- Photos and sketches start the project; a controlled drawing releases production.
- A measured value is not necessarily the original nominal value.
- A 3D scan still needs parametric reconstruction and tolerancing.
- Verify interchangeability with mating parts, functional tests and a master sample.
Values in this guide are practical starting points for RFQ, DFM and prototype validation. They do not replace load calculations, regulations, material certificates, qualified procedures or approved production drawings.
Start with a Minimum Evidence Set
Supply front, side, top, bottom and joint-detail photos. Include a ruler or known reference, but never derive precision dimensions from image scale alone. A sketch should show overall envelope, material thickness or tube size, hole diameters and centers, bend angles and mating parts. State load, movement, outdoor exposure, contact media, cosmetic faces and quantity.
Separate Measured Values from Design Values
Use calipers for routine dimensions, a surface plate and height gauge for datum-based dimensions, an angle gauge for bends, and a profiler, CMM or 3D scan for complex geometry. Measuring at least three same-lot samples helps reveal process variation. With one old sample, record wear, corrosion, coating thickness, weld shrinkage and permanent deformation. A measured 23.86 mm may represent a nominal 24.0 mm design.
A 3D Scan Is Not a Production Drawing
Scanning efficiently captures surfaces and overall form, but hole axes, datums, symmetry, tolerances, material and functional intent still require engineering reconstruction. Clean, align and fit features to the mesh, then create parametric CAD. A dense STL mesh should not normally drive cutting, bending or machining directly.
Reconstruct Intent from Mating Parts and Function
Measure the mating frame, bolt, shaft, insert or adjacent assembly as well. Prioritize interfaces: hole pattern, insertion depth, running clearance, stops and bearing faces. For interchangeability with installed products, use go/no-go gauges or actual mating assemblies. Visual similarity alone does not prove interchangeability.
Freeze the Drawing and Master Sample
Prototype approval should produce an approved drawing revision, material/finish definition, dimensional report, assembly result, functional test and cosmetic reference. Every sample change creates a new revision; do not rely on verbal edits to an old drawing. If a golden sample is retained, identify, sign and protect it, and define whether the drawing or sample controls in case of conflict.
PROJECT START CHECKLIST
- Multi-angle photos and dimensioned sketch
- Physical sample and at least one mating part
- Environment, load, movement and life requirement
- Interchangeable interfaces and CTQs
- Permitted destructive-measurement scope
- Ownership of prototyping, testing, revision and drawing approval