1. Decide what you want at the end
The result may be a clean 2D drawing set, 3D parametric models, or both. It may also feed a new design, a spare-parts catalogue or a manufacturing process. The use decides how much detail, how much accuracy and how much structure the models need.
Write the end use down. A model for a catalogue picture needs far less than a model that will drive tooling.
2. Gather and grade the inputs
Collect every source: paper drawings, scans, photographs, old electronic files, sketches and the parts themselves. Sort them by quality: readable, partly readable or unreadable.
Note drawing revisions. Where two sources disagree, tell your partner which one is authoritative, or agree who will decide.
3. Choose the route: redraw, scan or measure
When drawings are complete and readable, models can be rebuilt from the dimensions on them. When drawings are missing, the part can be measured or scanned and the shape rebuilt from the measurements.
Rebuilding from a scan captures the part as it is, including wear and manufacturing variation. Decide whether you want the as-made shape or the intended design, because they are not always the same. See our reverse engineering and scan-to-CAD service.
4. Set accuracy and tolerance expectations
State which dimensions are critical and what accuracy you need. A mating surface may need tight accuracy while a cosmetic edge does not.
Agree how missing dimensions will be handled: assumed from standards, taken from a measured part or raised as a question. A list of open questions is a healthy part of the process.
5. Agree model structure and standards
Share your CAD standard: naming, units, layers, feature structure, material callouts and the drawing format. Models built to your structure are easier to edit later.
Decide whether the models should be parametric, so a dimension can be changed and the shape follows, or a simple solid shape. Parametric models cost more to build and are far more useful for future variants.
6. Build in review
Check a first batch before the rest is built. Compare model dimensions with the source, check mass properties where you know them, and check that assemblies fit.
Keep a correction log. Repeated errors point to a misunderstanding that is cheaper to fix early.
7. Plan the hand-over
Agree file formats, the folder structure, the revision method and how open questions are closed. Keep the source files with the models so that anyone can see where each dimension came from.
Store the finished models and drawings in your document system, and mark the old paper files as superseded so that the team uses one source.