UNIT 9 TOOLS FOR BASIC LAYOUT
Tools for Basic
Layout
Structure
9.1
Introduction
Objectives
9.2
Tools for Scribing Layout
9.3
Layout Accessories
9.4
Summary
9.5
Key Words
9.1 INTRODUCTION
The process of making reference mark on the workpiece is called layout. Laying out
includes marking the straight lines, center point, circles, arcs on the surface of the
workpiece to indicate the position of hole to be drilled and the amount of material to be
removed by shaping or milling machine. These marks indicate shape, size and features of
the workpiece. Layout marks are often indicated on the surface where machining will
take place. Operator uses these marks as a guideline for machining during checking of
workpiece by actual measurement. Workpiece may cut according to layout mark. The
layout should be made from the base line or the machined edge to ensure the accuracy of
the layout and correct position of dimensions with respect to each other. The accuracy of
a finished job is generally determined by the amount of care taken while laying out.
The layout is very important for cutting the stock, filing and offhand grinding, drilling,
milling etc. One of the jobs of the operator is to measure and layout at the place, where
the stock will be cut. This kind of layout may be marked by pencil or chalk. Layout
marked by pencil or chalk, is called as semi-precision layout. Semi-precision layout is
generally done by steel ruler, which gives tolerance up to 0.5 mm. Precision layout can
be complex and requires sophisticated tools for operation and generally done by tools
that give tolerance up to 0.025 mm or finer. The reference points, reference plane,
reference lines are indicated by laser and optical instruments in aircraft and ship building
industries.
Objectives
After completing this unit, you should be able to understand
•
various types of tools required for layout,
•
the necessity for accurate layout, and
•
the purpose of layout tools such as scriber, dividers, squares etc.
9.2 TOOLS FOR SCRIBING LAYOUT
Surface Plate
It is very important tool for layout operation. It provides an accurate reference
plane. The reference plane is that plane from which measurements may be made
for both layout and inspection. A surface plate may be used for large amount of
work. The surface plate used for large work is called as layout table. Surface plate
should be covered when it is not in use and kept clean when it is in use. Further, it
should never be blown by hammer. This will affect the accuracy of the reference
surface. Surface plate may be made of cast iron or granite. Surface plate of cast
iron is shown in Figure 9.1. Cast iron based surface plate is made from good
quality casting. When the working surface of the casting has been finished to
desired degree of flatness, the distortion will be reduced by the age hardening.
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Layout Design for
Tool Engineering
Then casting has been allowed to age hardened to relieve internal stresses. The ribs
are provided on underside of the surface plate for rigidity. The large cast iron plate
is mounted on a heavy stand or legs with provision for levelling. The plate is
levelled periodically to ensure that its working surface remains flat.
Figure 9.1 : Surface Plate
Granite is superior to cast iron as granite is harder, denser and also gives resistance to
water. The surrounding flat surface will not get affected, if it is chipped. Due to such
excellent properties, granite is often used now-a-days. Also granite is aged in the
earth for long time which results in relieving of internal stresses in earth itself. The
temperature withstanding capacity of granite is also more than other material.
Layout Dyes
Layout dyes are used to make the layout marks visible on the surface of the
workpiece. Layout dyes may be blue, white or red in color. Different dye colors
may be used depending upon the surface color of the workpiece.
Scriber
The Scriber is a tool used for making layout lines on metal surfaces. The scribers
are made of tool steel with hardened and tempered points. The point of scriber
should be sharp in order to mark fine, clear layout lines. The pocket scriber has
removable tip that can be stored in the handle. This allows the scriber to be carried
safely in the pocket. The pocket scriber is shown in Figure 9.2.
Figure 9.2 : Scriber
Divider
The divider is a tool with hardened steel points used for transferring
measurements, comparing distances and marking arcs and circles. Spring divider is
commonly used everywhere for the same purpose. Figure 9.3 depicts a spring
divider. Dividers are adjustable and are classified according to size, i.e. by
maximum opening between the two points. To set the divider to a size, place one
point on 1 cm of rule and adjust the other point until it splits the graduation line at
correct distance. The graduation lines on a ruler are V-shaped and a divider may be
set more exactly by “feeling” that the point is on the graduation line than by seeing
it visually.
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Tools for Basic
Layout
Figure 9.3 : Divider
Hermaphrodite Caliper
It is a caliper having one straight leg and other bent leg. The tip is adjustable for
length. A straight leg has a point so that it can be used to scribe lines parallel to an
edge or shoulder. It can also used to locate the centers of round workpieces. The
hermaphrodite caliper is shown in Figure 9.4. To set this tool, place bent leg on the
end of a ruler and adjust until the pointed leg is at the desired graduation. The bent
leg is placed against the round workpiece and arc is marked at the end of
workpiece. The tangent marks can be laid out by adjusting the leg spacing. And the
centre of workpiece can be located by marking four arcs at 90o.
Figure 9.4 : Hermaphrodite Caliper
Square
It is used to layout lines at right angles or parallel to machined edge. It is also used
to check accuracy of surface which must be at right angle to each other and to set
up workpiece for machining. Square is shown in Figure 9.5. Square should be
handled with extreme care to preserve their accuracy.
Figure 9.5 : Square
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Layout Design for
Tool Engineering
Bevel Protractor
The bevel protractor is used to layout and check the angle. The protractor can be
adjusted from 0 to 180o. The scale may be graduated from 0 to 90o from both right
and left side. The accuracy of the bevel protractor is ( ± 5° ).
