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Surface Modeling Palette gibbscam

Clicking the Surface Modeling button in the Top Level palette opens the Surface Modeling palette, which is shown below. Surface modeling and sheets are primarily used when working with imported surface files, and are not generally required for building bodies.

The Surface Modeling palette includes various methods for creating sheets, including planes, revolved sheets, lofted sheets, Coons patch sheets, swept sheets, and sheets from faces as well as the ability to trim/untrim, stitch/unstitch, and extend sheets.

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Plane

This button is used to create planes. When no geometry is selected, using this function will create a flat planar sheet based on the current coordinate system at a depth of zero. Triggering this function with a closed shape selected will create a sheet bounded by the selected geometry at a depth of zero in the coordinate system. If the closed shape is not planar, a plane will still be created by projecting the geometry to a depth of zero in the current coordinate system.

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Revolve

This button will open the Sheet Revolve dialog which allows users to revolve a shape around the horizontal or vertical axis by a specified number of degrees to create a sheet.

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Sheet Revolve dialog

Select an open, terminated shape or a closed shape to be revolved. The axis buttons specify which axis the selected shape will be revolved about. If the horizontal axis is selected for the axis of revolution, a vertical value must be entered to specify the position of the revolution axis. Likewise, if the vertical axis is the axis of revolution, a horizontal value must be entered to specify the position of the revolution axis. The value entered in the A text box is the angle (specified in degrees) the selected shape will be revolved around the selected axis. A positive angle value will revolve the shape in a counter-clockwise direction and a negative angle in a clockwise direction based on the positive axis of revolution.

Loft

This button will open the Sheet Loft dialog which allows users to create a sheet through a series of open or closed shapes. The system will blend all the selected shapes into a smooth sheet. Sheet lofting produces ruled surfaces when only two shapes are selected and sculptured surfaces when three or more shapes are selected.

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Sheet Loft dialog:

Select a series of shapes to be blended into a smooth sheet. These can be closed shapes or open, terminated shapes. The shapes act as the cross-sections through which the final sheet will be created. The system will blend the selected shapes into a sheet using C0 points (corners) as alignment points. If the Close checkbox is selected, the system will attempt to blend the first and last shapes together to form a closed sheet.

Coons Patch

This button creates a sheet called a Coons patch through either three or four selected open, terminated shapes. A Coons patch is a surface type that uses boundary shapes (typically splines) and blends a smooth surface between them. Either three or four shapes must be designated as boundary shapes. Each shape can be any size or orientation as long as the endpoints are coincident (in the exact same location in X, Y and Z) and each shape is continuous and does not contain any sharp corners. The selected shapes represent the boundary of the sheet.

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In some cases, connected splines or features can be selected to create a Coons patch. Also, if trimmed splines that do not have coincident points at the edges are imported, a Coons patch can be created provided that the ends of each trimmed spline are coincident. Often times, a Coons patch surface can be created if there are more than three or four line segments but the connected splines have three or four distinct corners.

Sweep Sheet

The Sweep Sheet function is nearly identical to the Sweep Solid function described in Solid Modeling Palette. The only difference involves the alignment rules for the drive curves. Swept sheets do not use alignment or sync points selected on the drive curves to determine how the drive curves will be blended together. Only one alignment point per drive curve needs to be selected for the Sweep Sheet function. Refer to Solid Modeling Palette for additional information.

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Sheet from Face

This option creates a sheet from the face of a solid or sheet. A face is one surface of a solid or sheet that is bound by an edge loop. Using the Face Selection mode accessed from the Taskbar, users can select individual faces of a body. Selecting a face or faces and clicking on this button will create a sheet based on the face and bound by the edge loop of the selected face. Neighboring faces will produce stitched faces in the resulting sheet.

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Trim/Untrim Surfaces

This button performs both the trim and untrim functions depending on the entities selected when the button is clicked. If a sheet and geometry are selected, the system will attempt to perform the trim operation. The trim function breaks a single sheet into two separate sheets at the selected trim geometry. The geometry selected for the trim operation must completely cut the selected sheet into two pieces. If the geometry does not lie on the selected sheet, the geometry will be projected onto the selected sheet and the trim operation will be performed. Holding down the Alt key while clicking the Trim/Untrim button will perform both the trim and untrim operations at once. The system will untrim the selected one-faced sheet and then trim that sheet to the selected geometry in one step, never attempting to create a valid face from the untrimmed surface.

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If only a sheet is selected, the system will attempt to untrim. The Untrim function only works with single-faced sheets. The edge loop is what bounds the underlying surface definition into a finite bounded surface. The Untrim function removes the bounding edge loop so that the underlying surface definition replaces the selected surface. The untrimmed surface will be bound by the workspace stock size.

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This is useful when working with imported IGES files that are not stitching or solidifying due to edge loops of neighboring surfaces not joining within the specified tolerance. If this is the case, the user can select the problem sheet, untrim it to create the underlying surface definition and then trim that surface with the extracted edges from neighboring sheets.

Stitch Sheets

This button will open the Stitch Sheetsdialog. This dialog provides different methods for stitching sheets together as well as tools to analyze stitched sheets. In order to stitch sheets, the user must select all the sheets to be stitched, choose a stitching method from the Stitch Sheets dialog and click the Stitch button.

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Surfaces are stitched at their edges. When surface files are imported into the system, each surface is represented as a single-faced sheet. A face is a trimmed surface with an edge and knowledge of its neighboring surfaces. An edge is the trim curve that bounds a face. For sheets to successfully stitch to their neighbors, the edges of these sheets must align with each other within a specified tolerance; otherwise, there are holes (gaps) and adjoining sheets that are separated by a gap cannot be stitched.

