jigs and fixture design lecture note by Aragaw Gebremedhin

education is a key for everything so the objective of this slide is to share knowledge to the glob in my area of specialization.
This lecture note is basically designed for mechanical Engineering Manufacturing stream students and Instructors.

1. Jigs and Fixtures Design
Lecture note
By: Aragaw G/Medhin (Mscin manufacturing Engg.)
Email:[email protected]
From Ethiopia
1

2. CONTNTS
Chapter-1: Introduction
Chapter-2: Jigs and Fixtures design
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3. TEXT BOOKS
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4. CHAPTER-ONE
Introduction
CONTENT
Introduction to Tool Design:
Tools classification and design of tools
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5. 1.1. Introduction to Tool Design
Tool design is a specialized phase of tool
engineering.
The word "tooling" refers to the hardware
necessary to produce a particular product.
Tooling, as viewed by the tool designer, consists
of a vast array of cutting devices, jigs, fixtures,
dies, gages, etc.,used in normal production.
The basic task of the tool designer is to provide
drawings of a tool or set of tools to produce the
work piece.
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6. Cont’d
The tool designer may have to produce a
complete set of drawings showing:
1.An assembly drawing,
2.One or more subassemblies, if the design is
complex,
3.A detail drawing of each part,
4.A complete list of parts needed to make the tool.
❖These are given to the toolmakers, whose task is
to make the tools.
The tool designer must know manufacturing
procedures( how the work piece is to be made).
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7. Cont’d
Thetooldesignermusthaveknowledgeof
standardsandprocedures.
Thegreatesteconomycanbeeffectedwhere
standardparts(screws,bushings,handles,clamps,
andsoon)canbeworkedintonewtools.
Thetooldesignermustunderstandhowtools
performtheirfunction.
ForthisheneedsAgoodbackground:
✓Inmechanicsandmathematics.
✓Physicalpropertiesofmaterialsusedinmakingtools.
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8. Cont’d
TOOL DESIGN
Tooldesignistheprocessofdesigningand
developingthetools,methods,andtechniques
necessarytoimprovemanufacturingefficiency
andproductivity.
Itgivestotheindustrythemachinesandspecial
toolingneededfortoday'shigh-speed,high-
volumeproduction.
Itdoesthisatalevelofqualityandeconomythat
willensurethatthecostoftheproductis
competitive.
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9. TOOL DESIGN OBJECTIVES
The main objective of tool design is to lower manufacturing
costs while maintaining quality and increased production.
To accomplish this, the tool designer must satisfy the
following objectives:
➢Provide simple, easy-to-operate tools for maximum
efficiency.
➢Reduce manufacturing expenses by producing parts at the
lowest possible cost.
➢Design tools that consistently produce parts of high quality.
➢Increase the rate of production with existing machine tools.
➢Design the tool to make it foolproof and to prevent improper use.
➢Select materials that will give adequate tool life.
➢Provide protection in the design of the tools for maximum
safety of the operator. 9Aragaw G/Medhin

10. REQUIREMENTS TO BECOME A TOOL
DESIGNER
To perform the functions of a tool designer, an
individual must have the following skills:
➢The ability to make mechanical drawings and sketches
➢An understanding of modern manufacturing methods,
tools, and techniques
➢A creative mechanical ability
➢An understanding of basic tool making methods
➢A knowledge of technical mathematics through practical
trigonometry
➢File management
➢CAD drafting skills
➢Electronic communication skills
➢Geometric dimensioning and tolerancing 10Aragaw G/Medhin

