The short answer
On a CNC RFQ, **heat treat after machining** and **machine after heat treat** are not the same quote package. Post-machine heat treat can relieve stress, raise hardness, or meet a drawing callout—but it adds distortion risk, extra ops, and inspection gates. Silence on **sequence** (HT before vs after finish size) is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands—not the blank grade alone.
This guide is for buyers packaging steel and stainless RFQs where drawings mention hardness or temper without a clear op order. Illustrations use an **Example part** only—not a customer tooling plate. Related notes live in [heat treating steel after CNC machining](https://3dwk.com/resources/heat-treating-steel-after-cnc-machining) and [prototype vs production CNC quotes](https://3dwk.com/resources/prototype-vs-production-cnc-quotes); here we focus on **when to specify heat treat after CNC** so estimators do not guess.
What “heat treat after CNC” means for quoting
Post-machine HT typically means: rough or near-net CNC → stress relieve / harden / temper → optional grind or skim to finish. Pre-HT machining means cut already-hardened stock (slower feeds, more tool wear). Process pages for tooling and robotics steel ([CNC 3-axis Steel 1018 tooling](https://3dwk.com/en/cnc-3axis/steel-1018/tooling.html), [CNC 5-axis Steel 1018 robotics](https://3dwk.com/en/cnc-5axis/steel-1018/robotics.html), [CNC turning Steel 1018 robotics](https://3dwk.com/en/cnc-turning/steel-1018/robotics.html)) assume sequence notes when lots mix hardness callouts and tight finish sizes.
Do not bury “HRC 28–32 somehow” inside a notes cloud. Put **HT AFTER ROUGH CNC — STRESS RELIEVE + TEMPER; FINISH SKIM AFTER HT** (or **MACHINE HARD — NO POST HT**) on the PDF and mirror it in RFQ text. Background: [DFM checklist before an online CNC quote](https://3dwk.com/resources/dfm-checklist-before-online-cnc-quote), [what files to send for a CNC quote](https://3dwk.com/resources/what-files-to-send-for-cnc-quote).
Distortion, stock and skim allowances
Heat treat can move thin walls, long spans, and unbalanced sections. Leave skim stock on critical faces if finish size must survive HT; name that stock on the drawing. Soft stock (PA66 time coeff ×0.8) rarely needs HT—steel and PH stainless do. Harder alloys (17-4PH ×1.4, IN718/IN625 ×2.5) amplify both HT value and distortion risk; aggressive “harden then hold ±0.01 without grind” asks frequently auto-route toward **needs_manual** when mid-line bands exceed planning thresholds under **rates.v1.1** estimates.
If grind or hone follows HT, say so—those ops change the planning family. Related: [how workholding changes a CNC quote](https://3dwk.com/resources/how-workholding-changes-cnc-quote), [datum schemes for multi-setup CNC parts](https://3dwk.com/resources/datum-schemes-for-multi-setup-cnc-parts).
Bar $/kg planning bands (estimates only): PA66 ~5, 17-4PH ~9, IN718 ~55. Material cost is rarely the HT story—sequence, distortion stock, and inspection are.
When post-machine HT is worth calling
Call HT after CNC when: (1) the drawing hardness cannot be met in the as-machined condition, (2) stress relieve is needed before final skim to hold flatness, or (3) wear surfaces need case/harden after near-net geometry. Skip or defer HT notes on pure prototypes if hardness is “nice to have”—see [prototype vs production CNC quotes](https://3dwk.com/resources/prototype-vs-production-cnc-quotes). For stainless that is only passivated, do not confuse passivation with HT—see [passivation vs electropolishing stainless](https://3dwk.com/resources/passivation-vs-electropolishing-stainless); keep passivation out of the HT block.
Tolerance and inspection traps
Hardness callouts without location (surface vs core), missing temper range, and finish sizes that ignore HT movement fight automatic bands. Default non-critical envelope to ISO 2768-m and put functional tolerances only on post-HT faces. Related: [GD&T callouts that raise CNC quote bands](https://3dwk.com/resources/gdandt-callouts-that-raise-cnc-quote-bands), [CMM sampling plans for CNC lots](https://3dwk.com/resources/cmm-sampling-plans-for-cnc-lots), [what needs_manual means](https://3dwk.com/resources/what-needs-manual-means-preliminary-quote).
Illustration 1 shows an **Example part** with labeled rough CNC → HT → finish skim sequence versus machine-hard stock with no post HT.
Example part walkthrough
**Example part:** Steel 1018 plate ~200×120×25 mm tooling base, flatness 0.05 on top after HT, HRC callout on wear pads, ISO 2768-m elsewhere. Lot qty 12. With STEP + **ROUGH CNC → STRESS RELIEVE → FINISH SKIM TOP; HARDNESS ON WEAR PADS PER NOTE**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent CAD and “heat treat / hold all sizes” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“HT to print”) versus a labeled sequence block and the clearer estimate path.
What widens bands fastest
Unlabeled HT before vs after, finish sizes with zero skim stock, hardness without location, and 100% CMM of every face post-HT. Quantity breaks help unit HT lotting but do not erase distortion risk—see [how quantity breaks change CNC unit cost](https://3dwk.com/resources/how-quantity-breaks-change-cnc-unit-cost).
What to do next
Mark **HT AFTER CNC** or **MACHINE HARD**, name skim stock and hardness locations, 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. If the UI shows **needs_manual**, answer the sequence questions rather than forcing a fake firm price.
Common questions
Does every steel RFQ need post-machine HT?
No. Many 1018 fixtures ship as-machined or with a light stress relieve only. Call HT when hardness or stability is functional—under **rates.v1.1** estimates unused HT adds cost and lead gates.
Can I heat treat and still hold tight positional tolerances without grind?
Sometimes on thick rigid parts; often not on thin plates. Plan skim or grind stock and say so on the RFQ.
How do stainless PH grades change the story?
PH stainless (e.g. 17-4) often needs a defined age condition. Name the condition and whether aging is before or after finish size—tool-wear coeffs rise when cutting aged stock.
Should prototype lots skip HT?
Often yes if hardness is not yet locked. Production lots should freeze sequence early—see [prototype vs production CNC quotes](https://3dwk.com/resources/prototype-vs-production-cnc-quotes).