When a part is already catalogued, a request is easy to answer: a part number and a quantity are enough to come back with a price and a lead time. When the part has to be made, those same two lines leave almost everything undecided, and the reply you get back is a range rather than a number.
The gap is rarely about willingness. It is about the number of open questions, and each one of them moves the price.
Why the first reply is often a range
A quotation is a commitment. Before it can be firm, the supplier has to be able to answer four questions: what exactly has to be made, from what, to what tolerance, and how it will be shown to conform. A request that answers three of the four produces a quotation with conditions attached — and a conditional quotation is what a range looks like from the outside.
The items that decide the answer
| Item | What it settles | Typical effect if missing |
|---|---|---|
| Drawing or sample | Geometry, interfaces, features | Nothing can be quoted |
| Material specification | Cost, machinability, treatment | Price moves by a wide band |
| Tolerances and finish | Machine time, inspection method | Assumed worst case, priced high |
| Quantity and repeat pattern | Setup amortisation | One-off pricing on a repeat order |
| Required documentation | Traceability, test scope | Added later at a higher unit cost |
| Delivery date and destination | Routing, packaging, freight | Freight excluded, then renegotiated |
The drawing is the contract
A dimensioned drawing settles more than any description can. Where a drawing does not exist — a worn part, a competitor's item, an assembly that has to be matched — a physical sample plus a written statement of the interfaces is the next best thing, provided the sample is identified and its condition is stated. A photograph alone is a starting point, not a basis for manufacture.
Where a part number from another manufacturer is being used as the reference, say so explicitly. The number identifies the item being replaced; it is not a manufacturing instruction, and the drawing controls what is actually made.
Material and process
Two requests for the same shape in two materials are two different jobs. State the material by specification where one exists. Where it does not, state the property that matters — strength at temperature, wear resistance, weight, corrosion behaviour — and let the material be proposed back to you for approval.
If a surface treatment, heat treatment or coating is required, say whether it is called out on the drawing or expected by convention. Conventions travel badly between organisations.
Tolerances, finish and inspection
The tightest tolerance on a drawing sets the inspection method for the whole part more often than it should. Where a tolerance is functional, keep it tight; where it is inherited from a template, loosening it is the single easiest way to reduce cost without changing the part's behaviour.
State how conformity is to be shown: a certificate of conformity, dimensional report, material certificate, first-article inspection report, or a combination. Each one is a distinct piece of work and appears in the price.
Documentation and traceability
Ask early, not at delivery. If the part will be installed on an aircraft, the documentation that has to accompany it is decided by the airworthiness framework the operator works under, not by the supplier's default. Name the requirement in the request and it can be built into the process; raise it after despatch and it becomes a separate job.
What a supplier sends back
A firm quotation answers the four questions above and states the assumptions it rests on. If the assumptions are wrong, the number changes — so read them. Where a request is genuinely incomplete, the useful reply names the specific gaps rather than pricing the widest interpretation of every open point.