# Bonus Tolerance

Bonus tolerance is a benefit of geometric tolerancing and dimensioning.  In this article we will see how you can tolerance a fit while using the benefit of bonus tolerance to reduce manufacturing cost.

There are five types of geometric tolerances that can have bonus tolerance:

• Straightness
• Angularity
• Perpendicularity
• Parallelism
• Position

## Straightness

Bonus tolerance is only available if maximum material condition (MMC) is specified.  It is used for axis tolerance and diameter deviating from MMC.  There is no datum reference.

Two types of straightness:

1. Surface straightness
2. Axis straightness

Bonus tolerance is available for axis straightness when MMC is specified.

Go/No Go Gauge Diameter = 1.005 + .002 = 1.007

Max Bonus Tol = 1.005 – .998 = .007

## Angularity

Perpendicularity and parallelism are special cases of angularity where the angle is 90o and 0o respectively.  Angularity has a basic dimension, the angle.  The angle is referenced to a datum.

Two types of angularity:

1. Surface angularity
2. Axis angularity

Bonus tolerance is available for axis angularity when MMC is specified.

Go/No Go Gauge Diameter = .998 - .003 = .995

Max Bonus Tol = 1.005 – .998 = .007

## Perpendicularity

Perpendicularity is a special case of angularity where the angle is 90o.  There is no basic dimension since the angle is always 90o.  Perpendicularity is referenced to a datum.

Two types of perpendicularity:

1. Surface perpendicularity
2. Axis perpendicularity

Bonus tolerance is available for axis perpendicularity when MMC is specified.

Go/No Go Gauge Diameter = .998 - .003 = .995

Max Bonus Tol = 1.005 – .998 = .007

## Parallelism

Parallelism is a special case of angularity where the angle is 0o.  There is no basic dimension since the angle is always 0o.  Parallelism is referenced to a datum.

Two types of parallelism:

1. Surface parallelism
2. Axis parallelism

Bonus tolerance is available for axis parallelism when MMC is specified.

Go/No Go Gauge Diameter = .998 - .003 = .995

Max Bonus Tol = 1.005 – .998 = .007

## Position

Commonly referred to as true position.

The position deviation is calculated by:

Note that when the diameter symbol is applied to the position tolerance, the tolerance zone is cylindrical.  If not used, error is limited to the x and y directions (a square).

RFS

In a regardless of feature size (RFS) material condition, the part is out of tolerance since .009 > .008 position tolerance.

MMC

For maximum material condition (MMC), as the hole gets larger and approaches LMC there is a bonus tolerance available.  MMC is used to apply bonus tolerance when fitting a mating hole/shaft.

The bonus tolerance is:

Bonus tol = 1.001 – .998 = .003

Adding bonus tol to position tol, the new position tolerance is:

Total position tol = .008 + .004 = .011

For MMC, the part is within tolerance since .009 < .011.

LMC

For least material condition (LMC), as the hole gets smaller and approaches MMC there is a bonus tolerance.  LMC is used differently than MMC.  LMC is used to maintain a minimum wall thickness, for example.  When fitting parts together is important, MMC must be used.

The bonus tolerance is:

Bonus tol = 1.005 - 1.001 = .004

Adding bonus tol to position tol, the new position tolerance is:

Total position tol = .008 + .004 = .012

For LMC, the part is within tolerance since .009 < .012.

Note that if a pin was required to fit in the hole, using LMC is not going to allow more tolerance to fit.  LMC is used to make sure that a minimum wall thickness of the hole is maintained.

### MEboost

MEboost has a bonus tolerance calculator that will guide you through these calcuations effortlessly.