Inspection

 Nominal dimension
 Tolerance
9. Inspection and Gaging Tools  Use
 Appearance
 Cost

 Datum or Reference

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Basic principles of gaging Gage maker tolerances

 Measurement  Class XX – closest tolerances – master gages
 Measuring can be defined as the determination of  Class X – next best – master and inspection
a dimension. gages
 Gaging  Class Y – next best – inspection and working

 Gauging is defined as the acceptability of a given gages

dimension whether it lies in its specified or  Class Z - lowest – working gages with coarse
allowable limits or not. tolerances
 Gage tolerance
 10% work tolerance
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Table 9-1 Standard Gage Maker’s Tolerances Gage tolerances

Above To and Class (in)  Plug gage for 1  0.0006 inches
(in) including (in) XX X Y Z
 Gage tolerance = 0.00012 inch
0.010 0.825 0.00002 0.00004 0.00007 0.00010
 From table Z class
0.825 1.510 0.00003 0.00006 0.00009 0.00012
 If Plug gage for 1  0.0006 inches
1.510 2.510 0.00004 0.00008 0.00012 0.00016  Gage tolerance = 0.00006 inch

2.510 4.510 0.00005 0.00010 0.00015 0.00020  From table X class

4.510 6.510 0.000065 0.00013 0.00019 0.00025

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 Gage tolerances Allocation of gage tolerances
 Plug gage for 1  0.0075 inches  Bilateral system
 Gage tolerance = 0.0015 inch  The GO and NOGO gage tolerance zones are
divided into two parts by the high and low limits
 From table Z class
of the workpiece tolerance zone
 Smaller degree of gage tolerance means more
expensive
 Gage tolerances should be realistically applied.

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Maximum
Work
Tolerance
Allocation of gage tolerances
limit
 Hole to be gaged 1.2500  0.0006 inch
Work tolerance zone

 Work tolerance = 0.0012 inch

Bilateral

 Hole size from 1.2506 to 1.2494 inch

 Gage tolerance (10%) = 0.00012 inch

 Z-class tolerance zone

 GO gage size 1.2494  0.00006 inch

Minimum  NOGO gage size 1.2506  0.00006 inch

Work
Tolerance
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Table 9-1 Standard Gage Maker’s Tolerances Allocation of Gage Tolerances

Above To and Class (in)  Unilateral system
(in) including (in) XX X Y Z  The work tolerance zone entirely includes the
0.010 0.825 0.00002 0.00004 0.00007 0.00010
gage tolerance zone
0.825 1.510 0.00003 0.00006 0.00009 0.00012  Work tolerance smaller by the sum of the gage

tolerance
1.510 2.510 0.00004 0.00008 0.00012 0.00016

2.510 4.510 0.00005 0.00010 0.00015 0.00020

4.510 6.510 0.000065 0.00013 0.00019 0.00025

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 Maximum
Work
Tolerance
Allocation of gage tolerances
limit
 Hole to be gaged 1.2500  0.0006 inch
Work tolerance zone

 Work tolerance = 0.0012 inch

Unilateral
Bilateral
 Hole size from 1.2506 to 1.2494 inch

 Gage tolerance (10%) = 0.00012 inch

 Z-class tolerance zone

 GO gage size 1.24940 + 0.00012 inch

Minimum  NOGO gage size 1.25060 - 0.00012 inch

Work
Tolerance
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Maximum
Allocation of gage tolerances Work
Tolerance
limit
 Commercial gages

Work tolerance zone

 Allocate gage tolerance negatively with reference

Commercial
to both the maximum and minimum limits of the

Plain plug
Commercial
workpiece tolerance (C)

Plain ring
 NOGO gage tolerance is divided by the maximum
limit of the workpiece tolerance and the GO gage
tolerance is held within the minimum limit of the
workpiece tolerance.
Minimum
Work
Tolerance
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Allocation of gage tolerances Gage Wear Allowance

 The objectives in choosing an allowance  Wear allowance is an amount added to the
system should be the economic production of nominal diameter of a GO-plug and
as near 100% usable parts as possible, and the subtracted from that of a GO-ring gage.
acceptance of the good pieces and rejection of  It is used up during the gage life by wearing
the bad. away of the gage metal.

