GlossaryKind of term: Manufacturing termChamfer
What is a chamfer?
A chamfer is an edge cut back at an angle and a fillet an edge replaced by a radius; both turn a sharp edge into a dimensioned shape.
A chamfer is an angled cut across an edge, dimensioned as a length and an angle (0.5 × 45°) or as two lengths. A fillet replaces the edge with a radius, such as R2; on an outside edge many drawings call it a round or simply a radius. On an outside edge, both make the part less prone to damage and safer to handle, and a chamfer at the mouth of a bore or the end of a shaft eases assembly. In an inside corner, such as the shoulder between a shaft and a collar, a fillet reduces stress concentration. A note such as ‘break sharp edges’ with no shape or size is not a chamfer but an edge requirement.
How is a chamfer or fillet made?
How a chamfer or fillet is made depends on where the edge sits, the process and the size. On a milling machine, a chamfer is usually cut with a chamfer mill or spot drill following the contour, often in the same setup as the contour itself. An outside radius calls for a corner-rounding cutter of that radius or a toolpath with a ball-nose cutter. On a lathe, the chamfer or radius comes from the toolpath. Edges on the underside or at the far end of a through bore need a back-cutting tool, another setup or handwork. An internal corner radius in a pocket is a different case: it is set by the cutter radius, not chosen as a fillet.
How does a chamfer work in practice?
Whether chamfers and fillets add noticeable time depends on the number of edges, access, tooling and setups. Edges you can reach in a setup that is there anyway often cost little: one more contour pass. Edges on a side the tool cannot reach need an extra setup, a special tool or manual deburring; which is cheaper depends on quantity and how consistent the result has to be. A general edge note applies to every edge of the part and is easily overlooked when quoting. Anodising, and hard anodising in particular, builds up poorly on a sharp edge, which is why drawings often specify a small radius there.
What is a chamfer often confused with?
A chamfer is not a fillet: one is angled, the other round, and they usually need different tools. Chamfering is not deburring either: deburring removes the burr without creating a dimensioned shape. And an edge requirement such as ‘break sharp edges’ sets limits on the edge without fixing its shape, whereas a chamfer defines it.
Frequently asked questions
Is ‘break all sharp edges’ free?
Not automatically. Edges reachable in an existing setup often cost one more contour pass. Edges on an unreachable side need an extra setup, a special tool or handwork. What it costs depends on the number of edges, the quantity and the rate.
Should edges be chamfered on the machine or at the bench?
On the machine when the edge can be reached in an existing setup: the result is more consistent. At the bench when an extra setup for those edges alone costs more than the handwork. Quantity and the edge requirement also count.
Why is there a fillet in an inside corner?
To reduce stress concentration in that corner, for example at the shoulder between a shaft and a collar. On a turned part the radius follows from the tool nose radius or a form tool; a perfectly sharp inside corner cannot be turned.