Tool Centre Point Control (G43.4 / G43.5)

In simultaneous 5-axis cutting, the rotary axes move while the tool is cutting — and every degree of rotation swings the tool tip away from where the linear axes put it, because the tip sits some distance from the machine’s centre of rotation. Tool centre point control (TCP, sometimes TCPC) is what makes that manageable: with it on, you program the tool tip (or the tool-axis direction) against the part, and the control continuously moves the linear axes to keep the tip exactly on your programmed path as the rotaries turn. Without it, the same program gouges. Fanuc offers two types — G43.4 and G43.5 — plus related tool-length commands for tilted and nutating heads. This page is derived from FANUC’s Series 30i/31i/32i-B Plus Operator’s Manual (B-64724EN), §22.1.

The Two Types: G43.4 and G43.5

H_ selects the tool-length offset, as with ordinary G43. The essential difference from plain tool length compensation is that TCP is dynamic: it recomputes the linear-axis compensation every interpolation step as the rotaries turn, so the programmed point stays on the tool tip throughout the move — not just at the block endpoints.

The Rest of the G43 Family (Tool Length in a Tilted/Nutating Axis)

Two related commands handle tool length when the head is tilted but you’re not running full TCP:

Think of it as a ladder: G43 (length along Z) → G43.1 (length along the tool axis) → G43.3 (length along a nutating axis) → G43.4/G43.5 (full dynamic tip control while the rotaries move).

TCP vs. G68.2 vs. G54.4

Parameters by Axis Configuration

TCP can only hold the tip on path if it knows the machine’s rotary geometry, and that geometry is described by the same configuration-dependent kinematics parameters as tilted working plane (FANUC B-64730EN §4.104). Parameter No. 19680 declares the machine type — 2 tool/head rotation, 12 table rotation, 21 mixed — and that decides which position/offset vectors you populate:

Common to every type: No. 19681 / 19686 (rotation-axis numbers), No. 19657 (master rotation axis), No. 19696 (rotary config), No. 1006 #0 (mark them rotation axes). The axis pair (AB / AC / BC) isn’t chosen by which offset components you set — it’s the direction codes No. 19682 / 19687 (1 = X, 2 = Y, 3 = Z); the offset vectors are full measured geometry. The position vectors must be set for TCP to place moves correctly; the axis-intersection offsets are the accuracy dial-in on a real machine. The TCP-specific behaviour parameters in §4.104 (feed handling, singular-posture avoidance, tolerances) are MTB-configured. This is the same kinematics setup covered in tilted working plane (G68.2) — including its axis-direction table — a machine set up for one is set up for the other.

See also: the cross-control overview is in 4th/5th Axis, Tilted Work Planes & TCP. The same idea on other controls: Siemens keeps the tip on path with TRAORI; Heidenhain with FUNCTION TCPM (or the legacy M128). Neighbouring Fanuc features: tilted working plane (G68.2) and workpiece setting error compensation (G54.4).

Sources: FANUC Series 30i/31i/32i-MODEL B Plus Operator’s Manual (Common to Lathe/Machining Center), B-64724EN/01 — §22.1 Tool Centre Point Control, plus the G43.1/G43.3 tool-axis-direction commands; and FANUC Parameter Manual B-64730EN/01 — §4.104 Parameters of Tool Centre Point Control.