Nota BCP

Definition

Marking out is the accurate transference of dimensions from
drawings or specifications to a workpiece. Accurate marking
out is fundamental to all metal working processes.

Marking out tools

1. Surface plates and tables

advantages of the surface plate made of granite?
Harder than cast iron
Permanently true size stress free
Antimagnetic
No rusting
Smooth sliding
Easier to maintain

Steel rule

• A steel rule is a direct measuring instrument mostly used in 300
mm length.

During measuring.
• Place the rule either directly onto the length to be measured or at

right angles to the reference plane.
• Use a contact face if possible and read off measurements by

looking at the point from directly above.

Scriber
• A scriber is used for marking out by scratching or scribing very fine lines

on the workpiece

Square
• A 90 0 back square should be used if a second reference surface is

available

Protractor
• In a- simple protractor, the pointer-like measuring arm} can be set against

a circular degree scale from 00 to 180°. The measuring error is around 1
degree (1°).

Marking with templates
• used for marking in mass production or when the shape of the workpiece is

complicated. These are placed on the workpiece and outlined with a

scribing point.

Dividers
• Dividers have two legs with needle points. The points are harder than the

material which has to be marked. The legs are of equal length

Centre punch
• The layout or prick punch and the centre punch differ only in the angle of

the point. The prick punch is ground to an angle of 45° (30° to 60°) and is
used to mark permanently the location of layout lines. The narrow angle
of this punch makes a smaller and neater indentation in the metal

surface.

The accuracy of the centre punch mark depends on:
• exact marking out
• the ground point of the centre punch
• the placing of the centre punch position
• the correct use of the hammer

FILING
• The purpose of filing is to shape workpieces accurately so as to achieve

smooth surfaces. Files can be used to cut work to prescribed dimensions

and shapes as well as to obtain a desired surface finish.

Classification of Files
• Files are classified according to:
• Shape
• Cut of teeth
• Coarseness of teeth
• Size (armfile, handfile, wardfile and needle file)

Classification of Files According to Shapes

Classification according to the cut of teeth:

• single-cut
• double cut
• rasp-cut
• curved-cut

Classification according to coarseness of teeth:

File selection
• Many factors must be considered in selecting the file if maximum

efficiency is to be attained.
• 1. The nature of work (flat, concave, convec, notched etc)
• 2. Kind of material
• 3. Amount of material to be removed
• 4. Surface finish and accuracy demanded

• File safety
– A file should NEVER be used without a handle. This applies
especially to lathe work because the tang can be driven right through
a person's hand by force exerted by the moving parts of the machine.
– Clean files with a file card, NOT your hand. The chips can penetrate
your hand and cause a painful infection.
– Files are very brittle. They will break if used to pry!
– Do NOT clean the surface being filed with your finger. Short burrs are
formed in filing and can cause serious cuts.
– Never hammer on or with a file. It may shatter and chips can fly in all
directions.

• Avoid cleaning a file by slapping it on the bench. It may shatter

Height of vice
For correct body positioning for working

Tidiness in the working area

Holding large files
The right hand grips the file handle so that the end of the handle presses
against the ball of the thumb.

The left hand presses on the file blade with the ball of the thumb

Positioning of body Positioning of feet

Movement of the file

Radius filing

File provisional surfaces diagonally at right angles to the broad surface.
Turn the file about its longitudinal axis when round filing at right angles to the

radius.

Round filing of internal surfaces

Diagonal filing Transverse filing
Longitudinal filing

MANUAL SAWING

• Sawing is the removal of small chips by means of many chisel-type
cutting edges (teeth) arranged behind one another along the narrow
edge of a saw blade; a large number of these cutting edges are
effective at the same time. Sawing mainly serves to separate
materials and also to produce slits and grooves.

Saw teeth angles
• The sawing tooth is wedge shaped 13 = lip angle (beta)
• A = lip (beta)
• B = clearance (alpha)

• C = angle of rake (gamma

Free-cutting action

To prevent the saw blade from binding when penetrating the material,
the cut must be broader than the thickness of the saw blade. The saw

blade must cut freely.

