# SOLIDWORKS TECH TIP: Wave Washers Using Equation Driven Curves in 3D

*How model a Spring Washer using an Equation Driven 3D Curve*

If you’ve ever tried to model a Spring Washer (aka Wave Washer) and thought, “There has to be an easier way!” then here is a technique you might enjoy. SOLIDWORKS has the capability to create a 3D Sketch that is controlled by an equation, and with the proper inputs, you can use that sketch entity to model a wave washer similar to the images you see to the right.

The basic idea is a loft between two equation driven curves. To add some more detail to that, we start as a surface loft because we have open profiles, Thicken to make it a solid, then mirror to create the full shape.

The feature tree will look like this:

So let’s take a look at the equation we need to get the job done.

Start with a new part and create a 3D Sketch. Then go to **Tools**–> **Sketch Entities**–> **Equation Driven Curve**.

There are 5 basic lines needed, the values for X,Y,Z and the start and end values for the control variable (T).

Let’s start with the control variable. We only want to generate half of the geometry (if you try to go full circle, the equation doesn’t work) so we are going to set T1 to **0** and T2 to **pi**. Remember from Algebra class that a full circle is 2*Pi radians and we only want half a circle. If we set the X and Z values to be opposite trigonometric functions of one another and Y=0 we get an arc. So if X=Cos(t) and Z=Sin(t) and Y=0 you will get an arc.

So what size is it? well Cos(0)=1. That is a step in the right direction, but 1 what? Inches, millimeters, miles? It evaluates out to 1 of whatever units your model is set to. So in my case it is 1 inch and that is the radius of my washer. You can adjust the size simply by changing to 1.25*cos(t) to get an arc that is 1.25 inches.

Let’s now tweak the Y value to get the waves. In my example I used .09*cos(5*t). The .09 is half the height of my washer for a total height of .180 in the finished model. And the reason I used cos(5*t) is that I wanted 5 total peaks in the full circle. Once that is entered, you can close this sketch and create another one that will be almost identical, except the X and Z values will need to generate a different radius. In my model the inside radius is cos(0)=1 and the outside radius is 1.25*cos(t). So I have a .25 in wide wave. You can adjust those numbers to suit your application.

Once the two curves are complete, you can make a simple surface loft to create the wave. For those who have never worked with surfaces, you may not be aware that a surface has no thickness to it, it is just a face. So the **Thicken **feature will allow you to enter the material thickness. To finish the geometry, a simple mirror of the body will work. If you want to get even fancier, patterning of the body using **Move/Copy** and a **Linear Pattern** will get you the multi tier version shown above.

Enjoy!