TECH TIP – WORKING WITH COMPOSITE TOLERANCES

The use of Composite Tolerancing is a common practice in manufacturing. Using Composite Tolerance callouts allows the Engineer to Tolerance a component for machining and Tolerance the component's location to the final assembly using a single Feature Control Frame.

For example, a machined component is to be welded to a frame within 1/8” to the Datum Reference Frame. Still, the Tolerance of the hole pattern of the machined component is only 0.030” (from Feature to Feature, in this example, it would be the bolt hole pattern). It is possible to define tolerances required for both operations using a single Composite Control Frame using Composite tolerancing.

Another example would be a Hole Pattern; you can use a composite tolerance to specify the Hole Pattern's Diameter and the Diameter of each Hole using a single Composite Control Frame.

2. Composite Tolerances always apply to patterns.
   
3. Composite tolerances specify two tolerances for the same geometric characteristic of a feature(s) with unique datum requirements.
   

1. One Tolerance relates to a pattern of features, and the other Tolerance relates to each feature within the pattern. Typically, the individual feature tolerance is tighter than the pattern tolerance.
   

Composite Tolerance Feature Control Frame Description – based on ASME Y14.5 – 2009.

When using Composite Tolerances, each Feature Control Frame segment below uses the first line to refine the Tolerance Zone and Constraints of the last line using the same precedence order as the previous segment (seen in the example below).

1. Composite Tolerances are defined by up to four lines (segments) in the Feature Control Frame, using a single GD&T symbol (as shown above).
   
2. The upper segment is the pattern-locating control known as the Pattern-Locating Tolerance Zone Framework (PLTZF).
   

3. This Control Frame defines rotation and translation relative to the specified datums.
   
4. The Control Frame specifies the larger positional Tolerance for pattern location and features size as a group.
   
5. The upper segment can also control Orientation if not including a lower segment in the Feature Control Frame.
   

3. Use the lower segments to control feature relationships known as Feature–Relating Tolerance Zone Framework (FRTZF).
   

1. Controls the smaller positional Tolerance for each feature of size within the pattern (a feature to feature relationship).
   

3. Basic Dimensions used to relate the (PLTZF) to specified datums do not apply to the location of the FRTZF.
   
4. Datums specified in a lower segment control the rotation of the FRTZF relative to the datums and within the boundaries established and controlled by the PLTZF.
   
5. Where datum feature references are specified;
   

2. One or more datum feature references specified in the upper frame segment are repeated, as applicable, and in the order of precedence, to constrain the rotation of the FRTZF.
   
3. In some instances, the repeated datum feature references may not constrain any degrees of freedom; however, they are necessary to maintain the identical datum reference.
   

4. When not specifying datum references in a lower segment, the FRTZF is free to rotate and translate within the boundaries established and controlled by the PLTZF.
   

For full details on Composite Tolerances, see the ASME Y14.5-2009 (Revision of Y14.5M-1994) Dimension and Tolerancing specification. Visit www.ASME.org for more information

Using a single segment control frame provides for the Position shown here, and Diameter tolerance; controls the Orientation (translation, rotation) of the holes using datums A|B|C.

2. The component does not use refined tolerances for Orientation to Datums A|B or distance between the two holes.
   
3. In this example, the Diameter is +/- 0.0010” while Position and Orientation are 0.010”.
   

To Report in Verisurf, select the measured Cylinder or Circle and select to report; Diameter and Position (must have defined CAD Nominals, enter Tolerances as required) for required Features and then generate a report.

When adding a second segment to the Feature Control Frame, the Hole pattern Orientation controls define datums; in Verisurf, a Best Fit is used to control the Orientation.

Tip: Use Inspect/Build to collect your data; in this case, you can construct Cylinders from the objects saved by Inspect/Build.

4. The entire Hole pattern must fall within the Tolerance defined.
   
5. In the example, the holes' Perpendicularity is constrained to Datum A (as shown in the Front View).
   
6. In the example, holes are constrained to Datum B (parallel) to ensure they align with each other.
   
7. In this example, the Best Fit would require constraining (“Lock”) the YZ Translations to evaluate the 0.003 tolerance for A|B.
   

See later in this document for a suggested methodology for Reporting both segments of this Composite Position.

The third segment in a Feature Control Frame further refines the Orientation of the feature. Refer to the previous example for details on the second segment of the Feature Frame.

Using our example, this segment of the Feature Frame refines the holes' Perpendicularity to Datum A.

2. The previous Control Frame constrains the hole group within 0.003 to Datum A. They are now individually located to Datum A within 0.001, which “tightens” up the holes' Perpendicularity to Datum A.
   
3. Use the best fit, constraining (locking), X, Y, Z for Translations, and C for rotations to verify this segment of the Feature Frame.
   

See later in this document for a suggested methodology for Reporting both segments of this Composite Position.

The fourth segment of the Feature Control Frames constrains the overall pattern of all the features defined by the Control Frame.

This example shows 10 sets of holes, with 4 holes in each set.

