Rest machining for remaining material in CNC Programming

Introduction

Rest machining helps remove leftover material after a rough cut. It makes the final shape more precise and saves time.

After rough machining leaves small areas of material that need finishing.

When using different tool sizes to clean up hard-to-reach spots.

To avoid re-cutting large areas already finished.

When you want to improve surface quality by focusing only on leftover material.

Syntax

CNC Programming

G71 P<start_block> Q<end_block> U<allowance> W<allowance> F<feedrate>
G70 P<start_block> Q<end_block>

G71 is used for roughing cycles with rest machining.

P and Q define the start and end of the machining block range.

Examples

This runs a roughing cycle from block 100 to 200 with 0.5 mm allowance, then a finishing cycle on the same blocks.

CNC Programming

G71 P100 Q200 U0.5 W0.5 F0.2
G70 P100 Q200

Rest machining with smaller allowance and slower feedrate for finer finish.

CNC Programming

G71 P50 Q150 U0.2 W0.2 F0.1
G70 P50 Q150

Sample Program

This program rough machines leftover material between blocks 200 and 220 with 0.3 mm allowance, then finishes it.

CNC Programming

N100 G71 P200 Q220 U0.3 W0.3 F0.15
N110 G70 P200 Q220
N120 M30

Important Notes

Rest machining saves time by only cutting leftover material.

Allowance values (U and W) control how much material is left for finishing.

Always verify tool paths in simulation before running on the machine.

Summary

Rest machining targets leftover material after rough cuts.

It uses block ranges and allowances to focus cutting.

This method improves efficiency and surface finish.