AutoCAD 2002 Bible

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Figure 23-29: Two extruded surfaces created using TABSURF


For the I-beam, you could have simply given the 2D polyline profile a thickness and achieved a similar result. However, the extruded surface on the left could only have been created with TABSURF because the extrusion is not perpendicular to the XY plane that contains the 2D polyline profile. TABSURF can extrude a shape in any direction.


When you select the vector object, your pick point determines the direction of the extrusion. AutoCAD starts the extrusion from the end of the vector closest to the pick point.


You use SURFTAB1 to control the number of lines AutoCAD uses to display the curve. If the curve is made up of polyline segments, AutoCAD displays one line at each segment vertex.


Note the I-beam in Figure 23-29. If you create an object by mirroring, stretching, and so on, you will see extra tabulation lines at the separate segments in the polyline definition. If you want a clean look, you need to draw clean. You might need to use the original shape as a guide to draw a new polyline on top of the old one, and then erase the original.


You should use a nonplanar view when using TABSURF to check that you have accurately defined the extrusion vector into the third dimension. Any of the preset isometric views will be helpful.


To draw an extruded surface, follow these steps:


1.    Draw the object to extrude — a line, arc, circle, polyline, ellipse, or elliptical arc. This is the path curve.

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