limit,fits,tolerance & types of gauges, ,limit fits & tolerances ,geometric tolerance ,unilateral tolerance • bilateral tolerance ,clearance ,interference ,transition ,hole basis ,shaft basis ,taylor principle ,classification of plain gauge

1. Limit, Fits, Tolerance and
Gauges
By
Prof N D Sadaphal
Assistant Professor
Sanjivani College of Engineering,
Kopargaon (Maharashtra State) 423601
Mechanical Engineering

2. 7/21/2016
1
Limits, Fits & Tolerances
Limit -
These are the extreme permissible sizes within which
the operator is expected to make the component.
Fit –
It is the general term used to signify the range of
Looseness and Tightness of mating parts
Tolerances –
Allowable variations from the specified part
dimensions that are permitted in manufacturing.
Spring 2005
Limit Fits & Tolerances

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Tolerance Dimensioning
•Tolerance is the total amount that a specific
dimension is permitted to vary;
•It is the difference between the maximum and the
minimum limits for the dimension.
•For Example a dimension given as 1.625 ± .002
means that the manufactured part may be 1.627”
or 1.623”, or anywhere between these limit
dimensions.
Why is tolerancing necessary?
It is impossible to manufacture a part to an exact size
or geometry
Assemblies: Parts will often not fit together if their
dimensions do not fall within a certain range of values

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Types of Tolerances
A Geometric tolerance is the maximum or minimum
variation from true geometric form or position that may
be permitted in manufacture.
Geometrical Tolerances (Form)
Spring 2005
Types of Tolerances
The tolerance for a single dimension may be specified with the
dimension based on one of the following methods
• Unilateral tolerance
• Bilateral tolerance
Specific Tolerances

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Spring 2005
Specific Tolerances
Unilateral Tolerance
Variation from the specified dimension is permitted in only one direction,
either positive or negative, but not both.
Spring 2005
Specific Tolerances
Bilateral Tolerance
Variation is permitted in both positive and negative directions from
the nominal dimension.
It is possible for a bilateral tolerance to be unbalanced; for example,
2.500 +0.010, -0.005

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Spring 2005
Fits between Mating Parts
Fit is the general term used to signify the range of
Looseness and Tightness
of mating parts
Spring 2005
Fits Types
Clearance Fit occurs when two tolerance mating
parts will always leave a space or clearance when
assembled.
Interference Fit occurs when two tolerance mating
parts will always interfere when assembled.
Transition Fit occurs when two tolerance mating
parts are sometimes an interference fit and
sometimes a clearance fit when assembled.

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Spring 2005
Important Terms
Nominal size: a dimension used to describe the general size.
Basic size: the theoretical size used as a starting point for the
application of tolerances.
Actual size: the measured size of the finished part after machining.
A specified system of fits for holes and shafts
Spring 2005
Tolerancing Holes and Shafts
- Hole basis
•Hole is kept constant and
Shaft sizes are vary to give
various types of fits.
• Uses the symbol “H” in the
tolerance specification
- Shaft basis
•Shaft is kept constant and Hole
sizes are vary to give various
types of fits.
•Uses the symbol “h” in the
tolerance specification

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Spring 2005
Clearance and Interference fits between two Shafts and a Hole
Spring 2005
Transition fit between a Shaft and a Hole

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Spring 2005
Metric Symbols of Fits
Terms related to Metric Limits & Fits

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Some Definitions
•Deviation: is the difference between the basic size
and the hole or shaft size.
•Upper Deviation: is the difference between the
basic size and the permitted maximum size of the
part.
•Lower Deviation: is the difference between the
basic size and the minimum permitted size of the
part.
•Fundamental Deviation: is the deviation closest to
the basic size.
18
Gauges
•Gauges are inspection tool of rigid design, without a scale,
which serves to check the dimensions of manufacturing
parts.
• Gauge do not indicate the actual value of the inspected
part of the component.
• They are used to determine whether the part is made
within the specified limit.
Prof N D Sadaphal

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THE TAYLOR PRINCIPLE
• Go Gauge is designed to check the Maximum Metal Condition/limit
(MMC) while
No GO gauge should be designed to check Minimum metal
condition/limit.
• GO-gauge should check all related dimension (roundness, size etc)
NO-GO gauge should check one element of dimension at a time.
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Classification of Plain Gauge
Gauges are classified:
• According to their type :
(a) Standard gauges- made as an exact copy of mating part
(b) Limit gauges- made to the limits of the dimensions
• According to their purposes :
(a) Workshop Gauge: To Check Dimension after manufacture.
used by operator during manufacturing.
(b) Inspection Gauge: To check part before final acceptance.
used by inspector after manufacturing.
(d) Purchase Inspection Gauge: To check part of other factory
(c) Reference or master gauges: To check the dimension of Gauge
Prof N D Sadaphal

12. 7/21/2016
11
21
Classification of Plain Gauge
According to the form of the tested surface :
(a) Plug gauges
for checking holes.
(b) Snap and ring gauges
for checking shafts.
Prof N D Sadaphal
TAPER GAUGE
• The most satisfactory method of testing a taper is to use taper Gauges.
• They are also used to gauge the diameter of the taper at some point.
• Taper gauges are made in both the plug and ring styles and in general, follow
the same standard construction as plug and ring gauges.

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Screw Thread Gauge
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To Check Circular Shaft
Ring Gauge
Should be used
as Go Gauge
Length should be
equal to the
length of the
shaft
Prof N D Sadaphal

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SCREW PITCH GAUGE
RADIUS AND FILLET GAUGE

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Feeler Gauge/Thickness Gauge
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KEY WORDS
Standard Gauges : These are made to the nominal size of the parts
to be tested.
Limit Gauges : These are “Go” and “No Go” gauges.
Plug Gauges : These are used for checking holes of many different
shapes and sizes.
Ring Gauges : External diameter measuring gauges.
Taper Gauges : Taper testing gauges.
Snap Gauges : These are used for checking shafts.
Thread Gauges : These are used for pitch diameter of the thread.
Form Gauges : These are used to check the contour of a profile.
Feller Gauges : For checking the clearance between the mating
surfaces.
Indicating Gauges : To measure the position of the surfaces.
Prof N D Sadaphal