Guide
How do you run an engineering change notice with an outside machining or casting supplier?
An engineering change notice is the controlled document that tells everyone who builds, inspects or buys a part exactly what changed on its drawing or model, which revision is now current, from which order or lot the change takes effect, and what happens to parts already made to the old revision.
By Saola Manufacturing engineering team · Published · Updated
Inside one company, an engineering change often moves through a PLM workflow that every department can see. Across a company boundary that visibility disappears. The supplier sees a PDF in an email, a purchase order that may or may not name a revision, and a pile of castings or bar stock already cut to the previous drawing. Many wrong-revision parts are not machining mistakes at all: the supplier built faithfully to a drawing that was no longer current, because nothing in the paperwork told them to stop. This guide is about the interface, not your internal change board: what the notice to an outside shop must say, how to set effectivity and disposition, why cast-and-machined parts need extra care, and what to write on the PO so the current revision is the only one that can ship.
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What is the difference between an ECR, an ECN, an ECO and a deviation?
An engineering change request (ECR) proposes a change, an engineering change order (ECO) is the internal approval to make it, and the engineering change notice (ECN) is the release that announces the approved change to the people who must act on it. A deviation or waiver is different: it accepts a departure from the current drawing for a stated quantity or period without changing the drawing at all.
Companies use these labels inconsistently, and some use ECN and ECO as synonyms. The ideas underneath are stable, whatever the names. The configuration-management guidance in ISO 10007:2017 treats change control as proposing, evaluating, approving and then implementing and recording a change, and the SAE EIA-649C standard also handles a temporary departure from released requirements as its own controlled item, separate from a change to the requirement itself. What matters for a supplier is that the document they receive is unambiguous about which of these it is.
The distinction has teeth. A supplier who receives an ECR for review should quote the impact and keep building to the current revision. A supplier who receives an ECN must change what they build from the stated effectivity. A supplier who receives a deviation keeps the old drawing as the requirement and simply has permission to ship a defined quantity outside it. Sending a marked-up drawing with “please use this going forward” in the email body is none of the three, and it is the most common root of wrong-revision disputes because nobody can later prove which document governed which lot.
Deviations also flow the other way. When a supplier finds a feature it cannot hold, it should ask for a written deviation for a specific quantity, not quietly ship and hope. If the same deviation is requested twice, the drawing probably needs a real change, and that belongs in an ECR.
Does a change need a new revision letter or a new part number?
If parts made to the old and new drawings are still fully interchangeable in form, fit and function, revise the drawing and keep the part number. If old parts can no longer be used everywhere new ones can, the part needs a new part number, not just a new revision letter.
This rule comes from US drawing practice, where ASME Y14.35 governs how revisions are identified and recorded and ASME Y14.100 governs when a part must be re-identified. It matters more with an outside supplier than in house, because the supplier, your receiving dock and your stockroom usually track parts by part number alone. If a non-interchangeable change only bumps the revision, old and new parts end up in the same bin with the same label, and the first warning is an assembly that will not go together.
Revision letters themselves follow a convention worth copying even if you do not cite the standard. Recent editions of ASME Y14.35 skip the letters I, O, Q, S, X and Z because they are easily misread as numerals or placeholders, and continue with double letters after Y. A supplier reading a scanned print should never have to guess whether “REV O” is a letter or a zero.
| Change on the drawing or model | Old and new parts interchangeable? | Identification and supplier action |
|---|---|---|
| Clarification only: note reworded, title block fixed, view added, no requirement changed | Yes | New revision letter; supplier updates the controlled copy, no first article needed |
| Tolerance opened, cosmetic note relaxed, finish alternative added | Yes | New revision letter; old-revision stock usually usable as is; confirm in the disposition |
| Tolerance tightened, feature added or moved, material or finish changed but mating parts unaffected | Usually yes, check every assembly that uses it | New revision letter; partial first article on the changed characteristics; disposition required for stock and work in process |
| Mating interface changed, so old parts no longer fit where new ones do | No | New part number (or dash number); new purchase order line; full first article; old part number closed or kept only for service |
| Temporary acceptance of a nonconforming lot | Not applicable | Deviation or waiver for a stated quantity; drawing and revision unchanged |
What should an engineering change notice to a supplier contain?
It should identify the part and both revisions, describe every change in a way the shop floor can act on, state the effectivity and the disposition of existing material, and ask for a written acknowledgment. Anything the supplier has to infer by comparing two PDFs is a future nonconformance.
