Conversions
NNS Model vs Hi-Fi CAD — definitions
What an NNS Model (STL + AI STEP) and a Hi-Fi CAD model (STEP + PRT) are, and which one you need.
Last updated 25/08/2026
Voluminate gives you two levels of result: the NNS Model (Near-Net-Shape Model) produced automatically by the AI, and Hi-Fi CAD (High-Fidelity CAD) built by the 3D Spark reverse-engineering team from your sources, your part brief and any feedback you gave on the NNS candidates.
NNS Model (Near-Net-Shape Model)
An NNS Model is the AI-generated reconstruction produced automatically from your uploaded drawing or photos. A run typically returns it in two formats: an STL mesh for visualisation, 3D printing, ROM quoting and manufacturability checks, and an AI-generated STEP solid that opens in any CAD system. The STEP being a solid does not make it verified — both formats carry exactly the same AI-reconstruction caveats.
The name reflects the goal of the reconstruction, a model close to the final part's shape, but actual quality varies with your input. For a clean, well-dimensioned drawing with an isometric view, or a set of 4 photos taken 90 degrees apart, the result can genuinely approach near-net-shape accuracy. For a rougher photo or an incomplete drawing, it's more accurately described as a conceptual model: correct in overall form and proportions, but not dimensionally reliable. Because it's AI-generated, an NNS Model can also hallucinate, showing features that aren't actually on the part, or omitting features that are. Every NNS Model includes a quality score to help you judge which end of that range you've received. It is not a parametric CAD model and has not been reviewed by a design engineer.
Finishing the AI STEP yourself
The AI STEP is a boundary-representation solid without a feature tree. That is still a real head start: a design engineer can import it into any CAD system, verify and correct the dimensions against your drawing, and rebuild or patch the features that matter — instead of modelling the part from a blank sketch. The end result is a production-ready, dimensionally correct model.
This is the fastest and cheapest route when you have CAD capacity in-house and want full control over the final geometry. Hi-Fi CAD is the same destination with the work outsourced: 3D Spark's engineers do the finishing and verification for you, and you also get a native parametric PRT.
Hi-Fi CAD (High-Fidelity CAD)
Hi-Fi CAD delivers two files:
- a STEP model — a universal solid that opens in any CAD software, but carries no feature history
- a PRT model — a native, parametric CAD file with a full feature tree (sketches, extrudes, holes and other features), so a design engineer can pick up construction exactly where our reverse engineering left off
An expert design engineer builds and dimensionally verifies the geometry against your sources. The result is the same outcome as hiring a senior design engineer to reconstruct the part by hand, at a fraction of the cost.
Side by side
| NNS Model (STL + AI STEP) | Hi-Fi CAD (STEP + PRT) | |
|---|---|---|
| Best used when | You need a fast first assessment — for thousands of parts, or one urgent part | You need a final, verified model and decision for a selected part |
| Positioning | Fast, scalable first-pass analysis | Engineer-verified precision modelling |
| Core trade-off | Speed and scalability over precision | Precision and reliability over speed |
| Output quality | Approximate geometry, ranging from conceptual to near-net-shape | Dimensionally verified, parametric geometry |
| Geometric accuracy (bounding box) | ~2–20% deviation; features may be hallucinated — sufficient for initial assessment | Dimensionally verified against your sources by a design engineer; parametric, editable solid with full feature tree — suitable for production decisions |
| Path to production | Your own engineer finishes the AI STEP in your CAD system | We finish and verify it; native parametric PRT included |
| Decision reliability | Filters out clearly non-viable options | Enables confident make-or-buy and production decisions |
| Processing time | Seconds to ~10 minutes per part | ~24h typical (hours to 3 working days, complexity-dependent) |
| Scalability | High — bulk and on-demand | Limited — targeted use, more time and cost intense |
| Cost | 1 credit on download | 3 credits charged when you submit the request (plus complexity surcharge if applicable) |
| Output | Up to 3 candidate variants, as STL mesh and AI STEP | One verified model, delivered as STEP and native parametric PRT |
Complexity surcharge (Hi-Fi CAD only)
This applies only to Hi-Fi CAD orders — NNS Model runs are never surcharged.
Some parts are genuinely harder than others. If yours requires more work, we request 1–13 extra credits with a written justification (so a Hi-Fi CAD order costs at most 16 credits in total). You see this as a banner the moment you log in and can either approve it (work continues) or decline it (the order is cancelled and your 3 credits are refunded in full). Nothing is charged without your explicit approval.
Delivery
When the Hi-Fi model is ready it becomes the primary candidate on the part page automatically and you receive an email.