11. DUTIES OF TOOL DESIGN ENGINEER
Tool Design Engineer should take as a duty
to consider the following:
✓Manufacturing methods to be used.
✓Work piece material
✓Cutting tool materials
✓Tool Life
✓Cutting fluids to be used
✓Degree of accuracy required
✓Locating and clamping surfaces on part
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12. HUMAN FACTOR INVOLVED
Some of the human factors to be considered
while designing a tool are as follows:
✓Tool should crate smoothly
✓Controls and clamps should be convenient for the
operator to use
✓Use of foot can be made to minimize hand and arm
fatigue
✓All controls clamps should be located within easy
reach of the operator
✓Levers and handles, should be large enough to
reduce hand fatigue
✓Tool body should be rigid enough to resist all cutting
forces.
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13. 1.2. Tools classification and design of
tools
The most common classification of types of
tooling is as follows:
1.Cutting tools, such as
Single point cutting tools
Multi-point cutting tools. drills, reamers,
milling cutters, broaches, and taps
2.Jigs and fixtures for guiding the tool and
holding the work piece.
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14. Cont’d
3.Gages and measuring instruments
4.Sheet-metal press working dies for all types
of sheet-metal fabrication
5.Dies for plastic molding die casting,
permanent molding, and investment casting
6.Forging dies for hot and cold forging,
upsetting, extrusion, and cold finishing
❖Now let us see some of them in detail
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15. CHAPTER-TWO
Jigs and Fixtures design
CONTENTS
Introduction to Jigs and Fixtures
Types and Functions
Locating and Clamping Method
Design of simple Jigs
Design of fixtures for lathe and milling
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16. 2.1. Introduction to Jigs and
Fixtures
Jigsand fixturesare designed to hold, support
and locate the work pieces to ensure that each
part is machined within the specified limits.
Jigsandfixturesare production work holding
devices used to manufacture duplicate parts
accurately
Jigsand fixtures are so closely related that the
terms are sometimes confused or used
interchangeably.
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17. Cont’d
A Fixture is a production tool that locates, holds,
and supports the work securely so the
required machining operations can be
performed.
➢It does not guide the cutting tool. .
A Jigis a device which is used to hold and
position the work piece. In addition it provides
some means for guiding the cutting tool.
➢Jigs are usually fitted with hardened steel
bushings for guiding drills or other cutting tools
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18. Advantages of jigs and fixtures
The employment of jigs and fixtures has the
following advantages:
✓It is an important for production of articles in large quantities
with a high degree of accuracy and interchangeability at a
competitive cost.
✓To reduce machining times by eliminating time of handling
and setting up of the component parts.
✓Ensures the uniformity of finished product.
✓It facilitates the holding and supporting of the components, to
position the component properly and guide the cutters.
✓It becomes possible to accommodate several components at one
setting and multiple machining.
✓It makes possible to employ unskilled or semi-skilled
machine operators.
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19. 2.2. Types and Functions of jigs and
fixture
CLASSES OF JIGS
Jigs may be divided into two general classes:
boring jigsand drill jigs.
1.Boring jigs are used to bore holes that either
are too large to drill or must be made an odd
size .
2.Drill jigs are used to drill, ream, tap,
chamfer, counter bore, countersink etc.
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20. Figure 2-2-Boring jigs
Figure 2-3-Drill jigs
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21. 2.2.1. TYPES OF JIGS
Drill jigs may be divided into two general
types, open and closed.
1.Open jigs are for simple operations where work
is done on only one side of the part.
Example: Templetjig, Plate jig, Table jig, etc
2.Closed, or box jigs are used for parts that must
be machined on more than one side.
Example:Boxjig,Sandwichjig,Leafjig,etc
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22. 1.Template jigsare
normallyusedforaccuracy
ratherthanspeed.
Thistypeofjigfitsover,on,or
intotheworkandisnotusually
clamped(Figure2-4).
Templatesaretheleastexpensive
andsimplesttypeofjigtouse.
Theymayormaynothave
bushings.
TherearedifferenttypeofT.J
CircularTemplateJigs
LayoutTemplateJigs
Flat-PlateTemplateJigs
TYPES OF JIGS
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23. Cont’d
2. Plate jigs are similar to templates
The only difference is that plate jigs have
built-in clamps to hold the work.
These jigs can also be made with or without
bushings, depending on the number of parts
to be made.
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24. 3. Table jigs:
Plate jigs are sometimes
made with legs to raise the
jig off the table for large
work.
This style is called a table
jig
Cont’d
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25. 4. Sandwich jigs
Are a form of plate jig with a back plate.
This type of jig is ideal for thin or soft parts that
could bend or warp in another style of jig.
The use of bushings is determined by the number of
parts to be made.
Cont’d
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26. 5. Angle-plate jigs
Are used to hold parts that are machined at right
angles to their mounting locators (Figure 2-8).
Pulleys, collars, and gears are some of the parts that use
this type of jig.
A modified angle-plate jig, which is used for machining
angles other than 90 degrees (Figure 2-9).
Cont’d
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27. 6. Box jigs, or tumble jigs,usually totally
surround the part (Figure 2-10).
This style of jig allows the part to be
completely machined on every surface
without the need to reposition the work in
the jig.
Cont’d
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28. 7. Channel jigs: are the simplest form of box
jig (Figure 2-11).
The work is held between two sides and
machined from the third side.
In some cases, where jig feet are used, the work
can be machined on three sides.
Cont’d
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29. 8. Leaf jigs: are small box jigs with a hinged
leaf to allow for easier loading and unloading
(Figure 2-12).
Cont’d
▪Themaindifferences
betweenleafjigsandbox
jigsaresizeandpart
location.
▪Leafjigsarenormally
smallerthanboxjigsand
aresometimesmadesothat
theydonotcompletely
surroundthepart.
▪Theyareusuallyequipped
withahandleforeasier
movement.
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30. 10. Trunnion jigs: are a form of rotary jig for
very large or odd-shaped parts (Figure 2-14).
The part is first put into a box-type carrier and then
loaded on the Trunnion.
This jig is well suited for large, heavy partsthat must
be machined with several separate plate-type jigs.
Cont’d
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31. 11. Pump jigs:are commercially made jigs that
must be adapted by the user (Figure 2-15).
The lever-activated plate makes this tool very fast to load
and unload.
Since the tool is already made and only needs to be
modified, a great deal of time is saved by using this jig.
Cont’d
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32. Cont’d
▪Themainfeatureofthisjig
ishowitlocatesthework.
Whileonepartisdrilled,
anothercanbereamedand
athirdcounter-bored.
▪Thefinalstationisusedfor
unloadingthefinishedparts
andloadingfreshparts.
▪Thisjigiscommonlyused
on multiple-spindle
machines.
12. Multi station jigs: are combined type of jigs
discussed previously (Figure 2-16).
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33. CLASES OF FIXTURES
Fixturesare normally classified by the
type of machine on which they are used.
Fixtures can also be identified by a sub
classification. For example,
If a fixture is designed to be used on a milling machine,
it is called a milling fixture.
If the task is intended to perform straddle milling, it is
called a straddle-milling fixture.
If the task is intended to perform turning, It is called a
lathe fixture.
If the task is welding it is called as welding fixture
Cont’d
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34. 2.2.2. TYPES OF FIXTURES
Jigs and fixtures are made basically the same
way as far as locators and positioners are
concerned.
The main construction difference is mass.
Because of the increased tool forces,
fixtures are built stronger and heavier than a
jig would be for the same part
Fixture type fall generally in to six groups:
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35. 1. Plate fixtures: are the simplest form of
fixture (Figure 2-17).
The basic fixture is made from a flat plate that has a
variety of clamps and locators to hold and locate the part.
The simplicity of this fixture makes it useful for most
machining operations.
Its adaptability makes it popular.
Cont’d
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36. 2. Angle-plate fixture is a variation of the plate
fixture (Figure 2-18).
With this tool, the part is normally machined at a right
angle to its locator.
While most angle-plate fixtures are made at 90 degrees,
there are times when other angles are needed.
In these cases, a modified angle-plate fixture can be
used (Figure 2-19).
Cont’d
Set Block
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37. 3. Vise-jaw fixtures: are used for machining small
parts(Figure 2-20).
Vise-jaw fixtures are the least expensive type of
fixture to make.
Their use is limited only by the sizes of the vises
available.
Cont’d
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38. 4. Indexing fixtures: are very similar to indexing
jigs (Figure 2-21).
These fixtures are used for machining parts that must have
machined details evenly spaced.
Cont’d
▪Examplesofthepart
producedbyusesofan
indexingfixture.
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39. 5. Multi station fixtures: are used primarily for
high speed, high-volume production runs,
where the machining cycle must be continuous.
Duplex fixturesare the simplest form of multi station
fixture, using only two stations (Figure 2-23).
This form allows the loading and unloading operations to be
performed while the machining operation is in progress.
Cont’d
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40. 6. Profiling fixtures
Are used to guide tools for machining contours
that the machine cannot normally follow.
These contours can be either internal or external.
Cont’d
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41. SPECIAL TYPE OF FIXTURE
Modular Fixturing: is a work holding system that uses
a series of reusable standard components to build a
wide variety of special-purpose work holding devices.
Modular fixtures are assembled with a variety of
standard, off-the-shelf tooling plates, supports, locating
elements, clamping devices, and similar units.
The three primary types of modular work holding
systems used today are
1.The sub plate system,
2.The "T"-slot system, and
3.The dowel-pin system.
41
Cont’d
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42. 42
Cont’d
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43. ADVANTAGE OF MODULAR FIXTURE
The primary advantages of using a modular
work holding system are:
✓Reduced lead time in building work
holders
✓Reusability of the various components
✓It reduce the setup time and storage space
✓A very high degree of accuracy can be
achived
✓It is very flexible or Versatility of the
modular construction 43Aragaw G/Medhin

