Various work holding attachments such as three jaw chucks, collets, and centers can be held in the spindle. The spindle is driven by an electric motor through a system of belt drives and/or gear trains.
FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA
Lathe cutting action(Source: Kelmar Associates)
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1. INTRODUCTION-(cont’d)
Spindle speed is controlled by varying the geometry of the drive train. The tailstock can be used to support the end of the workpiece with a center, or to hold tools for drilling, reaming, threading, or cutting tapers. It can be adjusted in position along the ways to accomodate different length workpieces. The ram can be fed along the axis of rotation with the tailstock handwheel. The carriage controls and supports the cutting tool. It consists of:
1. A saddle that mates with and slides along the ways.
2. An apron that controls the feed mechanisms.
3. A cross slide that controls transverse motion of the tool (toward or away from the operator).
4. A tool compound that adjusts to permit angular tool movement.
5. A toolpost T-slot that holds the toolpost.
FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA
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1. INTRODUCTION-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Lathe Machine
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1. INTRODUCTION-(cont’d)
Types of Lathes:The engine lathe has kept pace with technological changes in
order to increase productivity and improve part quality. The most common engine lathes are:
1.The Engine Lathe – the accuracy of work produced is controlled by the operator. An experienced operator will be able to produce work to within 0.02 mm of accuracy.
2.The Engine Lathe with Digital Readout – it helps to improve the accuracy and performance of a lathe machine. Accuracy is up to 0.002 mm.
3.The Conventional/Programmable Lathe – it is equipped with digital readout (DR) and limited programming features. DR shows the location of cutting tool and X and Z workpiece dimensions.
4.The Computer-Numerically Controlled Lathe (CNC Lathe) – all movements are CNC controlled. Specially designed for production work that requires great precision and high productivity.
FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA
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2. MACHINE FUNCTION
Main Functions of a Lathe Machine:The main function of a lathe machine is to provide a means of rotating a workpiece against a cutting tool, thereby removing metal. All lathes have the same 3 basic functions:
1. A support for the lathe accessories or the workpiece.
2. A way of holding and revolving the workpiece.
3. A means of holding and moving the cutting tools.
Headstock - headstock supports spindle which rotates on ‘Zero Precision’ tapered roller bearings. Work holders are mounted on spindle nose.
Chuck - chuck is mounted on spindle nose. Adjustable jaws permit holding of larger diameter workpieces.
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2. MACHINE FUNCTION-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Tailstock - tailstock center supports right end of work held ‘between centers’. It can be offset to cut tapers, lock in any position along lathe bed, and has hand wheel feed for tailstock tools.
Apron - apron controls are centrally grouped with selector lever for power longitudinal and cross feeds, friction clutch for engaging feeds, half nut lever for thread cutting, and hand wheel for hand traverse of carriage.
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3. SAFETY PRECAUTIONSFAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
General Turning:1. Wear approved safety goggles.
2. Confirm that all guards are in place.
3. Before starting the lathe, turn the spindle by hand to insure that it turns freely. If the spindle is locked in a stationary position with the back-gear lever as well as the bull-gear pin, release one of these devices for the desired kind of drive and speed.
4. Stop the machine to make adjustment.
5. Stop the machine if you need to make measurement.
6. Stop the machine to remove chips. Do not remove them with the hands - always use a brush or stick.
7. Stop the machine for oiling.
8. Always stop the machine when adjusting the tool in the tool post.
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3. SAFETY PRECAUTIONS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
General Turning:9. Keep the machine clear of long chips, rags, and
unnecessary hand tools.
10. Use the right type of cutting tool for the job.
11. Adjust the feed, speed, and depth of cut according to the size and type of metal.
Turning Between Centers:12. Be sure that the tailstock and the tailstock ladle are
locked securely.
13. When available, use a safety dog to drive the work piece. Select the smallest dog which will do the job and clamp it tightly.