By the setting of the teeth. By the wave form of the saw blade

Guiding the Hacksaw
When sawing with the hand hacksaw, the movement starts from the arms and

is assisted by a corresponding movement of the body

Countersinking and Counterboring

• Countersinks and counterbores are boring tools, which normally
have two or more cutting edges. A wide variety of types is
available, thus enabling a very wide range of operations to be
carried out.

Countersink

• A countersink has cone shaped cutting edges and is used to cut a
chamfer round the edge of a hole so that the conical heads of
countersink screws can be accommodated.

• Countersinks can only be used to deburr the edges of holes





Counterbore

• A counterbore has parallel cutting edges and is used to
open out holes so that screw heads can be
accommodated flush with the workpiece surface.
Counterbores are available with interchangeable pilots
which enable the cutter to be an adapter for
counterboring holes of various sizes.



BENCH AND PEDESTAL GRINDERS

1)PURPOSE OF GRINDING.

Sharpening is the process of grinding and whetting of tool after their
manufacture in order to prepare the cutting edges for use mainly in cutting
processes . Furthermore , dull , worn out tools are made serviceable again by this
technique . There are two different techniques : Off-hand sharpening and
sharpening by means of fixtures of special grinding machines .

By off-hand sharpening , the following tools can be sharpened :

Steel scribers and scribers of beam trammels , punches , chisels
and drills of all kinds , screw drivers , scrapers and turning and shaping
tools .

2)MAIN PARTS OF PEDESTAL GRINDER

3)FORMS OF GRINDING WHEELS

The following are features, in list form, which must be specified
when ordering a grinding wheel. (Not all will be used on every
wheel.)

1. Abrasive type (aluminum ode, silicon carbide, etc.)
2. Grit size (8-600) (course to one)
3. Grade (A-Z) (soft to hard) (the bond, not the abrasive.)
4. Structure (0 or 1-12) (spacing of grains) (The larger the number,

the wider the grain spacing.)
5. Bond type (V Vitrified, S-Silicate, B-Resinoid, R-Rubber, and E-

Shellac)
6. Diameter
7. Width
8. Bushing size
9. Shape

4)RULES OF PEDESTAL GRINDER

1-Use only the face of the grinding wheel
2-Move the workpiece with a sufficient pressure across the face to keep

the wear on the wheel even
3-Avoid grinding on the corners of the wheels
4-Use the side of the grinding wheels only to straighten the main

clearance flank and the end clearance flanks

Position of the tool rest

5)INSPECTING THE WHEELS

-When a suitable wheel has been selected for the operation required ,
Carefully check the wheel for visible flaws .
-Look for :
.Broken and chipped pieces , cracks , damaged mounting bushes ,

damaged washers .
-Testing the wheel for cracks
The crack can be test by this method : Support the wheel with one
finger trough the bore or suspended on a piece of string . Allow the
wheel to hang free .
Tap the side of the wheel with a non-metallic object such as a small
wooden mallet or handle .
a) a clear ringing sound indicates a wheel free from cracks
b) a dull sound means a cracked

6)CORRECTLY MOUNTED WHEEL

#Grinding wheels for off-hand grinding are fitted with a lead or plastic
Center bush . The hole should have a free fit on the machine spindle .
Never force a wheel on to the spindle .
#A grinding wheel must be mounted on the spindle between steel
flenses of equal size
#They should be half the diameter of the wheel , never less than one third.
#The flanges are recessed on the side in contact with the wheel.
#The inner flange is firmly fixed to the spindle to give a positive drive.
#After mounting the wheel , tighten the nut sufficiently . Reset the work
rest and the wheel guards .

7)OBTAINING SATISFACTORY RESULT FROM AN ABRASIVE
WHEEL

LOADING
Small particle of the material being ground become embedded in the
space between the grains of the wheel. the surface of the wheel become
clogged or loaded. This reduce the cutting efficiency of the wheel.
A loaded will can easily recognized. The first indication will be :-

1.A rapid reduction of the cutting action of the wheel
2.Normal pressure of the work against the wheel has little effect
3.The volume of sparks produced by the wheel is reduced. Increased

pressure of the work against the wheel result in.
4.The work heating up.

