TURNMATE / TECHNICAL GUIDE · Updated 2026-10-28
G70 finishing cycle vs. G71 roughing cycle on a CNC lathe
At a high level, G71 can organize roughing passes around a profile in a particular control format; G70 can invoke a target profile range for finishing on the corresponding system. This process distinction does not mean any G71 program can safely be followed by G70.
Different roles in the process
Roughing removes material in passes while leaving an allowance; finishing follows the target profile to approach final dimensions. They may appear in one process plan, but the control defines profile references, modal behavior, and start conditions for each cycle.
Why the code number is not enough
Controls may use the same code number but differ in address words, units, profile constraints, direction, and machine options. FANUC and Haas publications both list G71/G70 turning cycles, but a Haas address definition is a Haas-specific instruction, not a portable FANUC or domestic-control template.
- Identify control brand, series, software revision, and machine-builder options.
- Check that G71 and G70 point to the intended profile start and end blocks.
- Match roughing allowances with the finishing tool, offsets, material, and dimensional tolerance.
- Review tool, spindle, feed, coolant, and coordinate modes between the cycles.
Plan the operation before composing blocks
First record the stock, roughing tool, rough allowance, finishing tool, target dimensions, and inspection method in the process plan. Then map those choices to the cycle format supported by the target controller. Use a verified machine template or manual for block order and address details.
Verification path
Check profile continuity and direction, inspect the cycle result in the target control’s graphics, then follow the machine builder’s procedure for dry run, single block, and first-article measurement. A simplified 2D illustration or static check does not model the whole chuck, turret, fixture, and machine dynamics.
Review checklist
- Identify the roughing and finishing tools and their offsets.
- Verify profile block references, coordinates, and stock allowance.
- Check feed/speed modes, RPM limits, coolant, and safe retracts.
- Validate with the target control graphics, dry run, and first-article measurement.
Sources and scope
- FANUC Series 0i-TC Operator’s Manual B-64114SP/01 (public mirror) — Contains roughing and finishing cycle sections for 0i-TC; verify against the target machine revision.
- Haas Lathe Programming Workbook — Haas ST/TL controller reference only.