A runout is basically a composite control.
When the form, orientation and location of a part feature is controlled simultaneously then it is known as composite control.
There are two runouts.
- Circular runout.
- Total runout.
Let’s deep dive into circular runout.
Datum axis establishment for Runout.
The three ways to establish a datum axis for runout are as follows:
- A single diameter having sufficient length.
- Two coaxial diameters having sufficient distance.
- A surface and diameter at right angles.
Establishing a Datum Axis for Runout
In the above figure, the three ways to establish a datum axis is mentioned.
Part shape and functional requirements are the criteria for selecting any of the methods stated above to establish a datum axis.
Mostly a single diameter is used when the diameter is large enough to orient the part.
Two coaxial diameters are used when orientation is important.
A composite control which affects the form, orientation and location of the part is known as circular runout.
The geometric tolerance which controls the amount of circular runout is known as circular runout control.
Circular runout is applicable to each element of a diameter.
The location of circular elements of a diameter is controlled by circular runout.
The visualization of tolerance zone shape of circular runout is quite simple as they consist of two coaxial circles whose centers are located on the datum axis.
The radial distance between the coaxial circles is equal to the tolerance value.
Circular Runout Tolerance zone
The above figure shows the size of a circular runout tolerance zone.
A dial indicator is used to verify a diameter controlled with circular runout.
The part is rotated by 360° and the dial indicators helps to find out the error.
CIRCULAR RUNOUT: COMPOSITE CONTROL
The best example of composite control is the circular runout.
Circularity, orientation and axis offset diameter are limited by this control.
The worst case boundary is affected by the control.
A dial indicator is used to verify the circular runout.
The errors associated with circular runout are shown in the below figure.
Circular Runout as composite control
A part contains a circular runout which is shown in the above figure under section A.
In the section B, a part is taken which is perfectly round and coaxial with the datum axis.
In this case, gage reading (runout value) will be zero.
In section C, a part is taken which contains out of round shape.
The part is still within the limits of the diameter.
A runout error is obtained when a dial indicator is used, and the part is rotated by 360°.
In section D, a part is taken which is perfectly round.
When the part is rotated by 360°, a runout error is obtained with the help of dial indicator.
In this situation, the runout error is produced from the axis offset.
CIRCULAR RUNOUT APPLICATIONS
The following conditions are applicable when a circular runout control is stated.
- Size requirements must be equal to the diameter.
- Worst case boundary is affected.
- RFS of a part is controlled by this runout.
- Runout is applicable to each circular element.
- Tolerance zone is equal to the two coaxial circles 0.2 apart.
- Maximum possible axis offset is 0.1.
Circular Runout applied to a diameter
The above figure shows an application of circular runout applied to a surface which is perpendicular to the datum axis.
The following conditions are applied.
- Runout control is applicable to the RFS.
- At each circular element of the surface a runout is applicable.
- The shape of the tolerance zone is the two coaxial circles.
- Orientation of the surface is not controlled by the circular runout.
LEGAL SPECIFICATOIN TEST
- Mentioning a datum in the feature control frame is important.
- Proper datum axis must be specified.
- This control must be applied to a surface element that surrounds the datum axis.
- Runout control must be applied on an RFS.
- There should not be any modifiers.
Verifying Circular Runout
In the above figure, a circular runout is stated on the diameter.
Three checks must be done to verify the diameter.
- Size of the diameter.
- Rule 1.
- Runout of diameter.
The other way to verify is shown in the next section of the image.
The part is mounted on a chuck or collet which helps in establishing the datum axis A.
Then a dial indicator is placed perpendicular to the surface of the diameter.
The part is then rotated by 360°.
The dial indicator is moved to a different location and another reading is taken.
Inspector’s judgement decides the number of circular elements to be checked.
A composite control which affects the location, orientation and form of the part relative to the datum axis is known as total runout.
A geometric tolerance which limits the total runout is known as total runout control.
It is also applicable to the complete length of the part.
The control is mostly used to control the location of the diameter.
Two coaxial cylinders is the tolerance zone shape of this control whose centers are located at the datum axis.
Tolerance value is the radial distance between the two coaxial cylinders.
The size of the largest cylinder is the radius which is maximum from the datum axis.
The difference between the largest and smallest cylinder is equivalent to the tolerance value.
To verify the total runout a dial indicator is used.
The part is rotated by 360° to check if there are any runout errors associated with the part.
TOTAL RUNOUT: COMPOSITE CONTROL
The worst case boundary is affected by the total runout.
All the 3 types of errors are included while verifying the total runout.
The dial indicator helps to verify the error in feature roundness.
Straightness and taper are also verified by the dial indicator as it moves along the axis.
The form errors are also directed by the dial indicator.
Total Runout as Composite control
TOTAL RUNOUT APPLICATION
- Size requirements must meet the diameter.
- There is an effect to WCB.
- Runout control applies to RFS.
- This control is applied simultaneously to all elements of the diameter.
- Tolerance zone is two coaxial cylinders.
Total Runout applied to a diameter
LEGAL SPECIFICATION TEST
The legal specification test of total runout is similar to the legal specification test of circular runout.
TOTAL RUNOUT VERIFICATION
Verifying Total Runout
In the above figure, a total runout is applied to a diameter.
Three checks must be done:
- Rule 1.
- Runout of the diameter.
Here is the link to check the size and Rule 1 boundary.
The part is mounted on a chuck or collet to establish datum axis A.
Then a dial indicator is used on the part.
The part is rotated by 360° and the dial indicator is moved axially along the surface.
In the below figure, a total runout is applied to a surface.
The part is held by the collet or chuck which establishes the datum axis A.
The dial indicator is placed perpendicular to the part surface.
The part is then rotated as the dial indicator is moved radially and the reading is taken.
Verifying Total Runout
COMPARISON BETWEEN CIRCULAR AND TOTAL RUNOUT
Coaxial diameters are toleranced with the help of circular and total runout.
There are some differences between the two control which we would discuss in the next part.
- Both the runout control has two coaxial cylinders as the tolerance zone.
- Circular runout has low cost to produce the part as compared to total runout.
- The cost of inspection is more for total runout as compared to circular runout.
- Location, orientation and circularity is controlled by circular runout while location, orientation and cylindricity is controlled by total runout.