44. 2.3. LOCATING AND CLAMPING
METHOD
2.3.1. Location
The termlocating, as used in the language of the tool
designer, refers to the dimensional and positional
relationship between the workpiece and the cutting tool
used on the machine.
The locating device should be so designed that each
successive work piece when loaded and clamped will
occupy the same position in the work holding device.
In the design of jig and fixtures the location of the
component is very important aspect as the correct
location influences the accuracy of the finished
product.
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45. 2.3.2. Clamping
Once a workpiece is located, it is necessary to press
it against the locating surfaces and hold it there
against the forces acting upon it. The tool designer
refers to this action as clampingand the
mechanisms used for this action are known as
clamps.
The method of clamping will depend upon the
type of locating device and vice versa.
The selection of locating and clamping
methods and devices will depend upon the
machining operation and the configuration of
the part.
Cont’d
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46. Cont’d
2.3.3. Degree of Freedom(DOF)
A body in space have twelve degrees of freedom i.e. it
is capable of moving into the space in the twelve
different directions as shown in Fig. below.
The body can move in either of two
opposed directions along three mutually
perpendicular axis (XX,YY& ZZ) as 9-
12,8-10 & 5-11and may rotate in either
of two opposed directionsaround each
axes clockwise and anti-clockwise (1-2,
3-4 & 6-7) Each direction of movement
is considered as one degree of' freedom.
Thus there are twelve degrees of
freedomfor any workpiece in space(6-
Rotational and 6 Translational).
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47. Example:Determine the degrees of freedom
arrested by V locator with a stop pin of a
cylindrical work piece shown in Fig. below.
Cont’d
▪7-DOFwill be arrested
1.The horizontal base plane
will restrict 3-DOFrotational
mov’t 1, 2 and translator
movement 3.
2.The vertical plane will
restrict 3-DOFrotational
mov’t 4, 5 and translator
movement 6 .
3.The stop pin will restrict 1-
DOF translator movement 7.
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48. Cont’d
48
MOTIONS
+X-X+Y-Y+Z-Z
TOTAL
DOF
TRANSLATIONAL
✓ ✓✓ ✓ ✓ 5
CCCW CCCW CCCW
ROTATIONAL
   ✓✓ 2
HOW MANY DOF THE
CYLINDER HAVE?
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49. Cont’d
HOW MANY DOF THE
CYLINDER HAVE?
49
MOTIONS
+X-X+Y-Y+Z-Z
TOTAL
DOF
TRANSLATIONAL
 ✓  ✓✓ 3
CCCW CCCW CCCW
ROTATIONAL
   ✓✓ 2Aragaw G/Medhin

50. Cont’d
9-DOF are constrained
Only the object have 3-
DOF
50
MOTIONS
+X-X+Y-Y+Z-Z
TOTAL
DOF
TRANSLATIONAL
   ✓ 1
CCCW CCCW CCCW
ROTATIONAL
   ✓✓ 2
HOW MANY DOF THE
CYLINDER HAVE?
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51. 2.3.4. LOCATING AND SUPPORTING
PRINCIPLES
2.3.4.1. BASIC RULES FOR LOCATION
The basic rules for locating the component are as follows;
1.Locators should be spaced as far apart as possible.
2.Locators should be positioned to contact the work on a
machined surface.
3.Locators provided should be fool proof i.e., the component
can only be loaded into the fixture in the correct position.
4.Location features should be swarf traps(chips proof) and
should have clearance provided where necessary to clear
machining burrs.
5.Locating devices should reduce the degrees of freedom to zero
with no redundant location feature.
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52. When designing locations and supporting
components A tool designer must keep the
following points in mind while designing the
tool:
1.Positioning the locators
2.Part tolerance
3.Fool proofing
4.Duplicate location
Cont’d
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53. 1.Positioning the locators
Whenever possible, locators should contact the work on
a machined surface.
Locators should be spaced as far apart as possible. This
permits the use of fewer locators and ensures complete
contact over the locating surface
Where chips or foreign matter may become a problem,
the locators should be placed to avoid this interference. If
this is not possible, the locators should be relieved.
Cont’d
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54. Cont’d
2. Part tolerance
When designing a tool, the designer must keep the part
tolerance in mind.
Locators must be designed to fit the part at any size
within the part limits
As a general rule, the tool tolerance should be between
20 and 50 percent of the part tolerance.
54
▪For example, if a hole
in a part must be located
within ±0.010 inch, then
the tolerance of the hole
in the jig must be
between ±0.002 inch and
±.005 inch (Figure 3-2).
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55. 3. Fool proofing.
Fool proofing is a means by which the tool
designer ensures that the part will fit into the
tool only in its correct position.
Fool proofing devices must be simple. If not, they
tend to complicated an easy task.
Cont’d
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56. 4. Duplicate location
The use of duplicate locators should always be avoided.
Locator duplication not only costs more but also could
cause inaccuracies.
For example on the figure below:
The flange in Figure 3-5A is located on both the underside
of the flange and the bottom of the hub This is called
Duplicate location. But it can be corrected as:
➢If the reference surface is the flange, as in Figure 3-5B
➢If the hubis the reference surface, as in Figure 3-5C
Cont’d
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57. 2.3.4.2. PRINCIPLE OF LOCATION
3-2-1 Principle of Location
3-2-1principleis also known as six point locationprinciple
which is used to constrain or prevent the body from
moving in any direction along three axes XX, YY&ZZ.
By providing six locating pins three in a base plane, two in
a vertical plane and one in a plane perpendicular to the first
two the nine degrees of freedom are controlled as
shown in Fig. 2-26.
3-2-1principleor six-point locating
method is the most common external
locator for square or rectangular
parts.
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58. Pins A, B, C will restrict the body from
rotating about X and Y axes and the
body cannot move downward along Z
axis.
DOF 1, 2, 3, 4 and 5.
Pins D and E will prevent from rotating
the body about Z axis and also it can
not move along -veY-axis.
DOF : 6,7 and 8 will get restricted
Pin Fwill be able to restrict the DOF-9
Three DOF 10, 11 and 12 will remain
unrestricted.
These three DOF can be restricted by
providing three more pins but then the pins
will entirely enclose the workpiece which
is not desirable and thus the DOF 10, 11
and 12 may be restricted by means of
clamping devices
Cont’d
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59. When a workpiece having holes is located, the holes
provide an excellent method of locating the
complete part.
As shown in Figure2-27the center hole is used as a
primary locator,and one of the other holes is used as a
secondary locator.
Here the primary locator is a round pin, and the
secondary locator is a diamond pin.
The base plate with the round pin positioned in the
center hole will restrict 9-DOF (1-4, 2-
5,7,8,10,11,and 12).
The diamond pin, located as shown, further restricts
another two degrees of movement (6 and 3).
Together, these locators restrict 11-DOF.
Cont’d
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60. Cont’d BACK
60
BACK
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61. 2.3.4.3. CHOOSING A LOCATING
SURFACES
Thetooldesignermustbeabletoaccuratelylocate
eachpartregardlessofhowitismade.
Todothis,thetooldesignermustknowthevarious
typesoflocatorsandhoweachshouldbeusedtoget
thebestpartplacementwiththeleastnumberof
locators.Themethodsarecategorizedas:
I.Locatingfromaflatsurface
II.Locatingfromaninternaldiameter
III.Locatingfromanexternalprofile
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62. I. LOCATING FROM A FLAT SURFACE
There are three primary methods of locating work
from a flat surface:
1.Solid supports,
2.Adjustable supports, and
3.Equalizing supports.
These locators set the vertical position of the part, support
the part, and prevent distortion during the machining
operation.
Cont’d
1.solid supports,
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63. Cont’d
2. Adjustable supports
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64. 3. Equalizing supports(Equalizing Jacks) .
Provide equal support through two connected contact points.
As one point is depressed, the other raises and maintains
contact with the part.
This feature is especially necessary on uneven cast surfaces.
Cont’d
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65. II. LOCATING FROM AN INTERNAL
DIAMETER
Locating a part from a hole or pattern is the most effective way
to accurately position work.
Nineof the twelve directions of movement are restricted by
using a single pin, and elevendirections of movement are
restricted with two pins. ***
When possible, it is logical to use holes as primary part
locators.
Several types of locators are used for locating work from
holes. Figure 3-16 shows a few locators used for large
holes.
Figure 3-16 : Internal locator
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66. 1. Pin-type locators: are used for smaller holes and for
aligning members of the tool (Figure 3-17).
When the pins are used for alignment, special bushings
should also be used so that they can be replaced when
they wear.
Pins used for part location are made with either tapered
ends or rounded ends, allowing the parts to be installed
and removed easily(Figure 3-18).
Cont’d
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67. 2. Diamond or Relieved pin:which is normally used
along with the round pin to reduce the time it takes to load
and unload the tool.
It is easier to locate a part on one round pin and one diamond
pin than to locate it on two round pins.
In use, the round pin locates the part and the diamond pin
prevents the movement around the pin.
Cont’d
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68. Cont’d
Diameter of
diamond(d) pin can
be calculated using
this formula
Where:
•D=bore diameter of
w/p
•V= tolerance b/n
center of holes
•W= width of pin
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69. 3. Split contact locator:
It is a type of relieved locator used for thick
workpieces.
Here, the locator is relieved in the middle, and only the top
and bottom areas of the locator contact the workpiece.
This design provides full location and makes the
locator less likely to bind in the workpiece.
Cont’d
69Aragaw G/Medhin

