Fillet and Chamfer

Overview#

Fillet rounds edges; Chamfer bevels them. Both remove sharp corners for strength, safety, appearance, and manufacturability. Sharp internal corners concentrate stress and cannot be machined with a round cutter; sharp external edges cut hands and chip.

Rules of thumb: add fillets late in the timeline (after the main shape is stable) because fillets add many faces and are the most common cause of broken downstream features when upstream geometry changes. Do not fillet inside sketches if a feature fillet will do the same job; sketch fillets are fine for 2D outlines you will extrude. (This is general modeling advice, not Autodesk guidance.)

Where to find it#

• Workspace: Design.
• Tab / panel: Solid tab > Modify > Fillet and Modify > Chamfer (Autodesk's help path is Design > Modify > Chamfer).
• Shortcut: F opens Fillet. Autodesk's Chamfer reference lists no shortcut.
• Quick alternative: Press Pull (Q) on an edge, which works as a fillet, but loses advanced options.

Step by step#

Fillet#

1. Press F.
2. Click edges, faces, or features. Selecting a face fillets all its edges. Tangent-continuous chains are picked with the edge when Tangent Chain is checked. Holding Ctrl (Windows) or Command (macOS) lets you modify the selection set after the preview appears.
3. Type a Radius or drag the arrow.
4. Pick the Type (Fillet, Rule Fillet, or Full Round Fillet) and, for each selection set, the Radius Type (Constant, Chord Length, Variable, or Asymmetric) and Continuity (Tangent G1 or Curvature G2). Add another selection set with the plus button for a different radius.
5. For variable radius, switch the Radius Type to Variable, then define a start point, an end point and any additional points between them, setting a Radius at each and a Position for the points between the start and end.
6. Choose Corner Type (Rolling Ball or Setback) where three fillets meet.
7. Click OK.

Chamfer#

1. Choose Modify > Chamfer.
2. Select edges (tangent chain optional).
3. Choose the Type: Equal Distance, Two Distance, or Distance And Angle.
4. Enter distances or angle, flip direction if needed.
5. Choose the Corner Type (Chamfer, Miter, or Blend) where chamfers meet, then OK.

Worked example: a rounded block#

1. Extrude a 50 x 30 x 20 mm block.
2. Press F, click the top face to select all four top edges, enter 4 mm. Add a second edge set for the four vertical edges at 6 mm.
3. Notice the corner. Change Corner Type from Rolling Ball to Setback and compare the vertices.

Options reference#

Tips and pitfalls#

Tip: Fillet large radii first, small radii last. Filleting 1 mm edges and then a 10 mm edge that includes them often fails.

Tip: Select the face to fillet the whole perimeter in one action. It stays robust when you add holes later because the selection is by face, not individual edges.

Warning: A fillet radius larger than the adjacent face allows will fail. Reduce the radius or fillet adjacent edges together as one edge set.

Warning: Filleting early and then editing sketches downstream can break the timeline. If a fillet breaks, drag it to the end of the timeline, or delete and recreate it.

• General guidance for plastic parts (not Autodesk data): inside corner radius at least 0.5 times wall thickness, outside corner radius inside radius plus wall thickness.
• A constant-radius fillet whose adjacent faces are not tangent along the entire edge may leave a cusp. Use variable or setback fillets.
• Chamfers are cheaper to machine than fillets on external edges.
• General 3D-print guidance: chamfer the bottom edge of a print (an elephant's-foot chamfer) to avoid first-layer squish, 0.4 to 0.8 mm.
• Fillet surfaces are tangent to neighbors; use Inspect > Zebra Analysis to check smoothness.
• To fillet an edge between a solid and a freshly joined body, join first, then fillet.
• Rule Fillet is a listed Fillet Type; use it when you want every edge matching a rule (for example Fillets Only on all inside corners) to update automatically.

