The short answer
CNC **unit cost** drops as quantity rises—but not on a smooth curve. Setup amortization, bar drops, fixture reuse, and inspection sampling all create **quantity breaks**. Package your RFQ so [quote-new.php](https://3dwk.com/quote-new.php) can apply **rates.v1.1** planning bands to the qty you actually intend to buy, not a single optimistic number.
This guide is for buyers comparing prototype versus bridge qty on CNC RFQs. Illustrations use an **Example part** only—not a customer invoice.
What “quantity break” means on a CNC line
A quantity break is where unit cost steps down because fixed work (programming, fixturing, first-article attention) is spread across more pieces, or because bar/plate nesting and tool life improve. It is not a retail “buy 10 get 10% off” coupon. Related buyer context: [CNC cost drivers](https://3dwk.com/resources/cnc-machining-cost-drivers-buyer-guide), [reading a preliminary quote](https://3dwk.com/resources/reading-preliminary-online-quote-min-mid-max), [CNC lead time](https://3dwk.com/resources/cnc-machining-lead-time-buyer-guide), [what needs_manual means](https://3dwk.com/resources/what-needs-manual-means-preliminary-quote).
Fixed versus variable cost in the estimate
**Mostly fixed per lot:** CAM, fixture design, first setup prove-out, heat-treat lot fees when selected (e.g. 17-4PH H900/H1025 often ~+$60/lot under **rates.v1.1** estimates), finish batch minimums.
**Mostly variable per piece:** spindle time, stock consumed, insert wear, piece inspection.
Prototype qty 1–5 is dominated by fixed work. Bridge qty 25–100 starts to look different. Production hundreds may need fixtures or process changes the automatic band never assumed—those lines often go **needs_manual**.
How to ask for breaks without gaming the mid
State the quantities you might order as a ladder: e.g. 2 / 10 / 25 / 50. Do not upload qty 1, screenshot the mid, then claim you “always meant 100.” Re-parse when qty changes. If revisions differ by qty tier, say which Rev applies to which tier.
Illustration 1 shows an **Example part** unit-cost curve sketch with setup-heavy early qty and flattening later—rates.v1.1 planning only.
Material and process effects on break shape
Soft aluminum and PA66 (machine-time coeff ×0.8 under **rates.v1.1** estimates) often show earlier soft breaks because variable time is lower. 17-4PH (×1.4), IN718/IN625 (×2.5), and CoCr (×2.2) keep variable time high, so unit cost falls more slowly. Bar $/kg planning bands (estimates): PA66 ~5, 17-4PH ~9, IN718 ~55, IN625 ~60; SLM powder bands differ when additive is in play. Hot-alloy or CoCr lines above configured USD thresholds auto-route to **needs_manual** regardless of a pretty qty ladder.
Packaging the RFQ for honest bands
- One STEP + PDF datums per revision
- Material + condition (not “steel”)
- Qty ladder and need-by windows per tier
- Finish list only where functional
- Note if qty 1 is for fit-check and qty 25 assumes same process
Incomplete packs still upload; they produce wider bands. See [DFM checklist before an online CNC quote](https://3dwk.com/resources/dfm-checklist-before-online-cnc-quote).
Lead time is not the inverse of unit cost
Higher qty can improve unit cost while stretching calendar time (more spindle hours, finish queue, CMM sampling). Ask for need-by per tier. Parallel SLM vs CNC trade studies belong on separate lines—do not paste an aluminum mid onto an Inconel qty-50 fantasy. Background: [CNC vs die casting vs injection molding by volume](https://3dwk.com/resources/cnc-vs-die-casting-vs-injection-molding-by-volume).
Illustration 2 contrasts a single vague qty note versus a laddered RFQ and the estimate clarity that follows.
When automatic breaks stop and humans start
Automatic bands assume continuous CNC process assumptions. If qty 200 needs dedicated fixtures, multi-spindle thinking, or a different stock form, expect **needs_manual**. That is not a rejection—it is where engineer ranges replace the parser. Do not invent a firm PO price from a neighbor line’s mid.
Example part walkthrough
**Example part:** 6061-T6 bracket, ~80×60×12 mm, ISO 2768-m, four M4 through, Type II optional. Ladder qty 2 / 10 / 25 with the same STEP. Expect clearer planning bands on [quote-new.php](https://3dwk.com/quote-new.php) than a lone “qty TBD.” Same geometry in IN718 qty 25 with “tight all over” often lands manual—without inventing customer invoices.
What to do next
Build a qty ladder that matches purchasing reality, 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 min/mid/max as planning ranges under **rates.v1.1**, not invoices.
Inspection and sampling as hidden break drivers
Qty 2 often implies near-100% dimensional attention on mates. Qty 25 may allow sampling plans if your quality agreement allows it. If the PDF says “100% CMM all dims,” the unit-cost curve flattens because inspection stays variable-heavy. Say whether FAIR is required once per lot—see [first article inspection reports](https://3dwk.com/resources/first-article-inspection-reports) and [CMM vs optical measurement](https://3dwk.com/resources/cmm-vs-optical-measurement-machined-parts).
Stock form and nesting notes
Plate vs bar vs near-net blanks change how breaks appear. A thin plate nest may improve at qty 10; a large bar drop may barely move until qty covers remnant waste. State preferred stock form when you care. Do not assume the parser will invent an optimized nest for an incomplete envelope note.
Finish batches and quantity
Anodize, passivate, powder, and plating vendors often have lot minimums. A qty 3 Type III hardcoat can carry nearly the same finish adder story as qty 10 if the line is finish-dominated. Call finish only where functional so finish minimums do not dominate a prototype ladder. Related: [powder coating vs painting](https://3dwk.com/resources/powder-coating-vs-painting-metal-parts), [zinc vs electroless nickel vs black oxide](https://3dwk.com/resources/zinc-plating-vs-electroless-nickel-vs-black-oxide).
Common questions
Should I always request 1 / 10 / 100?
Only if you might buy those tiers. Fake ladders waste review time and confuse lead-time notes.
Does doubling qty always halve unit cost?
No. Once variable time dominates, doubling qty cannot erase spindle minutes. Soft aluminum breaks harder early; hot alloys break slower.
Can I use yesterday’s mid for a new qty?
No—re-upload or update the line so the parser recomputes. Pasting old mids onto new qty is how PO disputes start.