Before ordering a first prototype, decide what you will do differently once you have tested it. Change the hole pattern? Choose a stiffer material? Move a fastener so someone can actually reach it?
Those decisions should shape the order. A prototype built to check assembly access needs a different specification from one intended for load testing.
This DFM checklist covers the review between finishing the CAD and authorizing fabrication. Its purpose is to make the part manufacturable by the chosen supplier and useful for the test you intend to run.
1. Write the test before choosing the process
Give the prototype a specific job. “Check the design” leaves too much open.
For a hypothetical motor bracket, the job might be to verify that the motor seats properly, its mounting screws are accessible, and the assembled belt can be tensioned. A separate test might measure bracket deflection under load. These are different questions, even if they concern the same CAD model.
Write down:
- The decision this build needs to support.
- The assembly and test conditions.
- The observation or measurement that counts as a pass.
- What this prototype will not establish.
Keep that last point with the test results. A successful assembly check should not quietly become approval for structural performance.
2. Confirm the process and exact material
Ask the supplier to confirm the manufacturing process, material grade, and supplied condition. “Plastic” or “aluminum” is not enough information to compare quotes or interpret a test.
For a functional part, list the properties the test depends on: stiffness, temperature exposure, wear, or repeated flexing. Check the relevant material datasheet and its test conditions rather than choosing by a familiar material name alone.
Post-processing belongs in this decision. For SLA resin parts, post-curing affects mechanical properties, and the appropriate conditions vary by resin. Agree on the delivered condition before testing. Formlabs explains the relationship between post-curing and material properties.
Confirm minimum walls, feature sizes, and achievable tolerances with the selected supplier for this geometry. Treat another process's design limits as a different specification.
3. Mark the dimensions that decide whether it works
Identify the features that locate, seal, slide, rotate, or fasten to something else. Give them explicit requirements, then ask whether the supplier's general tolerances are suitable for the remaining geometry.
Use functional reference surfaces or axes when establishing datums. A hole's position relative to the mounting face can matter more than its distance from an arbitrary outside edge. Protolabs Network recommends highlighting critical dimensions and using common baselines or datums where appropriate. See its technical drawing guidance.
Review the mating components too. For the motor bracket example, check the actual motor drawing, fastener heads, washers, and installation tool, not just the bracket's hole diameters. Decide which parts will be supplied with the prototype and which your team must have ready.
4. Check how the features will be made
For machining, inspect deep pockets, narrow internal corners, thin walls, and features hidden behind other geometry. Ask how the cutter will reach them and how the part will be held. Protolabs flags restricted tool access, deep internal features, and thin geometry as issues that can affect machining. Its machining DFM toolkit explains these constraints.
For printed parts, discuss orientation and cleanup access. Mark surfaces that must mate or look presentable. Formlabs recommends keeping critical mating and cosmetic surfaces away from SLA supports where possible, and addressing drainage in enclosed hollows. See its orientation guidance.
Record any proposed geometry changes before accepting them. A supplier's sensible manufacturing adjustment may affect the feature you intended to test.
5. Specify what “finished” means
Check whether the quote includes support removal, deburring, washing, curing, sanding, coatings, or installed inserts, as applicable. Do not assume the photographed sample represents the quoted finish. Xometry, for example, distinguishes between SLA finishes with different levels of sanding and surface treatment. Its finish descriptions show why the selected option matters.
State whether critical dimensions apply to the final finished part. Identify interfaces that may need masking or another agreed treatment. If appearance is being evaluated, agree on acceptable tool marks, support marks, and the surfaces on which they are allowed.
6. Choose quantity and inspection together
Assign a purpose to each unit before placing the order. You may need separate parts for assembly, destructive testing, and a demonstration. Decide whether a damaged test sample would prevent the remaining work.
Then define the receiving check. Which dimensions will be measured, with what equipment, and by whom? Will the supplier provide results, or will your team inspect the parts? A requirement that nobody can verify needs attention before fabrication.
For the hypothetical bracket, receiving inspection might cover the mounting interface and hole locations, followed by assembly with the actual motor. Record the part revision and test setup alongside the result so the next iteration has a useful comparison.
7. Release one unambiguous file package
Put the order in a single release folder containing:
- Matching revisions of the model and drawing, with units stated.
- Supplier-accepted file formats, reopened to check the export.
- Part numbers, quantities, material, and finish requirements.
- Assembly references, purchased components, and any bill of materials needed.
- Agreed inspection requirements and accepted supplier deviations.
- A named contact who can approve changes.
Remove superseded files from that package. Resolve any model-to-drawing discrepancy and confirm document precedence with the supplier rather than relying on an informal assumption.
8. Keep prototype approval separate from production approval
A printed or machined prototype does not verify an eventual injection-molding route. Moldability requires its own review of draft, wall sections, undercuts, and gate and ejection arrangements. Protolabs' molding DFM guidance covers these production-specific considerations.
Note those unresolved issues in the release record. When the prototype returns, its results can support the next decision without implying that every production question has been answered.
Need help reviewing the files before fabrication? Explore GoBigCAD's prototyping support or contact GoBigCAD with your CAD, intended process, and the question the prototype needs to answer.