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 Gage Wear Allowance (5%)
 Hole diameter 1.5000  0.0006 inch
 Work tolerance = 0.0012 inch
 Gage tolerance (10%) = 0.00012 inch
 GO gage size 1.49940 + 0.00006 = 1.49946
inch
 Add gage maker tolerance as shown
previously, 1.49946 +0.00012 and –0.00000 as
limits

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Gage Materials Surface Plate

 Chrome plated  Main horizontal reference plane
 Tungsten carbide tipped  Rigid block of granite or cast iron
 Generally have three-point suspension to
prevent rocking when mounted on uneven
surface
 Two types
 Cast-iron plates
 Granite surface plates

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Surface Plate Advantages of Granite Plates

 Cast-iron plates  Not appreciably affected by temperature
 Well ribbed and high strength change
 Good wear-resistance qualities  Will not burr, therefore, accuracy not impaired
 After machined, surface scraped by hand to flat  Nonmagnetic
 Operation long and cost high
 Rustproof
 Granite surface plates  Abrasives will not embed themselves as easily
 Manufactured from gray, pink, or black granite in the surface
 Several degrees of accuracy

 Extremely flat finishes produced by lapping

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 Template
 Specified profile
 Guide to the location of workpiece features
with reference to a single plane.
 A straight edge is a template for checking
straightness.
 Radius gages

 Screw pitch gages

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Fig 9-6 Gaging the profile of a workpiece with a

template

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Plug Gages
 A plug gage is a fixed gage usually made up of
two members
 One member is called the GO end and the
other the NO-GO or NOT-GO end
 AGD – American Gage Design standards

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Ring gages
 Ring gages are usually used in pairs, consisting
of go member and no-go member.

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Snap Gages
 For measuring length, diameter, thickness or
width

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 Amplification and Magnification of Error

 As the measurable error becomes small, it is

difficult for direct reading and hence some
means of magnification is required.
 Dial indicators

 Optical

 Pneumatic gauging

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Geometric Dimensioning and

Tolerancing
 ASME Y14.5-1994 (Rev. 2009)
 ISO 1101, 129, 3040

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Modifiers
 Maximum Material Condition (MMC) -
 Minimum diameter of a hole and maximum
diameter of a shaft
 Least Material Condition (LMC)
 Maximum diameter of a hole and minimum
diameter of a shaft

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 Flatness checking
 Checking process depends upon the accuracy
required
 Using a dial indicator

 After the surface is leveled, the indicator

explores the entire area and the full indicator
movement is a measure of flatness.

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Checking a Profile
 Follow a master part as shown in Fig 9-42.
 Number of dial indicators set in a plane
confirming the contour as shown in Fig 9-43.

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Checking for
Parallelism/Perpendicularity
 Parallelism can be checked by placing a part on
a surface plate and searching for out of parallel
condition with an indicator.
 Some times a special fixture may be required
as shown in Fig 9-49.
 Perpendicularity of a cylindrical feature and it
MMC can be checked with a functional gage as
shown in Fig 9-51.

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Fig 9-52 Gage for checking parallelism – cylindrical size Fig 9-52 Gage for checking parallelism – cylindrical size
feature feature

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Checking a Runout
 Total runout consists, by definition, of two
concentric cylinders that encompass a feature
about a defined axis.
 Generally, total runout is measured by taking
single runout at intervals along an entire
cylinder.
 The extremes of needle deflection for the
entire set of intervals yields total runout.

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Checking a Position
 Two holes that need to be gaged.
 Shown is a hole relation gage to check hole-
to-hole relationship.
 If RFS (Regardless of Feature Size) is used in
place of MMC, gaging will become difficult.
 To maintain the positional tolerance of 0.10 in
eleven gage pins will be required for all sizes
between MMC and LMC.

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Positional Tolerance Rules

 For parts with internal features, the nominal
gage feature size is directly determined by
subtracting the total positional tolerance
specified at MMC from the specified MMC
size of the feature to be gaged for location.
 For parts with external features, the nominal
gage feature size is directly determined by
adding the total positional tolerance specified
at MMC size of the feature to be gaged for
location.
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