Sizing fillets and chamfers with real numbers#

Pick sizes from manufacturing, not from what looks nice on screen. The table below is general manufacturing guidance, not Autodesk data; confirm against your shop's or supplier's rules.

The injection-molding outside radius works because a fillet of radius r on an inside corner has an offset curve of r + wall on the outside, keeping the wall uniform. Check this with Shell: shell a 40 mm box that has 3 mm outside fillets and a 2 mm wall, and the inside corner comes out at 1 mm automatically.

Chord length versus radius#

Chord Length measures the straight distance between the two tangent lines where the fillet meets the faces. On a 90 degree edge, chord c relates to radius r by c = r x sqrt(2). A 4 mm radius therefore equals a 5.66 mm chord, and a 10 mm chord equals a 7.07 mm radius. On non-90 degree edges the relationship changes, so chord length is handy when a drawing specifies the visible width but not the radius.

Variable radius example#

On a 100 mm long edge:

1. Select the edge, set Radius Type to Variable.
2. Set the start radius to 2 mm and the end radius to 8 mm.
3. Add an intermediate point at Position 50 percent with a radius of 3 mm.

The fillet stays tight for the first half and flares near the end, as on a handle grip. As a general rule of thumb, avoid very large jumps between neighboring radius values or the surface may pinch.

Chamfer numbers#

Equal Distance on a 90 degree edge at 1 mm gives a face 1.41 mm wide at 45 degrees. Two Distance with 2 mm on the top face and 1 mm on the side gives a shallower bevel: the angle from the top face is atan(1/2) = 26.6 degrees. Distance And Angle with 3 mm and 20 degrees is the quickest way to model a lead-in on a shaft or pin so it centers into a bore. Per Autodesk's reference, for Two Distance the first value you enter applies to both sides and any later adjustment changes only the side you modify, so set both values deliberately.

Corner treatment#

Where fillets meet at a vertex, Rolling Ball combines the rounded edges at the corner, while Setback blends the rounded corners into the adjacent faces; compare the previews when radii differ. For chamfers, Miter merges the beveled edges into a mitered corner point, Chamfer creates a chamfer joining the beveled edges, and Blend blends them into the adjacent faces.

Failure modes and fixes#

Tip: Fillet in this order: structural large radii, then medium, then small cosmetic edges, then chamfers on the free edges. Name the features "Fillet Structural" and "Fillet Cosmetic" so you can roll back to the half-finished state.

Practice exercise#

Create a molded enclosure base and a machined bracket, calculate each radius, and then provoke the errors.

1. Extrude a 80 x 50 x 30 mm block and shell it inward with 2 mm walls, open on top.
2. Fillet the four vertical outside edges at 3 mm before shelling (undo and redo in this order to see the difference). After shelling, measure an inside vertical corner with Inspect > Measure; you should get 1 mm.
3. Add a Fillet with three selection sets, each with its own radius: the floor edges 1 mm, the vertical inside corners 1 mm, and the outside bottom edges 1.5 mm.
4. Using Chord Length, fillet the top rim edge so the visible width is 1.41 mm; confirm this is a 1 mm radius.
5. Variable radius: on a separate 100 mm edge, create 2 mm at the start, 8 mm at the end and 3 mm at 50 percent.
6. Chamfer the bottom outside edges with Distance And Angle: 0.6 mm at 45 degrees, for the first-layer squish. Chamfer a 10 mm pin tip using 2 mm and 20 degrees.
7. Break it: try a 5 mm fillet on the top rim of a wall that is only 2 mm wide, record the error, then fix it by reducing the radius to 0.9 mm.

Expected result: a shelled base whose inside corner radius you confirmed numerically, a variable fillet, two chamfers with different parameters, and an error you diagnosed and fixed.

Related#

• Shell, Draft, and Scale
• Press Pull and direct modeling
• Hole and Thread (chamfered hole entries)
• Extrude (sketch fillets vs. feature fillets)