GLAZING

1. Caused by grinding hard materials on a wheel whose grade of bond
is too hard.

2. The abrasive particles become dull due to cutting the hard material.
3. The bond is too firm to allow them to break out. The wheel loses

its cutting effiency.The symptoms of a glazed wheel are very similar
to those of a loaded wheel.
4. When the wheel is inspected the surface has a smooth glassy
appearance.
5. Glazing may be prevented by selecting a wheel with a softer grade
of bond. Refer to the manufacturers handbook on wheel selection.

GROOVING

1. Grooves are worn in the surface of the wheel by pressure being
in
the one position.

2. Grooving may be prevented by moving the work across the full
face
of the wheel.

3. Avoid grinding on the outside edges of the wheel.
4. This will result in rapid wear and cause a curved surface on the

wheel.

OUT- OF- ROUND

1.Uneven application, bumping or vibration of the work against the
wheel will cause the wheel to wear out of round.

2.Carefully apply the work to the wheel face. Apply even pressure and
have the work well supported by the work rest. This will help prevent
the will from becoming out of round.

3.The condition of loading and glazing are cause by not using the
correct type of wheel for the material being ground.

4.Do not grind soft ductile material on a wheel that has been selected
for sharpening hard cutting tool. The result will be loading.

5.Do not sharpen a hard cutting tool on a wheel selected for grinding
soft materials. The result will be glazing.

DRESSING AND TRUING THE WHEEL

1.Dressing
Is the operation of cleaning or exposing new abrasive particles on the
cutting surface of the wheel.

2.Truing
Operation of removing material from the cutting face. This squares up
the surface of the wheel and makes it concentric with the axis. Loading
and glazing require dressing. Out of round and grooved wheel require
truing. Dressing a wheel face should also true the wheel. Truing a wheel
face will also dress the face. Most commonly used to true or dress a
grinding wheel consists of a revolving metal cutter or roller fitted with
a long handle. The revolving cutter is forced against the surface of the
wheel being dressed. The roller is to crutch the surface of the wheel to
free the abrasive particles.

SETTING THE WORK REST
1.Slide the rest away from the wheel far enough from the

lugs of the dresser to fit behind the rest.
2.Tighten the clamp.
3. Hold the dresser firmly back against the rest and clear of

the wheel .
4.Turn the wheel by hand full revolution to check that all is

clear.
5.Switch on the power at the isolator switch.
6.Switch on the grinding machine.
7.Hold the handle of the dresser firmly with both hands.

Dressing a Grinding Wheel

• Dressing is the process of restoring the sharpness of the grinding
wheel by breaking away the dulled abrasive crystals or by removing
the glazed or loaded surface of the wheel, thus presenting new sharp
cutting edges of the abrasive grains. This breaking away is caused by
the pressure of the dresser crushing the bond and releasing the dull
abrasive.

• This process should not be confused with truing, which refers to the
shaping of any part of the wheel to run true or to alter it to some
desired shape.

• The tools used for dressing are made in a variety of types and are
called dressers. The more commonly used off-hand dressers are: the
star type and the diamond stick .

SAFETY AND REGULATIONS

• The wheel guards must be securely fixed in place.
• The workrest must be adjusted and firmly clamped as

close to the wheel face as possible.
• Wear suitable clothing such as :-

Close- fitting overalls-buttoned up to the neck
No loose sleeves or ties
Safety goggles must be worn during all grinding
operations.
Support yourself comfortably on both feet by wear safety
boots

INTRODUCTION

• Tapping is the cutting of thread grooves in
the workpiece using a multi cutting-edged
tool with a particular cutting edge shape.

Screw,External&Internal Thread

• Screw is a ridge or uniform section in the form of
a helix on the external or internal surface of a
cylinder, or in the form of a conical spiral on the
external or internal surface of a cone.

• An external thread is a thread on the outside of
a member.

• An internal thread is a thread on the inside of a
member.

HAND TAPS

• Taps are cutting tools used to cut internal
thread.

• They are made from high-quality tool steel,
hardened and ground.

• Two, three, or four flutes are cut
lengthwise across the threads to form
cutting edges, provide room for the chips,
and admit cutting fluid to lubricate the tap.

Types of taps…

• Hands taps are usually made in sets of three:
>Taper
>Plug
>Bottoming taps

TAPER

• A taper tap tapered from the end
approximately six threads and is used to
start a thread easily.

• It can be used fir tapping a hole that a
goes through the work, as well as for
starting a blind hole (one that does not go
all the way through ).