CNC machining steel

Bilateral Tolerance vs. Unilateral Tolerance

What is Bilateral tolerance

Bilateral tolerance, also known as bilateral dimensioning or bilateral tolerancing, is a type of tolerance specification used in engineering drawings and design to define the acceptable range of variation for a specific dimension. It is represented by two tolerance values, one on each side of the nominal dimension.

In a bilateral tolerance, the tolerance range extends equally in both the positive and negative directions from the nominal dimension. The nominal dimension represents the target or desired measurement, while the tolerance values define the acceptable deviation or variation from that nominal dimension.

For example, if a dimension is specified as 50 ± 0.1 mm using bilateral tolerance, it means that the acceptable range for that dimension is from 49.9 mm (50 – 0.1) to 50.1 mm (50 + 0.1). Any measurement falling within this range is considered within tolerance and acceptable.

Bilateral tolerance is commonly used when it is important to control both the upper and lower limits of a dimension equally. It is often applied to features that require a balanced fit, symmetry, or where equal clearance or interference is desired.

It’s important to note that bilateral tolerance does not necessarily mean that the acceptable range is always symmetric around the nominal dimension. The tolerance values on each side may differ, but they still extend equally in the positive and negative directions.

Bilateral tolerance is typically represented on engineering drawings using the symbol “±” followed by the tolerance values. For the example given above, the dimension would be represented as 50 ± 0.1 mm.

By specifying bilateral tolerance, designers and manufacturers can communicate the allowable variation for dimensions, ensuring that the produced parts meet the required fit, form, and function within the defined tolerance limits.

What is Unilateral tolerance

Unilateral tolerance, also known as unilateral dimensioning or unilateral tolerancing, is a type of tolerance specification used in engineering drawings and design to define the acceptable range of variation for a specific dimension. Unlike bilateral tolerance, unilateral tolerance specifies the allowable deviation in only one direction from the nominal dimension.

In a unilateral tolerance, the tolerance range extends in only one direction, either in the positive or negative direction from the nominal dimension. The nominal dimension represents the target or desired measurement, while the tolerance value defines the acceptable deviation or variation in that specified direction.

For example, if a dimension is specified as 50 + 0.1 mm using unilateral tolerance, it means that the acceptable range for that dimension is from 50 mm to 50.1 mm. Any measurement within or below 50 mm is considered within tolerance and acceptable.

Unilateral tolerance is commonly used when it is important to control the tolerance on only one side of the nominal dimension. It is often applied to features that have specific fit requirements, clearance or interference requirements, or when a specific direction of variation is critical for the functionality of the part.

It’s important to note that unilateral tolerance does not inherently imply that the acceptable range is asymmetric around the nominal dimension. The tolerance range can be positioned on either the positive or negative side, depending on the design and functional requirements.

Unilateral tolerance is typically represented on engineering drawings using a plus (+) or minus (-) symbol followed by the tolerance value. For the example given above, the dimension would be represented as 50 + 0.1 mm.

By specifying unilateral tolerance, designers and manufacturers can communicate the allowable deviation in a specific direction for dimensions, ensuring that the produced parts meet the required fit, form, and function within the defined tolerance limits.

Leave a Comment