A machine stops because a small plastic component has broken. The machine is fifteen years old, the manufacturer no longer supports it, and the part is not available anywhere. The choice appears to be replacing an otherwise functional machine or improvising something.
This is one of the most practical applications of additive manufacturing, and it is underused largely because businesses do not know it is an option.
What is actually involved
The process is straightforward in principle. Capture the geometry of the original part, or of what remains of it. Build a clean CAD model from that capture. Choose a material appropriate to the application. Print, test and iterate.
The middle step is where the real work sits, and it is worth understanding why. A scan produces a mesh — a dense cloud of triangles describing the surface, including every scratch, wear mark and deformation. That mesh is not a usable engineering model. It has to be interpreted into proper geometry: flat faces made flat, holes made round and concentric, features restored to their intended dimensions rather than their worn ones.
You do not always need a scanner
For simple parts, digital callipers and a photograph are sufficient and often better. A bracket with a few holes and some flat faces can be measured directly in twenty minutes, producing a cleaner model than a scan would.
Scanning earns its place with organic or complex geometry — curved housings, ergonomic shapes, parts with many interrelated features — and with parts too large or awkward to measure reliably by hand.
If the part is broken into pieces, they can often be measured or scanned together and reconstructed. If a section is missing entirely, symmetry and the mating components usually let you infer it.
Getting the material right
The original was probably injection moulded in a material chosen for that process. The printed replacement does not have to match it, and often should not.
What matters is the actual service requirement: operating temperature, load and direction, UV exposure, chemical contact, whether it must flex, whether it contacts food or skin. A gear needs wear resistance and toughness. A bracket needs stiffness. A clip needs fatigue resistance in bending, which is a genuinely demanding requirement for printed parts and where naive replacements most often fail.
Remember the anisotropy. A part that will be loaded in a known direction should be oriented so the layers are not the weak point in that direction.
Improve it while you are there
Reverse engineering is an opportunity, not just a duplication exercise. If the original consistently broke in the same place — and there is often evidence that it did — thicken that section, add a fillet, or change the geometry. You are not obliged to reproduce the original design’s weaknesses.
The legal position, briefly
Worth stating plainly. Copying a part for repair of equipment you own is a different matter from manufacturing and selling copies of someone else’s product, and the second can infringe design rights, patents or copyright. Safety-critical components — anything in a braking system, a lifting mechanism, a pressure vessel, or a certified assembly — should not be casually replaced with an uncertified printed part. If a component’s failure could injure someone, get engineering advice.
The economics
Reverse engineering has real setup cost: measurement, modelling, test iterations. For a single small part it may be comparable to buying a replacement if one exists. It becomes compelling when no replacement exists, when the alternative is scrapping a functional machine, or when the part fails repeatedly and you will need more.
The second and subsequent parts are cheap, since the model already exists. Businesses that maintain ageing equipment often build a small library of digital spares over time, which is quietly one of the better returns available from having print capability.
What a bureau needs from you
Send photographs from several angles with a scale reference, the broken part itself if you can, the key dimensions you can measure, a description of what the part does and how it is loaded, and any information about the machine.
Most of these jobs start with a conversation rather than a file upload, since the requirement usually needs drawing out. If you are fielding a lot of these enquiries, note that they follow a predictable pattern of questions — which is why bureaus handling volume often route initial quote enquiries through an automated voice agent that captures the machine, the part and the urgency before a person gets involved.
Once you have a model of the part, our page on 3D printed replacement parts explains how to order it, what prints well, and when a printed replacement is not a good idea.