Fillet vs Chamfer: How to Add Them and When to Use Each

Two of the most common finishing operations in CAD are the fillet and the chamfer. They look similar in a menu, but they do different jobs. Here is the plain-English difference, a simple rule for which to pick, what size to choose, and how to add either one to your part in seconds.

Fillet vs chamfer: the one-sentence difference

A fillet rounds off an edge with a smooth radius. A chamfer cuts the edge off at an angle — usually 45° — to make a flat bevel. Both remove the sharp corner; they just do it with a different shape.

Fillet

A rounded transition defined by a radius (for example, a 2 mm fillet). Use it to reduce stress, make a part comfortable to handle, or give it a softer look.

Chamfer

An angled flat cut defined by a distance (and optionally an angle). Use it to break a sharp edge, help a part start into a hole, or guide a bolt or pin.

Both reduce sharpness

Either operation removes a knife edge that could chip, cut a finger, or concentrate stress. The choice between them is about function and looks, not safety alone.

Both are non-destructive

In parametric CAD, a fillet or chamfer is a feature you can edit or remove later. Change the radius and the model rebuilds — you do not redraw the part.

When to use each (a simple rule)

Most of the time you can decide in a few seconds:

Use a fillet on internal corners that carry load — a rounded internal corner spreads stress far better than a sharp one, so brackets, hooks, and structural parts last longer.
Use a fillet on outside edges of handheld parts, enclosures, and anything that should feel finished or look soft.
Use a chamfer on the leading edge of a hole or a peg so it self-aligns — a chamfered hole makes a bolt start straight, and a chamfered pin slides in without catching.
Use a chamfer on the bottom edge of a 3D printed part to fight elephant-foot, or where you just need to knock off a sharp edge cheaply.
Use a chamfer for machining — a 45° bevel is fast to cut on a mill or lathe, while a precise internal fillet may need a specific tool radius.

Rule of thumb for size

Keep the fillet or chamfer smaller than the thinnest wall it touches — typically 0.5–2 mm for small printed parts, scaling up with the part. A fillet larger than the wall it sits on will fail to build or eat through the wall. When in doubt, start small; you can always make it bigger.

How to add a fillet or chamfer with AI CAD

In traditional CAD you select edges one by one and type a value into a dialog. With PartWork.ai you describe what you want in plain English and the AI applies the feature to the right edges. For example:

“Add a 2 mm fillet to all the top edges.”
“Chamfer the bottom edge by 0.5 mm.”
“Round the four vertical corners with a 5 mm radius.”
“Add a 1 mm chamfer to the top of the bolt hole so the screw starts easily.”

Because the model is parametric, you can iterate: ask for a 2 mm fillet, look at it, then say “make it 3 mm” without starting over. To understand why edits like this rebuild cleanly, see What Is Parametric CAD. For the broader design workflow, see How to Design a Bracket for 3D Printing.

Reference: the fillet and chamfer tools

Want the underlying operation details? See the Fillet tool and Chamfer tool reference pages.

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Describe a part, then ask for the fillets or chamfers you need. PartWork.ai produces editable parametric solid geometry you can export for printing or machining — no software to install.

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