Rules to consider before beginning the ball corner procedure

• Ensure that the CVs are evenly distributed across the main surfaces.
• When trimming surfaces, ensure that any Curve on Surfaces are not cropped to the point where it is difficult to work with the trimmed edge.
• Because a ball corner must have a four-sided surface, the Patch Layout must be constructed in a similar fashion to avoid triangle surfaces.

Up until this point in the tutorial, high-quality model surfaces have been produced from a mathematical point of view. Single span surfaces (except the fillets), called Bezier surfaces, were utilized to guarantee a smooth curvature comb inside of a surface.

The correct use of single span surfaces requires a high degree of experience with the Object Edit > Align > Align 2008 tool, direct modeling, and handling Locators.

Because the experience required is outside of the scope of this tutorial, the ball corners created for this model will not use single span surfacing.

How to model a simple ball corner

1. Open the wire file Ball Corner.wire.
2. Use the prepared surfaces located in the layer entitled “work”.

   

3. Create a blend curve between the trimmed fillet surface and the front transition surface.
   NoteThe resulting blend curve should resemble the image below. Note also that it is possible that the left blend point projects from the surface in the wrong direction. To correct this problem, consult Steps 3 – 5.

   

4. Select the blend point.
5. Choose the BlendCrv Tools > Blend Curve Edit tool.
6. A manipulator will appear on the selected blend curve. Click on the axis that defines the desired direction.
   NoteA green U or V should appear on the desired axis. If a black sign is produced, click on the axis again.

   

7. Use the Viewing Panel to switch to the top view.
8. To produce a curve-on-surface, project the blend curve onto the top surface.

   

   

9. Set the options as follows, then, create a square surface with the projected curve set as edge # 4.

   Set this parameter...	To this value
   1 (rail_surf#5)	Set Continuity to CURVATURE and Rebld off
   2 (square#15)	Set Continuity to CURVATURE and Rebld off
   3 (fillet_srf)	Set Continuity to CURVATURE and Rebld off
   4 (square#14)	Set Continuity to CURVATURE and Rebld on
   Blend Type	LINEAR
   1-3 Boundary Blend	0.500
   2-4 Boundary Blend	0.500
   Explicit Control	off
   Max New Spans	10
   Insert at Midpoint	on
   Create History	on
   Auto Recalc	on
   Boundary Labels	on
   Continuity Check	on

   

10. Examine the span distribution of the square surface for irregularities.
    TipIn the above image, the span placements are irregular. Executing Step 11 will provide for a more even distribution of span lines.
11. In the Square Control box, use the Explicit Control option to change the arrangement of the square option box.
12. Set the Advanced options as follows:

    Set this parameter...	To this value
    1 (rail_surf#5)	Set Continuity to CURVATURE and Rebld off
    2 (square#15)	Set Continuity to CURVATURE and Rebld off
    3 (fillet_srf)	Set Continuity to CURVATURE and Rebld off
    4 (square#14)	Set Continuity to CURVATURE and Rebld on
    Blend Type	LINEAR
    1-3 Boundary Blend	0.500
    2-4 Boundary Blend	0.500
    Explicit Control	on
    U/V Sync Degree	off
    U degree	6
    V degree	5
    U spans	2
    V spans	7
    Max New Spans	0
    Insert at Midpoint	on
    Create History	on
    Auto. Recalc	on
    Boundary Labels	on
    Continuity Check	on

    

There may be slight differences in the appearance of your model and the model depicted in this tutorial. For this reason, you should explore the Square Control box to find the best possible arrangement for your surface.

Judge the surface by using an evaluation tool that shows you the stripes as projected by a lamp onto selected surfaces. Try moving the lamp using the blue, green, and red manipulators to find a lighting arrangement that best accentuates your model.

To use the IsoAngle tool

1. Select the surfaces to be evaluated.
2. Double-click the Evaluate > IsoAngle tool to open the option box.
3. Set the options as follows:

   Set this parameter...	To this value
   Type of Bands	Multiple
   Repeat Multiple Bands	25
   Shaded surface	on
   Visual Curves	off
   Blur	0.0100

4. Zoom out of the view to show the lamp.
5. Click on the colorized circle to move the lamp. Examine the highlights of the model surface.

   

At this point in the modeling process, the front-end of the model is complete. However, if you are not satisfied with the results presented by the Evaluate > IsoAngle tool, modify the ball corners using the direct modeling method. When direct modeling the ball curve, the number of CVs will have to be reduced, which in turn, will reduce the number of spans.

