Creating Complex Primitives AutoCad Help

As you learned earlier, you can convert a polyline into a solid using the Extrude option on the Solids toolbar. This process lets you create more complex primitives. In addition to the simple straight extrusion you’ve already tried, you can also extrude shapes into curved paths, or you can taper an extrusion.

Tapering an Extrusion

Next, you’ll take a look at how you can taper an extrusion to create a fairly complex solid with little effort.

  1. Draw a 3 x 3 closed polyline at the top of the current solid. Start at the backleft comer of the bracket at coordinate 3.5,3,1, and then draw the 3 x 3 closed polyline to fit in the top of the composite solid, as shown in Figure 18.16.
  2. Click the Fillet tool on the Modifytoolbar. At the Select first object or [Polyline/Radius/Trim] : prompt; type R to set the radius of the fillet.
  3. At the prompt for the fillet radius, type .5..
  4. At the command prompt, press,r to again issue the Fillet command, and then type p to tell the Fillet command that you want to chamfer a polyline.
  5. Click the polyline. The comers become rounded.
  6. Click the Extrude button on the Solids toolbar, or enter Ext.J at the command prompt.
  7. At the Select objects: prompt, pick the polyline you just drew and press button (As the prompt indicates, you can pick polylines or circles.)
  8. At the Specify height of extrusion or [Path]: prompt, enter 3.
  9. At the Specify angle of taper for extrusion <0>: prompt, enter 4 for 4° of taper. The extruded polyline looks like Figure 18.17.
  10. Now join the part you just created with the original solid. Choose Modify > BooIean > Union, and then select the extruded part and the rectangular solid just below it.
FIGURE 18.16

FIGURE 18.16

Extruding on a Curved Path

As demonstrated in the following execise, the Extrude command lets you extrude virtually any polyline shape along a path that is defined by a polyline, arc, or 3D polyline. .

  1. Choose View > Zoom > Extents and turn off the grid.
  2. Choose View > Hide. This helps you view and select parts of your model in the following steps.
  3. Start by placing the UCS on a vertical plane perpendicular to the back of the bracket. Choose Tools> Orthographic ues > Left.
  4. Start a polyline at the point shown in the top image of Figure 18.18. Use the Midpoint Osnap to make sure you select the midpoint of the vertical corner edge. After you locate the first point, enter the following coordinates:
    02<180
    01<270
    02<180
    When you are done, your drawing should look like the bottom image of Figure 18.18.
  5. Click the Fillet tool on the Modify toolbar, and then type R to set the fillet radius.
  6. Enter 4 for the fillet radius.
  7. Press button to reissue the Fillet command, and then type P to select the Polyline option.
  8. Click the polyline you drew on the backside of the solid.
  9. Choose Tools > New UCS > Y,and then enter 90. This rotates the UCS 90 degrees around the y-axis so the UCS is perpendicular to the front face of the solid.
  10. Draw a circle with a O.35-unit radius at the location shown in the second image of Figure 18.18.

At this point, you’ve created the components needed to do the extrusion, Next, you’ll finish the extruded shape. .

  1. Click the Extrude button on the Solids toolbar, click the circle, and then press button.
  2. At the Specify height of extrusion or [Path]: prompt, type P to enter the Path option.
  3. At the Select extrusion path: prompt, click the polyline curve. AutoCAD pauses a moment and then generate a solid “tube” that follows the path. The tube may not look like a tube because AutoCAD draws extruded solids such as this with a single line showing its profile.
  4. Click the Subtract tool on the Solids Editing toolbar or choose Modify > Solid Editing > Subtract, and then select the rectangular solid.
  5. Press button At the Select objects: prompt, click the curved solid and press button. The curved solid is.subtracted from the square solid. Your drawing will. look like Figure 18.19.

In this exercise, you used a curved polyline for the extrusion path, but you can use any type of 2D or 3D polyline, as well as lines and arcs, for an extrusion path.

Revolving a Polyline

When your goal is to draw an object that is circular, the Revolve command on the Solids toolbar is designed to let you create a solid that is revolved, or swept in a circular path. Think of Revolve’s action as similar to a lathe that lets you carve a shape from a spinning shaft. In this case, the spinning shaft is a polyline, and rather . than carving it, you define the profile and then revolve the profile around an axis.

In the following exercise, you will draw a solid that will form a slot in the tapered solid.

  1. Zoom in to the top of the tapered box, so you have a view similar to Figure 18.20.
  2. Turn the Snap mode off.
  3. Return to the WCS by choosing Tools > New UCS  > World.
  4. Next, choose Tools > New UCS  > Origin.
  5. At the Origin: prompt, use the Midpoint Osnap override and pick the midpoint of the top surface, as shown in Figure 18.20.FIGURE 18.20 
  6. Set the Snap distance to 0.25 and turn on Polar Tracking.
  7. Draw a polyline using Polar Tracking with the following polar coordinates:
    Start at -0.25,0
    0.75<90
    0.75<0
    0.70″71<:315
    0.5<0
    0.7071<45
    0.75<0
    0.75<270
  8. When you’ve finished, type C to close the polyline. AutoCAD will not revolve an open polyline. Your drawing should look like Figure 18.21.
  9. Click the Revolve tool on the Solids toolbar, or type Rev.J at the command prompt.
  • At the Select objects: prompt, pick the polyline you just drew and press button.
  • When you see the next prompt:
    Axis of revolution – Object/X/t/<Start point of axis>:
    use the Endpoint Osnap override and pick the beginning endpoint of the polyline you just drew.
  • Turn on the Ortho mode (press F8) and turn off the Snap mode (press F9) . Then pick a point to the far left of the screen so that the rubber-banding line is parallel with the x-axis of the current UCS.
  • At the Angle of revolution <full circle>: prompt, press button to sweep the polyline a full 360″.The revolved form appears, as shown in Figure 18.22.

 

You have just created a revolved solid that will be subtracted. from the tapered box to form a slot in the bracket. But before you subtract it. you need to make a slight change in the orientation of the revolved solid.

  1. Choose Modify > 3D Operation > Rotate 3D.
  2. At the Select objects: prompt, select the revolved solid and press button
  3. At the prompt
    Axis by Entity/Last/View/Xaxis/yaxis/Zaxis/<2point>
    use the Midpoint, Osnap and click the right-side edge of the top surface, as shown in Figure 18.23.
  • At the 2nd point on axis: prompt, use the Midpoint Osnap again and click the opposite side of the top surface, as shown in Figure 18.23.
  • At the <Rotation angle>/Reference: prompt, type 5 button. The solid rotates 5°.
  • Click the Subtract tool on the Solids Editing toolbar or choose Modify > Solids Editing > Subtract, click the tapered box, and then press button
  • At the Select objects: prompt, click the revolved solid and press button Your drawing looks like Figure 18.24.

Posted on November 9, 2015 in Mastering 3D Solids

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