Machining 2 STSENGS855 MEM09002B-interpret technical drawing - PowerPoint Presentation

Slide1

Machining 2

STSENGS855MEM09002B-interpret technical drawingMEM07005A-general machining

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Chapter 1

Determine job requirements: Slide3

Introduction

In order for parts of a product to fit together accurately, engineers need to be able to understand engineering drawings so that they can make the parts accurately.

In some cases, the parts to a product are not always manufactured in the same country. Therefore it is important that Engineering drawings follow the same format so that they can be understood all over the world.

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Planning

for Manufacture

In order to

make any product an Engineer will look at the engineering drawings for the product and use the information on these to plan the

sequence of manufacture. We need to plan the manufacture of a product so that accidents and mistakes are kept to a minimum.

Lots

of time could be wasted if materials, tools, equipment and staff are not available at the time when they are needed.

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1.1 Read and interpret mechanical

technical drawings.

When machining it is good practice to work from a drawing of the part or component.

Part Drawing

Engineering drawing are made up of several

elements

and

features.Slide6

Elements

FeaturesSlide7

Elements

of a part drawing

These are defined as ‘information aspects’ on the drawing.Material: in this case the material to be used is cast iron, however on some drawings you might come across the following:

BMS

– bright mild steel

Dimensions:

these values inform the engineer of the overall size of the finished part such as height, width and length.

Centre Line:

this tells the engineer where to start a particular machined feature.Slide8

Features

of a part drawing

These are identified by the shape and appearance of the designed part. Edges: the drawing tells us that the location piece needs to have two different machined slope features.

Hole:

the drawing tells us that we need a 10 mm drill bit

and that we need to drill a hole depth of 40 mm.

Radius:

The machine operator can plan ahead by making sure he has all the tools ready for cutting this type of feature.Slide9

Hidden edge line

Leader and arrowheads

Centre line

12 mm in length at an angle of 45 degrees

Outside radius measurement

Diameter of a holeSlide10

What the part is made from.

The name of the creator

The date the drawing was done

Completed once the part has been machined

The company details

Used for filing purposes

The description of the part being machined

The unit of measurement used to produce the drawing Slide11

Student Tasks:

Read and interpret mechanical

technical drawings.Slide12

Have a go at reading the engineering drawing you have just reviewed previously. The four key components have been extracted from the drawing to make easier for you. Drag the correct description and place it on top of the target.

What Material?

D

ate?

Company info?

Unit Slide13

Edge to centre

Hidden edge

Dia

10 mm

Centre lineSlide14

Through holes

Centre line

Leader line

Overall lengthSlide15

Nearest surface

Total depth

Highest surface

Hidden edgeSlide16

1.2 Determine and transfer

dimensions from given technical drawings

using datum points.

Machine operators are expected to produce engineering parts to the accuracy of the given drawing. Therefore it is important that the information regarding size and shape is clear and easy to interpret.Slide17

It is not good practice to work from an engineering drawing where no

conventions

and standards have been followed in relation to dimensioning. Here we can easily note it is difficult to determine which lines represent the outline of the shape.

DimensionsSlide18

A well-drawn part should follow the conventions opposite. These

linear dimensions

are vital to the machine operator as they will in most cases prepare a slightly

oversized

workpiece. This will reduce the amount of waste material after machining the part.Slide19

When reading an engineering drawing there is likely to be different methods used for dimensions of a circle. This will be determined by the surrounding detail.Slide20

The

steel flange

opposite illustrates the diameters are identified. PCD pitch centre line diameter

indicates the diameter of the circle on which the

pitch

of the holes is

centred

. The pitch of the circles is 60°.Slide21

Again, we can see that there are also a number of methods used to dimension arcs such as those that distinguish the radii outline of an irregular part.

Slide22

Tolerance is the allowable variation in weight or measurement of an object. It is important for a machine operator to work to a tolerance because it is not always possible to produce parts exactly to the specified measurements.

Tolerances

Piston in it’s cylinder of an engine

The

piston rings

have to be machined to a specific tolerance to prevent the engine from losing power

. If the diameter is greater then the piston will be subject to high levels of friction and visa versa.

