Give the first prototype one main question
Choose something that a physical object can help you decide. Does the enclosure feel comfortable to hold? Can the lid clear the component underneath? Is the display shape understandable at the intended size? Those are useful first questions because the result can change the next design revision.
A prototype intended to show appearance is not automatically a functional test article. If a load, temperature or other operating condition matters, describe it separately so the proposed design and manufacturing scope can be assessed. Avoid adding unspecified performance expectations after the part has been made.
Write the first test in plain language and state what you will do with the result. For an appearance study, that might mean choosing between two shapes. For an assembly study, it might mean revising an interface before considering a larger quantity.
Separate design work from printing work
| Starting point | Work to discuss | Approval before manufacture |
|---|---|---|
| Sketch or reference photographs | Creating and agreeing a dimensioned CAD model. | Approve the proposed geometry and unresolved assumptions. |
| Existing model that needs changes | A defined design revision, followed by manufacturing review. | Approve the changes and identify the superseded file. |
| File to manufacture as supplied | File review, manufacturing proposal and any separately agreed repair. | Confirm revision, dimensions, quantity and delivered finish. |
Commissioning CAD from a sketch is a separate deliverable from manufacturing a supplied file. Ask whether design assistance is available for your scope and how it will be quoted. Agree who will receive the editable model, what drawings or exports are included and how revisions will be handled.
List the file types you already have, without assuming that one particular format is required or accepted. A marked photograph can explain an idea, but the designer still needs dimensions and decisions that cannot be recovered reliably from perspective alone.
Dimension the relationships, not just the outside
Draw a top, front and side view if they help explain the shape. Label overall length, width and height, then show the positions of the features that matter. Use one clearly identified reference edge or centreline for related dimensions so the reader does not need to guess where a measurement starts.
Distinguish dimensions you have measured from dimensions you are proposing. If the new part must surround an existing object, provide that object’s envelope and explain whether it can be made available for a fit review. Identify cables, access paths and moving parts, since an object can fit inside an enclosure yet remain impossible to use.
Mark open questions on the sketch. “Opening position to be agreed” is more useful than an unlabelled hole that looks final. Do the same for appearance decisions such as corner shape, texture or lettering.
Check whether the dimensions describe one consistent object
Resolve which requirement takes priority before CAD approval. If the internal space must remain 100 × 70 mm, the outer plan changes. If the outer size is fixed, the internal space must be reconsidered. The 3 mm value here is only a proposed design dimension; it is not a recommended minimum wall or a printing capability.
Repeat this check around openings and mating features. Record intentional space between parts as a design question for review rather than assuming a universal allowance. The correct discussion depends on the selected process, geometry and the fit the test needs to examine.
Use two review checkpoints
First, review the proposed CAD against the sketch and brief. Check the dimensions, orientation, part count and the exact purpose of the first prototype. Ask for views that reveal hidden features. A polished rendering can still conceal an unresolved assembly detail.
Second, review the manufactured prototype against the agreed first test. Keep short notes and annotated photographs: what fitted, what obstructed assembly, what felt too large and what needs another look. Record the revision on the notes so observations do not get attached to the wrong design.
Decide the next revision from those observations before ordering repeat parts. If the first test changes the shape substantially, earlier manufacturing assumptions may also need review. The quotation guide helps separate design, printing, finishing and additional iterations.
Copy this sketch-to-prototype brief
Start with rapid prototyping. Once the geometry is agreed, use the CAD handover checklist to keep the approved revision, intended use and quotation aligned.