A notice that works across a language and time-zone boundary carries these fields, in this order:
- Identity. ECN number, part number, part name, superseded revision and new revision, and the file names of the drawing and model released with it. The model and drawing should carry the same revision; a mismatch is a common way for a supplier to end up machining the wrong geometry, as the machining RFQ guide explains for new parts.
- Change list. One numbered line per change, with the zone on the drawing, the old requirement and the new requirement. “Hole pattern updated” is not a change description; “Zone C4: four tapped holes moved, see view B, position tolerance unchanged” is.
- Reason, briefly. One sentence on why. A supplier who knows the change fixes an assembly interference will check the related features; one who only sees new numbers will not.
- Effectivity. The purchase order, release, lot or date from which the new revision applies (see the next section).
- Disposition. What to do with raw material, castings, work in process, finished stock and anything in transit at the old revision.
- Verification. Whether a full or partial first article is required, which balloons must be re-measured, and whether samples must be approved before production restarts.
- Acknowledgment. A named person at the supplier confirms receipt, confirms the old revision has been withdrawn from the floor, and states the first lot that will be built to the new revision.
On the drawing itself, the revision block should repeat the ECN number next to each revision letter so the two documents can always be matched. If you balloon drawings for inspection, keep existing balloon numbers and add new ones for new characteristics, as the guide to ballooned drawings and inspection reports describes, so that the first article at the new revision can be compared line by line with the old one.
How do you set effectivity and disposition so old-revision parts stop shipping?
Tie effectivity to something both sides can see on paper, usually a purchase order line or a release, rather than to “as soon as possible”. Then give a separate disposition for every stage of material, because a supplier will otherwise finish and ship whatever is already in process.
Date effectivity sounds simple but fails offshore: parts machined before the date may still be on the floor, on the water or in a consolidation warehouse after it. PO or release effectivity is cleaner. State that every PO line issued after the ECN calls out the new revision, and decide explicitly whether open lines on existing POs convert to the new revision or finish at the old one. If they convert, amend those PO lines in writing so the revision on the PO, the drawing and the packing list all agree.
For disposition, use the familiar categories and assign one to each stage of material:
- Use as is: old-revision parts are acceptable for all uses; ship them, identified as the old revision.
- Rework: old-revision parts can be brought to the new revision by an added operation, such as an extra drilled hole; the supplier quotes the operation and re-inspects the affected features.
- Hold: stop and segregate until the engineer decides, typically for work in process caught mid-routing.
- Scrap: parts cannot be used or reworked; agree in advance who carries the cost.
Write the disposition separately for raw stock, castings or blanks already made, parts mid-routing, finished parts at the supplier, and parts in transit. Then ask how old-revision parts will be marked if any ship after the change. A label or tag on the carton that names the revision, matched by the revision on the packing list and the certificate of conformance, lets receiving inspection catch a mix before it reaches the line. The certificate of conformance guide covers what that document should state.
Cost belongs in the same conversation. Under United States federal contracts, the FAR 52.243-1 Changes clause lets the contracting officer change drawings or specifications within the general scope of the contract by written order, and requires the contractor to assert its right to a price or schedule adjustment no later than 30 days after receiving that order. Commercial purchase orders rarely spell this out, which is why it helps to state in your PO terms how a supplier submits the cost and schedule impact of an ECN and who approves it before work starts.
Why are changes to cast-and-machined parts harder to control?
Because the part exists in two states, and a change can hit the casting tool, the machining program and fixture, or both. A revision that only moves a machined hole is a program edit; a revision that moves a cast boss is a tool modification that can also invalidate every casting already in stock.
The cleanest way to keep this under control is to release separate casting and machining drawings with their own revisions, so an ECN can say precisely which one changed. The trade-offs of that split are covered in casting drawing vs machining drawing. With a single combined drawing, every revision forces the supplier to work out whether the tool is affected, and a change that touches only machined features can still trigger an unnecessary question about the die.
For a part that goes through die casting and then secondary CNC milling, ask the ECN to answer four questions explicitly: does the casting geometry change; can existing castings be machined to the new revision (often yes when material is only being removed, rarely when it must be added); do datum features or targets move, which would mean new machining fixtures; and does the change affect the finish or masking. If the die must be modified, agree who owns the modified tool and who pays for it before the work is done, as discussed in die-casting tooling ownership, and record the tool's own revision so a later casting can be traced to the tool state it came from.
Finish changes deserve the same rigor. A switch from one plating or coating to another, or a new masking requirement on a bore or thread, is a revision even when no dimension moves, because it changes the routing and the finished size of coated features.
