Modeling Standard Wood and Sheet Goods in Fusion 360

1. The First Rule of Woodworking Design: Nominal vs. Actual

Before we even open Fusion 360, we need to cover the most critical concept when designing with wood: the dimensions you see on the label are not the dimensions you get. This is the difference between nominal and actual size.

• Nominal Size: This is the name of the lumber, like a "2x4". It refers to the rough-sawn size of the board before it's dried and smoothed.
• Actual Size: This is the final dimension of the board after it has been kiln-dried (which causes shrinkage) and planed smooth on all four sides (S4S - Surfaced Four Sides).

For example, a standard "2x4" in North America actually measures 1.5 inches x 3.5 inches. Modeling with the nominal size (2" x 4") will lead to significant errors in your final assembly. The same principle applies to plywood, where a "3/4 inch" sheet may be slightly thinner.

To understand this concept thoroughly, please read the following article. It provides the background on why this difference exists.

The image below provides a comprehensive reference chart for North American lumber sizes. This is a great resource to save for future projects.

Plywood also has a nominal vs. actual thickness. The image below provides a quick visual guide.

2. Modeling Standard Lumber and Sheet Goods

Now let's apply this in Fusion 360. The fundamental workflow for creating a piece of virtual lumber is:

1. Create a New Component for the piece of wood. This keeps your project organized.
2. Create a sketch of the board's cross-section using its actual dimensions.
3. Use the Extrude tool to give the board its length.

The following video from Dorset Design Build provides a clear, no-nonsense demonstration of this process for both dimensional lumber and a sheet of plywood.

This method is simple and effective. A key takeaway is the importance of using Components. As we move towards designing your desk, each piece of wood (each leg, the tabletop, each support beam) will be its own component, just like in a real-world assembly.

3. A More Robust Method: Using Parameters

While manually typing in dimensions works, a more powerful and flexible approach is to use Fusion 360's User Parameters. You can think of these as variables for your design.

Instead of typing "1.5in" every time you draw a 2x4's thickness, you can define a parameter named two_by_four_thickness and set its value to 1.5 inches. Then, you simply use the parameter name in your dimension fields.

Why is this better?

• Consistency: It guarantees you use the exact same dimension everywhere. No typos.
• Easy Updates: If you decide to switch from using 2x4s to 2x6s, you only need to change the parameter value in one place (two_by_four_width from 3.5in to 5.5in), and your entire model will update automatically. This is incredibly powerful for iterating on a design.

Given your background, the logic of using parameters should feel quite natural. Let's see how to set this up.

4. Your Turn: Model Your First Pieces of Stock

Let's combine these concepts into a practical exercise. You will create a couple of standard boards using a parametric approach.

Task (15 minutes):

1. Create a New Design in Fusion 360 and save it as "Wood Stock Practice".
2. Set Up User Parameters:
   • Go to Modify > Change Parameters.
   • Click the + next to User Parameters.
   • Create the following three parameters:
     • Name: ply_thick_3_4, Expression: 0.75 in
     • Name: lumber_2x4_w, Expression: 3.5 in
     • Name: lumber_2x4_t, Expression: 1.5 in
   • Click OK.
3. Model a 4-foot 2x4:
   • Create a New Component and name it 2x4 Board.
   • Create a sketch on an origin plane (e.g., the XY plane).
   • Draw a rectangle.
   • When adding dimensions, instead of typing numbers, type the parameter names: lumber_2x4_t for the thickness and lumber_2x4_w for the width.
   • Finish the sketch.
   • Extrude the profile to a length of 4 ft.
4. Model a Plywood Shelf:
   • Make sure you activate the top-level component in the Browser before creating a new component. This prevents nesting.
   • Create a New Component and name it Plywood Shelf.
   • Create a sketch on an origin plane.
   • Draw a rectangle with dimensions 2 ft by 4 ft.
   • Finish the sketch.
   • Extrude the profile. For the distance, enter the parameter name ply_thick_3_4.

You should now have a design with two separate components representing two standard pieces of wood, with their dimensions controlled by your user parameters. Try going back into the Parameters dialog and changing lumber_2x4_w to 5.5 in (the width of a 2x6) and watch your model update automatically.

Conclusion

Great work! You've just learned one of the most fundamental skills for designing real-world objects made from wood. This knowledge is the bedrock upon which we'll build your desk design.

Key Takeaways:

• Always design using actual dimensions, not nominal ones. A "2x4" is modeled as 1.5" x 3.5".
• Organize your designs by creating a new component for each individual piece of wood.
• Use User Parameters to define standard material dimensions. This makes your models robust, consistent, and easy to update.

Next Lesson Preview:
Now that we can create accurate virtual lumber, the next logical step is to join it together. In our next lesson, we will explore how to design and model common subtractive wood joints, starting with the butt joint, rabbet, and dado. This will be our first step into creating assemblies.