The short answer
On a CNC RFQ, **filleted** and **sharp** internal corners are not the same quote package. A fillet that matches a realistic end-mill radius is usually a standard 2.5D pocket plan. A true sharp internal corner often means EDM, a corner-relief drill, a smaller finishing tool, or an acceptance that the shop will leave a tiny radius anyway. Silence on corner intent is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands—not the pocket depth alone.
This guide is for buyers packaging prismatic aluminum RFQs. Illustrations use an **Example part** only—not a customer fixture. Related pocket and undercut notes live in [CNC pockets, thin walls and undercuts](https://3dwk.com/resources/cnc-pockets-thin-walls-undercuts), [when to call out undercuts on a CNC RFQ](https://3dwk.com/resources/when-to-call-out-undercuts-on-cnc-rfq), and [sharp internal corners CNC quotes](https://3dwk.com/resources/sharp-internal-corners-cnc-quotes); here we focus on **how to label fillet vs sharp** so estimators do not guess.
What “fillet” and “sharp” mean for quoting
A filleted internal corner has a controlled inside radius (often ≥ tool radius). A sharp internal corner asks for a near-zero inside radius that a rotating end mill cannot leave. For quoting, also say whether the corner is structural (stress / fatigue), cosmetic, or only a clearance pocket for a mating part. Process pages for aluminum robotics and automation parts ([CNC 3-axis Al 6061 robotics](https://3dwk.com/en/cnc-3axis/al-6061/robotics.html), [CNC 5-axis Al 6061 robotics](https://3dwk.com/en/cnc-5axis/al-6061/robotics.html), [CNC turning Al 6061 robotics](https://3dwk.com/en/cnc-turning/al-6061/robotics.html)) assume clear corner notes when lots mix pockets and locating bosses.
Do not bury “sharp corners somehow” inside a GD&T paragraph. Put **R≥…** or **SHARP / relief allowed** next to each critical corner 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).
Tool radius, reach and pocket depth
End mills leave a radius at least as large as the tool radius. Deep pockets with tiny corner radii force long slender tools, longer cycle time, and chatter risk. Soft stock (PA66 time coeff ×0.8 under **rates.v1.1** estimates) still needs clearance for chips in deep corners. Harder alloys (17-4PH ×1.4, IN718/IN625 ×2.5, CoCr ×2.2) amplify heat and finishing passes; aggressive sharp-corner asks on hot alloys frequently auto-route toward **needs_manual**, especially when the line mid exceeds configured planning bands (e.g. above ~$2000 for hot alloys/CoCr).
If the mating part only needs clearance, prefer a drill-dot or dog-bone relief over a true sharp. Say whether a small leftover radius is allowed on non-critical corners.
Bar $/kg planning bands (estimates only): PA66 ~5, 17-4PH ~9, IN718 ~55, IN625 ~60. Material cost is rarely the corner story—tool diameter and secondary ops are.
Stress, fatigue and fillet intent
Structural robotics brackets often benefit from a designed fillet that reduces stress concentration. Calling every corner “sharp” for cosmetic preference can fight that intent and raise finish time. If fatigue life matters, name the minimum inside radius from the FEA or hand calc, then let manufacturing round up to the next practical tool. Related: [deep pockets and tool reach CNC quotes](https://3dwk.com/resources/deep-pockets-and-tool-reach-cnc-quotes), [minimum wall CNC vs SLM for buyers](https://3dwk.com/resources/minimum-wall-cnc-vs-slm-for-buyers).
Tolerance and inspection traps
Tight true position next to a sharp corner forces probing strategies and may fight tool deflection. Default non-critical pocket floors to ISO 2768-m and put functional tolerances only on locating or sealing features. Related: [surface roughness Ra for machined parts](https://3dwk.com/resources/surface-roughness-ra-for-machined-parts), [datum schemes for multi-setup CNC parts](https://3dwk.com/resources/datum-schemes-for-multi-setup-cnc-parts), [GD&T callouts that raise CNC quote bands](https://3dwk.com/resources/gdandt-callouts-that-raise-cnc-quote-bands).
Illustration 1 shows an **Example part** with a labeled R3 fillet pocket versus a dog-bone relief on a “sharp” mating corner.
Example part walkthrough
**Example part:** 6061-T6 plate ~120×80×16 mm with one open pocket 40×30×10 mm deep, R3.0 floor fillet preferred, plus one mating slot corner marked SHARP with Ø3 dog-bone relief allowed, ISO 2768-m general, pocket floor Ra 3.2, boss true position 0.1 to Datum A. With STEP + clear fillet/sharp labels, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent CAD and “all corners sharp” often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“sharp corners everywhere”) versus a labeled fillet/relief block and the clearer estimate path.
What widens bands fastest
Unlabeled mix of fillets and sharp asks, “as sharp as possible” without relief options, conflicting thin-wall notes near deep corners, and 100% CMM of every pocket radius. Quantity breaks help unit cost but do not erase tool-reach risk—see [how quantity breaks change CNC unit cost](https://3dwk.com/resources/how-quantity-breaks-change-cnc-unit-cost) and [what needs_manual means](https://3dwk.com/resources/what-needs-manual-means-preliminary-quote).
What to do next
Mark every critical internal corner **R≥…** or **SHARP + relief allowed**, state pocket depth / tool-reach limits, 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 corner-radius questions rather than forcing a fake firm price.
Common questions
Can I mark every corner “sharp” to simplify the drawing?
No. Mislabeling fillets as sharp creates wrong tool plans and often scrap or **needs_manual** clarification. Label what the CAD and function actually require.
Do fillets always cost less than sharp corners?
Usually yes for prismatic CNC—matching a standard tool radius avoids EDM or micro-tools. Very large fillets that force big tools in tight envelopes can still widen the **rates.v1.1** band.
How do hot alloys change sharp-corner quotes?
Finishing and heat in IN718/IN625/CoCr raise machine-time under **rates.v1.1** coeffs (×2.5 / ×2.2 estimates). Expect wider bands or manual review when corner radius fights tool diameter.
Should undercuts follow the same labeling habit?
Yes. Function notes still help—see [when to call out undercuts on a CNC RFQ](https://3dwk.com/resources/when-to-call-out-undercuts-on-cnc-rfq)—but fillet vs sharp remains mandatory on pocket corners.