The short answer
On CNC housings, **boss height** (how far a cylindrical stand-off sticks up) and **draft** (the taper leftover from a molded ancestor, or a taper someone added “for tool relief”) are separate notes. Tall, skinny bosses chatter, need rest-milling or a second setup, and concentrate stress at a sharp root. Draft that a molding designer left in the CAD often adds 3D surfacing a prismatic CNC job did not need. Silence on **boss height vs diameter**, **root fillet** and **whether draft is required or should be removed** is what widens many [quote-new.php](https://3dwk.com/quote-new.php) **rates.v1.1** estimate bands—not the overall envelope alone.
This guide is for buyers packaging aluminum housing RFQs that migrated from a molded cover or accumulated tall fastener bosses. Illustrations use an **Example part** only—not a customer automotive ECU cover. Related notes live in [designing bosses and ribs for CNC housings](https://3dwk.com/resources/designing-bosses-and-ribs-for-cnc-housings), [five-axis aluminum housing design tips](https://3dwk.com/resources/five-axis-aluminum-housing-design-tips), and [CNC pockets, thin walls and undercuts](https://3dwk.com/resources/cnc-pockets-thin-walls-undercuts); here we focus on **boss height and draft labeling** so estimators do not guess tool reach and surfacing time.
What height and draft mean for quoting
**Boss height** drives tool stick-out, deflection and whether the boss can be roughed with the same end mill that finishes the floor. A short boss with a generous root fillet mills as a simple boss feature. A tall boss with a tiny diameter and a sharp inside corner behaves like a thin wall plus a deep pocket at the root—see sibling thin-wall notes above. **Draft** on a CNC housing is optional: unlike injection molding, prismatic CNC does not need 1–2° on every wall. If the CAD still carries molded draft, say whether to **machine as-modeled** (surfaces) or **de-draft to vertical walls** (often cheaper on 3-axis). Process pages for automotive aluminum ([CNC 3-axis Al 6061 automotive](https://3dwk.com/en/cnc-3axis/al-6061/automotive.html), [CNC 5-axis Al 6061 automotive](https://3dwk.com/en/cnc-5axis/al-6061/automotive.html), [CNC 3-axis Al 6061 robotics](https://3dwk.com/en/cnc-3axis/al-6061/robotics.html)) assume boss and wall notes are explicit when covers mix fastener towers with sealing floors.
Do not bury “bosses OK / draft as CAD” inside a notes cloud. Put **BOSS Ø8 × 10 HIGH, ROOT FILLET R1.0; NO MOLD DRAFT — VERTICAL WALLS** or **KEEP 1° DRAFT AS MODELED ON OUTER WALLS ONLY** 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).
Height-to-diameter, fillets and setups
A practical RFQ habit is to name height, outer diameter (or ID if it is a standoff with a tapped hole) and the root fillet. Threaded bosses also need tap depth—see [thread depth callouts on blind tapped holes](https://3dwk.com/resources/thread-depth-callouts-blind-tapped-holes-cnc) and [helicoil vs tapped holes CNC aluminum](https://3dwk.com/resources/helicoil-vs-tapped-holes-cnc-aluminum). Very tall bosses may need 5-axis or a second op to reach the root without a long, skinny tool; that is a planning input, not a capability claim. Workholding that lets the boss ring can widen bands—see [how workholding changes CNC quote](https://3dwk.com/resources/how-workholding-changes-cnc-quote).
Aluminum 6061 bar/plate $/kg planning bands sit in the mid-commodity range under **rates.v1.1** material tables; the boss story is tool reach and surfacing, not kg price.
When a little draft actually helps
Keep a small modeled draft or relief when a deep boss OD must avoid rubbing a long tool, or when the part will later be molded and this CNC lot is a prototype of the molded geometry. In that case write **PROTOTYPE OF MOLDED DESIGN — KEEP DRAFT AS CAD**. For production CNC housings that will never see a mold, removing leftover draft usually simplifies the 3-axis path. Do not leave both intents silent.
Vent or weep holes through a boss should be labeled separately: [vent, drain and weep holes in CNC housings](https://3dwk.com/resources/vent-drain-weep-holes-cnc-housings).
Tolerance and inspection traps
Calling “tall bosses as needed,” leaving a molded 2° draft on every internal wall without saying to keep or remove it, or stacking a tiny positional tolerance on a tall skinny boss without a datum that the shop can actually hold, all force **needs_manual**. Default non-critical envelope to ISO 2768-m and put functional position only on boss patterns that locate a mating cover. Related: [GD&T callouts that raise CNC quote bands](https://3dwk.com/resources/gdandt-callouts-that-raise-cnc-quote-bands), [sharp internal corners and CNC quotes](https://3dwk.com/resources/sharp-internal-corners-cnc-quotes).
Illustration 1 shows an **Example part** housing with labeled boss height, root fillet and a “no mold draft” note versus leftover tapered walls.
Example part walkthrough
**Example part:** Aluminum 6061-T6 cover ~120×80×18 mm, four fastener bosses Ø10 × 12 high with R1 root fillets and M4 blind taps, sealing floor, ISO 2768-m general. With STEP + **BOSSES Ø10 × 12 HIGH, ROOT R1; DE-DRAFT INTERNAL WALLS TO VERTICAL; TAP DEPTH NAMED**, expect a usable automatic planning band on [quote-new.php](https://3dwk.com/quote-new.php). Same geometry with silent molded CAD (2° everywhere, sharp boss roots, no height note) often lands DFM notes or **needs_manual**—without inventing any customer PO.
Illustration 2 contrasts a vague RFQ (“bosses as CAD / draft OK”) versus a labeled height-and-draft pack and the clearer estimate path.
What widens bands fastest
Unlabeled leftover mold draft on a “CNC housing,” tall bosses with sharp roots, boss height that forces a long tool next to a deep pocket, and tapped depth that conflicts with remaining floor thickness. Quantity breaks help unit minutes but do not erase surfacing ambiguity—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
Name **boss height, diameter and root fillet**, say **keep or remove draft**, 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 height/draft questions rather than forcing a fake firm price.
Common questions
Do CNC housings need draft like molded covers?
Usually no. Prismatic CNC prefers vertical walls unless you are prototyping a molded design or you have a documented tool-relief reason.
How tall is “too tall” for a boss?
There is no single number. What matters on the RFQ is height, diameter, root fillet and nearby pockets so the estimator can see tool stick-out. Label those instead of writing “as needed.”
Should I fillet every boss root?
A named root fillet (even a modest R) is easier to tool than a sharp inside corner and is kinder to thin floors. Silent sharp roots widen bands.
Does five-axis erase the height note?
No. Five-axis can reach some roots more cleanly, but the RFQ should still name height, fillet and draft intent so planning does not guess.