05.StraightnessMeasurement90

7/22/2019 05.StraightnessMeasurement90

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STRAIGHTNESS MEASUREMENT 1

Chapter 5

StraightnessMeasurement


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How many kinds of Straightness Tolerance

Specifications are there?

What are they?


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Interpret the geometric requirements of a,b & c


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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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(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 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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Interpret the geometric control requirement

Sketch how will you check the straightness

Story on Inspection


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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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Interpret the geometric tolerance requirement


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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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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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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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Straightedge method of checking for straightnessof noncylindrical parts?


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Measurement of Straightness of surface elementsby Two Block Method


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Where should the probe touch the part?


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Cf. V-Block Method Vs Two Block Method


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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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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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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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* RFS?

*


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Interpret geometric tolerance

requirement (Difference?)


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Interpret geometric tolerance requirement


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Design a functional ring Gauge to inspect the part


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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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Locating the highest spot


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Axis Straightness by Differential Method


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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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Draw the end

view of thepart


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Draw the end

view of the

part


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Draw the end

view of the

part


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Draw the end

view of thepart


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Design a functional gauge to check this part


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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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RFS


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Straightness of a Centerplane: Differential

MeasurementMethod


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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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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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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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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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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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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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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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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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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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5.4

The tolerance zone for straightness of an axis is a --

-----------------------------------------


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5.4

The tolerance zone for straightness of an axis is a

cylinder


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5. 5.5The tolerance zone for straightness of a

centerplane is -----------------------------------------


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5. 5.5The tolerance zone for straightness of a

centerplane is two parallel planes


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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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

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05.StraightnessMeasurement90