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Prepared by : Mechanical Teacher Module 1: Introduction to Machining 1

Institute of Applied Technology

Year 12

Machining

Semester 1

September 2013

Module 1: Introduction to Machining Prepared by : Mechanical Teacher 2

Machining

Module 1: Introduction to Machining

Prepared by : Mechanical Teacher Module 1: Introduction to Machining

Video 1 – The Lathe

Lets Warm Up – Think, Pair, Share

Minds On Activity


Objectives

After the completion of this unit, you will be able to:

1. Recognize the function and importance of machine tools.

2. Differentiate between the basic categories of machine tools.

3. Read and understand the main technical drawings’ symbols.

4. Take precise measurement using Vernier Caliper and Micrometer.


1.0 Introduction

How much a nation produces determines how well its people live.

Today, every known Product from a paper clip to a space vehicle

is a product of machine tools.

If machine tools are not used directly in the manufacture of the

product itself, machine tools are required to produce the

machinery and the equipment necessary for its processing.

Without machine tools, modern civilization could not exist.

Think of what would the world be without the automobile,

electric power generators, aircrafts… etc. Fig. 1.1.

Fig. 1.1


1.1 What is Machine Tool?

A machine tool is a power-driven machine not

portable by hand, used to shape or form metals or materials by cutting, impacting, forming, eroding, or a combination of these processes.

Example of machine tools is shown in Fig. 1.2

Fig. 1.2: CNC milling is one of

the machine tools


2.0 Basic Machine Tools

There are three main categories of machine tools:

1. Non-chip producing machine tools.

2. Conventional chip producing machine tools.

3. New Generation of machine tools.

Non-chip producing machine tool

2.1 Non-chip producing machine tools This type of machines shapes metals by shearing, pressing, and drawing to a desired shape. Fig. 1.3



2.2 Conventional chip producing machine tools

Machines of this type shape metal to a size and contour by cutting away the unwanted portions in form of metal chips. Fig. 1.4

The collection of material-working processes in which conventional machine tools are used is called conventional machining.

This is the type of machine tools that we are going to cover in this course.

Process of Chip removal



Machine tools products

Fig. 1.5 shows many parts of different shape that made by this type of machine tools.

These parts could be used in the production of engines, machines or any industrial product.

With conventional machine tools, the operator uses machine hand-wheels to manually control the table or spindle movements to produce the part. Fig. 1.6

The accuracy of the part produced depends upon the skills of the operator or machinist.

Hand wheels of conventional machine tool



Lathe and Milling machines are examples of this type of machine tools.

Fig 1.7 (a) shows lathe machine.

Fig. 1.7 (b) shows milling machine.

Conventional lathe machine

Conventional milling machine



2.3 New Generation of machine tools

To increase the rate of production as well as

preciseness of machined parts, automatic programming has also been added to conventional

machines and called NC or CNC (Computer Numerical Control) machines.

With Computerized Numerical Control machine tools (example, CNC lathe and CNC milling), the programmer

programs the machine control unit (MCU), through

the use of symbols, letters, and numbers

(coded instructions) which automatically control the machine tool movements to produce the desired part.

Fig 1.8

Computerized Numerical Control machine tool



The cutting action of CNC machine tools is similar to conventional machining.

Fig 1.9 (a) and 1.9 (b) show a CNC milling

machine and CNC lathe machine respectively.

Electric discharge machines (EDM) and

electrochemical machines are also examples

of new generation machine tools but are

completely different in construction and in the

way they shape metals so they will not be part

of this course. (b) CNC lathe machine

Fig. 1.9 (a) : CNC milling machine


Video 2 – Thread Cutting

Lets increase our knowledge!


3.0 Skills required to use Conventional Machine Tools

In order to machine any part using the chip removal machine tools, you need to:

1. Acquire certain skills, ex: for the part shown in Fig. 1:10.

2. Have the skills of drafting, read drawings and taking precise measurements.

Machined Part

Drilling bit

Module 1: Introduction to Machining Prepared by : Mechanical Teacher

Show and Tell

WHOEVER PARTICIPATES & WINS,

PLENTY OF BONUS MARKS!

Think Fast…


3.1 Engineering Drawing

Engineering drawing is a common language by which drafts persons, tool designers, and engineers indicate to the machinist and toolmaker the physical requirements of a part.

Drawings are made up of a variety of lines, which represent surfaces, edges, and contours of a workpiece.

By adding symbols, dimension lines and sizes, and word notes, the draftsperson can indicate the exact specifications of each individual part. Fig. 1.11

Technical Drawing


Recap from AutoCAD



3.1.1 Orthographic Projection:

Orthographic Projection is a way of drawing a 3D object from different directions.

Usually a front, side and top view (Three standard views) are drawn so that a person looking at the drawing can see all the important sides.

Orthographic drawings are useful especially when a design has been developed to a stage whereby it is almost ready to manufacture. Fig. 1.12.