The system must be in Edge Selection mode in order to view edges. The Show Internal Edges checkbox provides a method for only viewing the external edges of a part. The internal edges are edges that can be viewed from the inside of the model looking out, while the external edges are ones that can be viewed from the outside. The external edges are the edges that need to be stitched together. After performing a stitching operation, the only external edges that will be visible are the edges that could not be stitched together because of the tolerance gap. All stitched edges become internal edges.

Once the problem edges have been identified, if the gap is large, the user can build a sheet using Coons Patch or another Surface Modeling tool to fill the hole. Often times the gaps are small and can be fixed by applying a looser tolerance to select edges. This is accomplished by selecting the problem edges, entering the looser tolerance in the Edge Tolerance text box, and clicking on the Set Edge button. Applying a different edge tolerance to certain edges often aids the system in stitching together all the sheets together.

There are three stitching methods offered in this dialog 1 Pass, Multiple Passes and Multiple Tries. Each of these methods uses the Tolerance value entered in the dialog. The tolerance can be thought of as the maximum gap that can exist between the edges of two sheets that the system will still stitch together. For example, the edges of two adjoining sheets are 0.002mm apart. If the tolerance set is 0.002mm or greater, the two sheets will be stitched together and the result will be a single sheet. If the tolerance is less than 0.002mm, the two sheets will not be stitched together and remain two separate entities. The minimum tolerance is set by the system and is 0.00002mm or 0.00000079″. The tolerance specified by the user cannot be less than this value.

1 Pass:

When the 1 Pass option is selected, the system will attempt to stitch all selected sheets at the given tolerance. The system will take one pass at the specified tolerance in this attempt. The system will analyze each sheet, its neighbors and its edges and if they fall within the tolerance, stitch the sheets together. If all edges stitch together at this tolerance into a single closed sheet, the system will solidify the sheets, thereby creating a solid. Otherwise, the result will be a multi-faced sheet composed of all of the sheets that could be stitched together.

Multiple Passes:

When this option is selected, the system will attempt to stitch together all selected sheets by performing a series of single passes. The system will begin at the minimum tolerance (0.00002 mm or 0.00000079″) and attempt to stitch the sheets at that tolerance. The tolerance entered by the user provides the maximum tolerance that the system will go to in its attempt to stitch the sheets. Multiple passes will be taken at incremental tolerance steps ranging from the minimum tolerance (set by the system) to the maximum tolerance (set by the user). On each pass, the system will stitch together all the sheets that it can at that tolerance and then proceed to another pass at the next tolerance, attempting to stitch any remaining sheets. The progress bar, located on the right side of the Taskbar, displays the number of sheets remaining to be stitched and the tolerance being used on the current pass. When all of the passes have been completed, if the sheets stitched together into a single closed sheet, the system will automatically solidify the sheets, resulting in a solid. Otherwise, the result will be a multi-faced sheet or sheets.

Multiple Tries:

This option is similar to Multiple Passes in that it takes incremental passes ranging from the minimum tolerance (0.00002 mm or 0.00000079″) to the maximum tolerance, which is the Tolerance value entered in the dialog. The system will attempt to stitch all the sheets together at each tolerance increment, starting over after each pass that does not stitch all the selected sheets together. The system is looking for the smallest single tolerance that will stitch the entire part. This is similar to taking a series of one-pass steps and undoing after each one. The stitching process will stop when all the selected sheets have been stitched together into a single sheet even if this occurs before the maximum tolerance is reached.

Face Check:

Clicking the Face Check button will perform a face validity check on the selected sheets. This is identical to the face validity check that is run when the Solids > Tools > Check Body Validity item is selected. The face check produces an error message for each invalid face and also deselects the problem faces. It is useful to run a face check if stitching has failed to identify problem areas before attempting to stitch again. When a face fails the check, it must be deleted and re-created in order for future stitching attempts to be successful.

Unstitch Sheets

This button will unstitch or detach faces of a sheet. This will also convert solids into sheets. The faces will be unstitched at the edge loop which bounds the selected face or faces. Example of unstitching a sheet illustrate an example of unstitching. The first row of pictures shows geometry revolved to create a single multi-faced sheet with the edges displayed to differentiate between the faces of the sheet. In the second row, multiple adjoining faces are selected to be unstitched.

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1. Original Sheet
2. Edges of sheet which separate the faces
3. Selected face to be unstitched
4. Resulting Sheet
5. Resulting Sheet

Example of unstitching a sheet

Untrim & Extend Surfaces

This function untrims and extends sheets to the user-specified point(s), effectively eliminating all trimmed loops and plugging in any holes that exist in the sheet. After selecting a single-faced sheet, click this button to open the Untrim & Extend Surface dialog. The system offers three methods for untrimming and extending sheets: To A Point, by All Sides Outside Cuboid specified by two points, and by All Sides By Approximate value. This will not change the shape of the surface, and is most useful when attempting to heal surfaces.

To A Point:

The surface will be untrimmed and extended to the specified point along the chosen axis. Note that multiple edges may be extended depending on their proximity to the specified point.

All Sides Outside Cuboid:

The surface will be modified (either reduced or enlarged) to fit within the cuboid, specified by entering its minimum and maximum point. The default coordinates for the cuboid coincide with the boundaries of the stock.

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