What to Clarify When a Drawing Revision Changes
This guide is for engineers who release drawing changes, buyers who amend orders and quality engineers who inspect against the new definition.
A revision letter tells a supplier that something changed, not what changed or which parts it applies to. The sections below cover what to send, what a revision can affect and how to keep old and new parts apart.
What a Revision Letter Tells a Supplier, and What It Does Not
A revision letter identifies a state of a document. On a well-kept drawing, the revision table adds a short description of each change, often with the drawing zone where it appears, and the changed area is flagged or clouded. Conventions for this are set out in standards such as ASME Y14.35, but practice varies between companies, and sometimes between drawings from the same team.
What the letter cannot tell a supplier is how far the change reaches into work already planned, whether parts at the old revision are still usable, which orders the new revision applies to, or whether the 3D model was updated at the same time. Those answers sit with the design owner. Without them the supplier has to guess, and different suppliers guess differently.
Related: Factory and production
Interchangeability rule
in many companies, a change that stops old and new parts from being interchangeable requires a new part number, not just a new revision. State which rule your drawings follow.
What to Send with a Revised Drawing
A revised drawing reaches a supplier in the middle of something: a quote, an open order or a batch already on the machines. A short cover note sent with the files saves several rounds of questions, makes the supplier's impact review faster and more reliable, and leaves your team with a written record of what was communicated and when.
the drawing and 3D model at the same revision, with superseded files clearly withdrawn.
each changed feature, its zone, and the old and new requirement.
which orders, quantities or dates the revision applies to.
whether parts at the previous revision remain usable, and for which builds.
your preferred handling of parts already in progress or in stock.
characteristics that need a new or partial first article.
How a Revision Moves Through Quote, Manufacturing and Inspection
On the supplier side, a revision is usually handled as a short sequence: the new files are compared with the previous revision, the change is classified by what it touches, price and schedule are confirmed, and only then are programs, fixtures and inspection plans updated.
The classification step decides which programs, fixtures and checks a revision reaches — concept illustration
Asking a supplier to describe its own sequence is a fair way to see how changes are controlled.
The classification step decides the rest. A note change may affect only the documents. A tighter tolerance on an existing feature may change the measuring method and the order of operations. A moved hole or new pocket affects the program, possibly the fixture, and the first article. Material or finish changes reach purchasing and subcontractors. Ask for the classification in writing with the revised quotation.
Related: Factory and production
- 01Compare
old and new files checked feature by feature, or overlaid.
- 02Classify
documents only, inspection, program and fixture, or material and finish.
- 03Confirm
revised price, schedule and handling of open work.
- 04Update
programs, fixtures, inspection plan and identification.
- 05Verify
a first article or partial first article on the changed features.
What Different Changes Typically Affect
The effect of a revision depends on what it touches rather than how large it looks on the drawing. A one-line finish note can reach a subcontractor and the appearance reference, while a visible geometry change may need only a program edit. The table gives general patterns; the actual effect on a given part comes from the supplier's review of that part.
| Type of change | What it can affect | What to re-confirm |
|---|---|---|
| Tighter tolerance on an existing feature | Operation sequence, measuring method, scrap risk | Price, inspection method and records |
| New, moved or resized feature | CAM program, fixture clearance, tooling | Price, schedule and a partial first article |
| Datum scheme changed | Setups, fixtures and the whole inspection plan | A full first article and fixture changes |
| Material, condition or form | Stock on hand, purchasing, certificates | Stock status, documents and source approval |
| Finish or masking | Subcontractor instructions, final size, appearance | Finish records and the reference sample |
| Notes or title block only | Documents and labels | Revision on the order, labels and records |
Parts in Progress and Stock at the Previous Revision
Most revisions arrive while something is already in progress: material bought, blanks cut, parts half machined or finished parts waiting to ship. Each group needs a decision, and the decision is commercial as well as technical. The usual options are to complete at the old revision where those parts remain usable, rework to the new revision where the geometry allows, hold pending a decision, or scrap.
Ask the supplier for a count of each group and the cost of each option, then give a written disposition by quantity. Record it against the order so that invoicing, inspection and later questions refer to the same decision. Avoid open-ended instructions such as 'use up old stock', which can leave old-revision parts arriving months later inside a delivery labeled with the new revision.
Keep it in writing
a disposition agreed on a call is easily remembered differently by each side. A short email listing quantities per revision is enough.
Keeping Revisions Apart on Parts, Labels and Documents
Parts at two revisions can look identical, so the separation has to be physical and written.
Separate bags and labels keep two revisions of a similar-looking part apart through packing and receipt.
Where the drawing calls for part marking, the revision is often part of the mark. Bags and cartons should carry the part number, revision and quantity, and old and new revisions should not share a carton unless each bag inside is labeled and your receiving team has agreed to it.
Check that the documents follow the same revision. The inspection report should be made against the drawing revision of the parts it covers, and the packing list and certificate of conformance should name it too. When a mismatch reaches receiving inspection, either the parts or the paperwork may be wrong, and both take time to untangle.
Related: Packaging and identification requirements for machined parts
Re-Confirming Price, Schedule and Inspection on the Order
A revision usually needs a matching change on the order itself. Amend the purchase order line so it names the new revision, the quantity at each revision and the revised price and delivery date, and confirm that the quotation the supplier is working from refers to the same revision. A quote issued against an earlier revision does not automatically cover the new one.
Then confirm inspection. Ask whether the inspection plan and any measuring program have been updated, which characteristics a partial first article will include, and which report will come with the first delivery at the new revision. If your program requires a specific first article format, say so when the change is sent, not after the parts arrive.
Related: Small-batch production · Quality and inspection
Repeat orders
a repeat order placed months after a revision should still name the revision. Suppliers often keep several revisions on file, and the part number alone does not choose between them.
Related Pages
Continue with the closest related part family or guide.
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From an Approved Prototype to a Controlled Batch
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Evaluating Evidence from a CNC Machining Supplier
Which supplier information verifies a factory, its site and its manufacturing scope, and what photos, lists and certificates cannot prove.
Drawing Revision Questions
Does every revision need a new first article?
Not always. A note or title block correction may need no new inspection, while a change to a feature usually needs at least a partial first article on the changed and related characteristics. A change of datum scheme or material often justifies a full one. Agree the scope for each revision rather than applying one fixed rule.
Can the supplier continue at the old revision while we decide?
Only if you say so, and preferably with a quantity limit. Continuing to make old-revision parts adds to the stock that later needs a disposition. Holding the affected operations while unaffected work continues is often cheaper than finishing parts that may end up scrapped or reworked.
Why did the price change when the change looked small?
Because the effect depends on what the change touches. A tighter tolerance may add an operation or a slower measuring method; a moved feature may need a fixture change; a finish note may change a subcontractor's price. Ask for the price difference to be broken down by those items so it can be checked.
What if the model and the drawing show different revisions?
Treat it as an open question and resolve it before work continues. Suppliers often program from the model and inspect from the drawing, so a mismatch can produce a part that matches one and fails the other. Send both at the same revision, and state which governs if a conflict is ever found.
Discuss a Revised Drawing for Your Part
Send the new drawing and model with a short note of what changed, which orders it applies to and how parts already in progress should be handled.
Sales contact (pending)
Name, role and photo to be confirmed
Drawings are optional for an initial discussion.
Start with the information you have; file exchange can be arranged afterward.
Name to be confirmed
Sales, company name to be confirmed
- The effect on price, schedule and inspection can then be reviewed against the revision you intend to build.
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