Piston

Cylinder

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Suppose a simple rectangular block has

nominal

dimensions of 300 x 150 mm, but it is acceptable for the manufactured item to be 1 mm over or 2 mm below the nominal size. This can be shown in two ways on an engineering drawing.

Rectangular block

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Nominal Deviation of

Tolerances - LinearSlide24

The first method shows how much the measurements can

deviate

from the nominal dimension (between plus 1 mm and minus 2 mm).

The second way of indicating these tolerances is to specify the

limits

directly on the component.Slide25

The diagram shows how tolerances are indicated on an

angular

measurement. The angle is nominally 35°, but the drawing indicates that it is allowable for it to be up to 1° over or 2°under the nominal size

Nominal Deviation of

Tolerances - AnglesSlide26

In some cases there will be two different surface textures on a machine part. Engineers need to be made aware of which the smooth and surface textures required. These need to be measurable and indicated on the drawing.

Surface finish

The diagram shows how surface texture is indicated on engineering drawings. The value has been stated in

micrometres

alongside the symbol. A surface texture of 3 micrometres is required all over the surfaces of the part.Slide27

The machine operator needs to know a number of factors before he/she can start work such as:

The material to be used.

If a component of an assembly, then the fitting method to be used.

Any heat treatment.

This type of important detail is conveyed on the drawing using symbols, written notes which are placed near to the feature

Manufacturing detail

Piston drawing 002Slide28

Although a part may be dimensionally accurate and within tolerance, the object’s geometric features such as flatness,

concentricity

may need further definition.

Geometrical tolerance

This diagram shows the side view of a part whose perfect flatness is indicated by the dashed line. However in reality the shape may be more like that shown by the solid blue line. Therefore the uppermost line show that geometric tolerances have been applied to specify how much variance is allowed.Slide29

This image shows how it would be shown on a drawing.

Geometrical tolerance

Here a number of

geometric tolerancing

symbols that are likely to be on drawings.Slide30

Datum

is the origin from which the location or geometric characteristic of features of a part is established. It is represented by an axis, plane or exact point. In a drawing it is symbolized by a letter in a triangle.

Datum and Datum points

In machining we refer to a feature as a physical portion of a part such as a surface pin, hole or slot. To machine these features, we have to exact points, axes or planes which are known as datums.

A datum plane

ASlide31

M

aximum Material Condition

(MMC) refers to a feature-of-size that contains the greatest amount of material, yet remains within its tolerance zone. Some examples of MMC include:

Maximum Material

Condition (MMC)

MMC is symbolized on a drawing by the letter ‘M’ in a circle.

Smallest

hole size

M

Largest pin diameter

http://www.engineeringessentials.com/ege/tol/inch_tol.pngSlide32

Least Material Condition

(LMC) least material condition (LMC) refers to a feature of size containing the least amount of material, yet remains within its tolerance zone:

Least Material

Condition (LMC)

LMC is symbolized on a drawing by the letter ‘M’ in a circle.

Largest hole size

L

Smallest pin diameter Slide33

Regardless of Feature Size

(RFS): RFS is the

default modifier. So if there is no modifier symbol shown in the feature control frame, it means RFS is the default modifier. RFS is used when the size feature does not affect the specified tolerance.

Regardless of feature size (RFS)

RFS is applicable

MMC and LMC’s symbols are modifiers in this caseSlide34

On an engineering drawing you may find one of these three symbols which are all used to identify a datum.

On some cases there might be a different letter used however letter I, O and Q are not used.

Application

A

A

ASlide35

The

Feature Control Frame

is like a basic sentence that can be read from left to right.It defines characteristic type, geometric tolerance and value and datum references.The number of compartments in the feature control frame can vary. This is dependent on the characteristic type used, whether single or related and what the functional requirements are.

Feature Control Frame

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In the drawing we can see the Feature

C

ontrol Frame in use. Datum references indicated on the right end of the feature control frame which are read from left to right. The three letters signify datum preference. They establish the three mutually

perpendicular planes.

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Feature Control Frame Slide37

In the diagram opposite the perpendicular planes (two surfaces that are 90° to each other) are the datum references.

