Creo EZ Tolerance Analysis > Summary and Stackup Details Tables > Stackup Details Table
  
Stackup Details Table
Click next to the stackup in the Summary table to open the Stackup Details table:
A description of the Stackup Details table follows:
• The graphical symbols in the first column indicate the dimension path through these parts and features. Each feature is represented with a symbol that indicates the type, such as a flat surface, a cylindrical feature of size, or a planar feature of size such as a slot.
The previous image shows how the dimension attaches to the feature. For features of size, you can modify the assumed attachment. Many dimensions, however, are attached to the planar surfaces with no ability to modify the attachment option. Right-click the symbol next to the Results row to open a list of attachment types and select one of the following types.
1. Indicates where the dimension origin should be attached to the size of the feature above the dimension row.
2. Indicates where the dimension should be attached to the size of the feature below the dimension row.
When both the feature above and below the dimension are features of size, the list has nine options. If only one of the features is a feature of size, the list has three options.
You cannot change the attachment for dimensions with tolerances linked with tolerances on the part files. To change the attachment type of such dimensions, you must first unlink them.
• Name—Name of the part, feature, dimension, calculated assembly shift, or calculated datum shift. The second last row shows the name of the stackup.
• —A dimension is used in more than one stackup. Place the pointer on this icon to open the list of stackups in which the dimension is used.
• Sens—Sensitivity and direction of the dimension in the stackup. It is 1 or -1. If the dimension loop passes from the outer edge to the center of a feature of size, it is ½ or -½.
• Nominal—Nominal value of the dimension between the two features calculated from the geometry. You cannot edit the nominal values except for the offsets that are added between parts using the Add Offset tool. In that case, double-click in the cell to edit the value.
• Tolerance Type—Type of a tolerance objective. Right-click the type symbol to select a different tolerance type for defining the upper and lower objectives of the stackup. The following types are supported:
◦ ± (symmetric)—Bilateral value applied relative to the nominal value.
◦ +/- (plus-minus)—Non-symmetric values applied relative to the nominal value. The +/+ and -/- definitions are supported.
◦ Limits—Definition of absolute upper and lower limits for the objective independent of the nominal value.
◦ ≤ (upper limit)—Definition of a single upper limit.
◦ ≥ (lower limit)—Definition of a single lower limit.
◦ Geometric Tolerance—Opens the Add Geometric Tolerance dialog box. For more information, see To add geometric tolerance.
• Tolerance value—Values associated with the Tolerance Type. Double-click in the field to edit the limits of dimension in the Edit Tolerance dialog box.
 
• In the specified objective values, the number of digits determine the precision to be used. However, if you specify a value without a decimal, the precision is not changed.
• The sign and value of the number that you specify are evaluated to determine if it must be placed in the upper or lower segment of +/- and Limits objective types. If you do not specify a sign, the existing sign designated for the field is applicable.
• Datum—Feature that is used as the datum feature. This feature is placed above or below the dimension row. Datum feature is applicable for geometric tolerances.
• (link) or (break link)— In feature or dimension rows, appears when either of the following conditions are met:
◦ When the dimension in the EZ Tolerance Analysis stackup is associated with the dimension in a Creo Parametric part.
◦ When two subsequent features in the stackup are associated with a Datum Feature and an annotation controls the other feature back to the Datum Feature.
EZ Tolerance Analysis uses the tolerance information found in Creo Parametric and creates a link. Changes made to the tolerances in EZ Tolerance Analysis, result in changes in the associated tolerance in the Creo Parametric part file.
To change the tolerance without updating the tolerance values in the Creo Parametric part, click to break the link. replaces , indicating the link is broken. To restore the link, click . The tolerance displayed in EZ Tolerance Analysis is pushed into the equivalent Creo Parametric part file.
• Cp—When the analysis type is either RSS or Statistical, indicates the Cp values for the parts and the dimensions. These Cp values are used to assume a standard deviation for the variation of each of the input dimensions for the calculation of the distribution characteristics of the stackup result. For Statistical analyses, EZ Tolerance Analysis incorporates a hierarchy of settings to give you control over the assumed statistical distributions. Only Normal or Gaussian distributions are supported, but you can control the standard deviation defined by the tolerance applied through the specification of an assumed Cp quality metric.
You can define the Cp quality metric at the following levels:
◦ Application level—Through the definition of Default Model Cp option in the Options dialog box. It is recommended to set this at 1.0 unless you have most of your parts produced at a different quality level.
