CNC Outsourcing Quotation Guide

• 1
  How a machine shop turns a drawing into a price
• 2
  Why ±0.005 mm is not free, and when you do not need it
• 3
  When a part needs 5-axis work and when 3-axis is enough
• 4
  Quantity breaks: the number that changes everything
• 5
  Finishing and outside services in the quote
• 6
  How to read a quote that looks too low
• 7
  What each quote line actually covers

A quote is not a guess. A shop reads your drawing, picks a machine, estimates cycle time, adds material and outside services, then spreads setup and programming across the batch. When you compare two quotes, you are really comparing five numbers: cycle time, setup, material, finishing, and the margin the shop needs to keep the spindle running.

Cycle time dominates. On a 3-axis part with simple pockets, cutting might take 8 minutes. Add a deep 0.5 mm slot with a 3 mm end mill and the same feature can run 25 minutes because the tool has to run slower and clear chips more often. Same geometry, triple the time.

Setup and programming are fixed costs. A 5-axis part with a complex datum scheme may need 4 hours of programming and 2 hours of first-article setup. Spread over 10 parts, that is 36 minutes per part. Spread over 500 parts, it is 43 seconds. This is why the same drawing gets a very different unit price at different quantities.

Material is quoted at the size you actually need, not the size you drew. A part that fits in a 100 × 80 × 30 mm block should be quoted from that block, not from a 150 mm bar. Bar stock with a 6 mm cleanup allowance on every face can add 25% to the material line on a small part.

• 1
  Cycle time scales with features, not volumeThin walls, deep pockets and tight radii cost more time per cubic millimeter removed.
• 2
  Setup amortizes over quantityUnit price drops fast between 1 and 50 pieces, then flattens.
• 3
  Material is sized to the blankOversized stock quietly raises the quote on small parts.

Tolerance is the single biggest lever on a quote after cycle time. General machining holds ±0.05 mm all day. Tightening a bore to ±0.005 mm changes the process: you need a temperature-stable room, a finishing pass with a sharp tool, and in-process gauging. That bore may take three times longer than a ±0.05 mm bore on the same part.

Only tolerance that is actually measured should be tightened. If a bore is a slip fit for a dowel pin, ±0.01 mm is justified. If it is a clearance hole for a bolt, ±0.1 mm is fine and costs nothing extra. Engineers often copy tolerance blocks from a legacy drawing without asking which dimensions the assembly actually controls.

Surface finish behaves the same way. As-machined Ra 1.6–3.2 μm comes free with a normal finishing pass. Ra 0.2–0.8 μm needs a slower feed, a smaller stepover, or a secondary polishing step. If the surface is not a sealing face or a sliding fit, the finer finish buys you nothing but a higher invoice.

A useful habit: mark the 3 to 5 dimensions that matter for function and leave the rest at general tolerance. Shops quote against the critical callouts, and the price reflects real work instead of defensive inspection on every dimension.

• 1
  General tolerance is the baseline±0.05 mm on most dimensions adds no cost.
• 2
  Each tightened callout has a price±0.005 mm needs stable temperature and gauging.
• 3
  Match finish to functionRa 0.8–1.6 μm for fits; Ra 0.2–0.8 μm only for seals or optics.

Axis count is a quoting decision before it is a machining decision. A part with features on four or more faces, or with contoured surfaces that cannot be reached from two setups, is usually cheaper on a 5-axis center because it avoids multiple fixtures and re-datuming. A part that is essentially prismatic with holes on one face belongs on a 3-axis machine.

The trap is quoting a simple part as 5-axis because the shop has the capability. A 5-axis machine has a higher hourly rate and programming takes longer. If a bracket can be made in two 3-axis setups with a soft jaw fixture, that route is usually faster and cheaper, even with the extra setup.

Deep features change the math. A pocket deeper than 4× its tool diameter forces a long-reach tool, which deflects and chatters. The shop either reduces feed, which raises cycle time, or adds a roughing pass with a smaller tool. Both show up in the quote. If you can open the corner radius from 1 mm to 3 mm, cycle time can drop by 20–30% on that feature.