70. 4. Raised contact locator:
Is an example of relieving a locator for better function.
This design reduces the contact area and raises the point where
the locator and work-piece touch.
Moving this contact point off the base plate, to the middle of
the workpiece, helps reduce the effects of dirt, chips, or burrs.
Cont’d
The raised contact design
supplies a complete locating
surface and reduces the chance
of the locator binding in the
hole.
70Aragaw G/Medhin

71. III. LOCATING FROM AN EXTERNAL
PROFILE
Itis the most common method of locating work in the
early stages of machining.
Profile locators position the work in relation to an
outside edge or the outside of a detail, such as a hub or
a boss.
The following are examples of the most common
ways a part can be located from its profile.
1.Nesting locators
2.Vee locators
3.Fixed-stop locators(machined or Installed locators)
4. Adjustable-stop locators etc.
Cont’d
71Aragaw G/Medhin

72. 1.Nesting locators: position a part by enclosing
it in a depression, or recess, of the same shape
as the part.
➢Nesting is the most accurate locating device for
profile location.
➢It is very expensive to design for complicated
shapes.
The most common type is
➢The ring nest -for cylindrical profiles.
➢The full nest-shapes other than cylindrical.
➢The partial nest-encloses only a part of the
workpiece
Cont’d
72Aragaw G/Medhin

73. Cont’d
73Aragaw G/Medhin

74. 2. Vee locators:
Are used mainly for round work.
They can locate flat work with rounded or angular ends
and flat discs (Figure 3-29).
The Vee-block locator is normally used to locate
round shafts or other work pieces with cylindrical
sections (Figure 3-30).
One advantage vee locators have over other locators is
their centralizing feature.
Cont’d
74Aragaw G/Medhin

75. Cont’d
3. Fixed-stop locators
Are used for parts that cannot be placed in either a nest or a vee
locator.
They are either machined into the tool body (Figure 3-32), or
installed(Figure 3-33).
Installed locatorsare normally more economical to use
because of the time it takes to make the machined locators. It
can be replaced when worn, the entire tool body does not have to
be made again.
75Aragaw G/Medhin

76. 4. Adjustable-stop locators:
can also be used to keep the cost of a tool to a
minimum (Figure 3-36).
Since these stops are adjustable, their position
on the tool body does not have to be as closely
controlled.
Cont’d
76Aragaw G/Medhin

77. One common way to locate parts is to use both fixed
stops and adjustable stops.
The tool in Figure 3-37 shows how the fixed locator is
used to reference the end of the part while the adjustable
locators are used on both sides.
Cont’d
Using adjustable locators for
this jig allows the part to be
positioned exactly.
If adjustment is necessary because
of wear or misalignment, it can be
easily corrected.
Another advantage of the
adjustable-type locator is its
ability to double as a clamp.
77Aragaw G/Medhin

78. Cont’d
5. Sight locators:align rough parts in a tool for
approximate machining (Figure 3-39).
There are two methods of referencing a part by sight
location:
1.By lines engraved on the tool, as in Figure 3-39A, or
2.By slots, also shown in Figure 3-39B.
In both cases, the part is aligned with the marks until it
is in the approximate center. It is then clamped and
machined.
78Aragaw G/Medhin

79. 2.3.5. CLAMPING AND
WORKHOLDING PRINCIPLES
The main purpose of a work holder, or clamping
device, is to securely hold the position of the part
against the locators throughout the machining cycle.
To do this, the clamp used must meet the following
conditions:
1.The clamp must be strong enough to hold the
part and to resist movement
2.The clamp must not damage or deform the part.
3.The clamp should be fast-acting and allow
rapid loading and unloading of parts.
79Aragaw G/Medhin

