The short answer
Some **GD&T callouts** are cheap insurance; others quietly push CNC lines into wider [quote-new.php](https://3dwk.com/quote-new.php) bands or **needs_manual**. Know which frames buy function versus which ones mainly buy inspection minutes under **rates.v1.1** planning estimates.
This guide is for buyers reviewing drawings before upload. Illustrations use an **Example part** only—not a customer FAIR. Baseline literacy: [GD&T basics for buyers](https://3dwk.com/resources/gdt-basics-for-buyers). Multi-setup datum context: [datum schemes for multi-setup CNC parts](https://3dwk.com/resources/datum-schemes-for-multi-setup-cnc-parts) once live, and [flatness / parallelism / perpendicularity](https://3dwk.com/resources/flatness-parallelism-perpendicularity-machined-parts).
Callouts that usually stay in automatic bands
- ISO 2768-m (or equivalent) general tolerance on non-mates
- A single coherent datum scheme (A|B|C)
- True position on bolt patterns with generous but real MMC modifiers when function allows
- Flatness on one sealing face with a shop-realistic value
- Simple perpendicularity between a bore and a primary face
These still need clean STEP+PDF packaging—see [what files to send](https://3dwk.com/resources/what-files-to-send-for-cnc-quote) and [DFM checklist](https://3dwk.com/resources/dfm-checklist-before-online-cnc-quote).
Callouts that commonly raise bands
- Profile of a surface on every organic wall “just in case”
- Runout / total runout stacked with position on the same diameters without a turned process note
- Composite position frames with tiny tolerances on large envelopes
- Flatness tighter than the process can hold without scrape/lap notes
- “100% CMM all GD&T” on qty 50 without sampling language
Illustration 1 shows an **Example part** callout heat map: green = mates; orange = cosmetic walls overloaded with profile.
Why inspection narrative moves the mid
Parsers and reviewers translate GD&T density into inspection time. A frame that requires a rotary table, custom soft jaw, or optical+CMM combo is not free. Related: [CMM vs optical measurement](https://3dwk.com/resources/cmm-vs-optical-measurement-machined-parts), [first article inspection reports](https://3dwk.com/resources/first-article-inspection-reports), [surface roughness Ra](https://3dwk.com/resources/surface-roughness-ra-for-machined-parts).
Hot alloys amplify the effect: **rates.v1.1** CNC time coeffs (estimates) include 17-4PH ×1.4, IN718/IN625 ×2.5, CoCr ×2.2; bar $/kg bands PA66 ~5, 17-4PH ~9, IN718 ~55, IN625 ~60. The same profile frame on CoCr hurts more than on PA66 (coeff ×0.8). Lines above configured USD thresholds auto-route to **needs_manual**.
Datum schemes vs frame spam
Ten position frames referencing three conflicting datum systems are worse than three frames on one scheme. Fix datums first—see multi-setup guidance—and only then tighten mates. Mill-turn hybrids need frames that match process order—[milled and turned features on one CNC part](https://3dwk.com/resources/milled-and-turned-features-on-one-cnc-part).
Illustration 2 contrasts a spam-heavy title block versus a mates-only GD&T block and the clearer estimate path.
Material-specific traps
- **17-4PH:** age condition (H900/H1025) plus tight position after heat treat—note sequence; lot heat-treat often ~+$60 under **rates.v1.1** estimates. See [17-4PH H900 vs H1025](https://3dwk.com/resources/17-4ph-h900-vs-h1025-what-buyers-choose) and [tolerances CNC 17-4PH](https://3dwk.com/resources/tolerances-cnc-17-4ph-what-buyers-specify).
- **Plastics (PA66):** moisture swell can make tiny position frames unmeasurable in uncontrolled humidity—see the PA66 moisture guide in this batch theme.
- **SLM + machine:** do not apply wrought-style profile to as-built walls.
Packaging RFQs so bands stay honest
- One datum scheme drawing-wide
- GD&T only on functional mates
- Separate cosmetic notes from metrology notes
- State inspection level (FAIR once / sampling / 100%)
- Avoid “aerospace GD&T” as a sticker without frames that match function
Ambiguous packs still upload; they produce wider bands—see [what needs_manual means](https://3dwk.com/resources/what-needs-manual-means-preliminary-quote) and [reading a preliminary quote](https://3dwk.com/resources/reading-preliminary-online-quote-min-mid-max).
Example part walkthrough
**Example part:** 6061-T6 manifold plate, ~120×80×20 mm, four M5 patterns true position 0.1 to A|B|C, sealing face flatness 0.05, ISO 2768-m elsewhere, no profile on pocket walls. Expect a clearer planning band on [quote-new.php](https://3dwk.com/quote-new.php) than the same plate with 0.02 profile on every pocket wall and “±0.01 all over.” No customer metrology reports invented.
What to do next
Audit frames for function, then upload on [quote-new.php](https://3dwk.com/quote-new.php). Service pages: [CNC machining](https://3dwk.com/cnc-machining-service.php), [materials](https://3dwk.com/materials.php). Treat **rates.v1.1** min/mid/max as estimates, not invoices.
Process capability versus wishful frames
If a frame implies grind/lap/EDM and your RFQ says “CNC mill only,” the estimate path breaks. Match callouts to process family: turned runout on journals, milled flatness on sealing faces, position on drilled patterns. When capability is unclear, ask for a planning band first on [quote-new.php](https://3dwk.com/quote-new.php) rather than asserting aerospace-grade frames on a prototype housing. Related: [3-axis vs 5-axis](https://3dwk.com/resources/3-axis-vs-5-axis-cnc-for-buyers), [CNC lead time](https://3dwk.com/resources/cnc-machining-lead-time-buyer-guide).
Title-block hygiene
Put general tolerance, datum scheme, and finish notes where reviewers look first. Buried GD&T on a detail view nobody opens still counts as inspection risk once discovered. Keep one revision letter consistent between STEP and PDF so frames are not quoting yesterday’s envelope.
Common questions
Is MMC always cheaper than RFS?
Often on patterns that allow bonus tolerance—but only if function allows MMC. Do not add MMC to force a lower mid when the joint cannot use bonus.
Does more GD&T always improve quality?
Only if it is measurable and functional. Unmeasurable frames create disputes without improving the part.
Will deleting all GD&T lower the quote?
It can hide function and force clarification later. Prefer honest mates-only frames over a blank title block with tribal knowledge in email.
How do quantity and GD&T interact?
Dense 100% inspection at qty 50 flattens unit-cost breaks—see [how quantity breaks change CNC unit cost](https://3dwk.com/resources/how-quantity-breaks-change-cnc-unit-cost).