Centre Head
The head forms a center square when clamped to the rule. It can be used for
locating centers of round, square and octagonal stock. The centre head should be
used only on workpiece which is true in shape.
Square Head
The square head and rule is used to layout lines parallel and at right angles to an
edge. It may be used as a depth gauge or for checking 45o and 90o angles. The
square head can be moved along the ruler to any position.
Steel Rule
Steel rule is used as a straight edge or for measuring. It may be fitted to the center
head, bevel protractor or to the square head. Metric combination steel rulers are
generally graduated in 1 mm and 1/2 mm while imperial combination set rules are
generally graduated in inch, i.e. 8th or 16th on one side and 32nd and 64th on other side.
Combination Set
It is one of the most useful and versatile tools in the machine shop. The set consist
of steel ruler, bevel protractor, centre head and square head. Figure 9.6 shows
combination set.
Protractor
Head
Steel
Rule
Centre
Head
Square
Head
Scriber
Figure 9.6 : Combination Set
Prick Punch
A prick punch also known as layout punch is made of tool steel in which both ends
are hardened and tempered. It has an included point angle of 30o. The prick punch
is shown in Figure 9.7.
Included Angle of 30
o
Figure 9.7 : Prick Punch
The slim point provides easy location of the punch on a scribe line. It is usually
used to layout mark along layout lines, to mark centers for drilled holes and also to
mark center for divider point. The prick punch is the punch which is used only to
preserve the location of a layout mark while creating minimum damage to the
workpiece. The punch mark may affect the surface finish of the workpiece.
Center Punch
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Center punch is also layout instrument made of tool steel in which both ends are
hardened and tempered. It is same as that of prick punch but only difference being
that it has an included point angle of 90o. It is used to mark the workpiece before
drilling. It is generally used to enlarge the mark made by prick punch so that drill
may be started easily and accurately. Following points should be remembered
while using prick or center punch :
(a)
Hold the punch at an angle of 450 and place the point on layout line.
(b)
Insure that the point of punch should be sharp.
(c)
Examine the position of the punch mark and correct it if necessary.
(d)
Bring the punch to a vertical position and tap it gently with a light
hammer.
Tools for Basic
Layout
Surface Gauge
The surface gauge is the instrument which is used on a surface plate or any flat
surface for scribing lines in layout work. It consists of heavy base and an upright
spindle to which a scriber is clamped. The base of the surface gauge has a
V-groove which allows it to be used on the cylindrical work as well as on the flat
surface. Surface gauge has pins in the base which may be pushed down so that the
surface gauge can be used against the edge of a surface plate or a slot. A surface
gauge can also be used as a height gauge and for leveling work in a vise. A surface
gauge may be set to a size or dimension by using combination square which is
most accurate for most of the layout work.
SAQ 1
(a)
What is the purpose of laying out the workpiece?
(b)
Why should all layouts be made from a base line or machined surface?
(c)
Explain prick and centre punch?
(d)
Explain layout tools with neat sketch.
9.3 LAYOUT ACCESSORIES
Angle Plate
An angle plate is a precision tool having L-shape. It is made of cast iron or
hardened steel, machined to an accurate angle of 90o with all working surfaces and
edges ground. Angle plate is used to hold the workpiece parallel and at right angle
to the surface. C-clamp is generally used to fasten the workpiece with an angle
plate. Slots and tapered holes are provided with some angle plate for clamping the
workpiece.
Parallels
Parallels are used in layout operation for raising the workpiece to a suitable height.
It provides a solid seat for workpiece. The work surface is held parallel to the top
of the surface plate by using the parallel.
Clamps
C-clamps are used to fasten the workpiece to an angle plate or drill press table. It is
also used for holding two or more pieces of metal together. C-clamp is widely used
for this purpose. C-clamp is shown in Figure 9.8. The shape of C-clamp is of letter
“C”.
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Layout Design for
Tool Engineering
Figure 9.8 : C-clamp
V-block
V-block is made of cast iron or heat-treated steel in a wide range of sizes. They are
machined with a 90o V-shaped slot on the top and bottom. V-block is shown in
Figure 9.9. Some V-blocks are provided with U-shaped clamps to hold the
workpiece securely. They are used for laying out round work and to hold it for
machining.
Figure 9.9 : V-block
SAQ 2
(a)
List various layout accessories with uses.
(b)
What is V-block? Explain the purpose of V-block?
(c)
Explain angle plate, parallel with figures.
9.4 SUMMARY
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Laying out includes marking the straight lines, center point, circles, arcs on surface of
workpiece to indicate the position of hole to be drilled or the amount of material to be
removed by shaping or milling machine. These marks specify shape, size and features of
workpiece. Scriber, divider, surface plate, squares, calipers, prick punch, center punch
etc. are used for layout purpose. Surface plate provides accurate reference plane.
Hermaphrodite caliper is used to scribe lines parallel to an edge and to locate the centers
of round workpieces. The bevel protractor is used to layout and check the angle.
Combination set is used for laying out straight line. Center head can be used for locating
centers of round, square and octagonal stock. Angle plate is used to hold the workpiece
parallel and at right angle to a surface. C Clamps are used to tie the workpiece to an angle
plate or drill press table. V-blocks are used to hold the workpiece firmly.
Tools for Basic
Layout
9.5 KEY WORDS
Prick Punch
: A prick punch is used to layout mark along layout
lines, for drilled holes and to mark center for
divider point.
Center Punch
: A center punch is used to enlarge the mark made
by prick punch so that drill may be started easily
and accurately.
Surface Gauge
: Surface gauge is used on a surface plate or any flat
surface to scribe lines in layout work and to level
work in vise.
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