The order of the datum references starts with the first, then secondary and finally Tertiary planes

Datum references

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Part to be machinedSlide38

Drag the labels over the correct drawing elements.

Student tasks

Determine and transfer

dimensions from given technical drawings

using datum points

.

Projection line

Dimension

Projection line gap

Termination (arrow head)

In line arrowheads

Projection line extensionSlide39

Complete the different methods of dimensioning the diameter of these circles. Slide40

Work out the tolerances as values based on the nominal measurements and visa versa by matching them.

200

5

3

1

4

9

 Slide41

Match the geometric tolerancing symbols with the correct labels.

Cylindricity

Flatness

Concentricity

Straightness

CircularitySlide42

Focus on the Feature Control Frame to match the symbols with the correct descriptors.

Primary datum

Position

symbol

Tolerance

value

Diameter

symbol

Tertiary datum

Secondary datumSlide43

Chapter 2

Determine sequence of machining operations Slide44

Introduction

When it comes to machining parts, the chances are that you will need to carry out more than one operation.

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The most effective approach is to plan in the form of a sequence of operations.

Therefore it is important that you have thought about how you are going to produce the finished part to avoid any waste resulting from an error. Slide45

Planning resources

Before a sequence of operation can be planned, the machine operator will probably need to refer to a number of documents.

To machine affectively, we need to have:

A drawing

– tells us what the component or part needs

to

look like.

http://www.lucastechnical.com/wp-content/uploads/LTS-Engineering-Drawing-Example.pngSlide46

Planning resources

A

job card

– This document tells the operator what materials and resources are needed and breaks down the machining processes into tasks

.

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Planning resources

Data charts

- reference material which informs the operator on things such as machine speed, feed rate, Limits and fits, threads, etc.

The above documents are generated in different formats such as:

Hard copy Soft copySlide48

2.1 Plan a sequence of

stepsfor machining operationsThis should include reference to the process,

materials and tooling.

Drawing

Before the machining operations can be sequenced, the operator needs to understand what processes are going to be carried out.

5

1

4

6

3

Processes6 x threaded M4 holes.1 x 35 long x 3mm deep slot.4 radius corners.A 3.5mm deep step along all four edges.A 30 mm D blind hole.Material type and size.These are not in any order 2Slide49

Machining processes

Preparing the stock so that the material is square is the first stage of the operation.

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Then the drilling of the 6 through holes would be done next.

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The drilling and boring of the 30 mm diameter blind hole would then be machined.

Slide50

Machining processes continued

By using a slot drill in the milling machine we can machine out the blind slot.

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The perimeter step is machined using an end mill along with the radius corners with the aid of a rotary table.

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Materials

Different materials are specified for parts depending on the function of the part.

Here are some common materials that are machined on a lathe and milling machine.

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Aluminum

Brass

Mild steel

All three materials have different surface hardness properties.This hardness is considered when selecting cuttings tools , and setting the speed of rotation. Slide52

Data charts

The common materials that are machined on a mill have recommended cutting speeds which cutting tool manufacturers design their products around

.

These speeds are based on cutting tools manufactured from high speed steel (H.S.S

) however the speed rates are different for carbide tipped tools.

Material

Aluminum

Brass

Mild steel

Cast iron

High Carbon steel

Cutting speed in metre/min

100

45

25

20

15

Cutting speeds in metres per

minute M/MinSlide53

By calculating the speed and feed rates for each cutter the machine operator is able to work out how many parts they are likely to produce in given time frame.

By using a

simple formulae

we can calculate the

spindle speed

required for a number of cutting tools and materials.

N

= Number of revolutions per minute

S

= Cutting speed in meters/min

=

3D = Diameter of the cutter N =  Example: to calculate the speed required to cut a mild steel workpiece with a 8 mm diameter end mill the following needs to be done.N =

N

=

=

1041

Rev/MinSlide54

Feed rate

This

is the rate at which the workpiece moves into the revolving cutter which is expressed in millimeters per minute (mm/min).

To calculate the cutting feed

we need to determine the

number of teeth

on the cutting tool.