Three standard views in orthographic drawings


Recap from AutoCAD



3.1.2 Sectional Views:

Sectional views are used to clarify interior or hidden details on a multi-view drawing of an object. Fig. 1.13

Sectional views are located by creating a Cutting Plane Line in one view.

"Section Lining" or "Hatching" is added to the Section view mainly to distinguish the solid portions from the hollow areas of an object.

Sectional View


Recap from AutoCAD



3.1.3 Isometric drawing:

Isometric drawings consist of two-dimensional drawings that are tilted at some angle to expose other views and give the viewer the feeling that what he or she is viewing is a three-dimensional drawing. Fig. 1.14

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Isometric Drawing


3.1.4 Tolerance:

It is the permissible variation of specified size of a part.

The basic dimensions plus or minus the variation allowed is given on a drawing.

Example:

From Fig.1.15 the following can be calculated:

The largest permissible dimension = 70.1 mm (70 + 0.1 = 70.1 mm)

The smallest permissible dimension = 69.7 mm (70 – 0.3 = 69.7 mm)

The tolerance = 70.1 – 69.7 = 0.4 mm

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3.1.5 Allowance:

Allowance (Fig. 1.16) is the intentional difference in the sizes of mating parts, such as the diameter of a shaft and the size of the hole.

On a shop drawing, both the shaft and the hole would be indicated with maximum and minimum sizes to produce the best fit.

Fit is the range of tightness between two mating parts.

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There are two general classes of fits: 1. Clearance fits, whereby a part

may revolve or move in relation to a mating part.

2. Interference fits, whereby two parts are forced together to act

as a single piece.

Fig. 1.16: Largest and smallest dimensions of two mating parts



3.1.6 Common Symbols and abbreviations:

R: Radius of a circle. Fig. 1.17

Ø: Dia. = Diameter. Fig. 1.18

TYP: Typical dimensions. Fig. 2.18

P: Pitch of the thread Fig. 1.19

mm: the unit of measurement is millimeter

M: Metric Thread

Example: M10 X 1.5

M = metric thread (Screw)

10 = diameter, 1.5 = Thread pitch

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R: means radius

The diameter of the two similar holes is 5.5 mm

Pitch of a thread


Students Presentation

Each group of students teach/present the next few topics of module 1 followed by teacher’s lesson/clarification.

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3.2 Measurement There are two measuring systems:

1. International system of measurements

(Abbreviated SI from Systeme Internationale the

French version of the name).

Meter (m) is the basic unit of length measurement.

1m=100 cm=1000 mm

1cm=10 mm

Note:

In machine shop, most dimensions are in millimeters (mm).

Large dimensions are in meters (m) and millimeters (mm).

Fig 1.20 shows a steel ruler with mm scale at the top and inch scale on

the

bottom.

Steel ruler with two measuring systems


3.2 Measurement

2. Imperial system (Old system using Yard as basic unit of length)

1 yard = 36 inch

I inch = 25.4 mm

Note:

Care must be taken when using measuring tools. Most of tools have very sharp edges that may result in severe injuries. (Fig. 1.21),

Tools could be damaged easily if bended, twisted or screwed with extra force.

When using the graduated measuring tools, you must look at 90 degrees for accurate measurement.

Fig. 1.21 Sharp edges of tools may result in severe injuries


3.2 Measurement

3.2.1 Steel Ruler:

Metric steel rulers, are usually graduated in millimeters and half-millimeters, and used for making linear metric measurements that do not require great accuracy. Fig. 1.22

Metric steel ruler A: 12 mm B:31.5 mm


3.2 Measurement

3.2.2 Metric Vernier:

There are three basic types of Vernier caliper:

1. Standard, Fig. 1.23 – a

2. Dial, Fig. 1.23 - b

3. Digital, Fig. 1.23 - c.

GRP car frame


3.2 Measurement

The Vernier caliper is used to measure outside, inside and depth measurement as shown in Fig. 1.24 below:

31

Outside measurement Inside measurement Depth measurement


3.2 Measurement Reading – Vernier Caliper

The accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual (true) value.

1. The Vernier caliper with 10 divisions in Vernier scale (Vernier scale is

the bottom scale on the Vernier) is accurate to (1/10) ±0.1 mm.

Fig.1.25 (a)

32

reading = 15.8 mm


Examples of measurements

2. The Vernier caliper with 20 divisions in Vernier scale is

accurate to (1/20) ±0.05 mm.

Fig. 1.25 (b).

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reading = 31.85 mm

3. The Vernier caliper with 50 divisions in

Vernier scale is accurate to (1/50) ±0.02 mm. Fig. 1.25 (c).

reading = 19.26 mm


Main scale = 28.0mm

Vernier scale = 37 divisions (0.02) = 0.74mm

Total reading = 28.0mm + 0.74mm = 28.74mm

34

Extra examples of vernier caliper reading


The reading is 7.5mm Main scale = 7.0mm Vernier scale = 5 divisions (0.1) = 0.5mm Total reading = 7.0mm + 0.5mm = 7.5mm

Extra examples of vernier caliper reading


3.2 Measurement 3.2.3 Metric Micrometer:

A Micrometer is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades.

