About the Flat Pattern Preview Window
Use the Flat Pattern Preview tool to open a window with a preview of the sheet metal model in an unbent state. The preview is suppressed when you add or redefine features in a design. It is automatically resumed after the features have been added. The Preview window is not available when a Flat Pattern feature is in the model, but is available in Verify mode when creating or redefining most features.
To access the Flat Pattern Preview tool, click 
on the Graphics toolbar.
on the Graphics toolbar.These additional commands appear on the Graphics toolbar of the Flat Pattern Preview window:
• 
Flatten Forms—Toggles the flattening and unbending of form features.
Flatten Forms—Toggles the flattening and unbending of form features.• Overlapping Geometry—Toggles the display of overlapping geometry. (default)
Overlapping Geometry—Toggles the display of overlapping geometry. (default)• 
Bounding Box Dimensions—Toggles the display of the length and width dimensions of the unbent sheet metal part. The dimensions are associated with the SMT_FLAT_PATTERN_LENGTH and SMT_FLAT_PATTERN_WIDTH parameters.
Bounding Box Dimensions—Toggles the display of the length and width dimensions of the unbent sheet metal part. The dimensions are associated with the SMT_FLAT_PATTERN_LENGTH and SMT_FLAT_PATTERN_WIDTH parameters.• 
Create Instance—Opens the New Instance dialog box to automatically create a Family Table instance of the flat pattern.
Create Instance—Opens the New Instance dialog box to automatically create a Family Table instance of the flat pattern.Keep in mind the following points when using the Flat Pattern Preview tool:
• Corner relief appears as defined in the Relief area of the Sheetmetal Preferences dialog box, unless the Corner Relief, Flange, or Conversion tools are used to define feature-specific relief.
• You must set a fixed geometry reference for the preview, unless one is already defined for the part.
• Set the accessory_window_display configuration option to yes to open the preview in a docked window, or set it to no to open the preview separately.
• A preview does not appear for parts with the following geometry:
◦ Two or more distinct pieces
◦ Unmerged quilts
◦ One or more deformation areas that cannot be unbent
◦ Relief geometry that is not valid
◦ Hem geometry that is not valid
◦ Deformation areas that cannot be regenerated
◦ Sharp edges that cannot be unbent
◦ Surfaces that cannot be unbent
• Geometry that cannot be unbent is highlighted in a different color. To change the default color, click > 
Options > . Expand the Graphics branch and specify the required color for Secondary previewed geometry.
Options > . Expand the Graphics branch and specify the required color for Secondary previewed geometry.