Make the selections shown in the image of the dialog box shown below.
©2002 Winston Mitchell
This is an experimental tutorial. As I have never been happy with the format of the soccer ball tutorial, I have been experimenting with other formats. This is an attempt at a tutorial using an HTML format. Comments, suggestions, and questions about this material are most welcome. Please post them on the TurboCAD User Forum.
Since HTML with graphics doesn't print well, you can download a PDF version (309KB) of this page.
The geometry of the serpentine path of a baseball seam is a good vehicle for demonstrating the TurboCAD's ability to model seemingly complex objects with precision. It also offers the opportunity to demonstrate how workplanes can be used efficiently and how to take advantage of the fact that points in 3D space can be projected on the 2D workplane.
First, the problem needs to be reduced to its essentials. What is known about the geometry? We know that it has a circumference of 9 1/8 inches, that the closest approach that the seam's center line makes to itself, as it winds around the ball, is an arc length of 1 3/16 inches, and that there are 108 stitches. Beyond that, we have to make some observations.
Although the shape of the seam's path is not specified, inspection reveals that the path is composed of four circular arc segments and that the points on the ball's surface where the arc segments are joined describe a square that lies on a plane that bisects the ball. The resulting hemispheres are identical except that one is rotated 90° with respect to the other. This is sufficient information to draw the seam's path.
The Selector and Inspector Bar have two modes: 2D only and 2D/3D. This exercise requires the 2D/3D mode be invoked. To get access to the switch that controls mode selection, the Select tool must be active (KBD: Spacebar). In addition, there must be at least one object in the drawing to enable the Select tool.
To ensure that you are in the 2D/3D mode, please do the following:
Your screen or the central portion of it should look approximately the same as the image that accompanies step 1.
1. Draw the arc that identifies a point that represents the seam's closest approach to itself.
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2. Draw the square that identifies the four points where the seam arcs connect to each other.
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3. Rotate the square to final position.
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4. Establish the WorkPlane for the first seam arc.
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5. Draw the first seam arc.
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6. Replicate the seam arc.
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7. Replicate the last two arcs.
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8. Rotate two arcs and join all seam arcs.
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9. Draw a small circle and extrude it along the seam.
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10. Draw the ball.
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11. Replicate sphere and extrusion.
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12. Finish seam.
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13. Finish Ball
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14. Final render.
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Variations on the Theme |
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| Readers of this tutorial my want to create a somewhat more realistic seam as shown here. This was done by revolving a profile and replicating it as in steps 6, 7, and 8. The holes in the seam and cover are subtractions of a pair of cylinders radial copied around one seam arc and then replicated. Also, the sphere was shelled and then filled with a slightly smaller one to produce the tan color at the bottom of the holes. |
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| Stitches can then be added in a manner similar to that used to make the holes. |  |
Separating the halves of the cover requires a little different methodology. Only one cover is drawn and then replicated.
Referring to the cover on the right, it was made with cones instead of arcs. The right half of the cover was made by subtracting two cones from a hemisphere and the left half was made by intersecting two cones with a sphere. The halves were then added.
Then, after adding the seam, the cover was shelled by subtracting a slightly scaled-down copy. The standard shelling operation does not seem to work on this object.
All that was left to do was drill the holes, replicate the result, and position the copy.
