The Problem Starts at the Second Unit

While one person is building one prototype, documentation feels like overhead. The file on the desktop is the design. The problem appears the first time two people work from the same data, or the first time a factory builds a second batch. A contract manufacturer quotes from Rev B, you send Rev C without saying so, and 500 housings arrive with the old boss diameter. Nobody was careless; there was simply no mechanism to tell the two files apart.

Engineering documentation is not paperwork for its own sake. It is the mechanism that lets a design be built by someone who was not in the room, and rebuilt two years later after the original engineer has left.

Four Identifiers Every Product Needs

Get these four right and most documentation problems disappear.

  • Part number. One per unique physical item, including purchased parts. Use non-significant numbers, meaning a plain sequential number rather than a code that encodes material and size. Significant numbering always breaks: the day a part changes material, either the number lies or you renumber everything.
  • Revision. A letter or number tracking changes to the same part. A part number identifies what it is; the revision identifies which version of it. Both must appear on the drawing and, wherever possible, molded or laser-marked on the part itself.
  • Assembly and BOM structure. Every assembly gets its own part number, and its BOM lists child part numbers with revisions and quantities. A multi-level structure that mirrors how the product is actually built is what makes a bill of materials usable by purchasing rather than just by engineering.
  • Serial number or date code. Applied to the finished unit at production. Without it a field failure cannot be traced to a build lot, and a recall becomes a recall of everything you ever shipped rather than of 400 units.

What Goes Under Revision Control

More than the CAD. The full set that a factory needs to build the product without asking you a question:

  • Native CAD files and neutral exports. STEP for solids, and a clear statement of which is the master; the distinction matters and is covered in STL versus STEP.
  • Dimensioned 2D drawings with datums, tolerances, material, and finish. The drawing, not the model, is the contractual document, and GD&T practice is what makes it unambiguous.
  • Schematics, PCB layout, Gerbers, pick-and-place files, and the electronics BOM with approved manufacturer part numbers.
  • Firmware source, build configuration, and the exact binary shipped, hashed and archived.
  • Work instructions, test procedures, and inspection criteria.
  • Supplier approvals, material certificates, and test reports.
  • Labels, packaging artwork, and the user manual, which change more often than anything else and are the most frequently uncontrolled.

Bundled together, this is the manufacturing data package, and its completeness is what determines whether you can move production to a second supplier without redoing the engineering.

When to Bump a Revision

Two rules, and they are worth writing on the wall.

Any change to a released item requires a new revision. Released means anyone outside the design team has it: a supplier, a test lab, a customer. Before release, edit freely. After release, revise.

Form, fit, or function changes require a new part number, not just a revision. If the new version is not interchangeable with the old one, it is a different part. A wall thickness change that does not affect anything is Rev C. A mounting hole moved 2 mm is a new part number, because a stockroom holding both must not mix them.

Once a part has been released to a supplier, changes should route through a controlled engineering change order: what changed, why, what it affects, who approved it, what happens to inventory already built, and the effective date. On a small team an ECO can be a one-page form. What it cannot be is an email saying "use the attached instead."

Tooling: As Simple As You Can Get Away With

Full PLM systems cost real money and administrative effort, and a three-person team will not maintain one. Match the tool to the stage.

Early, one or two engineers: a shared cloud drive with a rigid folder structure, filenames carrying part number and revision, a read-only released folder, and one spreadsheet acting as the part number register and BOM. This works for longer than people expect, provided the released folder discipline is absolute.

Growing team: the vault built into your CAD system, plus Git for firmware. Check-in and check-out prevents the two-people-editing problem the spreadsheet approach cannot solve.

Production with multiple suppliers or a regulated product: a proper PLM, or a documented quality system doing the same job. Medical devices need this from the beginning, since the design history file is an FDA expectation, not an internal nicety.

Whatever the tool, one rule dominates: exactly one location is authoritative. The most expensive documentation failure is not having no system, it is having two.

Traps That Recur

  • Filenames as version control. housing_v4_final_FINAL_use_this.step. Everyone has seen it; it always eventually costs a tool change.
  • Redlined drawings that never get incorporated. The shop marks up a print, the change works, and the CAD never catches up. Six months later the model and the parts disagree and nobody knows which is right.
  • Undocumented supplier substitutions. The factory swaps a resistor or a resin grade because of availability and does not tell you. Require written approval for any deviation, and verify at first article inspection.
  • Firmware without a matching hardware revision. Record which firmware build ships on which board revision. Field updates go badly otherwise.
  • Design data held by the contractor. If the engineering firm owns the vault and you have only PDFs, you cannot change suppliers. Take delivery of native files at every milestone.

What This Is Worth in Money

A single wrong-revision production run of a molded part is typically a five-figure write-off plus a four to six week schedule slip. A recall traced to an untracked component substitution is worse. On the upside, complete documentation is what lets you quote a second supplier against the first, which is often a 15 to 30 percent cost reduction, and it is one of the first things examined in technical due diligence during a raise or acquisition. Buyers discount companies whose product exists only in one engineer's head.

Set the System Up Before You Need It

Projects House delivers documented data packages as standard: numbered parts, revision-controlled drawings, structured BOMs, and native files handed to the client at every milestone. If your project is running on a shared drive and a hope, send us the current state through our contact form and we will tell you what is missing before the factory finds it.