14. Lubricate the tailstock dead center properly and frequently.
15. Always cut toward the headstock whenever possible.
16. Before starting the power feed, make certain at the carriage has sufficient free travel to complete the cut without running into the lathe dog.
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3. SAFETY PRECAUTIONS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Turning Work in Chuck:17. Place a board under the chuck when mount ing it or
removing it from the spindle. Keep the fingers clear.
18. Be sure that the chuck is mounted tightly to the spindle.
19. Be sure that the work is mounted tightly in the chuck.
20. Always remove the chuck wrench or key from the chuck immediately after using it.
21. Turn the chuck one complete revolution by hand after the work is mounted to see that it clears the carriage and the ways.
22. Never allow the cutting tool or tool holder to come into contact with the revolving chuck jaws.
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3. SAFETY PRECAUTIONS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Turning Work in Faceplate: 23. Be sure the faceplate is secured tightly to the lathe
spindle.
24. Use the shortest bolts and clamps possible for clamping work to the faceplate, and clamp the work securely. The clamps should be supported at the outer ends and should be parallel to the faceplate.
25. Use a counterweight, if necessary, to balance an off-center work piece.
26. Before starting the machine, turn the work one complete revolution by hand to see that it clears the carriage and the ways.
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4. CUTTING TOOLSFAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Lathe Cutting Tools: Tool bits - types of tool bits include
right and left hand turning tools, facing
tools, cutoff tools and threading tools.
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4. CUTTING TOOLS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Common cuts made by various cutting tools:
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4. CUTTING TOOLS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Carbide tipped:
These tool are resharpened as needed, using special silicon carbide or diamond grinding wheel.
Indexable throwaway inserts: Made of carbide, ceramic and diamond When the initial cutting edge became dulled, rotate to
the next cutting edge, reclamp and continue cutting without any change of tool holder position.
Regrinding – generally more costly than replacing them. Discarded after all cutting edges become dulled
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4. CUTTING TOOLS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Standard shapes for indexable throwaway insert cutter
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4. CUTTING TOOLS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Cutting Tool Materials: Cutting tools for metalworking are made of high speed
steel, cast alloys and cemented carbide. Also made of ceramic and diamonds for special purposes. Cutting tool must be made of material with suitable
properties:
1. Must have sufficient hardness to cut other materials
2. Must be capable of retaining hardness at high
temperatures which are produced at the cutting edge.
3. Must have good wear resistance
4. Must posses sufficient toughness to prevent chipping or
fracturing.
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5. TOOLHOLDERSFAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Types of toolholder
Straight shank toolholder-hold tool bit parallel to the base of the toolholder shank-Intended for holding carbide tipped tool bit also cast alloy bit
Throwaway insert toolholder-Used to hold a carbide/ceramiccutting tool and chip breaker-Many types throwaway inserttoolholder are made to hold different insert.
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5. TOOLHOLDERS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Types of toolholder
Boring toolholders-Used for boring operations using lathe machine
Cutoff toolholders-Used for holding cutoff tool.-Used for cutting grooves, Cutting off stock.
Threading toolholders-Used for holding threading tool.
Knurling tool-Used for performing knurlingoperations
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6. LATHE OPERATIONSFAKULTI KEJURUTERAAN MEKANIKAL
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INSTALLING A CUTTING TOOL
1. Lathe cutting tools are held by tool holders. To install a
tool, first clean the holder, then tighten the bolts. [Video1]
2. The tool post is secured to the compound with a T-bolt. The
tool holder is secured to the tool post using a quick release
lever. [Video2]
POSITIONING THE TOOL
3. First, loosen the bolts securing the compound to the
saddle. Then rotate the compound to the desired angle
referencing the dial indicator at the base of the compound.
Retighten the bolts. Now the tool can be hand fed along
the desired angle. No power feed is available for the
compound. If a fine finish is required, use both hands to
achieve a smoother feed rate.