Cutting tool manufactures give

recommendations for cutting feed

stated as a

value per tooth

. Number of teethhttp://www.zps-fn.com/go_category_image.php?pid=166FlutesSlide55

End mill

Slot drill

Drill bit

Boring cutter

Vertical Cutter

types

Thread millSlide56

Feed per tooth in

millimetres

The table below demonstrates this:

Material

end mill

Slot drill

Face mill

Aluminum

0.40

0.06

0.2

Brass

0.30

0.05

0.2

Cast iron

0.30

0.05

0.1

Mild steel

0.20

0.05

0.1

High carbon steel

0.15

0.03

0.05Slide57

To calculate the

feed rate

in millimetres per minute (mm/rev)

the following equation is used:

f.t.p

=

Feed per tooth for a particular cutter and metal as given in the table

.

N

=

Number of teeth on milling cutter.Feed rate = f.p.t x N = mm/revExample: a 8 mm diameter end mill having 6 teeth is to be used for cutting mild steel the following needs to be calculated.mm/rev = x = 60.201.2Slide58

To calculate the

table feed

in millimetres per minute (mm/min)

the following equation is used

:

Feed/rev

=

Revolutions per minute of the milling cutter

.

f.t.p

= Feed per tooth for a particular cutter and metal as given in the table.

Table feed (mm/min) = Feed/rev x NExample: a 8 mm diameter end mill having 6 teeth is to be used for cutting mild steel using the spindle speed 1041 (rev/min) the following needs to be done.Table feed = x = 0.202081041Slide59

Finally, the operator needs to calculate the

cut time

which is done using the following formulae:Cut length (mm) ÷

Feed rate (mm/min)

= Cut

t

ime (min)

By referring to the original drawing at the start of this chapter we can see that the length of the perimeter step is:

310

mm

÷ = 2 min208 mm/min Slide60

Processses

Review the milling processes on this and the next slide, then label them with correct term below.

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Face milling

End milling

Pocket milling

Student tasksSlide61

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Boring

Tapping

DrillingSlide62

Cutting tool Teeth and flutes Slide63

J

Planning sheet for plate

Name: Plate

Date: 18/03/14

Material: Mild steel 90 x 65 x 13 mm

Stage

Description

Tools needed

Cutting

Speed (rev/min)

Feed

Rate

(mm/min)

Table

Feed

Rate

(mm/min)

Time taken

(min)

Safety precautions

1

prepare the stock so that it is square.

Hand

file and vice

2

Marking out of detail.

Marking out dye,

scriber, centre punch, hammer, square

3

Drill the 6 through holes.

5 mm HSS drill

bit (2 flutes)

1562

0.10

78

1

4

A 30 mm

Dia

blind hole.

16 mm

end mill (2 flutes) then 30 mm boring cutter (1 flute)

16

mm =

500

30 mm = 266

0.40

0.20

5

1 x 3

mm deep slot.

10 mm slot drill (2 flutes

806

0.10

40

1

6

Perimeter step

8 mm end

mill (6 flutes)

1000

1.2

200

2

7

Radius corners

8 mm end mill (6 flutes)

1000

1.2

200

1

8

Tapping the 6

through holes

M4 tap

(2 flutes)

Slowest speed

Hand

With any machining job the first stage is to prepare the stock so that it is square using two surfaces.Slide64

Chapter 3

Select and mount tools:3.1 Select appropriate tools for turning, facing grooving and milling.

3.2 Show how to mount lathe tools and milling cutters.Slide65

3.1

Select appropriate tools for turning and milling

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Introduction

Both the centre lathe and milling machines are universal in their operation.

They can perform several different cutting task. The type of task is determined by the feature requirements of the component or part being manufactured.The operator can then select or

adapt

existing cutting tools to suit.Slide67

Lathe cutting tools

http://www.youtube.com/watch?v=J63dZsw7Ia41.3 Machine Tool Basics -- Lathe Cutting Tools -- SMITHY GRANITE 3-in-1

The profile of the cutting tool determines the type of job it can do.

