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STRAIGHTNESS MEASUREMENT 1
Chapter 5
StraightnessMeasurement
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STRAIGHTNESS MEASUREMENT 2
How many kinds of Straightness Tolerance
Specifications are there?
What are they?
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STRAIGHTNESS MEASUREMENT 3
Interpret the geometric requirements of a,b & c
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STRAIGHTNESS MEASUREMENT 4
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STRAIGHTNESS MEASUREMENT 5
Straightness of surface elements callouts point directly
to the surface in a view on the drawing that will show
the direction of surface straightness control.
Straightness of an axis callouts are always next to the
size tolerance of the part and have the diameter
symbol in the feature control frame.
The diameter symbol clarifies that the tolerance zone
for straightness of an axis is a cylinder.
Straightness of a centerplane (for noncylindrical parts)will also be called out typically under the size
tolerance for the part.
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STRAIGHTNESS MEASUREMENT 6
(d) Is it possible to have the surface elements
straight with the axis bent?
(e) Conclusion?
Difference between Axis Straightness & Element Straightness
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STRAIGHTNESS MEASUREMENT 7
Straightness of surface elements applicationsinclude functional applications where
barrel- shaped, hourglass-shaped, or bowed surface
elements of a diameter (or surface) must be
controlled
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STRAIGHTNESS MEASUREMENT 8
Interpret the geometric control requirement
Sketch how will you check the straightness
Story on Inspection
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STRAIGHTNESS MEASUREMENT 9
Straightness is a unidirectional control. When applied to
the surface of a noncylindrical part, it will not control
flatness. Straightness, in this case, will only control the line
elements of the part surface in one direction
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STRAIGHTNESS MEASUREMENT 10
Interpret the geometric tolerance requirement
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STRAIGHTNESS MEASUREMENT 11
Inspection of the part requires that the surface elements of
the part be compared to an imaginary optimum line.
Straightness of surface elements (unlike certainstraightness of an axis or centerplane applications to
follow) cannot be gaged; it must be inspected.
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STRAIGHTNESS MEASUREMENT 12
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STRAIGHTNESS MEASUREMENT 13
Establishing
zero on part
surface at one
end
Place the precision
parallel over the
jackscrews with two
jacks at one end and oneat the other. Place the
part in a vee block and
then the vee block on
top of the parallel
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14
Rotate the part in the V block and repeat this procedure on another line
element of the shaft. It is recommended that at least four line elements
(900 apart) be inspected
Indicator traversed
along the surface
elements of shaft(at TDC)
for straightness
error measurement
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STRAIGHTNESS MEASUREMENT 15
Can there be an easier method to checkstraightness of surface elements of a cylindrical
part?
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16
A Precision straightedge used to check
straightness of surface elements when tolerances
are .(?)
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STRAIGHTNESS MEASUREMENT 17
Straightedge method of checking for straightnessof noncylindrical parts?
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STRAIGHTNESS MEASUREMENT 18
Measurement of Straightness of surface elementsby Two Block Method
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STRAIGHTNESS MEASUREMENT 19
Where should the probe touch the part?
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STRAIGHTNESS MEASUREMENT 20
Cf. V-Block Method Vs Two Block Method
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STRAIGHTNESS MEASUREMENT 21
Which is the most direct & accurate method to
check for straightness of surface elements of a
cylindrical part?
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Measurement Accuracy = f (X, LC of table)
Is there any limitation for this method?
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STRAIGHTNESS MEASUREMENT 23
On noncylindrical parts optical comparator cannot be
used visually since a line element of the noncylindrical
surface cannot be seen.
A comparator could be used for straightness of surface
elements on a noncylindrical part if the comparator were
equipped with (1) a tracer elementwith a reticle follower
shown on screen, and (2) an overlay that has two linesthat are the straightness tolerance apart (accounting for
the magnification power of the comparator). In this
manner, the tracer could follow a line element of the part
surface and the reticle follower could be viewed on the
comparator screen with respect to the two lines of
tolerance on the overlay.
