You can use 3D splines to draw the path for 3D sweeps, but if you’ve ever tried to do this you may have found that it’s difficult to make the profile perpendicular to the path. This short exercise will show you how to do this.

Quick 3D Command Review
You’ll use both the Line and Spline command in this exercise, so you’ll need to know how to use the commands. When you use either of these commands the 3D coordinate triad appears.

Click a point to start drawing a line or spline, and then click one of the planes on the triad. This will allow you to select locations for points on the line or spline within a 2D plane. You can also use the Default Work Plane and the Look At command to set the view to a planar view. When you’re finished selecting the points, right click and select continue to finish drawing the line or spline.

Start by Drawing 2D Geometry.
Before you enter 3D Sketch mode, draw the profile in a 2D sketch plane, and then draw a line perpendicular to the profile in a second 2D sketch.

The circular profile in this image was drawn in the first sketch plane, which is on the X-Y plane. The second sketch plane was created on the Y-Z Default Work Plane. The node in the center of the circle was projected to the second plane for referenced geometry for the line.

Create a 3D Sketch.

If the 2D sketch plane is still active, click the Return button to exit it. Once you’ve exited the 2D sketch plane, click the down arrow on the Sketch button, and then select 3D sketch.

Draw the 3D Path for the Sweep.
Draw the path for the sweep using either the Line command or the Spline command. Since the procedure for using the Spline command is more complicated, we’ll use the Spline command in this exercise.

Start by using the Include Geometry command to project the line from the 2D sketch onto the 3D Sketch. This line will be used to assure that the path is perpendicular to the profile.

The next step is to draw the spline. Click the Spline command, and then select the node on the end of the line.

Select the Y-Z plane on the triad, which is the plane adjacent to the blue and green axes. This will cause the grid to display, and you will be able to select point locations on the Y-Z plane. You might also want to change the view to a planar view by clicking the Look At command, and then select the Y-Z Default Work Plane in the browser.

Draw the spline by selecting three points along a straight line that's collinear with the line projected from the 2D sketch. This will create three relatively straight spline segments that extend from the end of the projected line.

Once you’ve selected 3 points on the line you can use the Rotate command to rotate the triad so that you can select another plane and draw other points. Try to make the next points you draw as far apart as possible because Inventor may issue a self-intersecting error when you try to perform the sweep operation if the points are too close together. Usually this happens when the spline makes a sharp turn.

When you finish adding points, right click and select Continue to stop drawing the spline, and then type the escape key to exit spline mode.

The last step is to add a tangent constraint to the projected line and the spline. When you do this, you will see the spline straighten up on the end near the projected line.

You can also see in this image why you have to add three points to the spline before you add the rest of the points. The three points help to keep the spline straight enough for you to successfully add the tangent constraint with the right orientation. When the points aren't present, the tangent constraint can create a hook shaped arc connecting the lines. The hook can be very small, so if you want to test this concept you may have to zoom into the end of the spline to see it.

Perform the Sweep Operation.
Now you’re ready to perform the sweep operation. The profile should already be selected for you, and all you’ll have to do is select the path and click OK.

The thickness of the sweep should be constant along the length of the sweep because the profile is perpendicular to the path.

Why is this Important?
When the profile of a sweep operation is not perpendicular to the path, the thickness and contour of the sweep can change along the path. This can make your sweeps look strange, especially if the sweep is supposed to be uniform along the path. For example, electrical wires in an assembly can be constructed by using the method described above.