80. 2.3.5.1. BASIC RULES OF CLAMPING
I.Positioning the Clamps
Clamps should always contact the work at its most rigid
point. To prevents from bending or damaging the part.
The part must be supported if the work is clamped at a
point where the force could bend the part. The flange in
Figure 4-1 shows this point.
The ideal place to clamp the part is from its center hole.If it is
held by the outer edge, the part must be supported (Figure 4-2).
Clamps are also positioned so they do not interfere with the
operation of the tool or machine.
Cont’d
80Aragaw G/Medhin

81. Cont’d
II.Tool Forces
Tool force are forces generated by the cutting action.
They are caused by resistance of the workpiece being cut or
sheared by the tool.
To clamp a part correctly, the tool designer must know how
tool forces, or cutting forces act in reference to the tool.
The drill jig in Figure 4-3 is an example of how the cutting force
is used to hold the work.
In this drill jig, the forces that cause the part to revolve are restricted
and held by the locators. This leaves the climbing action to be
restrained by the clamp.
81Aragaw G/Medhin

82. III.Clamping force
It is the force required to hold a part against the locators.
In the case of the bored ring in Figure 4-4, if the ring is
clamped as shown at view A, the part can bend. If it is held
as at view B, this possibility is reduced.
Cont’d
Clamping pressure, as
a general rule, should
only be enough to hold
the part against the
locators.
The locators should
resist the bulk of the
thrust.
82Aragaw G/Medhin

83. 2.3.5.2. TYPES OF CLAMPS
Various methods of clamping are common to
both jigs and fixtures.
The type of clamp the tool designer chooses is
determined by
1.The shape and size of the part,
2.The type of jig or fixture being used, and
3.The work to be done.
The tool designer should choose the clamp that is
the simplest, easiest to use, and most efficient
Now let us see some common types of clamps:
Cont’d
83Aragaw G/Medhin

84. Cont’d
1.STRAP CLAMPS
Strap clampsare the simplest clamps used for
jigs and fixtures (Figure 4-5).
Their basic operation is the same as that of a
lever. Strap clamps can be grouped into three
classes (by the position of fulcrum), each
representing a form of lever (Figure 4-6).
Most strap clamps use the third-class lever
arrangement.
84Aragaw G/Medhin

85. Whenastrapclampisused,theforceontheworkpieceis
alwaysproportionaltothepositionofthefastenerwith
respecttotheworkpieceandtheheelsupport.
Cont’d
85Aragaw G/Medhin

86. The arrangement shown in
Figure 4-9 is a better way to
clamp a single part.
Here the fastener is positioned
so that 1/3 of the strap length is
between the fastener and the
workpiece and 2/3 of the strap
is between the fastener and
the heel support.
The clamping pressure on the
workpiece with this setup is
twice as great as that on the heel
support.
Cont’d
86Aragaw G/Medhin

87. Strap clamps are used in almost every area of
jig and fixture design and construction.
Some more common types are the hinge
clamp, the sliding clamp, and the latch clamp
(Figure 4-10).
Cont’d
87Aragaw G/Medhin

88. 2. SCREW CLAMPS
Screw clampsare widely used for jigs and fixtures.
They offer the tool designer almost unlimited application
potential, lower costs, and, in many cases, less complex
designs.
The only disadvantagein using screw clamps is their
relatively slow operating speeds.
Cont’d
The basic screw clamp
uses the torque developed
by a screw thread to hold
a part in place either by
direct pressure or by its
action on another clamp
(Figure 4-15). 88Aragaw G/Medhin

89. 3. SWING CLAMPS
Swing clampscombine the screw clamp with a swinging
armthat pivots on its mounting stud.
➢The holding power with this
clamp is generated by the screw.
➢The rapid action needed is
achieved by the swinging arm
(Figure 4-16).
Cont’d
89Aragaw G/Medhin

90. 4. HOOK CLAMPS
Hook clampsare similar to swing clamps but they are
much smaller (Figure 4-17).
They are useful in tight places or where several small
clamps rather than one large clamp must be used.
A variation of the hook clamp is shown in Figure 4-18.
Cont’d
90Aragaw G/Medhin

91. 5. QUICK-ACTING KNOBS
Quick-acting knobsare useful for increasing the
output of low-cost tools.
These knobs are made so that when pressure is released,
they can be tilted and slid off a stud (Figure 4-19).
The knob is slid over the stud until it contacts the part.
It is then tilted to engage the threads and is turned until
tight.
Cont’d
91Aragaw G/Medhin

92. 6. CAM-ACTION CLAMPS
Cam-action clamps, when properly selected and used,
provide a fast, efficient, and simple way to hold work
(Figure 4-20).
Cam clamps, which apply pressure directly to the work, are
not used when a strong vibration is present. This might
cause the clamp to loosen, creating a dangerous condition.
It may be Direct-pressure cam clamps (Figure 4-20) or
Indirect clamping (Figure 4-2).
Cont’d
92Aragaw G/Medhin

93. Three basic cam types are used for
clamping mechanisms:
1.flat eccentric,
2.flat spiral, and
3.cylindrical.
Cont’d
93Aragaw G/Medhin

94. Cont’d
7. Wedge Clamps
Wedge clampsapply the basic principle of the inclined plane to
hold work in a manner similar to a cam.
These clamps are normally found in two general forms, flat
wedges and conical wedges.
Flat wedges, or flat cams,hold the part by using a binding action
between the clamp and a solid portion of the tool body
(Figure 4-26).
Large-angle, or self-releasing, wedges are used where more
movement must be made (Figure 4-27).
94Aragaw G/Medhin

95. Conical wedges, or mandrels,are used for holding
work through a hole (Figure 4-28).
Mandrels are available in solid form and expansion
form.
Cont’d
Solid mandrels
are limited in
use to one size
of hole.
Expansion
mandrels are
made to fit a
range of sizes.
95Aragaw G/Medhin

96. 8. Toggle-Action Clamps
Toggle-action clamps,shown in Figure 4-29, are made with four
basic clamping actions: hold down, squeeze, pull, and straight
line.
Toggle clamps are fast-acting.
They have the natural ability to move completely free of the
work, thus allowing for faster part changes.
Another advantage is their high ratio of holding force to
application force.
Cont’d
96Aragaw G/Medhin

