CNC Machining RFQ Guide

• 1
  What a CNC Machining RFQ Actually Prices
• 2
  What to Send With a CNC Machining RFQ
• 3
  How Tolerance and Geometry Pick the Machine
• 4
  Why Two Shops Quote the Same Part Differently
• 5
  How to Read a Quote Back
• 6
  From RFQ to First Article: The Sequence
• 7
  RFQ Detail versus What It Changes

A request for quotation is a translation step. You hand over a drawing and a quantity, and the shop turns it into time on a machine. Every line in the returned quote maps to a physical action: face the stock, rough the pocket, drill the holes, heat treat, anodize, inspect, pack. If a quote arrives as a single number with no assumptions listed, the shop either guessed or copied a similar job.

The three inputs that move the number are geometry, tolerance and quantity. Geometry sets which machine can reach the part. A bracket with features on five faces needs a 5-axis setup, while a flat plate with a few holes runs on a 3-axis mill in one pass. Tolerance decides how much of the cycle is cutting and how much is measuring. Quantity spreads the setup cost, which is why ten parts often cost far less than ten times one part.

Software turns those inputs into an estimate. CAM software calculates tool paths from the model, applies feeds and speeds for the material, and adds setup time per operation. The shop then overlays real constraints: fixture availability, machine capacity that week, and whether the tolerance can hold on the chosen machine. Two shops can quote the same part 40% apart and both be right, because they planned different processes.

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  GeometryFace count and feature depth decide the machine.
• 2
  ToleranceTighter bands add cutting passes and inspection time.
• 3
  QuantitySetup cost is fixed; cycle time is not.

Send a 3D model and a 2D drawing together. The model defines shape; the drawing defines intent. Features that look identical in CAD can carry very different tolerances, and the drawing is where that difference lives. A STEP file alone forces the shop to assume general tolerances, which usually means a looser part than the assembly needs.

On the drawing, call out the datum scheme first. Datums tell the inspector how the part sits in the fixture and in the assembly, so they drive both machining and measurement. Then mark the surfaces that matter: a sealing face at Ra 0.8–1.6 μm, a bearing bore at ±0.005 mm, a clearance hole at ±0.2 mm. Blanket tolerances across every dimension raise the price without improving the part.

Add material grade, surface finish, heat treatment and any secondary operations. Write aluminium 6061-T6, not aluminium. Write anodize hardcoat, not coating. Include thread class, edge break requirements, and whether you need milled radii or a sharp corner. These small words decide which tool the machinist reaches for, and they change the quote.

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  Model plus drawingSTEP for shape, PDF for tolerance and finish.
• 2
  Datum schemeSets both fixturing and inspection.
• 3
  Named materials6061-T6 and 7075 machine differently.
• 4
  Secondary opsHeat treat, plating and marking add lead time.

Tolerance and geometry work together to limit the process. A part that fits in a 500 × 500 × 450 mm envelope with features on three faces runs on a 3-axis mill. Add features on the fourth or fifth face and the part must be repositioned for each new setup, unless a 4-axis or 5-axis machine can reach them in one. Every extra setup adds a fixture, a re-datum, and a stack of positional error.

On our floor, 27 three-axis machines handle plate work and simple housings, 12 four-axis mills cover parts that rotate around one axis, and 16 simultaneous 5-axis centers cut complex contours without repositioning. For turned parts, 16 mill-turn centers combine turning and milling in one cycle, which removes a second operation and its re-clamping error. Maximum processing size is 4,000 mm, with travels from 500 × 310 × 200 mm up to 4,000 × 400 × 150 mm.

Tolerance is the second filter. General machining holds ±0.1 mm without effort. Moving to ±0.005 mm changes the plan: finer tools, smaller depth of cut, temperature control, and more frequent in-process checks. That band is achievable on the right machine, but it should be reserved for the two or three dimensions that actually need it. Applying it to the whole part multiplies cost for no gain.

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  Three-axisFlat parts, one setup, lowest cost.
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  Four-axisParts rotating around one axis.
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  Five-axisComplex contours, one setup, no re-datum.
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  Mill-turnTurned parts with milled features.

A wide spread between quotes is normal, and it usually comes from process choice rather than margin. One shop plans a single 5-axis setup with a custom soft jaw. Another plans three 3-axis setups with two fixtures. Both can make the part. The first has higher programming and tooling cost, the second has higher labor and positional error. The cheaper quote is not automatically the better one.

Quantity assumptions matter too. A shop quoting 50 pieces will plan a dedicated fixture and amortize it. A shop quoting 10,000 pieces will plan a fixture, a first article, and possibly a second source for raw material. If your RFQ states 50 but your program needs 5,000, ask for both price breaks and note where the process changes.

The third variable is inspection. A general-tolerance part might be checked with calipers. A ±0.005 mm bore needs a coordinate measuring machine and a controlled environment. If the quote does not mention inspection, ask. Unclear inspection scope is the most common source of rejected lots, and the cost lands on both sides.

Finally, watch the material line. Aluminium 7075 and 17-4PH stainless cost more and cut slower than 6061. Titanium and Inconel cut slower still. If two quotes assume different grades, the numbers are not comparable.

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  Setup strategyOne 5-axis setup versus three 3-axis setups.
• 2
  Quantity breakThe process plan changes at volume.
• 3
  Inspection scopeCMM time is a real line item.

A usable quote lists assumptions before it lists price. Look for the material grade, the finish specification, the tolerance standard and the inspection method. If the quote says the part will be made to your drawing, confirm that the drawing you sent is the revision referenced. Revision mismatches are a quiet and expensive error.

Then check the lead time breakdown. Quotation and free DFM analysis come back within 12 hours at our shop. Production can start within 24 hours of a released PO. Parts ship in 3–5 days for standard work. If a quote shows a much longer window, ask which step is the bottleneck: material purchase, heat treatment, or machine capacity.

Ask about the NDA if your design is sensitive. Uploads are secure and confidential, and a non-disclosure agreement is available on request. For regulated programs, confirm the quality system: we hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. Match the certificate to your industry before you release the PO.

One more check: does the quote mention the fixture? For a first run, fixture cost is often the largest single line. Ask whether it is reusable for the next order. If it is, the second order should be cheaper, and a supplier who cannot answer that question has not planned past the first batch.

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  Assumptions firstThey tell you what is being priced.
• 2
  Revision matchConfirm the drawing revision in the quote.
• 3
  Lead time by stepFind the real bottleneck.
• 4
  Fixture reuseAffects the next order's price.