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STRAIGHTNESS MEASUREMENT 24
Methods for checking Straightness of Surface
elements of conical parts:Precision Straightedge
Wobble plate, Sinebar & Vee block
Jackscrews?
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Interpret the design requirement by a magnified
sketch
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STRAIGHTNESS MEASUREMENT 26
* RFS?
*
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STRAIGHTNESS MEASUREMENT 27
Interpret geometric tolerance
requirement (Difference?)
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STRAIGHTNESS MEASUREMENT 28
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STRAIGHTNESS MEASUREMENT 29
Interpret geometric tolerance requirement
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STRAIGHTNESS MEASUREMENT 30
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STRAIGHTNESS MEASUREMENT 31
Design a functional ring Gauge to inspect the part
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STRAIGHTNESS MEASUREMENT 32
Functional gaging is allowed in cases when
features of size are controlled with a geometric
tolerance at MMC.
When MMC is stated in the feature control frame,
bonus tolerances on the control applied can be
used as the actual size of the controlled feature
departs from its MMC size toward LMC
The reason that bonus tolerances are allowed isthat the virtual condition (or worst case allowed)
never changes.
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STRAIGHTNESS MEASUREMENT 33
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STRAIGHTNESS MEASUREMENT 34
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STRAIGHTNESS MEASUREMENT 35
Locating the highest spot
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Axis Straightness by Differential Method
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STRAIGHTNESS MEASUREMENT 37
Measurement of axial locations or form at RFS is a
complicated procedure in open setup (or any setup for
that matter). The most significant limitations to thedifferential method are the following:
1. Out of roundness of the shaft can contribute to error
in the results.
2. The observer must be able to graph line elements
and interpret the differentialvalues of opposing
elements.
3. The differential method is very time consuming.
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Axis Straightness by Precision Spindle
Method
How Precise can the spindle rotation be?
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STRAIGHTNESS MEASUREMENT 39
Draw the end
view of thepart
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STRAIGHTNESS MEASUREMENT 40
Draw the end
view of the
part
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STRAIGHTNESS MEASUREMENT 41
Draw the end
view of the
part
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STRAIGHTNESS MEASUREMENT 42
Draw the end
view of thepart
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STRAIGHTNESS MEASUREMENT 43
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STRAIGHTNESS MEASUREMENT 44
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Design a functional gauge to check this part
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STRAIGHTNESS MEASUREMENT 46
In addition use a gap gauge also to check thickness
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Simulating a Functional Gage for Straightness of
Centerplane at MMC
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STRAIGHTNESS MEASUREMENT 48
Interpret the geometric tolerance requirement
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STRAIGHTNESS MEASUREMENT 49
RFS
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Straightness of a Centerplane: Differential
MeasurementMethod
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STRAIGHTNESS MEASUREMENT 51
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Interpret the geometric tolerance requirement
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STRAIGHTNESS MEASUREMENT 53
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STRAIGHTNESS MEASUREMENT 54
Key facts: Straightness ofsurface elements:
1. Datum references are not applicable to any straightness tolerances.
2. The tolerance zone for straightness of surface elements is twoparallel lines the stated tolerance apart.
3. Permissible error in the straightness of surface elements is not
additive to size tolerances. (The straightness tolerance must be less
than the associated size tolerance) The maximum boundary of perfect
form at MMC must not be violated. The worstcase condition (virtual
condition) of a size feature, in this case, is the MMC size.
4. Straightness of surface elements applied to the surface of a
noncylindrical part does not control flatness of the surface. The
tolerance is unidirectional.
Key facts: straightness of an axis:
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Key facts:straightness of an axis:
1. The tolerance zone for straightness of an axis is a cylinderof the
specified diameter.The diameter symbol precedes the tolerance in the
feature control frame.
