A CNC quote should start with an input review and end with an explicit pricing decision. Between those points, estimate stock, setup, machine and labour time, outside services, inspection and risk as separate lines. A single unexplained total is difficult to review and almost impossible to improve.
Review scope: this article passed an internal Kostira source audit for process consistency, terminology and product limitations. It is not an externally signed manufacturing engineer’s opinion; a competent person at the shop should approve process assumptions, rates and manufacturability for each part.
1. Qualify the request
Confirm that the request includes the 3D model, tolerance drawing, material, quantity, delivery expectation and quality requirements. A STEP model can represent the solid accurately, but it does not necessarily contain surface finish, heat treatment, coating or critical inspection requirements.
Record missing information instead of hiding it inside an estimator’s assumptions. If a tolerance or material grade is not confirmed, make the quote conditional.
2. Read geometry and choose stock
Bounding dimensions, volume and surface area from successfully imported geometry provide a starting point for stock selection and mass. Volume multiplied by density gives model mass only when the import produced a valid closed solid and the units and material density have been confirmed. It is not a quote-ready material cost. Add allowances for sawing, workholding, datums and the intended process. Purchased stock, not finished-part mass alone, drives the material line.
Include:
- purchased stock size and mass;
- cutting layout or nesting, scrap and the usable value of an available remnant;
- minimum order quantity and any full-bar, sheet or plate purchase;
- cutting and inbound freight;
- certification where the customer requires it;
- the current price per kilogram or piece.
For customer-supplied stock, identify the material as consigned instead of automatically setting the whole line to zero. Receiving, identification, storage, cutting and the absence of replacement stock can still create cost or risk.
Kostira reads STEP geometry and keeps stock inputs editable, so an estimator remains responsible for approving the blank.
3. Build the operation sequence
List operations in manufacturing order. A part may require sawing, datum preparation, several milling setups, drilling, grinding, heat treatment and final inspection. Every setup or machine change introduces preparation time and another source of variation.
Do not copy a cycle time from a similar part without checking access, pocket depth, thin walls, tool reach, number of orientations and tolerance. These factors can matter more than net material volume.
4. Separate setup from unit time
The estimate becomes much easier to scale when one-time work is distinct from per-piece work.
| Cost element | Typical treatment |
|---|---|
| CAM and process planning | for a new or revised process, program or operation; allocation depends on shop policy |
| Setup, datums and first-off approval | once per operation or batch |
| Machine cycle | per part × quantity |
| Operator attendance | according to how independently the cycle runs |
| Inspection and documentation | per batch and/or per part |
| Outside processing | supplier quote, mass or lot charge |
This structure explains the difference between quantities of 1, 10 and 100 instead of applying an arbitrary volume discount.
5. Use rates that belong to your shop
A machining-centre hour and a manual bench hour are different cost objects. Each process should use a rate based on the costs your business allocates to that resource. If the model is not established yet, work through the machine hourly rate guide and calculator.
Keep cost and price separate. Calculate expected manufacturing cost first. Then show a measurable contingency separately, followed by margin and other commercial decisions. This prevents a change in risk from distorting the resource rate or expected cycle time.
6. Make risk explicit
Avoid hiding every unknown inside an inflated cycle time. For each contingency, record:
- the event, such as remaking a first-off part after an unproven clamping step;
- the cost basis, such as replacement stock, repeat setup and repeat machining;
- probability and impact, or another documented shop method;
- the removal condition, such as tolerance confirmation or a successful process trial.
A foreseeable event can be included in expected cost when the shop can measure it reasonably. Less measurable uncertainty should be disclosed separately with the calculation basis. Margin remains a separate commercial decision, not another name for unexplained risk.
7. Review before sending
The final check should cover:
- material, quantity and currency against the RFQ;
- every operation and setup;
- rates and billing units;
- outside services and their lead times;
- total cost, margin and commercial conditions;
- whether the PDF or XLSX exposes internal notes.
Where software fits
Quoting software should retain assumptions and remove mechanical data entry. It should not make the manufacturing decision invisible. Kostira provides an editable starting point: it reads STEP geometry, applies the shop’s configured materials and process rates, and produces a cost breakdown plus PDF/XLSX output.
The user remains responsible for manufacturability, time estimates and the final price, especially for novel geometry, tight tolerances and requirements that are not contained in the 3D model.
Sources and related guides
- NISTIR 5808: A Machining Process Planning Activity Model — a primary model of NC process-planning functions and data flow.
- NIST: An Object-Oriented Manufacturing Process Model — a model covering operations, setup, handling, resources, and estimated time and cost.
- FAR 31.205-7: Contingencies — the primary rule distinguishing measurable foreseeable events from contingencies disclosed separately with their basis; we use it as a documentation pattern, not a general legal requirement for Kostira users.
- GAO Cost Estimating and Assessment Guide — guidance for documenting assumptions, sensitivity, risk and the basis of contingency; it is a programme-level guide, so we apply its documentation principles rather than its cost scales.
- What STEP contributes to a quote
- CNC machining cost drivers
- CNC machining cost estimation