4. The cross slide and compound have a micrometer dial to
allow accurate positioning, but the saddle doesn't. To
position the saddle accurately, you may use a dial indicator
mounted to the saddle.
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6. LATHE OPERATIONS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
TURNING
The lathe can be used to reduce the diameter of a part to a
desired dimension. First, clamp the part securely in a lathe
chuck. The part should not extend more that three times
its diameter. Then install a roughing or finishing tool
(whichever is appropriate). If you're feeding the saddle
toward the headstock (as in the clip below) use a right-
hand turning tool. Move the tool off the part by backing the
carriage up with the carriage handwheel, then use the
cross feed to set the desired depth of cut. In the clip below,
a finish cut is made using the power feed for a smoother
finish. Remember that for each thousandth depth of cut,
the work diameter is reduced by two thousandths. [Video3]
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6. LATHE OPERATIONS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
FACING
A lathe can be used to create a smooth, flat, face very
accurately perpendicular to the axis of a cylindrical part.
First, clamp the part securely in a lathe chuck [Video4].
Then, install a facing tool. Bring the tool approximately
into position, but slightly off of the part. Always turn the
spindle by hand before turning it on. This ensures that no
parts interfere with the rotation of the spindle. [Video5]
Move the tool outside the part and adjust the saddle to
take the desired depth of cut. Then, feed the tool across
the face with the cross slide. The following clip shows a
roughing cut being made; about 50 thousandths are being
removed in one pass [Video6]. If a finer finish is required,
take just a few thousandths on the final cut and use the
power feed. Be careful clearing the ribbon-like chips; They
are very sharp. Do not clear the chips while the spindle is
turning. After facing, there is a very sharp edge on the
part. Break the edge with a file. [Video7]
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6. LATHE OPERATIONS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
PARTING
1. A parting tool is deeper and narrower than a turning tool. It
is designed for making narrow grooves and for cutting off
parts. When a parting tool is installed, ensure that it hangs
over the tool holder enough that the holder will clear the
w/piece.
2. Ensure that the parting tool is perpendicular to the axis of
rotation and that the tip is the same height as the center of
the part. A good way to do this is to hold the tool against
the face of the part. Set the height of the tool, lay it flat
against the face of the part, then lock the tool in place [
Video8]. When the cut is deep, the side of the part can rub
against sides of the groove, so it’s especially important to
apply cutting fluid. In this clip, a part is cut off from a piece
of stock. [Video9]
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6. LATHE OPERATIONS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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DRILLING
1. A lathe also be used to drill hole accurately concentric with
the centerline of a cylindrical part. First, install a drill chuck
into the tail stock. Make certain that the back of the drill
chuck seats properly in the tail stock. Draw the jaws of the
chuck and tap the chuck in place with a soft hammer. [
Video10]
2. Move the saddle forward to make room for the tailstock.
Move the tailstock into position and lock the it in place.
Before starting the machine turn the spindle by hand.
Always use a centerdrill to start the hole. You should use
cutting fluid with the center drill [Video11]. Always drill
past the beginning of the taper to create a funnel to guide
the bit in. In this clip, a hole is drilled with a drill bit. [
Video12]
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6. LATHE OPERATIONS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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Boring on a Lathe
(www.eng.mu.edu)
BORINGIs an operation in which a hole is enlarged with a single point cutting tool. A boring bar is used to support the cutting tool as it extends into the hole. Because of the extension of the boring bar, the tool is supported less rigidity and is more likely to chatter. This can be corrected by using slower spindle speeds or grinding a smaller radius on the nose of the tool.
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6. LATHE OPERATIONS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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Threading on a Lathe(www.phantasmechanics
.com)
SINGLE POINT THREAD TURNINGExternal threads can be cut with a die and internal thread can be cut with a tap. But for some diameter, no die or tap available. In these cases, threads can be cut on a lathe. A special cutting tool should be used, typically with 60 degree nose angle. To form threads with a specified number of thread per inch/mm, the spindle is mechanically coupled to the carriage lead screw.
