Fillet
Glossary · Part Features
At a glance
- Category /
- Part Features
- Also called /
- radius, corner radius
- Related /
- 2 terms
- Source /
- Written in the shop
A fillet is a rounded internal corner where two surfaces meet, specified by its radius.
Also called: radius · corner radius
In practice
Where a chamfer cuts a corner off, a fillet rounds an inside corner. On a shaft, the fillet is the radius at the step between two diameters.
Why it matters
Sharp internal corners concentrate stress and are where fatigue cracks start. On a rotating shaft the fillet radius at a shoulder is frequently the single feature that determines fatigue life — which is why drawings call it out and why it should never be quietly reduced to make machining easier.
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