When two foundries quote the same casting and the numbers land 40% apart, the instinct is to assume one of them is expensive. Usually neither is. They answered two different questions, because the package they received left room for two different answers.
Almost everything published on this subject is written by foundries, so it reads as a list of files to send. This guide is the buyer's version: what goes in the package, what each field changes about the price you get back, and what it costs you to leave it out. It's written for the person who owns the RFQ but may not own the drawing, and it sits inside the wider process covered in our practitioner's guide to strategic sourcing.
What does a foundry actually need to quote a casting?
The minimum viable package is a 2D drawing with tolerances, notes and a revision level, a 3D model in a neutral format, the alloy or an allowed equivalent, annual volume plus first-order quantity, the machining scope, and the delivery terms. Everything else refines the number; these decide whether a number can be produced at all.
Here's the full package, with what each line does to the quote.
| Field | Why the foundry needs it | If you leave it out |
|---|---|---|
| 2D drawing with revision level | Carries tolerances, datums, notes, and which revision is current | The shop quotes an assumption, or no-quotes |
| 3D model (STEP) | Geometry, wall sections, feeding and gating study | Manual modelling time gets priced in, or added later |
| Alloy or approved equivalent | Melt availability, mechanical properties, heat treat | Silent substitution, or a premium for a melt they don't run |
| Tolerance grade and critical dimensions | Decides tooling, process control and scrap rate | Blanket tolerances price the whole part at the tightest feature |
| Surface finish requirement | Secondary operations and inspection method | Finish disputes at first article |
| Annual volume and first-order quantity | Tooling amortization and process choice | The quote answers the wrong question |
| Process preference, or "open" | Sand, permanent mould, die casting each price differently | You lose the cheaper alternative they'd have suggested |
| Machining scope | Whether they machine, subcontract, or ship as-cast | The largest single source of incomparable quotes |
| Required records (FAI, PPAP, certs) | Real cost and real calendar time | Discovered late, then requoted |
| Packaging and destination, with Incoterm | Freight, duty, and who carries them | Two quotes that can't be compared on landed cost |
A useful test before sending: could a shop that has never spoken to you produce a firm price from this package alone? If the honest answer is no, you're not sending an RFQ, you're starting a conversation. Both are fine, but they get different response rates. Standardizing the package is what RFQ templates are for.
How much detail does the drawing need?
Send the drawing and the model together, not one or the other. A model carries geometry but no tolerances, no notes and no revision control, so a model alone isn't quotable. The drawing is what makes the requirement contractual.
Three things belong on the face of it: the revision level, the datum scheme, and a clear separation between dimensions that are functional and dimensions that are reference. Foundries price risk, and an undated drawing with no datums reads as risk.
The most expensive sentence a buyer can put on a casting drawing is a blanket tolerance applied to every dimension. It tells the shop to hold the tightest number everywhere, which changes the tooling, the process control and the scrap rate on features that never needed it. The fix isn't to loosen everything. It's to call out the few dimensions that matter.
What tolerances should you specify, and under which standard?
Cite the standard properly, because the standard is what the foundry quotes against. ISO 8062-3 defines sixteen linear dimensional casting tolerance grades, designated DCTG 1 to DCTG 16, with geometrical tolerances handled separately as GCTG grades (ISO 8062-3:2007, clause 5.2). Two rules inside that standard catch buyers out regularly.
- Wall thickness gets one grade coarser. For wall thicknesses in grades DCTG 1 to DCTG 15, one grade coarser applies. A wall is not held to the same tolerance as a linear dimension, by design.
- The tolerance is symmetric by default. Unless stated otherwise, the casting tolerance is disposed symmetrically about the nominal dimension, half positive and half negative. If your feature needs a unilateral tolerance, that's a callout, not an assumption.
The standard is also explicit that where general tolerances don't fit, whether you need something tighter for function or looser for economy, individual tolerances must be indicated on the drawing in accordance with the GPS standards (ISO 8062-3, clause 5.1). That's the mechanism for a tight feature: one callout, not a tightened blanket.
High-pressure die casting works to a different reference. NADCA publishes two tolerance sets, Standard and Precision, across seven categories: linear dimensions, dimensions across the parting line, dimensions formed by moving die components, angularity, draft, flatness, and cored holes for threads. Standard runs roughly ±0.010 in on the first inch of length; Precision runs roughly ±0.002 in, and it's reached through tooling investment and tighter process control, not by asking (NADCA Product Specification Standards).