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Selecting lathe tools

Lets consider the lathe machining operations of the thumbscrew

As

we can see, there are a number required

features

. For purpose of this job, the machinist is able to select an off-the shelf cutting tool for each feature.

Step

Knurling

wheel

undercut

ThreadSlide69

Features

Knurling wheel

Step

Undercut

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Tools

Facing

http://www.micro-machine-shop.com/lathe_tools_std_shapes.jpgSlide70

Butt weld

Shank

Tool bit

Tool holder

So that metal may be cut effectively and efficiently, the tool cutting edge must be sharp, have enough support and be made from a suitable material. All lathe cutting tools must be hard enough to maintain a cutting edge and tough enough to

withstand shock and heavy pressure.

The three types of lathe cutting tools

Lathe cutting tool materials

High speed steel (H.S.S.)

High speed steel is the most widely used cutting tool material in machine shop

engineering. H.S.S. is used for lathe tools, drills, taps, and reamers.

H.S.S lathe tools can be either of the two types:

1. H.S.S. butt welded onto a medium carbon steel shank

.

2. H.S.S. tool bits held in tool holders.

 Slide71

Tungsten carbide

This material is very much harder than high speed steel, so higher cutting speeds are possible.

The two main types of tungsten carbide tools are:

1. The insert (tip) is brazed onto the shank. When the insert is worn, it must be removed, the tip turned and re-brazed back onto

shank.

Insert

Shank

Braze

2. The

tungsten carbide insert is clamped to the

shank. When

a cutting edge is worn the insert can be turned around and accurately clamped in position so that another cutting edge can be

used.

Insert

ClampSlide72

Sharpening lathe cutting tools

Both high speed steel (HSS) and Carbide tipped cutting tools when dull need to be sharpened. This is done using a grinding wheel on a bench grinder.

Cutting tool tip

Grinding cutting tools is a skill and takes some time to master. Bench grinders can be very dangerous if operated by untrained personnel therefore follow safety guidelines.

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Student task

Based

on the

tap wrench

below,

study the drawing and the machining stages then match them up with the correct cutting tool on the next

slides. Slide74

At the other end,

turn down a 45° chamfer.

Cut a diamond knurl along a section of the workpiece. Face-off

both ends to a length of

100

mm (check with digital calipers).

Drill

a

9.5

mm hole all the way through the centre of the workpiece.

Turn

down a to a diameter of 11 mm (check with digital calipers).Cut two profile grooves at the position shown on the drawing.http://www.da7c.co.uk/technical_torque_articles/drill_bit_2.jpgDrill bitSlide75

Drill bit

Turn

down a to a diameter of 11 mm

(

check with

digital calipers).

Drill

a

9.5

mm hole all the way through the centre of the workpiece.

At the other end,

turn down a 45° chamfer.Face-off both ends to a length of 100 mm (check with digital calipers).Cut a diamond knurl along a section of the workpiece. Cut two profile grooves at the position shown on the drawing.Slide76

The milling cutting tool

http://www.youtube.com/watch?v=ckzK-LbeZmY2.2 Machine Tool Basics -- Mill Cutting Tools -- SMITHY GRANITE 3-in-1

Again, the profile of a mill cutting tool determines the type of job it can do.

http://electron.mit.edu/~gsteele/mirrors/www.nmis.org/EducationTraining/machineshop/mill/mcutters.gifSlide77

To

manufacture the large jaw below there are a number of milling operations which require different cutting tools.

Again, the features required can be machined using off-the-shelf milling cutting tools.

Selecting milling tools

Facing

Corner rounding

Slot drillsSlide78

Features

Facing

Slot drills

Corner rounding

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Slot drills

http://www.harveytool.com/secure/Content/Images/Thread%20Mill%20Harvey%20Tool.JPGSlide79

Student task

As with the large jaw, study the drawing of a pen holder

and the machining stages then match them up with the correct cutting tool on the next slide. Slide80

Face-off the top surface of the workpiece.

Roll the workpiece forward so you can face-off at right-angles to the top surface.

Drill out the three different size holes.

cut

all four edges

to create a set radius value as stated on the drawing.

Cut an internal M8 thread in the

centre

hole.

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Face-off the top surface of the workpiece.