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7. SPEEDS & FEEDSFAKULTI KEJURUTERAAN MEKANIKAL
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CUTTING SPEED FOR LATHE WORK Correct cutting speeds is important for good tool life and
efficient machining. For lathe work, cutting speed refers to the rate in meter
per minute at which the surface of the workpiece moves
past the cutting tool. Condition that affect cutting speed:
1. Kind of material being cut
2. Kind of material the cutting tool is made
3. Shape of the cutting tool being used
4. Rigidity of the workpiece
5. Rigidity of the machine
6. Kind of cutting fluid being used
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Cutting speeds are determined using the formula:
rpm = v / (D x )
where
rpm = revolutions per minutev = cutting speed, in meter per minute (mpm)
D = diameter of workpiece
= 3.14
Example 1:
If the cutting speed is 12 mpm for a certain alloy steel and
workpiece is 5cm in diameter, find the rpm.
rpm = v / (D x )
rpm = 12 / (5x10-2 x 3.14)
rpm = 76
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Example 2:
What rpm should be used for a heavy cut of 30.5 mpm on
a piece of low carbon steel of 50.8 mm diameter.
rpm = v / (D x )
rpm = 30.5 / (50.8x10-3 x 3.14)
rpm = 191
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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CUTTING FEEDS FOR LATHE WORK Feeds is the distance a cutting tool advances per
revolution. Feeds are expressed in milimeters per revolution of the
spindle. Feeds are determined by the formula:
T = L / (f x N)
where
T = time, in minutes
L = length of cut, in milimeters
f = feed, in milimeters per revolution (mmpr)
N = lathe spindle speed, in rpm
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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Example:
A shaft is being turned at 130 rpm and feed 0.5 mmpr. If
the length of cut is 100 mm, calculate the time required to
make the cut.
T = L / (f x N)
T = 100 mm / (0.5 mmpr x 130 rpm)
T = 1.54 min
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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TURNING OPERATION
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
The rotational speed in turning is related, to the desired cutting speed at
the surface of the cylindrical work piece by the equation
N (rpm) = v / (Do x )
where N = rotational speed , rev/min
v = cutting speed, (m/min)
Do = original diameter of the part, (m)
The turning operation reduces the diameter of the work
from Do to final diameter Df . The change in diameter is
determined by the depth of cut d:
Do – Df = 2d
The feed in turning is generally expressed in mm/rev. This
feed can be converted to a linear travel in mm/min by the
formula
fr = Nf
where fr = feed rate in mm/min and f = mm/rev and
N = rotational speed, rev/min.
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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The time to machine from one end of a cylindrical workpart
to the other is given by
Tm = L/ fr
where Tm = time of actual machining, minute
L= length of the cylindrical work part in mm The volumetric rate of material removal can be most
conveniently determined by the following equation:
MRR = v f d
where MRR = material removal rate (mm3/min)
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Example:
A 60 mm long, 50 mm diameter aluminum rod being
reduced in diameter to 49 mm by turning on a lathe
machine. Find material removal rate (MRR) if cutting
speed 70 m/min and time to machine 2 min.
N (rpm) = v / (Do x )
= 70 (m/min) / [50x10-3 (m) x 3.14]
= 445.9 rev/min
Tm = L / fr
fr = L / Tm
= 60 mm / 2 min
= 30 mm/min
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7. SPEEDS & FEEDS-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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fr = Nf
f = fr / N (f = feed in mm/rev)
= (30 mm/min) / (445.6 rev/min)
= 0.0673 mm/rev
determined by the depth of cut d:
Do – Df = 2d
d = (Do – Df ) / 2
= (50 – 49) / 2
= 0.5 mm
MRR = v f d
= 70 m/min x 0.0673 mm/rev x 0.5 mm x
1000
= 2355.5 mm3 /min
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8. TOOL GEOMETRYFAKULTI KEJURUTERAAN MEKANIKAL
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TOOL GEOMETRY A cutting tool must posses a shape that is suited to the
machining operation. Important way to classify cutting
tools is according to the machining process. We have
turning tools, cutoff tools, drill bit, reamers, tap and many
other cutting tool that are name for operation. Cutting tools can be divided into two categories: Single
point tools and multiple cutting edge tools.
