Chamfer vs Fillet: Choosing the Right Edge for a Machined Part

Q: Is a chamfer cheaper to machine than a fillet?

On external edges, usually yes — a chamfer is cut with the same end mill or a spot drill in the main cycle, while a fillet radius needs a corner-radius end mill of matching size and can force a smaller, slower tool into corners. On internal corners the gap widens further: a chamfer relieves the corner with a simple angled pass, whereas a full internal fillet constrains the cutter radius and may require slower finishing passes. The cost difference is per-feature, so it matters most on parts with many edges.

Q: What chamfer sizes do you routinely machine?

C0.3, C0.5, C0.8, C1 and C2 are the everyday callouts on drawings we receive, with C0.5 and C1 the most common. Symmetric 45° chamfers are the default unless the drawing states otherwise. Non-45° angles and asymmetric chamfers are machined on our 4-axis and 5-axis centres. Tolerances follow the general drawing block unless the chamfer is functionally critical.

Q: Do you inspect chamfers and fillets on the CMM?

Yes, when they are dimensioned on the drawing. Chamfers are measured directly by angle and width; small fillet radii are verified with radius gauges and optical projection, and functionally critical radii are scanned on the 3D CMM. Every production run is inspected 100% before shipment with a dimensional report against the drawing.

A manufacturing view from Boyang Hardware · Zhongshan, Guangdong, China

Direct answer A chamfer is a straight 45° (or specified-angle) bevel across an edge; a fillet is a rounded transition. In CNC machining the choice is mostly about function: use chamfers to break sharp edges, aid assembly and lead pins into holes — they are fast to cut and easy to inspect. Use fillets where stress concentration, flow or mating radii matter — internal fillets soften corner stress but constrain tool selection. If the edge has no function beyond de-burring, a chamfer is almost always the cheaper callout.

C0.5 / C1most common chamfer callouts
45°default chamfer angle
54machine tools on site
100%inspection before shipment
1–2 dquotation turnaround

Decision table: which edge for which job

Table 1 — Typical edge-selection logic applied when we review customer drawings. Where the drawing is silent, we chamfer external edges at C0.5 as standard practice and confirm at quotation.
Situation	Better choice	Why
Breaking a sharp external edge for safe handling	Chamfer C0.3–C0.5	One pass, no special tool, universally understood
Screw or dowel pin must start into a hole	Chamfer C0.5–C1 on the bore	Leads the fastener; prevents thread shave
Part sees cyclic or impact load at a corner	Fillet (largest radius the design allows)	Reduces stress concentration factor
Two walls meet in an internal pocket	Chamfer to relieve, or fillet matching tool radius	Full internal fillet limits cutter diameter — see chamfer vs fillet vs bevel
Corner of a "round vs fillet" debate on a cosmetic face	Fillet	Rounded corners read softer and resist chipping — see round vs fillet corners
Sealing face preparation	Small chamfer per seal standard	Prevents seal lip damage on insertion
Die-cast or moulded part edge	Fillet	Radii fill and eject better in casting/moulding — relevant to our die casting work

What each costs to machine

An external chamfer on a prismatic aluminium part is cut in the main milling cycle — often with the same tool that faces the part, or a dedicated spot drill for bore entrances. It adds seconds, not minutes. A fillet needs the correct corner-radius end mill; if the specified radius is smaller than the natural tool for the pocket, the finishing pass runs slower with a smaller tool and higher wear. Internal fillets also tighten the corner-cleaning strategy: every internal radius must be ≥ the tool radius, or a secondary operation (plunge, EDM — we run 7 EDM machines) is needed.

On turned parts the picture reverses in one way: both features are single-point profile moves, so the cost difference is smaller and the choice can follow function almost freely.

Standard sizes we see on drawings

Table 2 — Frequent callouts in production drawings we machine across aluminium, brass, stainless steel and titanium.
Feature	Common callout	Typical tolerance treatment
Edge break	C0.3 / C0.5 / "break edges 0.3–0.5"	General tolerance block (e.g. ISO 2768-m)
Assembly lead-in	C0.8 / C1 / C2	Dimensioned; checked if functionally critical
Bore entry chamfer for threads	C1 × 45° typical	Checked for thread start integrity
Internal pocket fillet	R0.5 / R1 / R2	Must be ≥ finishing tool radius; flagged if not
External cosmetic fillet	R1–R3	Profile tolerance; surface finish carried over from the pass

Chamfer geometry is simple to verify: for a 45° chamfer, leg length equals the callout (C1 = 1 mm × 1 mm); for other angles, width = depth / tan(angle). See our tolerance capability detail in CNC machining tolerances.

How each feature is inspected

Chamfers are the easiest edge feature to verify: a CMM probe or optical system reads angle and leg width directly in two or three points. Fillets require more care — small radii are checked with radius gauges and projected optically; radii that carry a function (a seat radius under a bolt head, a stress-relief radius on a bracket) are scanned on the 3D CMM and reported. As with everything we ship, inspection is 100% before despatch with a dimensional report — see inspection and reporting.

Honest limits: we cannot give universal rules of thumb a certificate behind — edge selection is a design decision, and we will machine either feature to drawing. Two real constraints from our floor: internal fillets smaller than R0.5 are slow and fragile-tool territory, and knife-edge internal corners are impossible by milling — they need the wire EDM route, which changes lead time and price. If your drawing mixes both features freely, expect us to come back with comments during the 1–2 working day quotation.

FAQs

Is a chamfer cheaper to machine than a fillet?

Usually on external edges, and clearly so on internal corners. A chamfer is a simple angled pass; a fillet dictates tool radius and can slow finishing. The difference is per-feature, so it compounds on parts with dozens of edges.

What chamfer sizes do you routinely machine?

C0.3 to C2 at 45° are everyday work across our aluminium, brass, stainless and titanium jobs; other angles go through 4-axis and 5-axis set-ups.

Do you inspect chamfers and fillets on the CMM?

Dimensioned features are verified — chamfers by angle and width, fillets by gauge, optical projection or CMM scanning for critical radii. 100% of production is inspected before shipment.

Can I leave the edge treatment unspecified?

You can, but we will ask. A general note like "break edges 0.3–0.5" is usually enough for non-critical edges and lets us quote without back-and-forth. For design background on rounded options, see the fillet engineering design guide.