Roll the workpiece forward so you can face-off at right-angles to the top surface.

Drill out the

three

different size holes.

cut

all four edges to create a set radius value as stated on the drawing.Cut an internal M8 thread in the centre hole.Slide82

3.2

Show how to mount lathe tools and milling cutters.

http://www.micro-machine-shop.com/QCTP_14mm_crosslide_2.jpgSlide83

When a component is being turned it is usual for the operator to keep the various diameters concentric.

They try to ensure that all the diameters of a part or component have a common axis.

The three diameters shown in the left-hand drawing are

concentric

(they lie on the same axis and have the same centre of rotation.

Therefore the two diameters shown in the right-hand drawing are

eccentric

(they do not lie on the same axis therefore have different

centres

of rotation.

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Concentricity and eccentricityconcentric eccentricSlide84

Introduction

In order to cut a workpiece accurately there are a number of factors that need to be followed:The position of the cutting tool in the

toolpost.Centre the cutting edge.The safe setup of the cutting tool.

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The position of the cutting tool

In most turning applications the cutting tool needs to be perpendicular to the workpiece. There are

a number of toolpost types which are used to accommodate different cutting tools. The most popular one is the ‘quick-change’ toolposts as seen above.

To avoid inaccurate cutting and deflection, the cutting tool needs to be secured tight in the

toolpost

.

Cutting tool

Screw

s clamp the tool

http://www.robotroom.com/DualFan/ButtonTurning.jpg

http://www.youtube.com/watch?v=VkeW_Bcwj3E

Lathe Tool Post Slide86

Setting tool on centre height

To maintain the rake and clearance angles on the lathe tool, it is important that the tool is set to centre height. If the tool is set above or below centre height, then rake and clearance angles will change and affect the cutting action.

The overhang of the cutting tool should be kept to a minimum to avoid vibration of the tool when cutting.Slide87

Methods of setting a tool on centre height

All tools that are to be used on a centre lathe must be set to the centre line of the machine, which is called the

centre height. Shims are used to set the tool to the correct height.

a) Using a live or dead centre

Shims

b) Using a setting gauge

ShimsSlide88

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_misc/Lathe_tool-post1.jpg

Student task

Identify the parts of the quick-release toolpost by connecting the words to the features in the picture.

Height adjustment

screws

Tool block

Locking nut

Cutting tool

Tool holderSlide89

When it comes to mounting milling cutters there are a number of options depending on the tool holding system that is being used. However the principles are similar apart from the tools that are needed.

The following video clip demonstrates one of the most common ways of mounting milling cutters.

http://www.youtube.com/watch?v=r6MVhQtjN3I

Mounting

milling cutters Slide90

Student task

Identify the tools and parts of a vertical milling machine in relation to mounting the cutting tool by connecting the words to the features in the picture.

http://www.tormach.com/uploads/images/Gallery/products/order_by_partnumber/32336_Drawbar_Wrench_MG_9345.jpg

http://www.tormach.com/uploads/images/Gallery/products/order_by_partnumber/31911-Draw-Bar-for-Power-Draw-Bar_MG_7382.jpg

http://img.directindustry.com/images_di/photo-g/morse-taper-shank-roughing-end-mills-85149-4155389.jpg

http://www.toolmex.com/images/ecomm_images/Items/Large/3-185.jpg

Milling cutter

Draw-bar

Wrench/

hammer

Milling cutter holderSlide91

Chapter 4

Perform lathe machining operations(Intermediate) 4.1 Select

from a data table, an appropriate feedrate and speed for a given workpiece and tool type. 4.2 Secure a workpiece in the lathe chuck and demonstrate lathe

m

achining

operations for general turning, taper turning, grooving

and parting.

Make

sure that machining is performed in a

safe

manner

utilising all guards, safety procedures and personal protective clothing and equipment.Slide92

The safe setup of the cutting tool

Whilst setup takes place, all guards need to be engaged.

http://www.ferndalemachinery.com/img/repar/full-lathe-safety-guards.jpg

Machine Guards

http://www.ferndalemachinery.com/img/repar/milling_machine_safety_guard.jpg