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8. TOOL GEOMETRY-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Cutting Tool Terminology:
(Source: R. Kibbe, 2006)
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8. TOOL GEOMETRY-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
Cutting Tool Terminology: The tool shank is that part held by the toolholder. Back rake is important to smooth chip flow, needed for
uniform chip and good finish. The side rake directs the chip flow away from the point
of cut. The end relief angle prevents the front edge of the tool
from rubbing on the work. The side relief angle provides for cutting action by
allowing the tool to feed into the work material. The side cutting edge angle (SCEA) directs the
cutting forces. Also helps to direct the chip flow away from
workpiece. The nose radius is important in controlling surface
finish. It will vary according to the finish required.
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8. TOOL GEOMETRY-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
MECHANICS OF BASIC MACHINING OPERATION
The important parameter involve
1. The thickness of the uncut layer (t1)
2. The thickness of the chip produced (t2)
3. The inclination of the chip-tool interface with respect to the
cutting velocity (the face of the tool in contact with the
chip known as rake face) i.e the rake angle(α)
4. The relative velocity of the
workpiece and the tool (v)
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8. TOOL GEOMETRY-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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EFFECT OF RAKE ANGLE
The performance of a cutting tool is markedly affected by
its rake angle as follows:
1. Strength of tool and heat conduction
a. A tool with large rake angle is weak so that the point
may break off. Also the heat will not be conducted
away from the point of tool effectively.
b. The shape with negative rake angle results is stronger
tool with better heat conductivity.
2. Effect on cutting force. As the rake angle is decreased, the
shear plane angle Ф will be decreased and for the same
depth of cut, the extent of the shear plane will be
increased so that the cutting force will be increased.
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8. TOOL GEOMETRY-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
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TWO METHOD OF DETERMINING THE SHEAR ANGLE
1. Mathematical Analysis
The early study in determining the shear angle Ф
mathematically was done by Ernst and Merchant based on
the model of orthogonal cutting.2. Experiment technique
Using quick stop device to
freeze the tool on the
workpiece and the cutting
zone is captured by
photomicrography
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8. TOOL GEOMETRY-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
CHIP BREAKER Chip disposal is a problem that is often encountered in
turning and other continuous operations. Long, stringy
chips are often generated, especially when turning ductile
materials at high speeds. These chips cause a hazard to
the machine operator and to the workpart finish and they
interfere with automatic operation of the turning process. Chip breakers are frequently used with a single point tools
to force the chip to curl more tightly than they would
naturally be inclined to do, thus causing them to fracture.
Two principal forms of chip breaker design are commonly
used on single point turning tools.
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8. TOOL GEOMETRY-(cont’d)FAKULTI KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
2 Types of Chip Breakers:
1. Groove type chipbreaker designed into the cutting tool
itself.
2. Obstruction type chip breaker designed as an additional
device on the rake face of tool. The chip breaker distance
can be adjusted in the obstruction type device for different
cutting conditions.
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THE END
FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA
THANK YOU
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HUreyyy…..QUIZZ time…..
FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA
A 6-in. long, ½-in. diameter 304 stainless steel rod is being reduced in diameter to 0.480 in. by turning on a lathe. The spindle rotates at N = 400 rpm, and the tool is travelling at an axial speed of 8 in./min. Calculate the :
1) cutting speed, 2) Material removal rate, 3) time to cut, 4) power dissipated and 5) cutting forces.
GOOD LUCK!!!!!!
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