That last point is the one worth internalizing. Precision is something you buy. When a drawing carries precision-class tolerances by default, the buyer has made a purchasing decision without pricing it.
| If the part is | The governing reference | What to put on the RFQ | The cost lever |
|---|---|---|---|
| Sand or permanent mould | ISO 8062-3 (DCTG / GCTG); Aluminum Association standards for the process | The grade, plus individual callouts on functional features | Coarser grade, fewer callouts |
| High-pressure die cast | NADCA Standard or Precision | Which set applies, and to which dimensions | Standard everywhere except where Precision is functional |
| Machined after casting | The machining print governs the finished feature | Which features are as-cast and which are machined | Machine fewer features |
So what should a buyer actually write? Ask each foundry which grade it holds routinely on your process and part size, specify that as the general grade, and tighten only the features that need it. Sending a blanket tolerance and waiting to see what comes back is the expensive alternative, and it usually surfaces at first article rather than at quote.
Which alloy, and should you let the foundry substitute?
Name the alloy or name the properties, and say which one you mean. If you specify an alloy the shop doesn't run, you either pay for a melt set up for you or you get a substitution nobody told you about.
The safest construction is "specified alloy, or approved equivalent meeting the stated mechanical properties", with the properties actually stated. That gives the foundry room to quote what it melts weekly while keeping the requirement enforceable. Heat treatment condition is part of the specification too, not a note at the end.
For sand and permanent mould work, the Aluminum Association publishes the standards that govern the process, and referencing them beats improvising your own acceptance language.
How do volume and tooling change the quote?
Quantity isn't a detail on a casting RFQ, it's most of the price. Tooling is a one-time cost amortized across the parts that follow it, so the same drawing at 500 pieces a year and 50,000 pieces a year produces two legitimately different quotes, often at different processes.
Give both numbers: estimated annual usage and first-order quantity. They answer different questions. Annual usage tells the shop which process and tooling class makes sense. First-order quantity tells it what you'll actually buy on the first purchase order, which is what the amortization math needs.
Then ask three questions that decide whether quotes are comparable at all:
- Is tooling amortized into the piece price, or invoiced separately? This single difference can make the cheaper-looking quote the expensive one.
- Who owns the tooling, and where does it live? Tooling ownership is leverage at the next price review.
- What's the tooling lead time, separately from part lead time? They're different calendars, and the second one doesn't start until the first finishes.
Ask for the quote validity window in writing as well, along with the metal-price basis. That matters more in 2026 than it did: aluminium casting prices are being squeezed by tariffs, energy costs and a record Midwest premium, with foundry margins compressed on all three (AlCircle, 2026). Quotes that would once have held for a quarter now often hold for weeks.
Whether a category like this deserves a full sourcing event or a fast competitive round is a separate decision, and our strategic sourcing guide sets out the rule.
What about machining, finishing, and inspection?
Decide as-cast versus machined before the package goes out, because it changes who can quote. Near-net as-cast surfaces are cheaper and perfectly adequate where nothing mates; critical interfaces and datums usually want machining. The decision is yours to make explicit, not the foundry's to guess.
State the machining scope as a list, not as an adjective. "Machined" means every feature to one shop and the listed features to another, and that ambiguity alone produces the widest spread you'll see in a quote set.
Records belong in the RFQ, not in the purchase order. First article inspection, PPAP level if you need one, material certificates, certificates of conformance: each carries real cost and real calendar time. A foundry that discovers them after quoting will requote, and you'll have lost two weeks to find that out. The same principle drives our approach to RFQ validation.
Why do foundries no-quote?
A no-quote usually isn't a capacity problem. Shops triage incoming requests and decline the ones that aren't worth the estimating hours, weighing the clarity of the package, the order volume, the buyer's history and the relationship. Successful shops describe no-quoting as normal practice rather than an exception (Production Machining).
On castings specifically, the recurring triggers are predictable:
- No revision level, so the shop can't tell which drawing governs.
- Blanket tolerances that imply a precision job on an ordinary part.
- Missing volume, which makes tooling amortization unanswerable.
- A process the shop doesn't run, which a one-line process note would have caught.
- Inspection and documentation requirements discovered halfway through estimating.
- An RFQ that visibly went to fifteen foundries, which reads as a price-fishing exercise.
The counter-move isn't a wider net. It's three to five qualified shops and a package worth their estimating time. We cover the general pattern in why RFQs don't get answered on time and the mechanics in ten best practices for managing RFQs.
How do you keep the quotes comparable when they come back?
Comparability is built on your side, not delivered on theirs. Supplier-side quoting is still overwhelmingly manual, with roughly 90% of shops quoting from spreadsheets or by hand and only about 10% using estimating software (CNCCookbook, n=100, a vendor survey with self-selected respondents). What arrives reflects each estimator's own habits, not a common format.
