Reverse engineering: what it is, how it works and when it pays off
Missing a drawing and the part is worn out? We explain what reverse engineering is, what happens to the scan and when recreating a part makes sense.
Reverse engineering is the process of recreating the documentation and geometry of an existing part from the part itself. Instead of a drawing, you have a component from a machine. We measure it, build a CAD model and use it to produce a drawing or another piece. It is a digital reconstruction of the geometry, allowing the part to be remanufactured, modified or recorded in your documentation.
Below we explain what happens to the data after scanning, what decisions must be made beyond the geometry itself and when this approach makes sense. We describe the next steps of the service on our reverse engineering and 3D scanning page.
Reverse engineering: why we do it
It usually starts with a shortage. A machine is down and the worn part cannot be bought. The manufacturer has disappeared, discontinued the model or quoted a delivery time of several weeks. In that case, the part itself is the only ‘documentation’.
There are also reasons other than repair:
- Modification or upgrade. You want to change the material, reinforce a cross-section or adapt the part to a new assembly.
- Documentation for batch production. You have one good piece and need a drawing to order more.
- Tidying up the archive. The machine is years old and the drawings have been lost or no longer match the actual state.
From scan to drawing: what happens to the data
A scan alone is not yet a part. Between the scanner and the machine tool there are three forms of data, and each serves a different purpose.
Point cloud and STL mesh
The scanner records millions of points lying on the surface of the part. This is a point cloud. Software connects them into a triangle mesh, most often saved as an STL file. The mesh shows the shape well, but it is ‘frozen’: it does not recognise holes as holes or planes as planes.
Reverse engineering in CAD: parametric model
A design engineer recreates the part in CAD software — at ECAD, in Siemens NX or Solid Edge. Over the mesh, they draw planes, cylinders, radii and holes as dimensioned features. Such a model can be modified and then used to programme machining.
Manufacturing drawing
From the model, a drawing is created with dimensions, fits and tolerances. This is the document we use to prepare a quote, manufacture and inspect the part.
The difference is shown in the table.
| Criterion | STL mesh | Parametric CAD model |
|---|---|---|
| What it contains | triangles describing the surface | planes, cylinders, radii, holes with dimensions |
| Good for | viewing, comparisons, deviation inspection | manufacturing, design changes, drawings |
| Changing a dimension | practically impossible | changing a single parameter |
| Reproduces wear | yes, along with damage | no, if the design engineer corrects it |
| Tolerances and fits | none | added by the design engineer |
That is why a mesh alone is rarely enough for production. Machining requires a model in which someone has decided what the nominal dimensions are.
What needs to be decided beyond geometry
A scanner measures what is there. It does not know what the original designer intended. Those decisions remain with a human.
Design intent. Two surfaces that differ by a fraction of a millimetre on the scan may have been designed as a single plane. The design engineer assesses what is a feature of the part and what is the result of casting, welding or service in the machine.
Wear compensation. We measure a worn part, but we recreate the nominal dimension. A shaft with a worn journal or a bore ovalised by play will not yield the true dimension from a scan alone. The design engineer determines it from unworn areas, symmetry or the mating component.
Fits and tolerances. A scanner shows geometry, not the required clearance in a joint. Fits and tolerances are set by the design engineer based on the part’s function and the mating component.
Material and heat treatment. A scan alone will not tell you the steel grade or hardness. If the material is unknown, it must be determined from the machine documentation, markings, or material testing. Tell us what you know about the material in your enquiry.
3D scanning for reverse engineering vs manual measurement
A simple part can be measured with a caliper. With complex geometry, manual measurement quickly becomes complicated, and 3D scanning for reverse engineering starts to have the advantage.
| Criterion | Manual measurement (caliper, micrometer) | 3D scan |
|---|---|---|
| Best for | simple solids, a few dimensions | freeform surfaces, castings, complex shapes |
| What you get | a list of dimensions | complete surface geometry |
| Curved surfaces | difficult and poorly repeatable | captured in full |
| Post-production verification | point by point | comparison of the entire part with the model |
| Operator influence | high | lower, though the design engineer still builds the model |
| Where it suffices | simple bush, flat bar, bolt | body, impeller, housing, blade |
3D scanning of machine components does not replace traditional measurement where a single dimension with a tight tolerance is critical. In such cases, the scan defines the shape, while critical dimensions are still checked with a conventional measuring instrument.
When reverse engineering pays off
It pays off when recreating a part is cheaper or faster than the alternative, or when no alternative exists:
- the part is no longer available from the manufacturer,
- the machine has been discontinued,
- the delivery time for the original part exceeds the downtime you can accept,
- you want to modify the part rather than just replicate it,
- you need documentation to order a batch.
It does not pay off when the part is an off-the-shelf catalogue item: a bearing, seal, bolt, circlip, or other standard component. Buying it is cheaper and faster than recreating it. Similarly, when a critical tolerance cannot be deduced from a worn part and you have neither the mating component nor data on its operation. In such cases, it is worth agreeing on the scope and risks before commissioning the recreation.
It is also worth checking copyright and patent protection for the part if you plan series production of a third-party design. This responsibility lies with the ordering party, not with the geometry.
What a scan might not capture
Optical scanners have limitations that are worth knowing before placing an order.
- Shiny and transparent surfaces can cause reflections or gaps in the point cloud. Matting spray can help, provided it can be applied to the given part.
- Internal channels and deep holes may be invisible to the scanner because the beam cannot reach inside. Such features are measured by other methods or reconstructed from other sources.
- Sharp edges and fine details require the design engineer to decide whether they are an actual part feature or measurement noise.
These are general characteristics of optical scanning. For a specific job, we assess them directly on the part.
How we do it at ECAD
At ECAD, we combine scanning, modelling, and manufacturing under one roof. We scan using a Scantech NimbleTrack-C Gen2 3D scanner at our facility at ul. Elektronowa 6 in Lodz or on-site at the client’s premises, including parts still mounted in a machine. The model and documentation are prepared by our design office in Siemens NX or Solid Edge. We manufacture the part by milling, turning, cutting, bending, or welding across our own machine park (more: CNC machining), and verify dimensions using a 3D scanner, on a granite surface plate, and with a Mitutoyo height gauge (3D quality inspection). You do not need a drawing for reverse engineering. A physical part – even a worn one – is enough, or if you cannot send it, photos with a reference dimension. Looking for an end-to-end service from scan to finished part? We describe the scope and next steps on our reverse engineering and 3D scanning page. We prepare quotes based on the part, photos, or documentation.
Frequently asked questions
Is a drawing needed for reverse engineering?
No. A physical part, whether original or worn, is enough. We also accept photos with a reference dimension, such as a ruler or caliper, as well as partial documentation.
Can you scan a part while it is mounted in a machine?
Yes, we scan both at our facility and at the client’s site, including parts mounted in a machine. Surface accessibility depends on the mounting location. During quoting, we determine whether the part needs to be dismantled.
What is the scan accuracy compared to the part tolerance?
These are two different things. The accuracy of the Scantech NimbleTrack-C Gen2 scanner is up to 0.020 mm, but this is not the tolerance of the manufactured part. Tolerances stem from the part’s function and are specified on the drawing by the design engineer. Surface condition and wear also affect the result.
How long does it take?
Lead time depends on the part’s complexity, condition, and project scope: whether you need model reconstruction alone or manufacturing as well. We provide the delivery date with the quote, and the quote itself is free of charge, usually within 48 hours.
What do I receive: a model, a drawing, or a part?
It depends on your order. Most often we handle the entire process: scan, CAD model, and manufacturing of the finished part in a single order. We agree on the scope at the quoting stage.
