In Part I of this series, we looked at how the smoothness of curves can be analyzed and controlled. Now we’ll be taking a look at some additional analyses tools to further evaluate our surfaces as well as ways to improve our curvature continuous connections.

The **zebra stripes** tool (**view>display>zebra stripes**) allows us to see small changes on a surface that may be hard to see with a standard display. This tool mimics the reflection of long stripes of light on a very shiny surface. With zebra stripes, we can verify that two adjacent faces are in contact, are tangent, or have continuous curvature. As can be seen in the image below, the zebra stripes for contact do not have the same direction or size. The zebra stripes for tangent have the same direction, but change sizes where the tangency occurs – there are two points of tangency. And the curvature continuous stripes share the same direction and the same size throughout the entire surface.

We can even use our **curvature** display tool to further analyze our surface. The curvature display tool (**view>display>curvature**) displays the local radius of curvature in different colors based off of the curvature value. Surfaces with the least amount of curvature are displayed in black and the colors change through blue, green, and red as the curvature values increase (red indicating surfaces with the most curvature).

There are different ways to optimize curvature continuous connections between splines. One way is by using the **equal curvature** sketch relationship. This matches the radius of curvature and the direction between two splines, ultimately creating a smoother transition between the two entities.

Another way to create a smoother transition between entities is by using the **curvature control** tool (**right click a spline>add curvature control**). The **curvature control** tool allows us to control the radius of curvature at a certain point on our spline. More importantly, it allows us to select an additional option which enables us to have a smoother transition between the entities. This option is called **raised degree** and is available in the property manager of the curvature control tool after it is placed on the spline. By selecting the **raised degree** option, SOLIDWORKS mathematically makes the spline smoother by adding additional control points. This option is automatically applied to splines that have equal curvature relations on both ends of the spline. As seen in the image below, the curvature combs have a smoother transition when the raised degree option is enabled versus not.

By utilizing all of these tools we can ensure that our surfaces will be as smooth as possible. If you want additional information on splines, specifically **style splines**, read the following articles: The Style Spline in SOLIDWORKS – Part 1, The Style Spline in SOLIDWORKS – Part 2 & The Style Spline in SOLIDWORKS – Part 3.

For more information, request a SOLIDWORKS 3D CAD quote or contact us at Hawk Ridge Systems today. Thanks for reading!

]]>The quality of a great surface lies within the curve that defines it. These curves are ideally created and controlled through splines. The **spline** sketch tool creates a smooth curve through the position of control vertices, or CV’s. Controlling the quality of our splines will ultimately control the quality of our surfaces. Splines can be analyzed using the **curvature combs** tool. The curvature combs tool graphically shows the amount of curvature at a given point on a sketch element. A smooth curvature comb is desired to produce the smoothest surface. As shown below, both splines look the same until we look at their curvature combs. The spline with the smoothest curvature combs (i.e. no flat spots or dips exist) will produce the smoothest surface.

To create smooth curvature combs, splines should be created with the least amount of points possible. Just as seen above, both of these splines are identical. The difference in curvature combs is due to the fact that the spline on the left was made with just 2 points, whereas the spline on the right was made with 5.

If multiple points are required, then the spline should be modified by using the **control polygon** tool as opposed to the spline handles. This can be activated by right clicking on your spline and clicking on **Display Control Polygon.** The control polygon will allow the spline to be manipulated while keeping the curvature combs as smooth as possible.

An even better method for creating a spline with multiple points is by using the **style spline** tool. This spline tool creates a spline by drawing its control polygon and using that control polygon to control the shape of the spline. This allows for smoother **curvature combs** since we’re using the control polygon instead of the spline handles. As stated above, controlling a spline through its control polygon allows for smoother control of the curvature combs which ultimately will create a smooth surface.

Curvature can be mathematically defined as the inverse of the radius (i.e. k=1/r where k is the curvature). There are three different degrees of curvature that we are concerned with in SOLIDWORKS. Curvature is defined as the The first degree is called **contact** (or C0 continuity) and is when two entities meet. These entities will ultimately create an edge, so there is no smoothness on the surface created by them. At the sketch level, this means the curvature combs will not touch or have a smooth transition between each other.

The second degree is called **tangent** (or C1 continuity) and is when two entities touch, and the angle of both curves are equal. This would be a situation where a tangent sketch relationship is created between two entities. Although this provides a smooth surface, the transition would be noticeable as seen in the image below. This situation would be acceptable for most applications, but is not aesthetically pleasing.

The third degree is called **curvature continuous** (or C2 continuity) which is when the two entities have the same curvature amongst each other. The radius of their curvature combs is equal as well as their angle. This type of curvature would provide the smoothest type of surface in SOLIDWORKS.

Part 2 of this series will further discuss how to further analyze surfaces and can be found. For more information, check out our YouTube channel, get a SOLIDWORKS 3D CAD quote or contact us at Hawk Ridge Systems today. Thanks for reading!

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