FANUC G12.4/G13.4 continuous-circle groove cutting: how F, pitch Q and tool diameter determine speed
The 30i-B continuous-circle groove-cutting rules relate groove advance to pitch per revolution. Two tool diameters and circular-acceleration limits show why commanded F cannot be equated directly with progress along the groove.
Contents
Continuous-circle groove cutting superposes a small circular motion on the groove-center path. A high programmed F does not necessarily mean rapid progress along the groove; a larger cutter can also lower the small circle's speed limit. Circular motion and center-path motion coexist here.
Four quantities differ from ordinary linear feed
The FANUC 30i/31i/32i-B machining-center operator's manual B-64484EN-2/03, §3.6, pages 30–37 and appendix pages 384–385 (public mirror of the original manual) defines I as groove width, K as tool diameter, Q as advance along the groove per circle, and F as tool-center speed for continuous circular motion. A machine-side enable signal is also required. This article analyzes a correctly configured function and provides no signal-enabling or parameter-changing procedure.
Calculate the time per circle
The commanded small-circle radius is r=(I−K)/2 and circumference 2πr. For F in mm/min, one circle takes T=2πr/F minutes. With Q millimeters of advance per circle, groove speed is v=Q/T=FQ/[π(I−K)]. F and v therefore describe different motions and are not interchangeable.
Original ideal command model: I=20 mm, Q=1 mm and F=1200 mm/min, all overrides 100%, initially ignoring other speed limits:
| Tool diameter K | Commanded small-circle radius r | Time per circle | Groove speed v |
|---|---|---|---|
| 12 mm | 4 mm | About 1.257 s | About 47.746 mm/min |
| 16 mm | 2 mm | About 0.628 s | About 95.493 mm/min |
The table uses commanded geometry. Page 34 of this edition notes that servo lag and post-interpolation acceleration/deceleration can make even the actual steady-state radius smaller than commanded. These values therefore guarantee neither actual trajectory nor groove width.
A smaller radius also lowers the circular F limit
The manual gives the circular-acceleration limit as maximum F=60√(ar), where a is the applicable acceleration limit, in mm/s² for metric units. For calculation only, take a=200 mm/s². Radii r=4 and 2 mm then give limits of about 1697.056 and 1200 mm/min. If the second tool is commanded at F=1600, this constraint allows only 1200 in the calculation; groove speed of 127.324 mm/min should not be expected.
A larger cutter thus reduces the small-circle circumference while the smaller radius lowers the circular speed limit. Evaluate effective circular speed before groove advance; extrapolating only from tool-diameter ratios misses the acceleration condition.
Pitch also has a geometric constraint
The manual requires tool diameter to exceed pitch; excessive pitch can leave material uncut. This is a necessary geometric condition for the mechanism, not sufficient proof of acceptable cutting load. The calculations also omit entry, exit, acceleration/deceleration and override changes, so steady-state time does not represent a complete machining cycle.
The actual-speed display includes the superposed motion and cannot simply be read as groove-center advance. Retain F, Q, I−K and effective limits separately for a meaningful comparison. Related resources are in the OPTION section.