97. 9. Power Clamping
Power-activated clampsare an alternative to manually operated
clamping devices. It is basically applied in CNC machine tools.
Power clamping systems normally operate under hydraulic
power or pneumatic power, or with an air-to-hydraulic booster.
The advantages of power clamps are better control of
clamping pressures, less wear on moving parts of the clamp,
and faster operating cycles.
The main disadvantageis cost. Typical applications of
power clamps are shown in Figure 4-31
Cont’d
97Aragaw G/Medhin

98. 10. Chucks and Vises
Commercially available chucks and vises offer
the tool designer devices that, when modified,
greatly reduce tooling costs.
Using standard chucks and vises for special tools can
save the tool designer a great deal of time and
money while increasing the efficiency of the job.
Cont’d
98Aragaw G/Medhin

99. 11. NON MECHANICAL CLAMPING
Non mechanical clamping is a term that is typically applied
to the group of work holding devices used to hold parts by
means other than direct mechanical contact.
The two principal forms of non mechanical clamping used
for production manufacturing are magnetic clamping and
vacuum clamping.
Magnetic chucksare most often used to hold ferrous metals
or work pieces made from other magnetic materials.
Vacuum chucksare another style of chuck used to clamp
difficult parts. While these chucks can hold almost any type
of non-ferrous material, they are typically used for nonmagnetic
materials or for parts that must be clamped uniformly.
Cont’d
99Aragaw G/Medhin

100. Cont’d
100Aragaw G/Medhin

101. 2.4. Design of simple Jigs
All tool design ideas begin in the mind of the tool
designer.
To determine the best possible tool design, a pre-design
analysis should be done to evaluate the workpiece and the
operations to be performed. This analysis should include:
✓Overall size and shape of the part
✓Type and condition of workpiece material
✓Type of machining operations required
✓Degree of accuracy required
✓Number of pieces to be made
✓Locating and clamping surfaces
✓Type and size of machine tools
✓Type and size of cutters
✓Sequence of operations
101Aragaw G/Medhin

102. DESIGN PROCEDURES
Once the tool designer decides that is the best jig or
fixture choice for a particular job, the design process
begins by following the planning processes outline and
the tool designer assembles and evaluates all the
necessary data.
The following are some common procedures:
STEP-1: Examining the part drawing and production plan
STEP-2: Locating the Part
STEP -3: Locating the Bushings
STEP -4: Initial Jig Design
STEP -5: Completing the Tool Drawing
Cont’d
102Aragaw G/Medhin

103. 2.4.1. Simple Jigs Design
EXAMPLE-1: Design a jig to the part drawing and the
production plan of a lock, which is to be drilled on mass
production, are given in Fig 2. Do the following:
A.Analyze the part drawing and production plan to design a
suitable jig
B.Prepare an initial sketch with all necessary dimensions
C.Draw the jig drawing including all necessary data needed
to manufacture the tool (Draw any two views of the jig
assembly).
D.Draw the detail drawing of the jig assembly
E.Give the materials list
103Aragaw G/Medhin

104. Fig-2: part
drawing and
production
plan
Cont’d
104Aragaw G/Medhin

105. SOLUTIONS
Part tolerance
Tolerance of shoulder
Maximum size = 32.08mm
Minimum size = 31.92mm
Tolerance b/n center
Maximum size = 27.1mm
Minimum size = 26.9mm
105
Cont’d
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106. DESIGN PROCEDURES
STEP-1: EXAMINING THE PART DRAWING AND
PRODUCTION PLAN
➢The part is flat disc, 86 x 20mm thick, with a
32mm shoulder in its center
➢The material is M.S
➢The only operation required of the jig is to drill
10-2 holes, 54mm apart.
➢The blank received for drilling is faced, turned to
the specific dimensions.
❖Based on the above information and the geometry of
the part the suitable type of jig is Templetjig
Cont’d
106Aragaw G/Medhin

107. Cont’d
107
STEP-2: LOCATING THE PART
A. Locating the part
The shoulder 32 +0.08mm can be selected as locating position
B. Size of Locator
First find the size of hole to use 32 +0.08mm as a locating element.
Use largest size shoulder as a guide
Hole size = Max. Diam. Of shoulder + clearance, let us take clearance
= 0.025mm = 32.08 + 0.025 = 32.105mm
Assume tool maker’s tolerance as +0.013mm, for jig body therefore:
Hole size = 32.105 +0.013mm
Max. Hole size = 32.118mmand Mini. Hole size = 32.092mm
Aragaw G/Medhin

108. CHECK: the tool tolerance is with in the part by taking center distance
The most possible conditions between the part and the tool can be
found as follows:
A) Largest shoulder size and minimum hole size should be compared
called maximum material conditions (MMC)
(Max. shoulder size –min. hole size = 32.08-32.092 =
-012mm) 0.012mm shift in each direction.
Cont’d
108
From the figure
The max. center distance b/n holes = 27.006mm
The min. center distance b/n holes = 26.994mm
Compare: Part toleranceand Tool tolerance
27.1 27.006
26.9 26.994
❖The tool tolerance is within the part tolerance, therefore
the selected size of hole is correct. Aragaw G/Medhin

109. B) Largest hole size and smallest shoulder size should be
compared called least material conditions (LMC)
(Max. hole size –min. shoulder size
= 32.118-31.92 = 0.198mm)
0.198mm shift in each direction.
Cont’d
109
From the figure
▪The max. center distance b/n holes =
27.099mm
▪The min. center distance b/n holes =
26.901mm
Compare: Part toleranceand Tool tolerance
27.1 27.099
26.9 26.901
❖The tool tolerance is within the part
tolerance, therefore the selected size of hole is
correct.
Aragaw G/Medhin

110. Cont’d
110
STEP -3: LOCATING THE BUSHINGS
Referring to the part drawing the following data gathered:
➢The first hole is positioned 27 +0.1mm from the center hole
center line
➢The second hole is positioned 54 +0.2mm from the center line
of the first hole so that Using these facts, the following
calculations must be made:
i.Maximum allowable distance between hole
centerlines
ii.Tolerance values that will ensure the desired precision
Aragaw G/Medhin

111. i.Maximum allowable distance between
hole centerlines
Largest hole size and smallest shoulder size (LMC)
selected to compute the allowable distance between hole
centers use tolerance 0.099mm for calculation
111
In the first case, the centerline of the part
and the tool is shifted to the maximum
allowable value of 0.099mm.
The nominal size of 27mm is then
added to the offset.
This value, 27.099mm, is then
subtracted from the largest allowable
size of 27.1mm, yielding a maximum
deviation of 0.001mm.
27 + 0.99 = 27.099mm
X = 27.1 -27.099 = 0.001mm
Aragaw G/Medhin

