Safety Precaution About Bench Fitting Shop and Concern to Tools and Equipment Used for

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  • Topic: Screw, Screw thread, Orthographic projection
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  • Published : February 21, 2013
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TRADE OF HEAVY VEHICLE MECHANIC

PHASE 2

Module 1

Induction/Customer Care/Bench Fitting/Welding

UNIT: 4

Bench Fitting and Drawing

Table of Contents
1.0 Aims and Objectives1
Learning Outcome:1
2.0 Introduction1
What is a fit in Engineering Terms?1
3.0 S I System3
4.0 Derived Units4
5.0 Basic Drawing Theory5
Graphical Methods5
Block Diagrams and Flow Diagrams5
Schematic Diagrams5
Circuit Diagrams5
Detailed Drawings6
Assembly Drawings6
6.0 Orthographic Drawing6
Oblique Views8
Isometric Projection8
Perspective Drawings9
7.0 Scale9
Dimensioning Drawings10
8.0 Sections11
9.0 Circuit Diagrams12
10.0 Block Diagrams and Flow Diagrams13
11.0 Hydraulics and Pneumatics14
12.0 Questions on the Background Notes15
13.0 Screw Thread Cutting18
Aims and Objectives18
14.0 Cutting and Repairing Threads18
Using a thread pitch gauge18
1. Preparation and safety18
2: Step-by-step instruction22
15.0 Repairing an external thread23
1. Preparation and safety23
16.0 Repairing an internal thread24
1. Preparation and safety24
Part 2: Step-by-step instruction25
17.0 Remove and Replace a Stud26
1. Preparation and safety26
2: Step-by-step instruction27
18.0 Using a screw extractor28
1. Preparation and safety28
2: Step-by-step instruction29
1.0 Aims and Objectives

Learning Outcome:

By the end of this unit each apprentice will be able to:
• State the function of common workshop tools and equipment and the safety precautions to be observed when using this equipment

• Measure and mark out metal work exercises

• Produce metal work exercises by cutting, drilling, tapping and screw threading

• Drill out and replace pop rivets as part of a metal work exercise

• Re-tap damaged threads on a vehicle component i.e. studs or stud holes

2.0 Introduction

In engineering you are usually concerned with a number of parts or components fitting together to make an assembly, so you must control the sizes of the parts to make sure they assemble correctly and will function as the designer intended. Even if you are only purchasing a bar stock you need to know that any unmachined surfaces are suitable sized for your application. In all theses cases the control of size and the assembly of components can be done with the help of a limits and fits standard of some kind.

What is a fit in Engineering Terms?

Imagine that you have drilled and reamed a hole 20mm in diameter in a piece of metal 14mm thick .[pic]
You are now going to machine a diameter on the end of a 30mm bar. If the machined diameter has to pass easily through the hole you could make it, say, 16mm. [pic]
There would be a gap, or technically clearance, between the diameter of the hole and the shaft. Alternatively you might want the shaft to be a tight fit in the hole and machine the shaft slightly larger than the hole –the method of determining the actual size will be discussed later! In this case you would need to force the shaft into the hole. The hole and shaft diameters interfere with each other. Notice that it was suggested carrying the fit by varying the size of the shaft. Because the hole is the fixed size this system is based on the hole and is known as a hole basis. The hole in our example could just as easily be a slot, groove, gap or similar internal feature whilst the shaft could be a tongue, tenon or similar external feature. [pic]

You could, however, decide on a shaft size and vary the hole sizes to give various fits. This would be known as a shaft basis. A particular base is a shaft having the same basic size throughout, which is designed to carry various parts required to assemble a shaft with different fits. Such variations in fit required by bearings, couplings, collars sliding members or other parts would involve expensive machining of the shaft in order to vary its diameter and to...
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