ATM-412 Machining M1 - Weebly

Machining

Module 1: Introduction to Machining

PREPARED BY

Curriculum Development Unit

August 2013

© Applied Technology High Schools, 2013

ATM 412 – Machining

2 Module 1: Introduction to Machining

Module 1: Introduction to Machining

Module Objectives

After the completion of this module, the student will be able to

Recognize the function and importance of machine tools.

Differentiate between the basic categories of machine tools.

Read and understand the main technical drawings’ symbols.

Take precise measurement using Venier Caliper and Micrometer.

Module Contents Topic Page No. 1 Introduction 3

2 What is a machine tool? 3

3 Basic machine tools 3

4 Non-chip producing machine tools 4

5 Conventional chip producing machine tools 4

6 New generation of machine tools 6

7 Skills required to use a machine tool 7

8 Engineering drawing 7

9 measurement 10

12 Prepare the blank part 15

13 References 16


Module 1: Introduction to Machining 3

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.

1. What is a 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

2. 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

Fig. 1.1: Aircraft is an example of a product of machine tools

Fig. 1.2: CNC milling is one of the machine tools



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.

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.

Fig. 1.3: Non-chip producing

machine tool

Fig. 1.4: Process of Chip removal

Fig. 1.5: Machine tools products



With conventional machine tools, the operator

uses machine handwheels 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.

Fig. 1.6: 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.

Fig 1.7 (b): Conventional milling machine

Fig. 1.7 (a): Conventional lathe 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

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.

Fig. 1.8 : Computerized Numerical Control machine tool

Fig. 1.9 (a) : CNC milling machine

Fig. 1.9 (b) : CNC lathe machine



3. Skills required to use Conventional

machine tools:

In order to machine any part using the chip

removal machine tools you need to acquire

certain skills, e.g for the part shown in Fig.

1:10, you need to have the skills of drafting,

read drawings and taking precise

measurements.

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

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 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

Fig. 1.10: machined part

Fig. 1.11: Technical drawing

Fig. 1.12: three standard views in orthographic drawings



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.

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

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 = 0.4 mm

(70.1 – 69.7 = 0.4 mm)

Fig. 1.13: Sectional Views

Fig. 1.14: Isometric drawing

Fig. 1.15: The basic dimension of the shaft plus or minus the



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.

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

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

variation allowed

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

Fig. 1.17: R: means radius

Fig. 1.18: The diameter of the two similar holes is 5.5 mm



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 will be given in millimeters (mm). Large dimensions will be given in meters (m) and millimeters (mm). Fig 1.20 shows a steel rule with mm scale at the top and inch scale on the bottom.

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.

3.2.1 Steel Rule Metric steel rules, are usually graduated in

millimeters and half-millimeters, and used for

making linear metric measurements that do

not require great accuracy. Fig. 1.22

Fig. 1.19: Pitch of a thread

Fig. 1.20 Steel rule with two measuring systems

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

Fig. 1.22 Metric steel rule

A: 12 mm B:31.5 mm



3.2.2 Metric Vernier There are three basic types of Vernier caliper:

standard, Fig. 1.23 - a

Dial, Fig. 1.23 - b

Digital, Fig. 1.23 - c

Fig. 1.23 – a Fig. 1.23 – b Fig. 1.23 – c

The Vernier caliper is used to measure outside, inside and depth measurement

as shown in Fig. 1.24 below:

The accuracy of a measurement system is the degree of closeness of

measurements of a quantity to that quantity's actual (true) value.

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)

Fig. 1.25 (a): reading = 15.8 mm

Fig. 1.24 (c) Depth measurement

Fig. 1.24 (b) Inside measurement

Fig. 1.24 (a) Outside measurement



The Vernier caliper with 20 divisions in Vernier scale is accurate to

(1/20) ±0.05 mm. Fig. 1.25 (b) .

Fig. 1.25 (b): reading = 31.85 mm

The Vernier caliper with 50 divisions in Vernier scale is accurate to

(1/50) ±0.02 mm. Fig. 1.25 (c).

Fig. 1.25 (c): Reading = 19.26 mm



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:

Outside micrometer. For external

measurement. Fig. 1.26 (a)

Inside micrometer, used to measure

the diameter of holes. Fig. 1.26 (b)

Depth micrometer, measures depths

of slots and steps. Fig. 1.26 (c)

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.

Fig. 1.26 (a) outside micrometer

Fig. 1.26 (b) inside micrometer

Fig. 1.26 (c) depth micrometer

Fig. 1.27 sleeve and thimble of

the micrometer



Example 1:

Fig. 1.28 (a) shows example 1 of a

micrometer reading.

Steps of solution:

Example 2:

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

micrometer reading.

Steps of solution:

3.2.5 Digital micrometers Digital micrometers are also available to give

direct reading. Fig 1.29

Fig. 1.28 (a): Micrometer

reading = 5.78 mm

Fig. 1.28 (b): Micrometer

reading = 5.28 mm

Fig. 1.29: Digital Micrometer

5.00 + 0.50 + 0.28 _______ 5.78 mm _______ _______

5.00 + 0.28 _______ 5.28 mm _______ _______



4.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).

Fig. 1.30: Power Hacksaw

For further reading, you can use the following links:

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

calliper-simulator-millimeter-05-mm.html

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

calliper-simulator-millimeter-02-mm.html

3. http://www.stefanelli.eng.br/webpage/en-aka-micrometer-caliper-

outside-millimetre-hundredth.html

4. 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



Student’s notes

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Worksheet 1. What is a machine tool?

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2. Mention two main differences between conventional chip removal tools

and CNC machine tools?

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3. Why sectional views are required in some cases to draw the part?

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4. Define the term “allowance”?

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5. Use the drawing below and answer the following questions?

a) What is the greatest permissible diameter?

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b) What is the minimum permissible diameter?

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6. Mention two types of measuring system?

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7. Mention two measuring tools used in the machine shop?

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8. Use the drawing below to answer the following questions?

a) What is the smallest diameter shown on the drawing?

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b) What is the largest diameter shown on the drawing?

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c) Explain: M20 X 1.5

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9. Find out the following readings of the measuring devices shown below?

A) ……………………mm B) ……………………mm

C) ……………………mm D) ……………………mm

d) The reading is …………………… mm

e) The reading is …………………… mm



f) The reading is …………………… mm

g) The reading is …………………… mm

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