Build to Print vs Build to Sample Wire Harness Assembly
Build to print means you own the drawing and the assembler builds exactly to it. Build to sample means the assembler develops the design from a physical sample or a performance brief. Print keeps design risk with the buyer; sample moves it to the supplier. That single difference drives cost, lead time and change control.
Both routes end at the same place: an approved harness in a box. The difference is who holds the acceptance criteria when the first unit comes off the bench and something does not fit.
What do build to print and build to sample actually mean?
Build to print is a manufacturing contract. You supply a controlled drawing package, the assembler supplies wire, terminals, labour and test, and conformity is judged against your drawing. Build to sample is a development contract: you supply something that works, or a description of what must work, and the assembler produces the drawing inside the quotation.
A print package is only complete when it carries all of the following. Missing any one of them turns a print contract into a sample contract by accident, usually after the first delivery.
- Wire style and gauge per circuit, by UL or VDE style number, not a colour name.
- Connector and terminal part numbers down to housing, seal, retainer and plating.
- Cut length, strip length and branch geometry with tolerances and one measuring convention.
- Splice locations, shielding, sleeving, heat-shrink and overmoulding call-outs.
- Test requirement: continuity, dielectric withstand, pull force, insulation resistance, report format.
- Marking, labelling and packaging, including any barcode or customer part number.
Build to print vs build to sample: a comparison table
The table is the version we use when a buyer asks which route is cheaper. Read it as a contract map, not a price list.
| Dimension | Build to print | Build to sample |
|---|---|---|
| Design ownership | Buyer | Assembler, approved by buyer |
| Input required | Released drawing, BOM, test spec | Working sample, photos, or performance brief |
| Who writes the drawing | Buyer’s engineering team | Assembler’s engineering team |
| Tooling and applicators | Quoted separately, often buyer-owned | Usually inside development cost |
| First article | Verification against drawing | Joint definition, then verification |
| Change control | Buyer issues ECN, assembler implements | Assembler proposes, buyer approves |
| Cost profile | Lower unit price at volume, higher engineering load on buyer | Higher first-lot price, lower engineering load on buyer |
| Time to first good unit | Shorter if the drawing is truly complete | Longer, because definition happens inside the project |
| Main risk | Drawing errors reproduced exactly and at scale | Scope drift between what was asked and what was built |
| Best fit | Repeat programs, transferred production, mature designs | New products, obsolete originals, cost-down work |
What does build to print require from you?
It requires a drawing a stranger can build from without asking a question. That is a higher bar than most internal drawings meet, because your own team fills the gaps from memory. An external assembler cannot.
Three things decide whether a print contract runs cleanly:
- A revision letter on every page. Two pages at different revisions is the most common cause of a wrong first lot.
- One measuring convention. State whether length is pin-to-pin, over the housing, or along the wire path. A 300 mm harness measured two ways can differ by 20 mm and both readings are defensible.
- A named approver for deviations. When a terminal is on 12-week allocation, someone must be allowed to say yes to an equivalent the same day.
Our specification checklist lists the fields we need before quoting, and the harness builder walks the same structure for buyers who have no drawing yet. If you already have a package, the custom wire harness page shows the format we accept.
When does build to sample make more sense?
Build to sample wins when the design is not written down yet. That covers a new product where the harness is still moving, a legacy machine whose original supplier has gone, and a cost-down project where the current part works but is over-specified.
It is also the normal route in repair and aftermarket work, where one sample and a photograph with a ruler in frame are often all that survives from a discontinued machine. Three signals point to sample rather than print:
- The harness interfaces with a housing or mechanism that is still being prototyped.
- You can describe the function but not the part numbers, because the connectors are unmarked.
- You want the assembler to propose a lower-cost construction, which means they must be allowed to change the design.
Houses that quote sample work keep an engineering function for it. Ours sits with the assembly services group, and the factory video page shows the cut, strip, crimp and test stations any drawing is written against.
How does sample approval change cost and lead time?
Sample approval adds a gate, and gates cost calendar time. A typical cycle runs three phases: definition, first sample, approved sample. Each ends with a document the buyer signs, and nothing moves until it is signed.
| Approval gate | What is fixed | Typical quantity | What the buyer signs |
|---|---|---|---|
| Definition | Wire styles, connector families, routing, test level | Paper only | Specification sheet |
| First sample | Build method, tooling, crimp settings | 3-5 pieces | Sample evaluation report |
| First article | Dimensional and electrical conformity | 3-5 pieces from production | FAI report, signed drawing |
| Production | Process frozen until an ECN | Order quantity | Release note per batch |
On cost, the sample route carries the engineering hour inside the first lot. That is why a 50-piece sample order can price 30-50% above the same harness at 5,000 pieces, and why the gap is not a negotiation position. Once the drawing exists it becomes a print job and the premium disappears.
