Home » How to fully define a spline in SolidWorks?

A SPLINE is a curve that is a combination of points that may or may not be collinear. In SolidWorks, we have two types of Spline: B-spline and style spline. B-spline is used to is preferred while making complex curves whereas style spline is used in the case which requires a smooth continuous curve. We also have another option in the Spline: “equation driven spline” i.e., based on any given mathematical equation.


Style Spline

This article will focus on using B spline and style spline. The objective of the article is to tell you how to fully define these two splines.

First, we need to locate the spline button on the sketch command manager. Once we go into the sketch window in the top left corner on the command manager we will find the spline option.


 To make a B-spline we need to take the cursor on the spline drop down and then choose the first option.

Once we click on the spline option we need to start making spline from the origin. Once we move our cursor from the starting point we will get a straight line but as soon as we click twice beyond the 2nd point we get to start getting a curvature.



In figure (a) we have a 2-point spline whereas in (b) we have a 4-point spline.  The blue color denotes under defined nature of the spline. To fully define a spline, we need to define the points of the spline. We need to press the escape key to come out of the editing spline window.

Below is a figure of an underdefined spline made up of 5 points. To fully define we shall follow the following steps.

  1. Define the endpoints first using smart dimensions. Fix its vertical and horizontal distance.
  2. Repeat the same process for the rest of the points by adjusting their position.
  3. When each point turns black the curve automatically becomes black thus indicating a fully defined Spline.

*The rightmost point is black thus indicating its fully defined.

*Note: You can edit the positions of the points using the tangents of the curve. We can also use a control polygon. The above-mentioned is a basic process to define a spline.


The position of the spline can also be adjusted using the tangent arrow.

*** A shortcut to fully define a spline is to right-click on the spline and choose the option of “fully define sketch”.  This is a shortcut to fully define the whole sketch but many times shows errors.


Style Spline:

Click on the 2nd option of the spline named “style spline”

On the left, in the insert spline window, we shall see 4 options.

Since we shall be dealing with the Bezier curve we shall choose the same.

The lines confine the curve in the style spline.

The steps followed to fully define the style spline are as follows.

  1. Define the line passing through the origin first.
  2. Now give a relation between each construction line.
  3. Use the smart dimension tool and give the desired dimension to the lines.
  4. When all the line turns black the spline will automatically become black i.e., fully defined.

Underdefined spline

The centerline is defined with respect to the origin.

Origin is the reference for defining the lines.

The above-shown figure shows us the relations existing in the sketch.