112. Cont’d
112
In the second calculation, the part
is shifted to the maximum amount
allowed in the opposite direction.
The offset is then subtracted from
27mm; the difference is
26.901mm.
The minimum allowable size,
26.9mm, is then subtracted from the
calculated value, resulting in
maximum deviation of 0.001mmin
the opposite direction.
27 -0.99 = 26.901mm
X = 26.901 –26.9= 0.001mmAragaw G/Medhin

113. ii.Tolerance values that will ensure the
desired precision
Tolerance X = 0.001mm; Assume wear tolerance =
0.05mm therefore the final tolerance can be X = 0.001
+ 0.05mm = 0.051mm
In other words, the first bushing must be placed
within a ±0.051mm tolerance range to properly
locate the hole in the part.
Allowing the toolmaker a ±0.05mm tolerance
permits a built-in ±0.001mm wear allowance,
which will lengthen the tool service life.
Cont’d
113Aragaw G/Medhin

114. 114
Once the position of the first
bushing has been decided, the
locational tolerance of the
second bushing must be
specified.
Following the general rule of
tool tolerance,the tool
designer should specify the
center-to-center distance
between the holes as 54 ±
0.1mm, or 50 percent of the part
tolerance.
Cont’d
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115. Based on the above standard since the hole to be drilled is 10mm
and the selected type of bush is Liner bush the dimension is b/n 8
to 10 mm so outside diameter is 16 mm and 12 mm length for
detail refer the above table on the right side.
Cont’d
115Aragaw G/Medhin

116. Cont’d
116
STEP -4: INITIAL JIG DESIGN
After calculating the locator and bushing values, the designer
is ready to plan the rest of the tool.
The first step in this initial design is rough-sketching the part.
Since the butt plate is a flat disc, only two views need to be
sketched (see Figure below).
Draw the rough outline of the jig plate
Finally add over all dimensions
Aragaw G/Medhin

117. STEP -5: COMPLETING THE TOOL
DRAWING
Once the initial sketch has been drawn and the tool
designer is satisfied that the tool will perform the desired
function, the tool drawing is started.
The tool drawing must include any special instructions
the toolmaker will need to fabricate the tool.
N.B:-The part drawing on the assembly
drawing must be drawn by a RED PEN with
phantom line
Cont’d
117 Aragaw G/Medhin

118. 2.5. Design of fixtures for lathe and
milling
2.5.1. Fixture Type and Design
Fixture types fall generally into six groups (it is discussed in section
2.2.2.):
1.Plate Fixtures
2.Angle-Plate Fixtures
3.Vise-Jaw Fixtures
4.Indexing Fixtures
5.Multi-Part or Multi-Station Fixtures
6.Profile fixture
In addition to their basic construction, fixtures may be classified in
respect to the process or machine tool to be used in the machining
process. The primary types include: Milling Fixtures, Lathe
Fixtures, Grinding Fixtures, Broaching Fixtures, Modular Fixturing
118Aragaw G/Medhin

119. 2.5.3. LATHE FIXTURES
A large majority of lathe operations can be accomplished
by using standard chucks and holding methods.
Many parts such as castings and forgings cannot readily
be mounted by any of the standard methods. It is
therefore necessary to manufacture special work-holding
fixtures for machining these parts.
Some of common types of lathe work holding/fixtures
are:
1.Standard chucks: Self-centering 3-jaw chuck,
independent 4-jaw chuck, combination chuck with
individual jaw adjustment. Standard jaws can be
replaced by special jaws or soft jaws
119Aragaw G/Medhin

120. 120
4-jaw chuck
Magnetic chuck
3-jaw chuck
Cont’d
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121. 2.Spring collets: Push-out collets [bar work], pull-in
collets [2
nd
operation], dead length collets, split-liner
collets.
121
Cont’d
COLLET CHUCK
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122. 3. mandrel
1.Plain Mandrel
2.Step Mandrel
3.Gang mandrel
4.Collar mandrel
5.Eccentric
mandrel
6.Screwed
Mandrel
7.Expansion
Mandrel
Cont’d
Aragaw G/Medhin 122

123. 4. Face platefixtures with balance weights.
123
Cont’d
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124. 2.5.4. MILLING FIXTURES
A milling fixture is used to hold the work
piece in correct relation to the cutter.
Milling fixture consists of following parts:
(i)Base
(ii)Clamps
(iii)Rest blocks or nest
(iv)Locating points
(v)T-Bolts
(vi)Gaging surfaces
Cont’d
124Aragaw G/Medhin

125. Types of Milling Fixtures
Various types-of milling fixtures are as follows.
I.String or line milling fixtures.
In this fixture number of components are
strung behind each other in a line.
The fixture, moves relative to the cutters as
shown in Fig. 9.88 and Fig. 9.89
Cont’d
125Aragaw G/Medhin

126. II. Eccentric clamp Fixture.
In this fixture an eccentric clamp is used to hold the
work piece against a serrated face clamp. Fig.9.90
shows a milling fixture with eccentric clamp.
Cont’d
126Aragaw G/Medhin

127. III. Hydraulic clamping fixture. Fig. 9.91
shows a milling fixture with hydraulic clamping.
In this fixture the work piece is located by reference
to a flat base and that flat surfaces of a key-way.
The holding force is directed against the irregular
upper surface of the works piece. Hydraulic force is
applied by means of pistons is used to operate
clamping levers.
Cont’d
127Aragaw G/Medhin

128. IV. Spring type fixture.
Fig. 9.92 shows a spring operated fixture to
hold the work-piece in position by means
of a screw clamp.
Cont’d
128Aragaw G/Medhin

129. V. Clamp type fixture.
Fig. 9.93 shows a milling fixture for
cutting key slots in circular shafts.
Clamp is used to keep the work piece in
position.
Cont’d
129Aragaw G/Medhin

130. FIXTURE DESIGN PROCEDURES
As a general rule the following can be taken as a
procedures but it is not applicable for all type of fixtures.
oSTEP-1: Examining the part drawing and production
plan
oSTEP-2: Locating the part
oSTEP -3: Supporting the part
oSTEP -4: Clamping the part
oSTEP -5: locating the cutters
oSTEP -6: Completing the tool drawing
130Aragaw G/Medhin

131. EXAMPLE:
Design a milling fixture for the part given in Fig 2. the
part drawing and the production plan of a butt plate ,
which is to be milled on mass production, Do the
following:
A.Analyze the part drawing and production plan to design a
suitable fixture.
B.Prepare an initial sketch to with all necessary dimensions
C.Draw the fixture drawing including all necessary data
needed to manufacture the tool (Draw any two views of the
fixture assembly).
D.Draw the detail drawing of the fixture assembly
E.Give the materials list
Cont’d
131Aragaw G/Medhin

