CAD

Using Reference Sketches to Create Advanced Geometry (Alibre Design Tips)

25 Jul, 2008 By: Ryan Montgomery

Control features used to create advanced geometry with reference sketches.


Editor's note: This tutorial courtesy of Alibre.

In today's tech tip we will use reference sketches to control features that are used to create advanced geometry like sweeps and lofts. We will demonstrate this practice by creating a wave spring.

We will start by creating our reference sketches. Open a new part and create a sketch on the xy plane. In this sketch, draw a circle with its center point on the origin. Use the Dimension tool to set the radius of the circle. The radius of your circle will ultimately represent the inner radius of your spring.

figure
Sketch a circle.

Using the Line tool, break your circle down into pie shapes. Draw one line on the x axis, one on the y axis, and two diagonally. Use figure 1 as reference for your sketch. When you finish the sketch, add a point that you will use later in the design process. Go to Sketch / Insert / Point and select one of the nodes that connects a line segment with your circle on the x axis. Hit OK.

Once you have your sketch completed, use the selection tool to drag a box around all of the items in your sketch. With all of the items highlighted, hit Ctrl + V or Edit / Copy. Exit your sketch.

Now create a new plane offset from your original plane. Go to Insert / New Plane, select the xy plane, and set your offset. This offset will represent the pitch of the waves in your spring. On this new plane, create a new sketch. In this new sketch, hit Ctrl + V or Edit / Paste. Exit sketch mode.

figure
Your reference sketches are complete.

With the reference sketches completed, we can create the actual sketches for our sweep. We will start with the profile sketch. Create a new 2D sketch on the x axis and draw a rectangle in this sketch. Use a coincident constraint to attach the inner side (the edge closest to the origin) of your rectangle to the point that we created earlier. Exit Sketch mode.

Now create your guide path. Create a new 3D sketch. In this scenario, it does not matter which plane you create your 3D sketch on, because all of our spline nodes will be attached to existing nodes/points. Start your 3D spline on the point that we created in sketch 1. Place your second spline node on the intersection of the diagonal line segment and the circle in sketch 2. Repeat this process, placing nodes around the circles in the reference sketches. Each time you place a new node, alternate between snapping it to sketch 1 and sketch 2. The guide path will be completed when you place your final spline node on the starting point, thus completing the circle. Exit your 3D sketch and create a sweep using the two sketches we just created. This completes the wave coil for our spring.

figure
Create a sweep.

Once your coil is complete, you can use the assembly module to create your spring. Create a new assembly and insert as many copies of your coil as you would like in the design. In your design explorer, right-click and select Show Reference Geometry on each of your coils. You can then use the reference geometry to constrain the coils together. Apply alignments between the z axis of your assembly and the z axis of each coil. This will center the coils. You can use mates and aligns along with the two sketch planes to stack each of the coils on top of each other. Use angle constraints with 45-degree offsets on the zx and zy planes to offset the rotation of each coil.

figure
The complete wave spring.


About the Author: Ryan Montgomery


AutoCAD Tips!

Lynn Allen

Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!
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