Loft

A loft is a blend or transition solid or surface that connects two or more cross sections. The cross sections, also called profiles, can be the same or different shapes. See Figure 24-1. The cross sections can also be projected along a path.

The most common drawing objects that can be used for the cross sections are 2D and 3D splines, 2D polylines, 2D solids, arcs, circles, ellipses, elliptical arcs, and lines. For a complete list, see the AutoCAD Help files.

The path must be a single open or closed object. The most common objects that can be used for the path are 2D and 3D splines, 2D and 3D polylines, helices, arcs, circles, ellipses, elliptical arcs, and lines. See AutoCAD’s Help.

 AutoCAD Command: LOFT

The LOFT command is used to create a solid or surface by blending two or more cross sections with the same or different shapes.

Shortcut: none

WORK ALONG: Using the LOFT Command

Step 1

Using the NEW command, start a new drawing using template: 3D Layout English.

Step 2

Save and name the drawing: AutoCAD 3D Workalong 24-1.

Step 3

Set the current visual style to 3D Wireframe, the current layer to Profile, the current view to SE Isometric, and the current UCS to Right.

Step 4

Using Figure Step 4A as a reference, draw a 12 × 12 inch closed pline. Start the bottom left corner at 0,0,0 as shown in the figure. (Figure Step 4A and 4B)

Step 5

Using the Properties window, ensure that the square is a closed pline.

Step 6

Copy the closed pline 6 inches in the positive Z direction. (Figure Step 6)

Step 7

Draw a 6 inch diameter circle exactly in the centre of the copied square. (Figure Step 7)

Step 8

Move the circle 8 inches in the positive Z direction. (Figure Step 8)

Step 9

Change the current UCS to Front and the set layer: Path as the current layer.

Step 10

Draw a pline 36 inches in the positive X direction and then 24 inches in the negative Y direction. Start it at the centre of the circle. (Figure Step 10)

Step 11

Fillet the pline with a radius of 12 inches. (Figure Step 11)

Step 12

Change the current UCS to Top and the set layer: Profile as current layer.

Step 13

Draw a 6 diameter circle locating its centre at the bottom end of the pline that you just drew. (Figure Step 13)

Step 14

After drawing the necessary construction lines, draw a 3 x 8 closed rectangular pline with its centre located at the end of the pline. (Figure Step 14A and 14B)

Step 15

Move the rectangular pline 10 inches in the negative Z direction. (Figure Step 15)

Step 16

Set the current view to SE Isometric. (Figure Step 16)

Step 17

Ensure that the system variable DELOBJ is set to 0.

Step 18

Set the current layer to Solid 4 and the system variable ISOLINES to 4.

Step 19

Enter the LOFT command, as shown below, and select the two squares for the cross sections. (Figure Step 19)

Command: LOFT

Current wire frame density: ISOLINES=4, Closed profiles creation mode = Solid

Select cross sections in lofting order or [POint/Join multiple edges/MOde]: 1 found

Select cross sections in lofting order or [POint/Join multiple edges/MOde]: 1 found, 2 total

Select cross sections in lofting order or [POint/Join multiple edges/MOde]: 2 cross sections selected

Enter an option [Guides/Path/Cross sections only/Settings] <Cross sections only>:

(Press Enter)

Command:

Step 20

Turn off layer: Solid Off. Change the layer of the solid that you just created in Step 18 to layer: Solid Off. (Figure Step 20)

Step 21

Using the LOFT command, create a loft selecting the square and circle as the cross sections. (Figure Step 21)

Step 22

Change the layer of the solid that you just created in the loft to layer: Solid Off.

Step 23

Enter the LOFT command, as shown below, to draw a loft between two cross sections that follow a path. Select the two circles for the cross sections, and the pline as the path. (Figure Step 23A and 23B)

Command: LOFT

Current wire frame density: ISOLINES=4, Closed profiles creation mode = Solid

Select cross sections in lofting order or [Point/Join multiple edges/MOde]: 1 found

Select cross sections in lofting order or [POint/Join multiple edges/MOde]: 1 found,2 total

Select cross sections in lofting order or [POint/Join multiple edges/MOde]: 2 cross sections selected

Enter an option [Guides/Path/Cross sections only/Settings] <Cross sections only>: P

Select path profile: 1 found

(Select the pline.)

Command:

Step 24

Using what you already learned in the workalong, change the layer of the solid created in Step 23 to layer: Solid off. Create a solid using the loft command between the circle and the rectangle. (Figure Step 24)

Step 25

Turn off layers: Profile and Path.

Step 26

Change the layer of all solids, that are on layer: Solid Off, to layer: Solid 4.

Step 27

Using the UNION command, union all solids to form a single solid. (Figure Step 27)

Step 28

Save and close the drawing.

Key Principles

Lab Exercise 24-1

Time allowed: 60 minutes.

Step 1

On layer: Solid 3, draw a solid model of the object shown in the figure by drawing cross sections and then using the LOFT command. (Figure Step 1)

Step 2

Draw the cross sections on layer: Profile.

Step 3

Union the solids to create one single solid model. (Figure Step 3)

Step 4

Save and close the drawing.

Lab Exercise 24-2

Time allowed: 60 minutes.

Step 1

On layer: Solid 2, draw a solid model of the object shown in the figure by drawing cross sections and then using the LOFT command. (Figure Step 1)

Step 2

Draw the cross sections on layer: Profile.

Step 3

Draw the text on layer: Text after you create the solid. Use the font: Tohoma. Select the height of your choice.

Step 4

Union the solids together to create one single solid model. (Figure Step 4)

Step 5

Save and close the drawing.