4. The first segment defines the Position of all holes to A|B|C.
   
5. The second segment refines the Orientation of all holes to A|B.
   
6. The third segment refines the Orientation of holes to A.
   
7. The fourth segment refines the entire hole pattern position (each group of 4).
   

1. To meet this requirement requires a Best Fit without any Translations or Rotations locked.
   

Using this simple example for an explanation of the inspection process:

1. Align with the Part using an AutoAlign or Feature Alignment.
   
2. Measure the Holes; there are two different methodologies available when performing this type of measurement work; the measurement collection method directly impacts the data analysis process.  Below, the process outlines the Hole measurement to Reporting to meet the Feature Frame controls.
   

Measurement Method used for Hole Inspection

Inspect/Build Mode record points on the surface of the Cylinder.

1. Create a Best Fit Analysis Object (for FRTZF callout for A|B).
   

After placing the Analysis object in the Report Manager, construct a Cylinder for reporting Diameter and first segment callout for A|B|C.

Measure as Cylinders

1. The Cylinder can be added to the Report Manager immediately for reporting Diameter and the first segment callout for A|B|C.
   

To Best Fit for the second segment, the points used to measure the Cylinder has to be exported and then Best Fit and Analyzed for A|B and then placed in the Report Manager.

Inspect/Build Points

Measured Cylinders

1. Best Fit the Analysis objects for each Hole, lock Y, and Z Translations.
   

1. Use Best Fit and Analyze Individually from the speed menu while in the Analysis Manager.
   

2. When the Best Fit is complete, use the Analysis button within the Best Fit Dialog to create two new Analysis objects; the Best Fit dialog is closed, close the Best Fit Dialog.
   

Note – you may want to rename the new Analysis objects.

3. Select the two original Analysis objects and select Best Fit and Analyze individually from the speed menu while in the Analysis Manager. When the Best Fit dialog opens, you may want to enter a unique name for the Best Fit (for Data Management).
   
4. Lock X, Y, Z for Translation; lock C for Rotations and run the Best Fit. When the Best Fit is complete, use the Analysis button within the Best Fit Dialog to create two new Analysis objects; the Best Fit dialog is closed, close the Best Fit Dialog.
   

Note – you may want to rename the new Analysis objects.

5. Place all six Analysis objects in the Report Manager.
   

1. Select the measured Cylinders and using the speed menu select Export - To Measured; this exports the probed points to the Data Tree.
   
2. Select the points for each Cylinder and using the speed menu select Tools - Merge Points and Clouds to create a Cloud for each Cylinder.
   
3. Go to Analysis Manager, select the two Pointclouds, and select Best Fit and Analyze individually using the speed menu. 
   
4. Lock Y and Z Translations and perform Best Fit.
   
5. When the Best Fit is complete, use the Analysis button within the Best Fit Dialog to create two new Analysis objects; the Best Fit dialog is closed, close the Best Fit Dialog.
   

Note – you may want to rename the new Analysis objects.

6. Go to Analysis Manager, select the two Pointclouds, and select Best Fit and Analyze individually using the speed menu.
   
7. Lock X, Y, Z for Translation; lock C for Rotations and run the Best Fit. When the Best Fit is complete, use the Analysis button within the Best Fit Dialog to create two 
   

Continued

6. In the Report Manager, Construct Cylinders on all six Analysis objects (consider naming conventions).
   
7. Using the Cylinders constructed from the original two Analysis objects not labeled `Best Fit’ select to report Diameter only, Position, ID MMC, and Angularity (rename the field to Perpendicularity) this completes the Segment 1 reporting.
   

Note: you can turn off all report details for the Analysis objects.

8. Segment 2 – using the two Cylinders labeled `Best Fit,’ report; Angularity (rename to Perpendicularity) and Position (if within tolerance 0.003,” Parallelism can be considered in Tolerance). If the Position is out of Tolerance, you may want to construct Lines if more detailed information is required.
   

Segment 3 – using the final two cylinders (constructed from the Analysis object from step 4), report Position, and Angularity (rename to Perpendicularity).

new Analysis objects; when the Best Fit dialog is closed, close the Best Fit Dialog.

Note – you may want to rename the new Analysis objects.

8. Place the Cylinders and the four Analysis objects in the Report Manager.
   
9. To complete Segment 1 reporting, select to report the two Cylinders. Report Diameter only, Position, ID MMC, and Angularity (rename the field to Perpendicularity).
   
10. Select the first two Analysis objects (created in step 5) and Construct Cylinders (rename for data management).
    

Note: you can turn off all report details for the Analysis objects.

11. Select the Analysis objects created in step 7 and Construct a Cylinder (rename for data management).
    
12. Segment 2 - Select the Cylinders created in step 10 and choose to report Angularity (rename to Perpendicularity) and Position (if within Tolerance, 0.003” is in Tolerance). If the Position is out of Tolerance, you may want to construct Lines if more detailed information is required.
    

