FANUC chamfer ,C and corner radius ,R: why the same value 3 produces different cut lengths
The 0i-D optional chamfering and corner R chapter distinguishes chamfer setback, connecting-arc radius and an arc command’s own R. Original geometry for 90° and 60° corners tests whether a short edge can accommodate the specified fillet.
Contents
Adding ,C3 or ,R3 at the end of a contour block does not merely replace the letter for the same dimension. The former describes chamfer endpoint positions; the latter defines the inserted arc radius. Their use of adjacent straight-segment length is especially easy to confuse when the corner angle changes.
Clarify the two dimensional meanings
The 0i-D / 0i Mate-D machining-center manual B-64304EN-2/01, §5.3, pages 90–93 (public mirror of the original manual) defines ,C as the distance from the hypothetical sharp-corner intersection to the chamfer start and endpoint, and ,R as the connecting arc radius. With the required function configured, a connection can be inserted at the end of the relevant G01 / G02 / G03 block. Motion on both sides must belong to the same plane.
The comma is part of this format. The R that defines an arc block itself and the trailing ,R that inserts a corner fillet have different roles; the same letter does not make them one item.
A 90° corner: identical endpoints, different connecting shapes
This original geometric example excludes tool compensation: travel along X toward the hypothetical corner (20,0), then leave along +Y. For C=3, the chamfer endpoints are (17,0) and (20,3), with straight connecting length 3√2≈4.243 mm. For R=3, the tangency points are the same, but they are joined by a quarter-circle arc of radius 3 and length 3π/2≈4.712 mm.
| Same stated value of 3 mm | Dimension represented | Connecting length in the 90° example |
|---|---|---|
| ,C3 | Distance from the sharp corner to each chamfer endpoint | 4.243 mm straight line |
| ,R3 | Connecting arc radius | 4.712 mm arc |
Even with identical endpoints, the intermediate contour differs. An acceptance check measuring only setback along the two adjacent edges may not distinguish whether the program produced a chamfer or a fillet.
Other than 90°: calculate the required straight-edge allowance
For interior angle θ between two intersecting straight lines, the tangency-point setback of an ideal tangent fillet is t=R·cot(θ/2). Here θ is the interior angle enclosed by the edges, not the change of travel direction. At R=3 and θ=60°, t=3√3≈5.196 mm; at θ=120°, it is only about 1.732 mm.
Thus, if one side has only 4 mm of available straight length, the 60° example cannot accommodate this fillet, even though R3 is less than 4. Page 92 of the original manual states that an inserted move extending beyond the original interpolation range causes an alarm. A specific program must also account for connections at both ends and length already used; comparing R with one edge's total length is insufficient.
Check the program against the drawing
First establish whether the drawing specifies a chamfer leg length, fillet radius or another dimension, then sketch the tangency points and actual connecting path. When both ends of a short edge have fillets, add their length requirements rather than judging each independently. This is ideal two-dimensional geometry; accessibility after cutter compensation still requires separate verification. See the OPTION section for fundamentals.