To reduce the number of spans

1. Choose Pick > Nothing .
2. Tumble the scene as shown in the image below.
3. Turn off the Evaluate > IsoAngle tool.
4. Make the top surface invisible.

   

   NoteFor this exercise, a curve-on-surface will not be used to create the ball corner because the result will involve a mathematical evaluation that could produce a high number of spans. Instead, this exercise will produce a ball corner using a blend curve that should produce fewer spans.
5. Create a square surface with the options set as follows:

   Set this parameter...	To this value
   1 (rail_surf#5)	Set Continuity to CURVATURE and Rebld off
   2 (square#15)	Set Continuity to CURVATURE and Rebld off
   3 (fillet_srf)	Set Continuity to CURVATURE and Rebld off
   4 (blend#17)	Set Continuity to FIXED and Rebld off
   Blend Type	LINEAR
   1-3 Boundary Blend	0.500
   2-4 Boundary Blend	0.500
   Explicit Control	on
   U/V Sync Degree	off
   U degree	6
   V degree	5
   U spans	2
   V spans	4
   Max New Spans	0
   Insert at Midpoint	on
   Create History	on
   Auto. Recalc	off
   Boundary Labels	on
   Continuity Check	on

   

   The newly created square surface has no connection to the top surface.

6. To project the edge of the new square onto the top surface, switch to the top view.
7. Project the edge of the ball corner onto the top surface.

   

8. To measure the POSITION Continuity (G0) between the projected curve-on-surface and the surface edge of the ball corner, double-click the Evaluate > Continuity > Surface Continuity tool to produce the options box.
9. Set the options as follows:

   Set this parameter...	To this value
   Find	Positional Continuity
   Check Spacing by	# Per Span
   Locator Persistence	on
   Check Interior	on
   Show Max Labels	on
   Show Edge Labels	on
   Show Comb	on

10. Press the Go button.
11. Pick the projected curve-on-surface.

    

The results from the Evaluate > Continuity > Surface Continuity tool show a small gap between the surface edge and the curve-on-surface. The surface will need to be aligned to the curve-on-surface.

To align the surface with the curve-on-surface

1. Choose Pick > Nothing .
2. Double-click the Object Edit > Align > Align 2008 tool to produce the options box.
3. Set the Advanced options as follows..

   Set this parameter...	To this value
   Modify	FIRST
   Continuity	CURVATURE
   Alignment Type	ALIGN BY PROJECT
   Explicit Control	on
   Create History	on
   Auto. Recalc	on
   Continuity Check	on
   Specify Contin. Check	on
   Continuity Check Type	CURVATURE

4. Select the edge of the ball corner surface close to the curve-on-surface.
5. Select the curve-on-surface.
6. Choose the Accept button.

   

It is possible that the alignment procedure will destroy the curvature continuity between the ball corner surface and the front-end transitional surface. To correct this problem, use the Object Edit > Align > Align 2008 tool again to restore the broken curvature connection. Before attempting another alignment, delete the construction history of the first alignment. The second alignment process could damage the results of the first alignment process; in this case, set the Continuity option to TANGENT instead of CURVATURE. If the alignment remains damaged after restoration attempts, a work-around can be executed.

A work-around for restoring a broken curvature connection

The mathematical behavior of a curve-on-surface derived from the Surface Edit > Create CurvesOnSurface > Project tool differs from a curve-on-surface derived from the Surface Edit > Create CurvesOnSurface > Project normal tool.

1. Delete the curve-on-surface of the top surface that was used to create the ball corner.
2. Choose the Surface Edit > Create CurvesOnSurface > Project normal tool. Project the ball corner edge onto the top surface to produce a new curve-on-surface, complete with a new mathematical behavior.
3. Repeat both alignment processes.

   

The last possibility to adjust the alignment of the ball corner is to directly manipulate CVs.

Begin by aligning the ball corner to the top surface.

Then, generate a TANGENT Continuity between the ball corner and the front-end transitional surface by using the PROJ (project) option in the Control Panel > Evaluate > Move CV tool.

Before you modify the CVs by hand, you must delete the construction history.

The end result of this exercise should be a balled corner with less spans than those created by the curve-on-surface used in the construction of the initial square.

To finish the rear ball corner

To create a square surface, use the edges of the transition surfaces, the fillet surface, and a curve-on-surface. Once you have a new square surface, experiment with the various options of the Surfaces > Boundary Surfaces > Square tool to find the best possible CV distribution.