Mehanical Engineering

8/22/2019 Mehanical Engineering

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MechanicalEngineeringTechnology.A synopsis for Grade 9


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Accidents DO happen in the workshop. But its

your duty to ensure and prevent accidents.

Always wear a shop coat or an overall that is notloose fitting; loose clothing can be caught onrevolving parts of a machine.

Always weargoggles, to protect eyes from: flyingobjects, dust, sparks etc.

N.B: its important to keep the workshop tidy; keep

all materials , machines and tools in order to preventaccidents. Prevention is better than cure!!!


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Picture of a MechanicalEngineer in Proper Clothing.


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The first step in the production of goodaccurate marking out is to produce good

lines that are clear, precise and n thecorrect places.


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Tools that can be used inMarking out.

The Combination set

Surface plateSurface gauge

Engineers Square/ Try Square

Straight edge

Inside CaliperOutside Caliper


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Depth Gauge

Scriber

Prick Punch/ Dot Punch

Centre Punch

Hammers: Ball Pein, Straight Pein andCross Pein.

Vee Block

Layout fluids: Preparation andApplication.

Dividers and Trammel-peints.


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The purpose of filing is to accuratelyreduce the size of any metal object to the

desired dimensions.

Filing is a method of removing metal.

Files are made from High Carbon Steelhardened and tempered. File is the chief

cutting tool used by the filter/mechanist.


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Types of files There are six (6) types of files for different

purposes. They are:

The hand file- has a safe or smooth edge.It is used in corners where one face is onlyfiled.


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The flat file

The flat file faces are double cut but theedges are only single cut. It is used for

general bench work. N.B. the difference between the hand and flat file is

that the hand file has an safe edge while the flat filedoesnt have any.


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The square file

The square file-has a square shape andhas teeth on all four sides , which are

parallel for two thirds of the file length. It isused for shaping square slots andgrooves.


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The round file

The round file-as its name implies, has around cross section. The round file is used

for enlarging holes and for working incurved areas. A picture of a round filebelow.


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The triangular file

The triangular file is sometimes referred toas three-square. It is double cut on each

sides. It has a section that has anequilateral triangle and this makes it usefulfor getting into sharp corners.


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The warding file

The warding file is similar to a flat file, but ithas a much thinner section. It is usually

used for filing very narrow slots, as in keys.

or


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Warding file


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Two methods of Filing: Cross filing : is used for general work ; roughing down,

squaring etc.


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Draw filing: is used for finishing. Most surface after beingcross filed then draw filed makes all the cross filed marksdisappear. The file is held at a right angle to the lengthof the metal and pushed back and forth along itslength. The diagram below shows the right way the fileshould be held.


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Grades of file cutCut Typical use

Rough Filing soft metals, plastics

Bastard Shaping steel and fettlingiron castings

Second cut Generally used for hardermetals and for good finish

Smooth cut Draw filing and finishing hard

metalsDead smooth Accurate filing with a high

finish


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Cares of file .1 To make files last, you need to handle them

with care.

Pinning is the clogging of the file teeth withparticles of metal causing the metal to looseits cutting efficiency and badly scar the work.

N.B to reduce pinning rub the file with chalk.Frequent rubbing of chalk reduces the cutting

power, which results in a smoother finish. Clean the file teeth as soon as they become

pinned.


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Cares of file .2 Never use a new file on welded joints , brazed

joints, surface of a casting or a burnt solderingbit.

Never allow the file to slip over the work it dullsthe teeth.

Never use a file without an handle itsdangerous.

Use new files on brittle metals like brass , soft

coat iron and steel. Never use a small file when a large file will do

the work better


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Chisels are sometimes referred as coldchisel, They are used to cut cold metals.

Chisels are made of cast steel oralloysteel, with hardened and temperedcutting edge.


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The four (4) common types ofchisels, they are:

The flat chisel, is used for general purposechiseling.


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The cross cut chisel

The cross cut chisel, is used for cuttinggrooves such as keyways, and for

chipping.


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The half round/round nosedchisel

The half round/round nosed chisel, is usedfor cutting grooves (which are either

curved or half round).


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The diamond point chisel

The diamond point chisel, is used forworking into corners and cutting small

grooves. A picture below of the diamondpoint.


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This has a steel frame, which can beturned at right angles for cutting deep

into the material. The blade is secured in the rigid frame.

The teeth points forward to enable thesaw to cut on the forward stroke.

Hacksaw blades are made of cast orhigh-speed steel.


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There are two types: all hard and flexible.The difference between two is that the all

hard snaps easily and is notrecommended for schools.

Hacksaw blades come in the followinglengths: 225, 250 and 300 mm. they are

also available with 14, 18, 24 and 32 teethper 25mm for cutting different materials.


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Continuing

The different types of hacksaws are: thehacksaw, the junior hacksaw, the sheet

saw and the piercing saw.


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Part 2 of Physical

Properties

Malleability: a property in metal whichallows it to be hammered or pressed into

shape without breaking. Brittleness: a property of metal which

allows it to break strain or shock.


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More topics will be looked at but whatwas stated in this PowerPoint is a preview

of the major topics that will be looked at.

Date post:	08-Aug-2018
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Mehanical Engineering

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