--- title: "G71 vs G72: Lathe Roughing Cycles Explained" description: "G71 roughs with passes along Z for shafts and long profiles, G72 roughs with passes along X for faces. Here is how each cycle works and which to pick." url: https://gcodepractice.com/journal/lathe-g71-vs-g72-roughing-cycle-practice/ canonical: https://gcodepractice.com/journal/lathe-g71-vs-g72-roughing-cycle-practice/ author: "Lawrence Arya" authorUrl: https://www.linkedin.com/in/vibecoding/ published: 2026-06-04 updated: 2026-06-04 category: "Code reference" tags: ["g71", "g72", "lathe", "canned-cycle", "roughing"] lang: en --- # G71 vs G72: Lathe Roughing Cycles Explained > **TL;DR** G71 is the lathe roughing cycle that cuts repeated passes parallel to the Z axis, the right pick for shafts and long external or internal profiles. G72 cuts its passes parallel to the X axis, the right pick for short, large-diameter parts where the stock mostly comes off the face. Both reference the same P to Q profile blocks and hand the finishing pass to G70. Roughing on a lathe is repetitive by nature: take a cut, step over, take another, until the part is nearly to size. The Fanuc-style roughing cycles fold that whole sequence into one call. You describe the finished profile once, and the control plans every pass. `G71` and `G72` are the two main cycles, and they differ in exactly one idea: which axis the passes run along. ## What does G71 do? `G71` is the **stock removal in turning** cycle. It strips the blank with repeated cuts parallel to the Z axis, stepping down in X after each pass, as the [G71 rough turning references](https://www.helmancnc.com/cnc-lathe-g71-rough-turning-cycle/) show. That motion suits the bread-and-butter lathe job described in any [lathe overview](https://en.wikipedia.org/wiki/Lathe): a shaft, a spindle, a long external profile, or a bore, where most of the metal comes off along the length of the part. The modern two-line format packs the cycle into a handful of words: ``` G71 U2. R1. (2 mm depth per pass, 1 mm retract) G71 P10 Q20 U0.4 W0.1 F0.25 N10 G00 X30. (profile start: X move only) ...profile blocks... N20 G01 Z-60. (profile end) ``` The second line points at the profile (`P10` to `Q20`) and leaves 0.4 mm in X and 0.1 mm in Z for finishing. ## What does G72 do differently? `G72` is the **stock removal in facing** cycle: identical idea, rotated 90 degrees. Its passes run parallel to the X axis, stepping along Z between cuts, per the [stock-removal cycle guides](https://www.helmancnc.com/cnc-lathe-stock-removal-in-turning-g71/). That fits a short, large-diameter part, a flange, a disc, a part whose profile mostly drops across the face, where facing strokes clear stock far faster than long turning passes would. One detail separates the two in the program besides the code itself: the first profile block. In a `G71` profile, the block at `P` approaches in X only; in a `G72` profile it approaches in Z only. The approach axis announces the pass direction, and mixing them up is a common first-week alarm. ## Which cycle should you pick? Decide by where the stock is, then let the geometry confirm it: | | `G71` (turning) | `G72` (facing) | | --- | --- | --- | | Passes run | Parallel to Z | Parallel to X | | Steps between passes | In X | In Z | | Best for | Shafts, long profiles, bores | Short large-diameter parts, flanges | | Profile start block at `P` | X move only | Z move only | | Verdict | Default for most turned parts | Pick when the face carries the stock | A concrete example: a 200 mm shaft turned from 50 mm bar is a `G71` job, because nearly every gram of chips leaves along the length. A 120 mm diameter brake-disc blank only 20 mm thick flips the logic: the profile lives across the face, so `G72` clears it with fewer, longer strokes. ## How do the cycles finish the part? Neither cycle cuts the final surface. Both leave the `U` and `W` allowances on the profile, and `G70`, the finishing cycle, replays the same `P` to `Q` blocks at finish feed and speed to bring the part to size. A third sibling, `G73`, repeats the profile in stepped offsets for blanks that already match the shape, like castings. The whole family works the same way the [mill drilling cycles G81 and G83](/journal/g81-vs-g83-drilling-canned-cycles/) do: one definition, automatic repetition, and a cancel or finish step at the end. Because these are lathe cycles, the usual lathe setup discipline applies around them, including the spindle-speed clamp covered in [G50 max spindle speed](/journal/g50-max-spindle-speed-crash-lathe/) when constant surface speed is active for the finishing pass. ## Bottom line `G71` roughs with passes along Z and suits shafts and long profiles; `G72` roughs with passes along X and suits short, wide parts where the face carries the stock. Both read one `P` to `Q` profile, leave `U` and `W` allowances, and hand the surface to `G70`. Learn the pass-direction difference and the profile's approach-axis rule, and the rest is filling in numbers. Locking those pairings in is what recall practice on the [G-code practice hub](/g-code-practice/) does, and the broader lathe-versus-mill code map lives in [how to remember lathe M-codes vs mill M-codes](/journal/how-to-remember-lathe-m-codes-vs-mill-m-codes/). ## Sources - [HelmanCNC: G71 rough turning cycle](https://www.helmancnc.com/cnc-lathe-g71-rough-turning-cycle/) - [HelmanCNC: stock removal in turning with G71](https://www.helmancnc.com/cnc-lathe-stock-removal-in-turning-g71/) - [Wikipedia: Lathe](https://en.wikipedia.org/wiki/Lathe) ## Frequently asked questions ### What is the difference between G71 and G72 on a lathe? The direction of the roughing passes. `G71` cuts parallel to Z for shafts and long profiles; `G72` cuts parallel to X for short, large-diameter facing work. Both repeat automatically until only the finishing allowance remains. ### How do G71 and G72 know what shape to cut? From the profile defined between the block numbers referenced by `P` and `Q`. The control plans the passes itself, leaves the `U` and `W` allowances, and `G70` replays the profile as the finish pass. ### When should you use G73 instead? When the blank already matches the rough shape, such as a casting or forging. `G73` repeats the profile in stepped offsets instead of slicing from solid, saving air cuts. ### What is the best way to practice lathe cycles like G71 and G72? Drill the cycle codes with active recall. A free app like G-Code Sprint quizzes `G71`, `G72`, and the other everyday codes and repeats whichever ones you miss. *G-Code Sprint is a study and practice tool only. Always follow your instructor, employer, machine manual, and shop safety procedures.* --- Source: https://gcodepractice.com/journal/lathe-g71-vs-g72-roughing-cycle-practice/ Author: Lawrence Arya — https://www.linkedin.com/in/vibecoding/