How do you stop the wrong revision being built in the first place?
Make the revision appear on every document that drives production, so a mismatch is visible before cutting starts. The purchase order, the drawing title block, the file name, the inspection report and the shipping documents should all carry the same revision.
The failures repeat across suppliers and countries, and each has a simple control:
- PO without a revision. Put “Part number, revision, drawing number” on every PO line and add a standard note: “Build to the revision stated on this PO line. If the drawing you hold shows a different revision, stop and contact the buyer.”
- Superseded copies on the floor. Ask the supplier how obsolete prints are withdrawn: printed travelers, tablets at the machine and files in the CAM folder all count. Ask that the acknowledgment confirm all copies at the old revision were removed or marked superseded.
- Model and drawing out of step. Release them together, with the revision in both file names, and state which governs if they disagree.
- Email-thread changes. A dimension agreed in a chat message never reached the drawing. Treat any agreed change as an ECR and close it with a released revision or a written deviation.
- Sub-tier suppliers. Plating, heat treatment or casting done by a supplier's own vendors also needs the change. Ask the supplier to confirm it has flowed the ECN down.
Verification closes the loop. A design change that affects form, fit or function should trigger a first article on at least the changed characteristics; the aerospace standard SAE AS9102C calls this a partial first article inspection, and the same logic works outside aerospace. The guide to first article inspection with an overseas supplier lists what that report should contain. Require the report header to name the drawing revision, and do not release production until it matches the ECN.
What does Saola do when you send a revised drawing?
A revised drawing goes through the same steps as a new one on the quality page: drawing review with a marked-up copy returned to you, then a first article measured against every toleranced dimension when new tooling is involved, before production runs to the verified routing.
The quality page lists a process routing sheet per part number, available on request, a first-article inspection report for the first piece off new tooling, and a dimensional inspection record with every lot, checked against your drawing. It also states that nothing moves forward on a verbal okay, and that an out-of-tolerance first-article measurement is reported to you with the measured value and a proposed fix before a sample ships. Those records are what let you confirm that a change has actually been built.
The site does not describe a separate, formal ECN procedure, so state your own requirements in the notice and the PO: the effectivity, the disposition of castings and stock at the old revision, whether you want a partial or full first article, and the acknowledgment you expect back. If the change affects the casting tool or the finish, say so; as with any quote, tooling cost is priced separately from the piece price. To price a revision or a new part number, send the revised drawing and model through the quote page with the ECN attached.
Frequently asked
Should the first release of a drawing be revision A?
Practice varies. Many companies following ASME Y14.35 show the initial release as a dash or as no revision and use A for the first change; others start at A or at a numeric revision. Either works with a supplier as long as the PO and drawing use the same scheme and nobody has to guess what “latest” means.
Can a supplier change our drawing?
No. A supplier can mark up a copy, propose changes through DFM feedback or request a deviation, but only the design owner releases a new revision. If a supplier's suggestion is accepted, it should come back to the supplier as your ECN and revised drawing, not as their marked-up copy.
Do we need a new first article for every revision?
Not for a clarification that changes no requirement. For anything that changes a requirement, a partial first article on the changed characteristics and anything that depends on them is the usual minimum, and a change of tooling, material source or manufacturing location calls for a new first article, full or partial, covering every characteristic the change could affect.
How do we handle a change while parts are already on the water?
Give in-transit parts their own disposition in the ECN, ask the supplier to confirm the revision on the packing list and certificate for that shipment, and flag the shipment for receiving inspection so the parts are segregated and either used as is, reworked or returned according to the disposition.
Is a redline on a PDF enough for a small change?
Only as a temporary deviation for a stated quantity. A redline that becomes the permanent requirement without a released revision leaves your own drawing out of date, and the next supplier, or the next buyer, will build to the old one.
Sources
- ASME Y14.35, Revision of Engineering Product Definition Datasets and Associated Documents, American Society of Mechanical Engineers, 2025 edition
- ASME Y14.100, Engineering Drawing Practices, American Society of Mechanical Engineers, 2017 edition
- ISO 10007:2017, Quality management – Guidelines for configuration management, International Organization for Standardization, 2017
- SAE EIA-649C, Configuration Management Standard, SAE International, 2019
- SAE AS9102C, Aerospace Series – First Article Inspection Requirements, SAE International, 2023
- FAR 52.243-1, Changes – Fixed-Price, Federal Acquisition Regulation, accessed October 2026