Segment 3 – using the final two cylinders constructed in step 11, report Position and Angularity (rename to Perpendicularity).

Inspect/Build Points

Measured Cylinders

Continued

Continued

1. Best Fit the Analysis objects for each Hole, lock Y, and Z Translations.
   

1. Use Best Fit and Analyze Individually from the speed menu while in the Analysis Manager.
   

2. When the Best Fit is complete, use the Analysis button within the Best Fit Dialog, this creates 5 new Analysis objects when the Best Fit dialog is closed, close the Best Fit Dialog.
   

Note – you may want to rename the new Analysis objects.

3. Select the five original Analysis objects and select Best Fit and Analyze individually from the speed menu while in the Analysis Manager. When the Best Fit dialog opens, you may want to enter a unique name for the Best Fit (for Data Management).
   
4. Lock X, Y, Z for Translation; lock C for Rotations. Run the Best Fit; when the Best Fit is complete, use the Analysis button within the Best Fit Dialog to create five new Analysis objects; when the Best Fit dialog is closed, close the Best Fit Dialog.
   

Note – you may want to rename the new Analysis objects.

5. Select the five original Analysis objects and select Best Fit and Analyze individually from the speed menu while in the Analysis Manager. When the Best Fit dialog opens, you may want to enter a unique name for the Best Fit (for Data Management).
   
6. Unlock all Translations and Rotations to allow for a full Best Fit calculation, run the Best Fit. When the Best Fit is complete, use the Analysis button within the Best Fit Dialog to create five new Analysis objects; the Best Fit dialog is closed, close the Best Fit Dialog.
   
7. Place all twenty Analysis objects in the Report Manager.
   
8. In the Report Manager, Construct Cylinders on all twenty Analysis objects (consider naming conventions).
   
9. To complete the Segment 1 reporting, use the Cylinders constructed from the original five Analysis objects. Report Diameter only, Position, ID MMC, and Angularity (rename the field to Perpendicularity).
   

Note: you can turn off all report details for the Analysis objects.

10. Segment 2 – using the five Cylinders from step 3; report Angularity (rename to Perpendicularity); Position (if within Tolerance, 0.003” Parallelism). If the Position is out of Tolerance, you may want to construct Lines if more detailed information is required.
    
11. Segment 3 – using the five cylinders (constructed from the Analysis object from step 4) report Position and Angularity (rename to Perpendicularity).
    
12. Segment 4 – using the five cylinders (constructed from the Analysis object from step 6) report Position only.
    

1. Select the measured Cylinders and using the speed menu Export - To Measured, to export the probed points to the Data Tree.
   
2. Select the points for each Cylinder and using the speed menu select Tools - Merge Points and Clouds to create a Cloud for each Cylinder.
   
3. Go to Analysis Manager, select the five Pointclouds and, select Best Fit and Analyze individually from the speed menu.
   
4. Lock Y and Z Translations and perform Best Fit.
   
5. When the Best Fit is complete, use the Analysis button within the Best Fit Dialog to create two new Analysis objects; the Best Fit dialog is closed, close the Best Fit Dialog.
   

Note – you may want to rename the new Analysis objects.

6. Go to Analysis Manager, select the five Pointclouds, and select Best Fit and Analyze individually from the speed menu.
   
7. Lock X, Y, Z for Translation; lock C for Rotations. Run the Best Fit; when the Best Fit is complete, use the Analysis button within the Best Fit Dialog to create two new Analysis objects; when the Best Fit dialog is closed, close the Best Fit Dialog.
   

Note – you may want to rename the new Analysis objects.

8. Select the five original Analysis objects and select Best Fit and Analyze individually from the speed menu while in the Analysis Manager. When the Best Fit dialog opens, you may want to enter a unique name for the Best Fit (for Data Management).
   
9. Unlock all Translations and Rotations to allow for a full Best Fit calculation, run the Best Fit. When the Best Fit is complete, use the Analysis button within the Best Fit Dialog to create five new Analysis objects; the Best Fit dialog is closed, close the Best Fit Dialog.
   
10. Place the Cylinders and the twenty Analysis objects in the Report Manager.
    
11. To complete Segment 1 reporting, select the five Cylinders to report Diameter only, Position, ID MMC, and Angularity (rename the field to Perpendicularity).
    
12. Select the five Analysis objects (created in step 5) and Construct Cylinders (rename for data management).
    
13. Select the five Analysis objects created in step 7 and Construct a Cylinder (rename for data management).
    
14. Select the Analysis object created in step 9 and Construct a Cylinder (rename for data management).
    
15. Segment 2 - Select the cylinders constructed in step 12 and choose to report Angularity (rename to Perpendicularity) and Position (if within Tolerance, 0.003 Parallelism). If the Position is out of Tolerance, you may want to construct Lines if more detailed information is required.
    
16. Segment 3 – using the five cylinders constructed in step 13, report Position and Angularity (rename to Perpendicularity).
    
17. Segment 4 - using the five cylinders constructed in step 14, report Position only.