2. Straightness of an axis (at MMC) is the only form tolerance where
bonus tolerances can be applied.
3. Straightness of an axis does not control surface elements, butstraightness of surface elements does provide inherent control of the
axis.
4. Straightness of an axis at MMC allows the option for functional
gage design and use
5.Straightness of an axis tolerance per unit length is identified by a
double feature control frame where the axial straightness tolerance of
the entire part is shown above and the per unit length tolerance is
shown below (along with the unit length applicable)
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Keyfacts: Straightness of a centerplane:
1. The tolerance zone for straightness of acenterplane is two planes the stated tolerance
apart
2. For straightness of a centerplane tolerance, theboundary of perfect form at MMC does not apply
(to the extent of the straightness tolerance)
3. Straightness of a centerplane at MMC allows
the option of functional gage design and use
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STRAIGHTNESS MEASUREMENT 57
Did we meet our objectives?
Upon completion of this chapter, the reader shouldbe able to:
1. Understand the difference between straightness
of surface elements, straightness of axis, andstraightness of center plane
2. Understand the various tolerance zones for each
straightness tolerance
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STRAIGHTNESS MEASUREMENT 58
Did we meet our objectives?
3. Measure straightness tolerances using direct ordifferential measurement methods
4. Understand the virtual condition and functional
gaging of certain straightness tolerances
5. Understand and measure straightness per unit
length
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STRAIGHTNESS MEASUREMENT 59
Questions & Answers on
Straightness Measurement
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5.1
It is possible for a part to have a diameterwhere the surface elements are crooked, but the
axis is perfectly straight. True orFalse?
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STRAIGHTNESS MEASUREMENT 61
5.1
It is possible for a part to have a diameterwhere the surface elements are crooked, but the
axis is perfectly straight.
True
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STRAIGHTNESS MEASUREMENT 62
5.2
Keeping the general rules of ANSI Y14.5 in mind,
what is the virtual size of a shaft that has a size
tolerance of .750" to .755" diameter and a
straightness of surface elements tolerance of.002"?
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STRAIGHTNESS MEASUREMENT 63
5.2
Keeping the general rules of ANSI Y14.5 in mind,what is the virtual size of a shaft that has a size
tolerance of .750" to .755" diameter and a
straightness of surface elements tolerance of.002"?
Answer: 0.755
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STRAIGHTNESS MEASUREMENT 64
5.3
The tolerance zone for straightness of surfaceelements of a cylindrical size feature is two
perfectly parallel ---------------------------------- the
stated tolerance apart.
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STRAIGHTNESS MEASUREMENT 65
5.3
The tolerance zone for straightness of surfaceelements of a cylindrical size feature is two
perfectly parallel lines the stated tolerance apart.
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STRAIGHTNESS MEASUREMENT 66
5.4
The tolerance zone for straightness of an axis is a --
-----------------------------------------
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STRAIGHTNESS MEASUREMENT 67
5.4
The tolerance zone for straightness of an axis is a
cylinder
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STRAIGHTNESS MEASUREMENT 68
5. 5.5The tolerance zone for straightness of a
centerplane is -----------------------------------------
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STRAIGHTNESS MEASUREMENT 69
5. 5.5The tolerance zone for straightness of a
centerplane is two parallel planes
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STRAIGHTNESS MEASUREMENT 70
5. 5.6
The diameter of a shaft has a size tolerance of.
750" to .760" and a straightness of axis tolerance of
.005" diameter. What is the virtual condition of the
shaft?
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STRAIGHTNESS MEASUREMENT 71
5. 5.6
The diameter of a shaft has a size tolerance of.
750" to .760" and a straightness of axis tolerance of
.005" diameter. What is the virtual condition of the
shaft?
Answer: 0.765
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STRAIGHTNESS MEASUREMENT 72
5.7
If the shaft in Question 6 had an actual diameter
of. 754" and the axis were out of straightness by
exactly .002", what is the actual virtual size of the
shaft?
