1. Tolerancing READING! - Today Lamit - Chapter 13 NEXT WEEK!
Review for Exam Unit 1-5
Due Thursday
Lab assignment #3
6.1
6.2M
6.7

2. Deviation:
The difference between the actual size and the corresponding basic size.
Go back to original GD&T drawing:
If you were to create this part at actual size after manufacturing it was
Deviation would be .2

3. 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 / 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
You can set up (establish)
various fits when establishing tolerances on part.
See NEXT SLIDE.
Thus it is your job (designer) to specify the allowance error that may be tolerated for a given dimension an still permit the satisfactory functioning of the part.
Greater accuracy costs money = therefore, as designer don’t specify the closest tolerance, but instead will specify as generous a tolerance as possible.

4. 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.

5. 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”

6. General Tolerancing Rules
All Tolerancing limits are considered to be absolute.
i.e.,
1.22 = …0
1.20 = …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.

7. 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.

8. Tolerance Accumulation
Chain
Baseline
Direct
Compares the Toleracne Values Resulting From Three Methods of Dimensioning.
Chain: Maximum variation between two features is equal to the tolerances on the intermediate distances.
Results in greatest tolerance accumulation.
Tolerance accumulation shown. (between X&Y)
Baseline: The maximum variation between two features is equal to the sum of the tolerances on the two dimensions from their origin to the features.
Results in a reduction of the tolerance accumulation.
Direct: The Maximum variation between two features is controlled by the tolerance on the dimension between the features.
Results in the least tolerance.
Tolerance accumulation is reduced. (between X&Y).

9. Functional Dimensions
Tolerances can have a cumulative effect.
Most important function needs to be considered.
Most Important: Fire Pin
Is to project far enough to detonate the primer
But not far enough to pierce the primer.
Plus - point must be fully below the bolt face - to prevent detonation in the cartridge.
This function controlled by dimension A
a direct dimension from the point face to the interface with the bolt in the full forward position.
Dim. B is established the same way.
Key Point
Dim. That affect function should be dimensioned directly to avoid tolerance buildup.

10. 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.

11. Tolerances and Machining Processes
This chart provides a chart of tolerance grades obtainable in relation to the accuracy of machining process.
Use as a guide as designer.

12. 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.

13. 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.

14. 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

15. Clearance fit:
The relationship between assembled parts when clearance occurs under all tolerance conditions.
There is always clearance.

16. 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.

17. 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.

18. Clearance, Transition, Interference Fits
A = Clearance Fit
B = Transition Fit
C = Interference Fit

19. 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
International tolerance grade = is a set of tolerances that varies according to the basic size.

20. 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 =
shaft =

21. Appendix C.13 - Basic Clearance Fits

22. Preferred Inch Fits
ANSI has issued the ANSI B (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.

23. 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)

24. ANSI - Running and Sliding Fits (Page A145)

25. 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
LC = Locational clearance fits -
stationary but which can be freely assembled or disassembled
range snug - loose
LC1 - LC11
LT = Location transition fits -
Between Clearance and Inferference fits
Location accuracy is important
but either a small amount of clearance or interference is permissible.
LN: Location Interference Fits-
Accuracy of location is prime importance
No special requirement for bore pressure.

26. Locational Fits

27. Force or Shrink fit Special type of Interference fit
Maintains constant bore pressure throughout the range of sizes.

28. Force or Shrink fit

29. Example: 2.0000” basic diameter with a Class R1 fit
embraces the ” basic size
“Limit of clearance” the values 0.4 and represents the maximum clearance between the parts in thousandths of an inch.
Conversion = multiply by 1000 or move decimal place three places. . .
Example: ”
Therefore:
Minimum clearance = .0004”
Maximum clearance = .0012”
Standard Limits (HOLE):
upper limit = +0.5 = .0005”
Lower limit = 0 = 0
Dimension the hole as /-.0000
Limits for Shaft: ”
-.0007”
Standard Limits (HOLE):
upper limit = +0.5 = .0005”
Lower limit = 0 = 0
Dimension the hole as /-.0000

30. Example (continued) 2.000” - .0004” = 1.9996 (upper limit)
Limits for Shaft: ”
-.0007”
2.000” ” = (upper limit)
2.000” ” = (lower limit)
Shaft dimensioned as /-.0003
2.000” ” = (upper limit)
2.000” ” = (lower limit)
Shaft dimensioned as /-.0003