# SolidWorks Tutorials – Part 2 – What is Parametric Modeling?

Welcome to the second of our **SolidWorks tutorials** for beginners. Part 2 of this **SolidWorks Tutorials** series is about parametric modeling. If you are new to CAD software, you may be wondering what the heck parametric modeling means, and why it is so important. The answer to this question can be understood by asking another basic question: what is SolidWorks, and what does it do? Our SolidWorks tutorials at www.video-tutorials.net teach you all about this.

SolidWorks is a 3D mechanical CAD software system. CAD stands for computer-aided design. Technically “SolidWorks is a parasolid-based solid modeler that uses a parametric, features-based approach to create solid models and assemblies.” So you’ve read this stuff in the SolidWorks tutorials blurbs, and what on earth is all that supposed to mean?

Parametric modeling refers to the use of parameters in fixing the model and its geometry in space and size. What are the parameters used to do this?

1) First, there are relations. These are the relationships between geometric elements of your work. A line that is parallel or perpendicular or equal to another line; a circle whose center is concentric with an arc, a rectangle with a vertex at the midpoint of one side of a cube. These are examples of the relationships you insert into the geometry while you’re sketching. That is, you define these relationships before you start working in the three dimensional part modeling environment. In SolidWorks, such relationships are called relations. In CATIA and Inventor, they are called constraints. The relations determine the shape of your geometry. In our SolidWorks tutorials, we cover this theory in our Essentials course.

2) The second type of parameter SolidWorks uses are dimensions. Dimensions are how you define the size of your geometry. The length of a line, the radius of a fillet, the length or angle of a chamfer: these are examples of dimensions.

When your modeling is parametric with both relations and dimensions, it makes your design and engineering work much more precise and thus suitable for manufacturing. The manufacturing process result in fewer errors when the source engineering data is modeled by parametric software.

There’s something else very cool about parametric modeling: the bidirectional associativity principle. When you update one parameter of your work, all the entities connected to it will update automatically, so that you don’t need to update anything manually. This saves a lot of time, and prevents a lot of errors. So, if you want to change the length of one side of a plate in your assembly, you just change the length in the source sketch, and the part as well as the assembly update automatically.

Below I’ve got pictured a plate in the SolidWorks graphic area. It’s 100 mm x 200 mm, and 10mm in height. There is a hole with diameter 50mm in the center of the plate:

**Fig 01 – 100 x 200 mm plate in SolidWorks, with 50mm diameter hole**

The source geometry for this model is controlled by parameters. There are dimensions that define the diameter of the hole, and the length, width and height of the plate. Then, there is a relation that positions the hole at the center of the plate. This means that even if the plate changes in size, in either length or width or both, the hole remains at the center of the plate.

When I double click on my plate, I can see the dimensions. When I left-click on one of the dimensions, I open the property manager for that dimension, and an editing box appears. I can change the value of the dimension right here, as shown in the image below:

**Fig 02 – Modifying a dimension on my model**

I click the green checkmark to accept the new dimension. Then I click the traffic light symbol to update the model. So how does the circle stay at the center of the plate?

Well, when I was drawing the rectangle, I also drew what is called a construction line. (A construction line is geometry that is not used when calculating a model; that’s why you don’t see it in the model). Construction lines are very helpful when sketching your designs; they help you position your geometry more accurately. This construction line was diagonal, from a top corner to a bottom corner of the rectangle. Then, I placed the center of the circle at the midpoint of this diagonal line, as shown below:

**Fig 03 – A diagonal construction line was used to constrain the hole to the center of the plate.**

This functionality that I’ve just demonstrated here, regarding both dimensions and constraints, is at the heart of parametric modeling. This concludes our introduction to parametric modeling, the second part of our SolidWorks Tutorials for Beginners series at our www.video-tutorials.net blog.