Reverse engineering

How to reconstruct missing documents


November 8, 2005


Typically, the idea for a fabricated product evolves into a manufacturing project from a complete set of engineering documents that define the product's scope, function, and limits and express its requirements. However, occasionally the necessary supporting documentation is unavailable and must be reconstructed.

For example, you might want to study an old sunken Roman or Viking vessel to gather information on ancient materials and technology and to understand a past civilization.

Small merchant ship in Viking Ship Museum, Roskilde, Denmark. Photo courtesy of Susanne Hfner.

You might obtain an old piece of machinery without related documentation. Perhaps you want to repair the machine, extend its operational scope, and create a new manufacturing line of similar products.

You might want to examine the latest product to improve your own, or to find out if any of your own details or secrets were copied by competitors.

The military might need to assess a foreign or hostile nation's technology, which may have been obtained by intelligence operations and lacks supporting documentation.

All of these activities require a special procedure called reverse engineering—reconstructing an acceptable set of manufacturing documents by systematically studying the final product to re-create the engineering design and bill of materials. The process can be complicated and expensive.


According to the Society of Manufacturing Engineers (SME), "Reverse engineering is the process of taking a finished product and reconstructing design data in a format from which new parts can be produced."

The Military Handbook MIL-HDBK-115 defines reverse engineering as "the process of duplicating an item functionally and dimensionally by physically examining and measuring existing parts to develop the technical data (physical and material characteristics) required for competitive procurement."

Besides taking something apart and analyzing its workings in detail, reverse engineering also is an invaluable teaching tool used by researchers, academics, and students in many disciplines to discover—by a constructive learning process—the operation, structure, and design of systems and products.

Reverse engineering's main objectives are to determine the functionality, the materials and their properties, and the manufacturing technology required to replicate production. Even if you have discovered relative movements and have imagined functions, you still could miss performance design limits and the operational envelope without adequate, possibly destructive, testing.

In certain cases, even if the documentation is available, just translating complex engineering documents from one dimensional system to another (for example, metric to British or U.S., or vice versa) with corresponding material standards and strength (resistance) ranges is a major engineering project that requires careful attention.

As long as the reverse-engineering study does not violate intellectual property laws, it is an accepted and widespread practice performed by the largest companies in the world.

There is a philosophical argument to the effect that even by studying all the elements—say, of a chess game—deeply and exactly, there is no chance of deriving, only from the pieces, the rules of the game and its purpose. The same reasoning sometimes applies to examining and reconstructing a product.

How to Proceed

First, before disassembling the item, take pictures; examine the external appearance, and record dimensions. Also examine any external finishing, coating, or paint.

Next, study the internal organs by radiography and by computed tomography. Name and list the different components.

If moving parts are involved, study the kinematics of the connected elements and document limits of movement and transmission ratios.

Carefully disassemble the item, being especially careful where interference fits are involved, because forceful disassembly might modify critical dimensions. Note possible permanent connections by welding or other methods that might have been performed during assembly.

If repairing the item requires substantial reconstruction or rejoining fractured parts, give special consideration to the mere possibility of welding. If the part was not welded when originally manufactured, be cautious about welding it now. Not all metals can be welded successfully.

With all the parts disassembled, sketch and record the dimensions of every piece, particularly mating or engaging elements. For irregular surfaces, you might need to use a coordinate measuring machine that allows you to collect sets of points to describe the item.

Chemical composition of the metallic materials can be investigated nondestructively by X-ray fluorescence. The same method can help identify plating or coating that could be present in critical wear surfaces. Nonmetallic elements, such as bushings and gaskets, should be examined by experts with relevant testing methods.

Using the correct nondestructive hardness testing method to determine mechanical properties is critical. It should be chosen for its applicability, limitations, and significance. Note that hardness can be measured on the surface only. Hardness gradients introduced by surface treatments, such as induction hardening, can only be suspected but not proved, in general, without destructive testing.

The assembled and recorded information is rough data only. Available materials may not be identical to the original product's materials, in which case, suitable alternatives should be selected. Reproducing the complete set of engineering documentation for manufacturing, including drawings, dimensions and tolerances, materials and processes, technology and methods, and finishing and testing, is a comprehensive project that ideally should include contributions from experts in many different fields.

Was It Worth Doing?

Reverse engineering is worth the effort only if the resulting documentation ensures economical production of durable items that perform as well as or better than the original product, or if the product repair is a success.

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