Thin walls have the same effect. Below about 1 mm in aluminum, the part moves during cutting and the shop has to take lighter passes. Tell the shop upfront if a thin wall is structural, or if it can be thickened without hurting the design.

• 1
  5-axis pays off with multi-face featuresOne setup beats three fixtures with re-datuming.
• 2
  Prismatic parts belong on 3-axisLower hourly rate, shorter programming.
• 3
  Corner radii drive cycle timeOpening a 1 mm radius to 3 mm can cut time 20–30%.

Quotes are usually tiered: 1, 10, 50, 100, 500, 1,000 pieces. The shape of that curve tells you more about a shop than the headline price. A healthy curve drops steeply from 1 to 10, flattens from 50 to 500, and only moves slightly beyond 1,000 because material and machine time stop shrinking.

A flat curve that barely moves between 1 and 100 pieces usually means the shop has quoted mostly material and machine time, with little setup. That is fine for simple parts. On complex parts, a flat curve may mean the shop did not account for programming, which leads to a surprise later.

Prototypes and production parts should be quoted together. If you order 1 piece now and 200 later, the shop keeps the program and fixture, and the second order skips the setup charge. Ask whether the quote includes fixture retention, because losing the fixture means paying setup twice.

Watch the material break at quantity. Some suppliers buy bar stock per order and pay a cut charge each time. At 500 pieces, buying a full bar or plate can drop the material line noticeably. Ask if the quote assumes remnant or full-length stock.

• 1
  Read the curve, not the priceSteep drop to 50, flat after 500 is normal.
• 2
  Quote prototype and run togetherKeeps the program and fixture alive for the second order.
• 3
  Ask about stock assumptionsRemnant versus full bar changes the material line.

Anodizing, plating, powder coating and laser marking are almost always subcontracted, even by shops that machine in-house. That means the finishing line in a quote contains a supplier price plus handling, and it carries its own lead time. Ask whether finishing is quoted from a specific supplier and whether color or thickness is guaranteed.

Hardcoat anodizing builds thickness, typically 25–50 μm, and can change a tight bore by more than the tolerance. If a bore is ±0.01 mm and gets hardcoated, the shop has to mask it or machine it undersize before coating. Both add cost, and masking is a manual step.

Laser marking has a practical limit: character height below 1.5 mm is hard to read and hard to repeat. If your part number is 20 characters and the marking area is 4 mm wide, the quote may include a second operation or a different marking method.

Bead blasting, tumbling and brushing are cosmetic and cheap per part, but they hide tool marks rather than remove them. If a surface is a sealing face, blasting is the wrong call. State the function of each finished surface so the shop does not blast a critical land.

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  Finishing is usually subcontractedIt adds handling and its own lead time.
• 2
  Hardcoat moves dimensionsMask or pre-machine tight bores before coating.
• 3
  Laser marking needs 1.5 mm minimum heightSmaller text adds a second operation.

A quote far below the others is not a bargain until you know what was left out. The usual omissions are setup, first-article inspection, finishing, and packaging. Ask for a line-item breakdown: material, machining, setup, finishing, inspection, freight. A shop that will not break it down is telling you something.

The second red flag is a missing DFM note. A competent shop will flag a 0.5 mm wall, a deep narrow slot, or a tolerance that cannot be held, before you place the order. If the quote has no comments on the drawing, either the part is genuinely simple or nobody looked closely.

The third is vague lead time. "3–5 days" or "2 weeks" without a start condition is not a commitment. Ask when the clock starts: on PO, on material arrival, or on drawing approval. Material lead time for 7075 or Ti-6Al-4V can be longer than machining time.

Finally, check the certification line against your industry. Medical work needs ISO 13485, automotive needs IATF 16949. A shop that lists certifications it does not hold will fail your supplier audit later, after you have already committed the tooling.

• 1
  Demand a line-item breakdownMaterial, machining, setup, finishing, inspection, freight.
• 2
  A quote with no DFM notes is suspiciousSimple parts get notes too, just shorter ones.
• 3
  Pin down when lead time startsPO date, material arrival, or drawing approval.