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STRAIGHTNESS MEASUREMENT 73
5.7
If the shaft in Question 6 had an actual diameter
of. 754" and the axis were out of straightness by
exactly .002", what is the actual virtual size of the
shaft?
0.756
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STRAIGHTNESS MEASUREMENT 74
5.8
When using two jackscrews to inspect
straightness of surface elements, the jackscrews
help the observer to establish the optimum -------
------------------------------------ for measurement.
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STRAIGHTNESS MEASUREMENT 75
5.8
When using two jackscrews to inspect
straightness of surface elements, the jackscrews
help the observer to establish the optimum line
for measurement.
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STRAIGHTNESS MEASUREMENT 76
5.9
The most effective methods for measuring
straightness of an axis (regardless of feature size)
use ----------------------------------measurements
to track the axis.
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STRAIGHTNESS MEASUREMENT 77
5.9
The most effective methods for measuring
straightness of an axis (regardless of feature size)
use differential measurements to track the axis.
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STRAIGHTNESS MEASUREMENT 78
5.10
When the surface elements of a cylindrical featureare being controlled, an optical comparator can be
used to measure surface element straightness.
True orFalse?
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STRAIGHTNESS MEASUREMENT 79
5.10
When the surface elements of a cylindrical featureare being controlled, an optical comparator can be
used to measure surface element straightness.
True
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STRAIGHTNESS MEASUREMENT 80
5.11
A noncylindrical part must be functionally gagedfor straightness of its centerplane at MMC. A hard
gage could be used, but cost is a problem. Can the
observer use surface plate accessories (such asgage blocks or precision parallels) to set up a
virtual boundary for worst-case gaging of the part?
Yes orNo?
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STRAIGHTNESS MEASUREMENT 81
5.11
A noncylindrical part must be functionally gagedfor straightness of its centerplane at MMC. A hard
gage could be used, but cost is a problem. Can the
observer use surface plate accessories (such asgage blocks or precision parallels) to set up a
virtual boundary for worst-case gaging of the part?
Yes
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STRAIGHTNESS MEASUREMENT 82
5.12
A shaft has a size tolerance of .500" to .505" and astraightness of axis tolerance of .002" at MMC. A
functional ring gage design has been chosen for the
functional gage. What is the nominal size of thehole in the gage (before allowing for gage-makers'
tolerance and wear allowance) to functionally gage
this part?
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5.12
A shaft has a size tolerance of .500" to .505" and a
straightness of axis tolerance of .002" at MMC. Afunctional ring gage design has been chosen for the
functional gage. What is the nominal size of the
hole in the gage (before allowing for gage-makers'tolerance and wear allowance) to functionally gage
this part?
0.507
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STRAIGHTNESS MEASUREMENT 84
5.13
When straightness of surface elements tolerance isapplied to surfaces of noncylindrical parts,the
straightness tolerance only applies in the direction
shown by the drawing. True orFalse?
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STRAIGHTNESS MEASUREMENT 85
5.13
When straightness of surface elements tolerance isapplied to surfaces of noncylindrical parts,the
straightness tolerance only applies in the direction
shown by the drawing. True
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5.14
With looser straightness of surface elementtolerances, feeler wire and a precision straight can
be used to measure straightness error. True / False
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STRAIGHTNESS MEASUREMENT 87
5.14
With looser straightness of surface elementtolerances, feeler wire and a precision straight can
be used to measure straightness error. True
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5.15
Straightness of an axis per unit lengthestablishes two different straightness tolerance
zones that apply to the part. One zone is for the
straightness of the entire length of the axis.Another zone applies to the straightness of each
specified length of the axis. True orFalse?
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5.15
Straightness of an axis per unit lengthestablishes two different straightness tolerance
zones that apply to the part. One zone is for the
straightness of the entire length of the axis.Another zone applies to the straightness of each
specified length of the axis. True orFalse?
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Thank You