There are three basic types of micrometers:

1. Outside micrometer, used for external

measurement. Fig. 1.26 (a)

2. Inside micrometer, used to measure the diameter of holes. Fig. 1.26 (b)

3. Depth micrometer, measures depths of slots and steps. Fig. 1.26 (c)

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Outside Micrometer

Inside Micrometer

Depth Micrometer


Zero Error > Not acceptable > False reading!

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Lets check our knowledge!!

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Video – Micrometer Reading

../videos/Reading a Metric Micrometer.mp4.mp4






3.2 Measurement 3.2.4 Reading the micrometer:

Each division on the upper scale on the sleeve

equal 1 mm. (Fig. 1.27)

Each line appears after the upper scale reading is equal to 0.5 mm.

The micrometer screw gauge also uses an auxiliary

scale (measuring hundredths of a millimeter) which is marked on a rotary thimble. (Fig.1.27).

The micrometers in our laboratory have a pitch of

0.50 mm i.e. the thimble must be rotated through two revolutions to open the jaws by 1 mm.

The rotating thimble is subdivided into 50 equal

divisions. This means each division on the thimble

= 0.01 mm

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Fig. 1.27 sleeve and thimble of the micrometer


Ex 1:

Fig. 1.28 (a) shows example 1 of a micrometer reading.

Steps of solution:

5.00 +0.50 +0.28 = 5.78 mm

40

3.2 Measurement

Ex 2:

Fig. 1.28 (b), shows example 2 of a micrometer reading.

Steps of solution:

5.00 + 0.28 = 5.28 mm

Fig. 1.28 (a)

Fig. 1.28 (b)


Sleeve reading up= 7 mm down=0.5 mm Thimble reading=22 x0.1=.22 mm Total reading= 7.72mm

Extra examples of micrometer reading


Sleeve reading =7mm

=0mm

Thimble reading= 38x0.1=38mm

Total reading=7+.38=7.38 mm

Extra examples of micrometer reading


3.2.5 Digital micrometers:

Digital micrometers are also available to give direct reading. Fig 1.29

43

3.2 Measurement

Digital micrometers


In class activity – Scavenger Hunts!

In groups of 4, follow your path and do the following:

a. Measure (in mm) the physical parts listed below with a (i) micrometer and (ii) vernier caliper.

b. Provide your accurate reading and show all step calculations.

1. Brass round tip specimen (outer diameter) – micrometer / vernier

2. Hand wheel on tail stock (inner diameter) – vernier

3. Gear (thickness) – micrometer

4. White Teflon specimen (height) – micrometer / vernier

5. 3-jaw chuck (inner diameter across flat) – vernier

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4.0 Prepare the blank part

Power hacksaw (Fig. 1.30) is used to cut the

blank part from a long bar (stock bar).

Cutting fluids must be used when cutting hard materials (steel).

(For practical tasks, the teacher will provide

each group of students with a ready blank

part).

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Power hacksaw


For further reading, you can use the following links:

1. http://www.stefanelli.eng.br/webpage/en-vernier-caliper-

pachymetercalliper-simulator-millimeter-05-mm.html

2. http://www.stefanelli.eng.br/webpage/en-vernier-caliper-pachymetercalliper-simulator-millimeter-02-mm.html

3. http://www.stefanelli.eng.br/webpage/en-aka-micrometer-caliperoutside-millimetre-hundredth.html

4. http://mdmetric.com/tech/surfruff.htm

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http://www.stefanelli.eng.br/webpage/en-vernier-caliper-pachymetercalliper-simulator-millimeter-05-mm.html






























http://www.stefanelli.eng.br/webpage/en-aka-micrometer-caliperoutside-millimetre-hundredth.html











http://mdmetric.com/tech/surfruff.htm


References

1. Technology of Machine Tools. Seventh Edition, McGraw-Hill Companies,

2. Machine shop operations and setups, 4th edition, Lascoe nelson Porter.

3 . Machine tool and Manufacturing technology, Steve F. Krar, Mario Rapisarda, Albert F. Check., Delmar Publishers.

4. en.wikipedia.org/wiki/Machining

* Teacher’s weebly site

http://misshannahsclassroom.weebly.com/

47

http://misshannahsclassroom.weebly.com/


IN CLASS WORKSHEET - 1

48

Finish in class worksheet

- Share your answers

and thoughts with your

partner


IN CLASS WORKSHEET2 – posted on weebly

49

Work on questions -

Share your answers and

thoughts with your

partner.


HOMEWORK M1 (worksheet back of module 1)

50

Given to students on

Wednesday Sept 11th, 2013.

Homework Due date – 2nd

week - Sunday Sept 13th,

2013


Quiz Module 1

51

TBD

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