How Successful People Make the Most of Their Concentricity.

DEFINTION

The condition in which the median points of all diametrically opposed elements of a cylinder come together with respect to the axis of the datum feature is known as concentricity.

The midpoint of a two point measurement is known as a median point.

A geometric tolerance that limits the concentricity error is known as concentricity control.

For this control, the tolerance zone is a cylinder.

This cylinder is coaxial with respect to the datum axis.

The tolerance value of concentricity control determines the diameter of the cylinder.

The median points must lie within the cylindrical tolerance zone.

The tolerance and datum reference are applied on an RFS basis when a concentricity control is used.

Below is an example of concentricity tolerance zone.

Example of concentricity control tolerance zone

Example of concentricity control tolerance zone

CONCENTRICITY APPLICATIONS

This control is used for unique applications when balance of the parts, similar wall thickness, or some other functional requirement is required we tend to use concentricity control.

Tolerance of position or runout must be considered before using this control.

In a runout control the variation is to a lesser extent of toleranced diameter.

The following conditions are applicable when a concentricity control is stated.

  1. Diameter must meet its size and Rule 1 requirements.
  2. Cylinder is the concentricity tolerance zone.
  3. Diameter of the tolerance zone is the tolerance value.
  4. All the median points must be within the tolerance zone.
Concentricity application

Concentricity application

DIFFERENCE BETWEEN CONCENTRICITY, RUNOUT AND TOLERANCE OF POSITION (RFS)

A number of geometric controls can be used for dimensioning coaxial diameters.

These geometric controls are common for the part which rotates.

The designer can choose between concentricity, total runout and tolerance of position (RFS).

The comparison is as follows:

1. Total Runout:

The tolerance zone is a two coaxial cylinders.

Tolerance zone is applicable to surface elements of a toleranced diameter.

Cost for production of the part is higher if this control is used.

Inspection cost is less.

It controls location, orientation and form.

2. Tolerance of position (RFS):

Tolerance zone is a cylinder.

Tolerance zone applies to the axis of the toleranced diameter.

Cost for production of the part is lesser as compared to total runout and concentricity.

Cost of inspection is also the cheapest.

It controls location and orientation.

3. Concentricity:

Tolerance zone is a cylinder.

Tolerance zone applies to the median points of the toleranced diameter.

Cost for production of the part is lesser as compared to total runout but greater than tolerance of position.

Cost of inspection is also the highest.

Location and orientation are controlled.

LEGAL SPECIFICATION TEST FOR AN ANGULARITY CONTROL

Following conditions must be satisfied for the concentricity control to be a legal specification.

  1. Application of feature control frame to a surface that is coaxial to datum axis.
  2. Datum references are essential.
  3. Diameter symbol must be present in the feature control frame.

If the above mentioned conditions are not fulfilled, then the concentricity specification is incomplete or incorrect.

CONCENTRICITY INSPECTION

Inspecting concentricity

Inspecting concentricity

The above image shows a concentricity control.

For inspecting large diameters, three checks are required:

  1. Size of the diameter.
  2. Rule 1.
  3. Concentricity requirements.

Inspecting concentricity is a bit different then runout or positional tolerance.

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