This is the third in a series of Tips and Tricks that will show you how to create and use 2D and 3D Splines. If you haven’t read the Drawing 2D Splines and Constraining Splines Tips and Tricks, you might want to read them before proceeding.

In this short exercise you will learn a general process for drawing splines that will increase the accuracy of your splines and assure that your splines are fully constrained.

Start the Sketch with Project Geometry.
The first step is to start the sketch with projected geometry.

If you’ve read my Tips and Tricks on Essential Templates, you can use the Fixed Point template. Otherwise follow these steps.

1. Open a new standard part file. 
2. Right click on the Center Point in the Browser and select Visibility.
   
3. Use the Project Geometry Command to project a node from the Center Point onto the sketch plane.
4. Right click on the Center Point in the Browser and deselect Visible.

Draw and Dimension Construction Lines.
The next step is to draw construction geometry that will control the shape of the spline.

1. Click the Construction Style icon on the Standard Toolbar.
2. Draw a line from the projected node vertically up about an inch. Be sure to use the green snap dot to constrain the beginning of the line to the node.
3. Draw a line from the vertical construction line horizontally to the right about one half of an inch. Make sure you don’t snap to the middle of the vertical line when you do this.
4. Draw a line from the vertical construction line horizontally to the left about one half of and inch. Be sure to use the green snap dot to snap to the end of the first horizontal line.
5. Use the Equal Constraint to make the horizontal lines equal to each other.
6. Add the dimensions shown in the image above.
7. Click the Construction Line Style icon to exit Construction Style mode.
8. Confirm that the sketch is fully constrained by clicking the Auto Dimension Command. The sketch should have zero constraints required.

Draw the Spline
Now that the construction lines are finished and fully constrained, you can draw the spline.

1. Select the Spline command from the 2D Sketch panel.
2. Click the nodes on the ends of the construction lines. Be sure to use the green snap dot to constrain the spline points to the nodes on the lines.
3. Type the escape key to exit Spline mode.

Why is this important?
Using construction lines before drawing the spline significantly increases your control over the shape of the spline. If you make sure that the construction lines are fully constrained before you draw the spline, the spline will be fully constrained and completely under control.