Normalize these lines before you compare anything.
| Line | What differs between foundries | How to normalize |
|---|---|---|
| Tooling | Amortized into piece price vs invoiced separately | Restate both quotes as tooling plus piece price at your EAU |
| Alloy | As-specified vs an equivalent they melt | Confirm the substitution and its properties in writing |
| Machining | All features vs listed features vs as-cast | Price the missing operations before comparing |
| Finishing | Included vs quoted as a secondary | Move it into the same column for both |
| Freight and duty | EXW vs FCA vs DDP | Compare landed cost, never piece price |
| MOQ and price breaks | Different break points | Evaluate at your actual order quantity |
| Validity | Days vs a quarter, different metal basis | Note expiry; a cheaper expired quote is not cheaper |
| Lead time | Tooling, first article and production quoted separately or together | Build one calendar per supplier |
Only after that does scoring make sense, and price shouldn't be the only column: capacity, past performance and lead-time reliability belong in the same view. The general mechanics live in our guide to supplier quote management, with practical shortcuts in quote comparison tips and supplier quote comparison with AI.
What changes when the casting is sourced overseas?
The package doesn't change. The risk around it does. Your drawing leaves your control, the metal-price basis and the Incoterm carry more weight, and the schedule inherits ocean reliability rather than a truck route. Global container schedule reliability was 64.1% in November 2025, so roughly one arrival in three runs off schedule (Sea-Intelligence Global Liner Performance, November 2025). A tooling calendar built on the assumption that the boat lands on time is optimistic.
Settle confidentiality before the drawing goes out rather than after, and decide what actually needs to be shared: full drawings, or a redacted package sufficient to quote. We cover that decision in when to transform and when to redact. Then compare on landed cost, and treat known shutdown windows as a scheduling input rather than a surprise. Our guide to managing overseas suppliers covers the lead-time side in detail.
FAQ
What information does a foundry need to quote a casting?
A 2D drawing with revision level and tolerances, a 3D model in a neutral format, the alloy or an approved equivalent, estimated annual usage plus first-order quantity, the machining scope, any required inspection records, and the destination with an Incoterm. Missing volume and missing machining scope are the two most common reasons a quote comes back wrong.
What tolerance standard applies to aluminum castings?
ISO 8062-3 defines sixteen linear dimensional casting tolerance grades, DCTG 1 to DCTG 16, with geometrical tolerances handled separately as GCTG grades. For wall thicknesses, one grade coarser applies. High-pressure die castings are normally quoted against NADCA's Standard or Precision tolerance sets instead.
Should I send a STEP file or a PDF drawing?
Both. The model carries the geometry a foundry needs for feeding and gating studies. The drawing carries the tolerances, datums, notes and revision level that make the requirement contractual. A model alone isn't quotable, and a drawing alone adds modelling time to your price.
Why did a foundry not respond to my RFQ?
Most no-quotes are triage rather than capacity. Shops weigh package clarity, order volume, buyer history and relationship before spending estimating hours, and decline the requests that don't justify them. Missing revision levels, blanket tolerances and absent volumes are the usual triggers on castings.
Why are two casting quotes so different?
Usually the difference isn't the piece price. It's tooling treated as amortized in one quote and separate in the other, a different machining scope, an alloy substitution nobody flagged, or EXW against DDP. Normalize those five lines and the real spread is generally much narrower than it first looks.
Key takeaways
- The minimum quotable package is a drawing with a revision level, a 3D model, the alloy or an equivalent, annual and first-order quantity, machining scope, required records, and destination with an Incoterm.
- Cite the right standard: ISO 8062-3 designates DCTG 1 to DCTG 16 for linear dimensions, wall thickness takes one grade coarser, and the tolerance is symmetric about the nominal by default.
- Precision is a purchase, not a request. NADCA's Precision set runs roughly ±0.002 in on the first inch against roughly ±0.010 in for Standard, and it's bought with tooling and process control.
- A blanket tolerance prices the whole part at its tightest feature. Specify the grade the shop routinely holds, then call out the features that matter.
- Give both estimated annual usage and first-order quantity, and ask whether tooling is amortized or invoiced separately. That one answer decides whether two quotes are comparable.
- No-quotes are a triage decision about your package, not a capacity problem (Production Machining). Send fewer, better packages to three to five qualified shops.
- Normalize tooling, machining, alloy, finishing and Incoterm before comparing anything, because roughly 90% of supplier quoting is still manual and arrives in whatever format the estimator uses (CNCCookbook).