Marking Out

Marking out is the scratching of lines on the surface of a workpiece, known as scribing, and is
usually carried out only on a single work piece or a small number of workpieces. The two main
purposes of marking out are:
to indicate the work piece outline or the position of holes, slots, etc. If the excess material will
have to be removed, a guide is given for the extent to which hacksawing or filing can be carried
out;
to provide a guide to setting up the workpiece on a machine. The workpiece is set up relative to
the marking out and is then machined. This is especially important when a datum has to be
established when castings and forgings are to be machined.
It is important to note that the scribed lines are only a guide, and any accurate dimension must be
finally checked by measuring.
Marking Out Equipment

In order to establish a datum from which all measurements are made a reference surface is required.
This reference surface takes the form of a large flat surface called a surface table upon which the
measuring equipment is used.

Surface plates are smaller reference surfaces and are placed on a bench for use with smaller workpieces.
For general use, both surface tables and surface plates are made from cast iron machined to various
grades of accuracy. A surface plate is shown below.

Surface Gauge
A surface gauge shown is used on surface plates for scribing lines on work pieces and checking
parallel surfaces and heights. The surface gauge is used also in finding the center of a cylinder
and determining whether a plane's surface is truly horizontal.

Angle plate

The angle plate as shown below is used to assist in holding the work piece perpendicular to the
table. The angle plate is provided with holes and slots to enable the secure attachment, clamping
and adjusting of work pieces.

Vee blocks
Holding circular work for marking out or machining can be simplified by using a vee block. The larger
sizes are made from cast iron, the smaller sizes from steel hardened and ground, and provided with a
clamp. They are supplied in pairs marked for identification. The faces are machined to a high degree of
accuracy of flatness, squareness, and parallelism, and the 90° vee is central with respect to the side
faces and parallel to the base and side faces.

Engineer’s square

An engineer’s square is used when setting the workpiece square to the reference surface or when
scribing lines square to the datum edge. The square consists of a stock and blade made from hardened
steel and ground on all faces and edges to give a high degree of accuracy in straightness, parallelism and
squareness. It is available in a variety of blade lengths.

Steel Rule
These are made from hardened and tempered stainless steel, photo-etched for extreme accuracy
and have a non-glare satin chrome finish. Rules are available in lengths of 150mm and 300mm
and graduations may be along each edge of both faces.

Dividers

Dividers are used to scribe circles or arcs and to mark off a series of lengths such as hole centres.
They are of spring bow construction, each of the two pointed steel legs being hardened and
ground to a fine point and capable of scribing a maximum circle of around 150mm diameter.

Larger circles can be scribed using trammels, where the scribing points are adjustable along the
length of a beam. Dividers and trammels are both set in conjunction with a steel rule by placing
one point in a convenient graduation line and adjusting the other to coincide with the graduation
line the correct distance away.

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Punches
The punch is a hard metal rod with a shaped tip at one end and a rounded butt at the other
end, which is usually struck by a hammer. The most commonly used ones for marking out
are:-
Centre punch: It is used as an aid to drilling operations. The centre punch forms an indent
in which the tip of the drill fits. A centre punch has a point angle of 90°.

Prick punch: It is used to produce a smaller indentation than a centre punch, which acts as a
useful datum (standard) point in layout operations. A prick punch has a point angle of 60°

Scriber
Scribers are used in metalworking to mark lines on work pieces prior to manufacturing.
They are used instead of pencils as the marks from pencils can rub off easily. Scribers
consist of a rod of steel that has been sharpened to a point at one or both ends and they are
used to draw shallow scratches on the surfaces of the work pieces.
There are two types of scribers: a) One-end scriber and b) Double-end scriber
Snips
Snips, also known as shears, are hand tools used to cut sheet metal and other tough webs. Their
grips are ergonomically designed for applying high pressures when required, allowing control for
precise cutting.

Pliers
Pliers are a hand tool used to hold objects firmly, or for cutting and bending tough materials such
as wires. There are different types such as flat nose pliers, long nose pliers, combination pliers
and circlip pliers. These types are designed to deal with different types of jobs.

1.Long nose pliers Long nose pliers are both cutting and gripping pliers used by electricians and
other tradesmen to bend, re-position and cut wire.

Combination pliers

These pliers incorporate side cutters, joint cutters and pipe grip.

Files
A file is a hardened piece of high-grade steel with slanting rows of teeth. It is used to cut, smooth
or fit metal parts. The size of the file is indicated by its length. Different types of files include:
Mill File, Flat File, Hand File, Square File, Round File, Half Round file etc.
Identifying files
To identify a file, it is necessary to know the following:
1. The length (measured from the point to the shoulder).
2. The shape of the file (the cross-sectional profile).
3. The grade the spacing and pitch of the teeth (smooth, second and coarse).
4. The type of cut or the patterns of cutting edge (single, double and rasp).
Hence Files are categorized according to Length, Shape, Grade and Cut
Patterns. File main parts are shown below.

Shapes of files
Files come in different shapes for carrying out different jobs. Some shapes include:
1. Hand File is the common file used for roughing and finishing. It is a rectangular in section and
parallel in width. It has double cut teeth on two faces, single cut teeth on one edge, and one safe
edge.

2. Flat File - is similar to a hand file rectangular in section, tapered slightly in width and
thickness towards the tip. It has double cut teeth on two faces and Single Cut teeth on two sides.

3. Half-round File - its cross-section is a chord of a circle with its taper towards the tip. It is used
for forming radii, grooves, etc. The flat side is used for finishing flat surfaces.

4.Mill files- are suitable as a sharpening file. Mill files are the best choice for filing where a
smooth finish is important. Also good for polishing and deburring work in lathes.
Mill files are widely used for sharpening tools. Two square edges. Single cut on sides and edges.
All sizes slightly tapered in width.
5. Round File – it has a round cross-section tapering toward the end. It is used for enlarging holes
and producing internal round corners. Usually double cut in the larger sizes, and single cut for
the smaller sizes.

6. Square File - is square in section and tapered towards the tip, usually double cut on all four
faces. It is used for filing rectangular slots or grooves.

7. Three Square File - is also known as triangular file. This is triangular in section, and tapered
towards the tip with double cut on both faces. It is used for filing corners or angles less than 90°.