◦ Part level—In the Stackup Details in the Cp column of the part row with tolerance included in the stackup results. Until you specify a part-specific value, the part assumes the default value defined at the application level. This existing value of Default Model Cp appears in parentheses in the Cp column. Right-click in the Cp column of part row and select Part level Cp to change this setting. The Default label is replaced with a real number that you can modify. Double-click the value and enter a new value, if required.
◦ Dimension and Feature level—In the Cp column of the dimension row with tolerance included in the stackup results. Unless you specify a unique value for a specific dimension or feature, Cp defined at the part level is considered. In the Cp column, the current Cp value of the part is shown in parentheses. Right-click in the Cp column of dimension or feature row and select Dimension level Cp or Feature level Cp. The Part label is replaced with a real number that you can modify. Double-click the value and enter a new value, if required. You cannot edit Cp values for RSS analyses.
The rows in the table consist of the following:
• Parts—One or more parts are included in the stackup definition. For each part, there is the following:
◦ Features—One or more features on the part appear in order of the stackup loop passing through the part. Features of size have a size dimension and tolerance shown in the same row. When there are four or more features included for a part, you can change the order of all except the first and the last feature. Change in order reflects a different series of dimensions. Drag onto to move the row up or down. When you press , it changes to the , and one or more appears indicating a place where you can move the respective row. The new dimensions are created between each of the features in the order they appear in the table.
If required, click to delete a row from the table. For example, you may want to remove a feature from the stackup so that the two dimensions between the surrounding features change to a single dimension.
◦ Dimensions and Tolerances—When two or more features are used from the part, a dimension between each indicates a tolerance and the distance that is the nominal dimension value between the features.
◦ Datum Shift contributors—When a datum feature is referenced at its Maximum Material Boundary or Least Material Boundary, an additional row appears with a light red background between the datum feature and the row with the Feature Control Frame. The value of tolerance in this row represents the permissible datum shift that can occur when the datum feature is at its ideal size, such as ½ way between the upper and lower specification limits for the size. Additional possible datum shift effects are accounted for in the modified sensitivity of the size dimension.
• Assembly Shift contributors—When EZ Tolerance Analysis detects the possibility of a clearance between the features of size, such as bolts or pins in clearance holes, controlling the location of two parts relative to one another, a row appears with a light purple background between the two parts. A prefix Asm shift and indicate such a shift. The tolerance value in this row represents the permissible assembly shift that can occur in each direction when both features are at their ideal size, such as ½ way between the upper and lower specification limits for their sizes. Additional assembly shift effects due to variation in the features of size, are accounted for in the modified sensitivity of the respective size dimensions.
The assumption of random placement, referred to as assembly shift or float, means that nothing influences the position of the parts relative to one another during assembly. However, when you determine whether two parts can be assembled, you must consider that the person who assembles the parts moves the parts around, using the clearances between the features described above, until they fit together. In such cases, instead of assuming random placement of the bolt into the hole, you would use the clearance to maximize the distance being analyzed in the stackup for fit. In such instances, the parts fail to get assembled due to interference, when the distance between two nearby surfaces decreases to 0 or less, despite the parts being moved as far apart as possible with the available clearance between them.
Right-click and select Maximize from the list to bias the Asm shift row such that these clearances maximize the stackup results. The label in the row reflects the options—Maximize or Minimize. The tolerance also changes to a single value in parentheses, indicating the amount of nominal bias. After you make this change, the stackup nominal value is changed to a larger value for Maximize, and a smaller value for Minimize, by the bias amount. To assume a random placement again, right-click the right arrow or the left-arrow and select Float in the list.
Changing of any Asm shift row from Float to Maximize does not impact the upper Worst Case or RSS limit. Similarly, changing Float to Minimize does not impact the lower Worst Case or RSS limit, because both analyses techniques consider that the part is shifted in the extreme positions when Float is selected.
• Offsets between parts—If one or more offset distance between two parts are defined in the stackup with the Add Offset tool, each defined offset in a row is highlighted with a gray background. Double-click the field to define a new nominal value or a tolerance value. Right-click the field to define a new tolerance type. To remove the offset, click .
• Results—The second last row after all the parts shows the results of the stackup analysis based on the defined Target Quality level. The results are presented in the same format used for the Objective definition, such as ±, +/-, or Limits. When Target Quality is set to use one of the statistical methods, the Results row includes the calculated quality of the stackup distribution compared with the defined Objective. For RSS, the row shows the Cpk label in the Cp column. For the general statistical analyses, EZ Tolerance Analysis reports the Predicted Quality using the same metric type as defined for the Target Quality. Double-click the name to edit it, if required.
• Objectives—The last row in the table shows the Objective for the stackup along with the Target Quality, such as the type of analysis and desired quality level for statistical analyses. You can change the analysis type and quality level.