On lead time the logic runs in reverse. A complete print package can go to the line almost immediately, while a sample job needs a definition round first. Common UL1007, UL1015, UL1061 and UL1569 constructions are normally available quickly; other wire styles and connector families typically take about seven days, and every harness is scheduled against its drawing and approved sample.
Why do most programs fail at the drawing, not the assembly?
Because assembly is mechanical and repeatable, while the drawing is a communication artefact. A crimp press either meets its pull-force window or it does not. A drawing that omits a retainer clip is a silent defect that passes every electrical test.
Four faults account for most rework on incoming print packages:
- Missing seal or retainer. The housing is listed, the secondary lock is not, and the harness unmates under vibration.
- Nominal-only dimensions. A length with no tolerance is not a specification; the shop picks a convention and you reject the lot.
- Wire style by trade name. “Thin-wall hook-up wire” is not a style. UL1007 at 80 °C and 300 V is, and it is a different part from 105 °C XLPE.
- Test level left to the shop. Continuity only, or continuity plus 1,000 V DC dielectric withstand and 500 V DC insulation resistance above 100 MΩ? The two price differently.
Where the drawing is genuinely incomplete, convert the job to build to sample and price the engineering openly. A print contract signed against a partial drawing pushes the gap into inspection, the most expensive place to find it. Our quality process describes the incoming review that catches these first.
How should you handle deviations and change control?
Write the rule into the purchase order before the first shipment. A workable one: no substitution without written approval, and every approved substitution recorded on the drawing at the next revision.
Three documents move between the two teams. A deviation note covers a one-off: this terminal, this batch, this quantity. An engineering change notice covers a permanent change and updates the revision letter. A first article report closes the loop by proving the changed part still meets the drawing.
The commercial detail that matters is who carries an obsolete batch. If you change the drawing after 5,000 housings were ordered against the old revision, that material is consumed or written off. Agree the liability cap, and agree how much finished stock the assembler may hold without a release.
How do you choose between the two?
Choose print when the design is stable, the volume is real and the drawing has survived at least one build. Choose sample when any of the three is untrue. Most programs do both in that order: sample for the prototype, print for production.
A practical test is to ask what you would do if the first lot failed. If the answer is “reject it against the drawing”, you are ready for print. If it is “argue about what we meant”, you need the sample route and a written specification first.
Volume changes the economics too. Two application examples show the split. Industrial control and machine wiring is usually print work, because the panel layout is fixed by the machine builder. Robotics and drag-chain harnesses more often start as sample work, because bend radius and strain relief are proved on a moving axis rather than on paper. The price drivers behind both are the same ones set out in the seven cost factors.
Frequently asked questions
Is build to print cheaper than build to sample?
At volume, yes. The engineering is already paid for and the unit price reflects material, labour and test only. At low volume the gap narrows, because setup and tooling spread over fewer pieces.
Can you build to print from a PDF drawing only?
Yes, provided the PDF is dimensioned and carries a revision letter. A 3D model or native CAD file shortens the review, but a complete dimensioned PDF is enough to quote and build.
What if a sample is the only documentation I have?
That is a normal starting point. We measure it, identify the connector families from the housings, confirm wire styles from the markings and insulation wall, and issue a specification sheet for your approval before any tooling is set.
Who owns the drawing produced during sample development?
Agree it before the first sample, because it is a commercial term rather than a technical one. The usual arrangement is that the buyer owns the drawing and the assembler retains process knowledge such as crimp settings and fixture design.
How many samples should I ask for?
Three to five. One is not enough to judge repeatability, and five lets you keep one for reference, test one to destruction and still have units for fit checks.
Does the route change the warranty?
It changes what is warrantable. On a print contract the assembler warrants conformity to the drawing. On a sample contract they also carry part of the design intent, so the specification sheet must define performance, not only dimensions.
Next step: send the drawing, or send the sample
Either input is enough to start. If you have a released drawing package, request a quotation and attach it; the review comes back with any gaps listed before pricing. If the design is still open, configure the specification in the harness builder and that document becomes the basis for a sample. For wire-only questions, the wire selector filters by voltage, temperature and approval, and the FAQ page answers the 25 questions buyers ask most often.
Suzhou Fuxi Electromechanical Equipment Co., Ltd. (Xinya) has built harnesses since 2008 and supplies 16 harness categories across 7 application groups, together with the wire: we are the authorised distributor of Xinya Electronic Co., Ltd. electronic wire, covering UL, VDE, PSE, CE, TUV, RoHS and REACH listings. Export packaging and labelling are agreed per order.