Transcript Multiview Drawings - Colorado State University

Tolerancing
Deviation:

The difference between the actual size
and the corresponding basic size.
Tolerance:


The total amount by which a specific
dimension is permitted to vary. The tolerance
is the difference between the maximum and
minimum limits.
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

The tolerance, or total amount of variation
“tolerated,” is .004
Example: Two mating parts

To control the dimensions of the
quantities of the two parts so that any
two mating parts will be
interchangeable, it is necessary to
assign tolerance to the dimensions of
the parts.
Allowance

Is the minimum clearance space (or
maximum interference) intended between the
maximum material condition (MMC) or mating
parts.
• Smallest Hole 1.250”
• Largest shaft 1.248”
• Allowance = .002”
General Tolerancing Rules

All Tolerancing limits are considered to be
absolute.
• i.e.,
1.22 = 1.22000…0
1.20 = 1.20000…0


All Dimensions and Tolerances are
understood to apply at 68 degrees
Fahrenheit.
The system of tolerances does not
necessarily require the use of any particular
method of production.
Setting Tolerances:

Unilateral: The tolerance is applied in one
direction, the other value is zero.

Bilateral: The tolerance is applied in both
directions from the nominal.
Tolerance Accumulation
Chain
 Baseline
 Direct

Functional Dimensions
Tolerances can have a cumulative
effect.
 Most important function needs to be
considered.

Reading Title Block Tolerances
Used where there is a uniformity in
tolerances.
 Nominal (Basic) dimension alone is
given on drawing face.
 Based on the number of decimal places
specified.

Tolerances and Machining
Processes
Limits and Fits
Production and inspection benefit from
the use of standard limits.
 ISO 286 has more than 500 possible
tolerance zones for holes and shafts.
 ANSI B4.2 has about 150 possible
tolerance zones for holes and shafts.
 Goals is to maximize standardization.

International Organization of
Standards (ISO)

Rapid growth to world\wide commerce has fostered
an international system of units - SI units • Seven basic units: 1) meter (length), 2) kilogram (mass), 3)
second (time), 4) ampere (electric current), 5) kelvin
(thermodynamic temp..), 6) mole (amount of substance), and
candela (luminous).


SI system gradually coming into use in the United
States.
Effort to convert all standards of the American
National Standards Institute (ANSI) to the SI units in
conformity with the ISO standards.
Fit:
Fit is the general terms used to signify
the range of tightness or looseness that
may result from the application of a
specific combination of allowances and
tolerances in mating parts.
 Clearance Fit
 Transition Fit
 Interference Fit

Clearance fit:
The relationship between assembled
parts when clearance occurs under all
tolerance conditions.
 There is always clearance.

Interference fit:
The relationship between assembled
parts when interference occurs under all
tolerance conditions.
 The internal member is larger than the
external member such that there is
always an actual interference of
material.
 Where there is always interference.

Transition fit:
The relationship between assembled
parts when either a clearance or
interference fit results, depending on the
tolerance conditions of the mating parts.
 Where there may be clearance or
interference based on where the parts
fall in the tolerance range.

Clearance, Transition,
Interference Fits
Preferred Metric System of
Tolerances and Fits
A system of preferred metric limits and
fits by the ISO in in the ANSI B4.2
standard.
 The system is specified for holes,
cylinders, and shafts.
 Terms for metric fits are similar to those
for decimal-inch fits.
 Use International tolerance grades

Examples: Close Running Metric Hole Basis Clearance Fits
50H8/f7
 50 = 50 millimeters in diameter
 H8 = hole deviation of 8
 f7 = shaft deviation of 7
 Refer to page A153 - Appendix C.13
(Lamit) for max. and min. deviations

• hole = 50.039 - 50.000
• shaft = 49.975 - 49.950
Appendix C.13 - Basic Clearance
Fits
Preferred Inch Fits




ANSI has issued the ANSI B 4.1 - 1967
(R1994), “Preferred Limits and Fits for
Cylindrical Parts”
Recommends preferred sizes, allowances,
tolerances, and fits in terms of the decimal
inch.
Used to produce similar performance
throughout the range of sizes (hole sizes)
Three groups: running and sliding fits,
locational fits, and force fits.
Running and Sliding Fits


Designed to provide a similar running
performance throughout the range of sizes.
Examples preferences:
• RC 1 = Close sliding fits are intended for the
accurate location of parts that must assemble
without perceptible play.
• RC 3 = Precision running fits are about the closest
fits that can be expected to run freely, and they ar
intended for precision work at low speeds.

RC1 - RC9 (close sliding - loose running)
ANSI - Running and Sliding Fits
(Page A145)
Locational Fits
Intended to determine only the location
of the mating parts.
 Divided into three groups

• LC = Clearance fits
• LT = Transition Fits
• LN = Interference Fits
Locational Fits
Force or Shrink fit
Special type of Interference fit
 Maintains constant bore pressure
throughout the range of sizes.

Force or Shrink fit
Example: 2.0000” basic diameter
with a Class R1 fit

Standard Limits (HOLE):
• upper limit = +0.5 = .0005”
• Lower limit = 0 = 0
• Dimension the hole as . . . 2.0000 +.0005/-.0000
Example (continued)



2.000” - .0004” = 1.9996 (upper limit)
2.000” - .0007” = 1.9993 (lower limit)
Shaft dimensioned as 1.9996 +.0000/-.0003