MEM07005Ageneral machining httpmachineshopcoedrexeledumachineshopequipmentmillingmachinesjpg Chapter 1 Determine job requirements Introduction In order for parts of a product to fit together accurately engineers need to be able to understand engineering drawings so that they ID: 675327
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Slide1
Machining 2
STSENGS855MEM09002B-interpret technical drawingMEM07005A-general machining
http://machineshop.coe.drexel.edu/machineshop/equipment/milling-machines.jpgSlide2
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.
http://kumasicenter.files.wordpress.com/2012/10/engineering-drawings.jpgSlide4
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.
http://upload.wikimedia.org/wikipedia/commons/b/b2/Engineering_drawings_with_Machinery%27s_Handbook.jpgSlide5
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
http://s1.hubimg.com/u/623790_f520.jpgSlide23
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
http://fr.norelem.de/en/productsimages/01160.jpg
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
http://docs.autodesk.com/ACD/2010/ENU/AutoCAD%202010%20User%20Documentation/images/PTDCPM/Gator-All/English/auw0999u.pngSlide36
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.
http://dealertraining.cat.com/suppliertraining/Printreading/prmod3/images3/m31109.gif
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
http://images.books24x7.com/bookimages/id_17892/fig7-1.jpg
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.
http://www.hsmworks.com/docs/cncbook/en/Project-3_square_block_step_5-back.png
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
.
http://jpkc.whut.edu.cn/ppkc/jxcadcam/include/editor/uploadfile/20130409212911365.gifSlide47
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.
http://www.henkel.de/de/content_images/Multan_cutting_fluid_278330_print_1772H_1772W.jpg
Then the drilling of the 6 through holes would be done next.
http://www.xstrange.com/bridgemachining450.jpg
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.
http://www.sandvik.coromant.com/SiteCollectionImages/Technical%20guide/Pablo/D%20milling/091689.jpg
http://grindaix.de/typo3temp/pics/114557b78c.jpg
The perimeter step is machined using an end mill along with the radius corners with the aid of a rotary table.
http://www.berryhillguns.com/mill.jpgSlide51
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.
http://img.directindustry.com/images_di/photo-m/cast-iron-rectangular-blocks-7884-3782031.jpg
http://ecx.images-amazon.com/images/I/71WAz7crclL.jpg
http://thumbs1.ebaystatic.com/d/l225/m/mwH_n1QLTs00hzEx25X3Ptw.jpg
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.
http://www.custompartnet.com/wu/images/milling/pocket-milling.png
http://www.custompartnet.com/glossaryimages.php?iid=1737
http://www.custompartnet.com/glossaryimages.php?iid=1771
Face milling
End milling
Pocket milling
Student tasksSlide61
http://www.custompartnet.com/glossaryimages.php?iid=1853
http://www.custompartnet.com/wu/images/milling/boring-mill.png
http://www.custompartnet.com/wu/images/milling/tapping-mill.png
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
http://electron.mit.edu/~gsteele/mirrors/www.nmis.org/EducationTraining/machineshop/lathe/cuttools.gif
http://www.efunda.com/processes/machining/images/mill/end_mill_types_1.gifSlide66
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.
http://1.bp.blogspot.com/-RSUTWNVS8tY/UJsLSf1sS4I/AAAAAAAAAXI/Ykwz51urV6U/s640/single_pt_lathe_tools.gifSlide68
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
http://collections.infocollections.org/ukedu/collect/ukedu/index/assoc/gtz103be/p05c.gif
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.
http://www.sherline.com/images/grndfg12.gif
http://4.bp.blogspot.com/-tRFLbpVZkjI/TxScdnysElI/AAAAAAAAA38/dkYGJH2tks0/s1600/Bench+Grinder+Safety+Gauge+-+Back+%2528Rockford+Systems%2529.PNGSlide73
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
http://imageserver.grainger.com/is/image/Grainger/4RKH4_AS01?$productdetail$
https://www.cromwell.co.uk/images/product/CTL/060/CTL0602353D_0.jpg
http://www.pw-tools.com/ekmps/shops/pwtools/images/20mm-hss-slot-drill-2-flute-milling-cutter-hsco-m42-cobalt-20mm-plain-shank-x-110mm-o-l-made-in-uk-241-p%5Bekm%5D433x324%5Bekm%5D.jpg
http://ecx.images-amazon.com/images/I/41Im7fE1rBL._SL500_AA300_.jpg
http://www.acutecsolutions.com/wp-content/uploads/2013/01/corner-rounding-cutter_no_bg.png
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.
http://www.chestermachinetools.com/ekmps/shops/juliechuk/images/-diameter-1-2-diameter--5675-p.jpg
http://www.maxtoolsin.com/www/media/products/24.jpg
http://www.engineeringsupplies.co.uk/images/my_images/metric-threadmill.jpghttp://www.maxtoolsin.com/www/media/products/24.jpgSlide81
http://www.maxtoolsin.com/www/media/products/24.jpg
http://www.maxtoolsin.com/www/media/products/24.jpg
http://www.chestermachinetools.com/ekmps/shops/juliechuk/images/-diameter-1-2-diameter--5675-p.jpg
http://www.maxtoolsin.com/www/media/products/24.jpg
http://www.engineeringsupplies.co.uk/images/my_images/metric-threadmill.jpg
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.
http://abtechmfg.com/wp-content/uploads/location-tolerance-concentricity-2.gif
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.
http://www.frets.com/HomeShopTech/Tooling/ToolHeightSet/toolheightset.jpg
http://www.poolewood.co.uk/acatalog/474644.jpg
http://www.tacrockford.com/images/accessories/LatheChuckShieldsHeader.jpgSlide85
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