132. Part drawing
Cont’d
132Aragaw G/Medhin

133. Cont’d
133Aragaw G/Medhin

134. SOLUTIONS
Part tolerance
Tolerance of Hole
Maximum size = 25.1mm
Minimum size = 24.9mm
Tolerance b/n center
Maximum C. size = 22.6mm.
Minimum C. size = 22.4mm
AND
Maximum C. size = 45.2mm
Minimum C. size = 44.8mm
134
Cont’d
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135. Cont’d
135
DESIGN PROCEDURES
STEP-1: EXAMINING THE PART DRAWING AND
PRODUCTION PLAN
➢The part is a flat disc that is 65mm in diameter and 20mm
thick.
➢The part has three holes, one 25mm hole and two 6mm
holes 45mm apart. The materialspecified is 1020 steel.
➢The operation required is milling two flats 45mm apart
and 8mm deep, parallel within one-half degree.
➢The size of the production run is 150 pieces.
➢The blank received for milling is turned, faced, bored,
and drilled.
Using this information, a suitable type of fixture is vise-held
fixturewhich is the most efficient and cost-effective tool to use
for a specific job, the tool design begins.
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136. STEP-2: LOCATING THE PART
As a general rule, when no machined detail such as a hole or
machined corner is available, the tool designer should use the
same point to initially locate the part that the drafter used
to dimension it.
To locate and position the butt plate accurately, the designer
should use the 25 mmcenter hole as the primary locator and
one of the 5 mmholes as a secondary locator.
In this case, the secondary locator, in addition to restricting the
radial movement of the part around the primary locator, sets
the proper relationship and position of the part in reference to
the milling cutters (Figure 10-5).
Cont’d
136Aragaw G/Medhin

137. A. Calculate diameter of primary locating pin
The hole 25 +0.1mm can be selected as primary locating
position so
➢Max. hole size = 25.1
➢Min. hole size = 24.9
Use smallest size hole as a guide and assume minimum clearance
= 0.01mm, the largest size of locator is:
➢Max. Pin size = Min. Diam. Of hole -clearance,
= 24.9 -0.01 = 24. 89mm
Using tolerance of +0.01mm on the locators size, the minimum
locator size can be:
➢Min. Pin size = Max. pin size –Total deviation
= 24.89 -0.02mm = 24.87mm
Thereforethe primary locator size= 24.88 +0.01
Cont’d
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138. B. To calculate the size(diameter) of secondary
locator which is the diamond pin
Take the small hole diameter is 5 +0.2mm = max. dia. = 5.2 and
min dia.=4.8mm
To calculate diamond pin diameter
Where D= minimum bore diameter = 4.8mm
V = tolerance b/n center = 0.1mm and
W = D/8 = 4.8/8 = 0.6mm
Therefore diameter of diamond pin d = 4.76mm
Cont’d
138Aragaw G/Medhin

139. The secondary locator on the vise-held fixture
should duplicate the position of the first
bushing on the template jig-that is, 22.5 ±0.05
mm from the primary locator (Figure 10-7).
Cont’d
139
HOME WORK
CHECK IF THE
TOOL TOLERANCE
IS WITH IN THE
PART TOLERANCE
OR NOT????
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140. Topreventjammingandpermiteasyloadingandunloading,the
primarylocatorshouldengageonlyone-halfthethickness
ofthepartwhichis10mm.
140
Cont’d
Thesecondarylocatorshould
berelieved1.5mmshorter
thantheprimarylocator,
whichallowstheparttobe
placedontheprimarylocator
firstandrevolveduntilitdrops
overthesecondarylocator.
(Figurel0-8).
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141. STEP -3: SUPPORTING THE PART
Special supports are not required, since the part is
completely machined and its thickness is sufficient
to resist bending.
In this case, to reduce costs the part is supported by
the base of the fixture.
Solid support buttons can be used, but any benefit
is offset by the cost of the buttons and the time to
install them.
Cont’d
141Aragaw G/Medhin

142. STEP -4: CLAMPING THE PART
Clamp type, style, pressure, and location are all
important factors in selecting a clamp.
In the case of the butt plate, the clamp should be
quick-operating and capable of moving clear off the
part for faster loading and unloading.
Using these requirements as a guide, the designer
chooses a cam-action strap clamp similar to the clamp
shown in Figure 10-9.
Cont’d
142Aragaw G/Medhin

143. Once all the tool details have been selected, they must be
placed in proper relation to each other to make sure the tool
will work. The best way to do this is by sketching, Figure 10-
10. For detail of each part refer the standard data's ****
In the case of this fixture, the base must be 70 mm wide and
152 mm long. To properly hold and support the part and tool
details, it should be at least 25 mm thick. To keep the cost
down, the base plate should be cut from the standard cast section
(Figure 10-11).
Cont’d
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144. STEP -5: LOCATING THE CUTTERS
The milling operation involved in fabricating the butt
plate requires parallel shoulders; therefore, the best
machining method is straddle milling.
Straddle millingmachines both sides at the same time
(Figure 10-12).
Cont’d
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145. Inthiscase,a3mmfeelergaugeisselected.Finally,thefeeler
gaugesizeissubtractedfromtheminimumbuttplatesizeto
determinethesizeofthesetblock.
➢The slot tolerance is 45±0.2
= Maximum 45.2mm and minimum 44.8mm
➢To find the size of set block take the minimum slot size and
subtract the filler dimension = 44.8-3-3 = 38.8mm
Sincethetoleranceforthepartis±0.2mm,thetotalallowable
errorinbothsizeandpositionofthesetblockshouldbeheldto
lessthan±0.1mm.
Againconsideringtheextremepermissibledimensions,the
toleranceforlocationshouldbeheldto±0.05mmfromthe
centerlineofthefixture.
Cont’d
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146. The size tolerance of the set block should be 38.8
±.0.05mm. Using these conditions affects the part size
by only 0.1mm, as shown in Figure10-13, which is
well within the part tolerance.
The set block is used to locate the position of one
cutter accurately.
146
Cont’d
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147. STEP -6: COMPLETING THE TOOL
DRAWING
When constructing the tool drawing, as shown in
Figure 10-14, two points must be noted on the
drawing.
➢First, the exact size of the collar that separates
the cutters is 45mm.
➢Second, the tool operator must be instructed to
grind the cutters together on the same arbor to
ensure that their size is identical.
Cont’d
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148. Cont’d
148Aragaw G/Medhin

149. 10Q
FOR UR ATTENTIONS!! 149Aragaw G/Medhin