Fusion Fillets: A deep-dive into how they work

The fillet command is one of the most used tools in 3D design software. It turns sharp edges into smooth, rounded ones. This makes parts look better and is safer, as it removes the sharp edges. Fusion offers many powerful options inside the fillet command. This guide will show you every option. You will learn how to create simple rounds and complex, flowing shapes. We will cover constant and variable fillets, tangency weight, corner types, and more.

How to Start a Basic Fillet

The fastest way to start a fillet is to pre-select an edge. Then, right-click. The fillet command will appear in the menu. You can also press F on your keyboard as a shortcut.

Once the command is open, you can drag the blue arrow. This gives you a visual preview of the fillet size. Start with a basic constant radius fillet. This gives the edge the same curve along its entire length.

For example, select an edge, start the command, and type 0.5. The edge will now have a smooth, rounded corner with a 0.5-inch radius.

Using Tangent Chain for Faster Selection

When you select one edge, you might see many edges highlight. This is because of the tangent chain option. It is turned on by default.

A tangent chain finds every connected edge that flows smoothly from your first pick, saving you time. You don't need to click every single edge.

You can turn this option off. Hold down the Ctrl key to select multiple edges one by one.

Matching an Existing Radius

A neat trick saves you from typing numbers. While dragging the blue arrow for a new fillet, hover your mouse over an existing rounded edge. A tooltip will say "Match Radius." Click on the original fillet. The new fillet will copy the same radius size.

Understanding Tangency Weight

The tangency weight controls the shape of the curve where the fillet meets the flat face. The default setting is 1. This creates a standard, smooth blend.

You can change this value from 0.1 to 2.

• Setting it to 2 makes the curve tighter. The fillet stays flat longer before curving sharply to meet the wall.

• Setting it to 0.1 makes the curve very shallow. It almost looks like a chamfer (a slanted cut).

Changing the tangency weight can give your parts a unique look. It is a simple way to customize a basic fillet.

Corner Types: Setback vs. Rolling Ball

When three fillets meet at a corner, Fusion handles them in two ways. You choose between Setback and Rolling Ball.

• Setback: This blends the rounded corners into the adjacent flat faces.

• Rolling Ball: This keeps a smooth, constant curve around the corner. Imagine a ball rolling along the flat faces of the edges. The ball's path is the shape of the fillet.

The Rolling Ball type maintains a perfect curve. You can easily switch between them to see which result you prefer.

Continuity Types: Tangent vs. Curvature

For a more advanced smooth look, you can change the continuity type. The two choices are Tangent and Curvature.

Both create a rounded edge. But they connect to the flat faces differently.

• Tangent (G1): This is the standard fillet. It creates a smooth join, but the transition can still be visible.

• Curvature (G2): This creates a much smoother, more gradual transition. It is less visible and creates a higher quality surface.

You can see the difference using the Zebra Stripe analysis tool under the Inspect menu. The black stripes will "connect" more evenly over a Curvature fillet.

Constant Radius vs. Chord Length Fillets

The Constant Radius fillet is the most common type. It makes a curve with the same radius value along the edge.

The Chord Length fillet is different. It keeps the straight-line distance across the curve the same. This is very useful on tapered or angled faces.

In some cases, a constant radius looks uneven. This happens on slanted surfaces. The fillet can look "bulgy" at one end.

Switching to Chord Length fixes this. It makes the fillet look even and professional on complex angles.

Creating Variable Fillets

A Variable Fillet lets you change the radius size along a single edge. To make one, select your edge and choose "Variable" as the type. A table will appear. You control the radius at the start and end points. You can also add control points along the edge. You can make the radius change size along the path, creating shapes that normally need a loft or sweep command. It is all done inside one fillet.

Here is a basic example of how the points work:

Point Location	Radius Value	Effect
Start (0%)	0.25 in	The fillet starts at this size.
Middle (50%)	0.75 in	It swells out to a larger curve in the middle.
End (100%)	0.1 in	It tapers back down to a small curve at the end.

You can drag the green midpoint dots to add points. Then, type in the exact radius you want at each spot.

Tips for Using Variable Fillets

1. You cannot select multiple edges for one variable fillet. You must make a new variable fillet for each edge.

2. Use the "Add Selection Set" button (+) inside the command. This lets you apply the same variable settings to another edge quickly.

3. A dropdown menu (three dots) remembers your last used numbers. This makes it fast to type the same start and end radii.

Using Asymmetric Fillets

The Asymmetric Fillet is a newer tool. When you select this type, two blue arrows appear. One arrow controls the "height" of the fillet. The other arrow controls the "depth."

You can pull one side much larger than the other. This creates a unique, flowing shape that is not symmetric.

The Power of Rule Fillets

Selecting many small edges is slow and tedious. The Rule Fillet solves this problem.

Instead of picking edges, you pick features or faces.

For example, you have a part with many small slots and cuts from one Extrude command. You want to round all those sharp edges.

• Start the fillet command.

• Change the type from "Fillet" to "Rule Fillet."

• Change the rule to "All Edges."

• Click on the Extrude feature in your timeline.

Fusion will automatically find every edge from that extrude feature. It will apply your chosen radius to all of them at once. This is a huge time-saver for complex parts.

You can also control exactly what gets rounded:

• Rounds & Fillets: Rounds over all convex and concave edges.

• Rounds Only: Only rounds over convex edges (outer corners).

• Fillets Only: Only rounds over concave edges (inner corners).

Creating Full Round Fillets

A Full Round Fillet is a special tool. It completely rounds over a face until it is tangent to two other faces.

Think of it as replacing a flat face with a perfectly curved one.

To use it, select "Full Round Fillet" as the type. Here's how you select the correct face:

1. Hover your mouse over the center face you want to round.

2. Slowly move your cursor. Two other faces will highlight in blue. These are the tangent faces the new curve will touch.

3. When the correct two tangent faces are blue, click your mouse.

The flat center face will become a full, smooth curve between the two side faces.

Why is this useful? If the part thickness changes, the fillet updates automatically. It always stays perfectly tangent. You don't need to recalculate any radius sizes.

Conclusion: Putting It All Together

The fillet command in Fusion is much more than a simple "round the edge" tool. It is a powerful suite for creating smooth, professional, and complex geometry.

Start with the basics. Master the constant radius fillet and the tangent chain. Use the match radius trick to work faster.

Then, explore the advanced options. Use variable fillets to add style to simple shapes. Apply chord length fillets to angled faces for a perfect finish. Try asymmetric fillets for unique designs.

For speed, use rule fillets on parts with many small features. This will save you a lot of clicking.

For smart, adaptive rounding, use full round fillets. They keep your model clean and update automatically.

Practice with these tools. Mix them together on a single part. You will find you can create complex, organic shapes starting from very simple 3D blocks.

The key is to experiment. Change a setting, see what happens. Use the visual previews. Soon, you will use the fillet command to make your designs look polished and ready for manufacturing.