Tolerances
Tolerances
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Tolerances are used in manufacturing to show how much a part’s size is allowed to vary from its ideal or nominal measurement. Instead of needing something to be the exact size, tolerances set acceptable upper and lower limits. For example, if a hole is meant to be 10 mm wide, a tolerance might allow it to be between 9.9 mm and 10.1 mm. This small range makes it easier and cheaper to produce parts, while still ensuring they work properly. Tolerances are important because they help parts fit together correctly, even when made by different machines or manufacturers.
Tolerance Application
Tolerance Application
Working out a tolerance
Working out a tolerance
Common
This way shows the overall maximum and minimum. The ‘math’ has already been worked out.
Asymmetrical
This way, the tolerances are shown separately. It shows that 0.25 can be added or 0.5 taken away. Therefore, the tolerance is between 44.5 and 45.25.
Symmetrical
This method only works when both tolerances are the same. It shows that 0.25 can be added or removed. Therefore, the tolerance is between 44.75 and 45.25
Functional
A maximum and minimum size that will allow the product to work correctly.
Non Functional
Dimensional variations that are not crucial for the part's functionality.
Measuring more than one part
Measuring more than one part
In an exam, you could be asked to work out the overall tolerance of the product. The product may be made of several parts.
To do this, you use these formulas:
MAXIMUM OVERALL = (length + maximum tolerance) + (length + maximum tolerance)
MINIMUM OVERALL = (length - minimum tolerance) + (length - minimum tolerance)
Regardless of the number of parts, you use the same formula!
For example:
Maximum Overall = (120+0.5) + (30+0.25) = 120.5 + 30.25 = 150.75
Minimum Overall = (120 - 0.5) + (30-0.25) = 119.5 + 29.75 = 149.25
Maximum Overall = (120+0.5) + (30+0.25) + (40+0.5) = 120.5 + 30.25 + 40.5 = 191.25
Minimum Overall = (120 - 0.5) + (30-0.25) + (40-0.25) = 119.5 + 29.75 + 39.75 = 189
Measuring the gap
Measuring the gap
In an exam, you could be asked to determine the maximum or minimum tolerance of a gap between product parts.
To do this, you use these formulas:
MAXIMUM GAP = Max overall length – smallest size – smallest size
MINIMUM GAP = Min overall length – largest size – largest size
The ‘smallest size’ is the length - min tolerance
The ‘largest size’ is the length + max tolerance
For example:
Maximum Gap = (15-0.25) + (15-0.25) = 14.75 + 14.75 = 150 - 29.5 = 120.5
Minimum Overall = (15 + 0.5) + (15 + 0.5) = 15.5 + 15.5 = 150 - 31 = 119
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