How to Scan an Object into CAD: Scanner to STEP File

To scan an object into CAD you capture its surface with a 3D scanner, clean the scan into a mesh, rebuild the geometry you need as CAD, check the model against the scan and export it in the format the next tool opens. The scanner measures the object; a person builds the CAD model from the measurement, and the modeling takes most of the time. This guide walks through the sequence for a mechanical part or an installed object, with the decisions that have to be made before the scanner is switched on.

Decide what the CAD has to do

Two people can scan the same pump bracket and need different files: one wants an editable solid to redesign the bracket, the other wants a dimensioned drawing a machine shop can quote from. The scan is the same; the work after it is not. So the first question is what the model is for, because that sets which features have to be exact, which can be approximate, and whether a worn surface should be recorded as it is or restored to the shape it was designed with. A scope that says “the mounting holes and the mating face must match, the outside profile matters, the cosmetic wear does not” saves the modeling hours that would otherwise go into surfaces nobody will use.

Pick the scanner for the object

Parts the scanner can be walked around, from a few centimeters to about four meters, are scanned with a handheld metrology scanner. The HandySCAN SILVER class is recommended by its brochure for parts from 0.05 to 4 m; it projects fourteen blue laser lines, is moved around the part by hand on a bench or wherever the part sits, and records geometry only. Its accuracy rating is given in the FAQ below.

Installed objects (a pump on its base, a railing, a tank) are scanned in place with a terrestrial scanner, because an installed part only makes sense together with what it bolts to. A scanner of the Trimble X7 class holds a 3D point accuracy of 2.4 mm at 10 m (one standard deviation) by its datasheet and records the object, its mounting points and the pipe and steel around it from the same stations. The 3D scanning for parts page describes the handheld work and the 3D laser scanning page the terrestrial.

Prepare the object

A scanner records what reaches its sensor, so the object has to be visible and still. Loose parts are cleaned of oil and swarf, and polished metal, black rubber and transparent plastic, which return the laser lines poorly, are coated with a thin matting spray that wipes off after the scan. Installed objects are scanned as they are, with the areas around them cleared where the facility allows, because anything leaning against the part ends up in the scan. Deep bores and internal passages are outside any surface scanner’s reach, so the openings are measured with gauges and the rest is taken from drawings or from a sectioned spare; the guide to internal features covers the options.

Scan and check coverage

The handheld scanner builds the mesh on the laptop as it moves, so a patch the lines have not covered shows as a hole and is filled before the scan ends; a part is turned over or held in a fixture so that every face is reached, and the two scans are aligned. The terrestrial scanner is moved from station to station around the installed object, and the stations are registered to each other with a report that lists the average error per station and the overlap between scans. Coverage is checked before leaving the site, because a missed face that is found a week later means a second visit.

Clean the scan into a mesh

The raw scan carries stray points from reflections and from whatever passed through the beam, and the fixture or the floor the object stood on. Cleaning removes those, closes the small gaps the scan left and orients the mesh to a sensible origin, usually a mating face or an axis of the part. The result, in STL or in OBJ or PLY, is a copy of the object’s surface, damage and all, and for some purposes that is the deliverable: a mesh can be printed or archived, and a new part can be designed around it, without ever becoming a solid model.

Scan to CAD: rebuild the geometry

A mesh is triangles, often millions of them; a CAD model is planes, cylinders, holes, fillets and the free-form surfaces that have no simple description, with the relationships between them that let the model be edited. Scan to CAD means fitting those features to the mesh and recovering the design intent behind them: a bore that measures 25.06 mm on a worn part was drawn at 25 mm, and a hole pattern that measures slightly uneven was laid out on a circle. The datum faces are set first, then the prismatic features, then the free-form surfaces fitted to the scan as NURBS. The scope decides which features are snapped to their nominal values and which follow the scan as measured, since a part that has to mate with an existing assembly keeps the measured positions of its mating features. The reverse engineering page describes that work and the propeller guide follows it on a part made of nothing but free-form blades.

Check the model against the scan

Before delivery the model is compared with the mesh it was built from, and a list says which features follow the scan and which were restored to their design shape. What the scan cannot tell you is not checked this way: material, heat treatment, wall thickness behind a face, thread specification and load capacity come from drawings, inspection or the engineer, never from geometry alone.

Export in the format the next tool opens

The CAD model is exported as a STEP file, ISO 10303-21, which CAD packages read, with native formats on request; the mesh as STL, OBJ or PLY; drawings for a shop in DWG and PDF on request; and the point cloud of an installed object as E57 and RCP/RCS. A quote for scanning an object into CAD arrives within one business day of your sending photographs, the approximate size and what the model is for. Reverse engineering of a single part starts at about $1,000 for the scan and the model; a part is usually scanned in a day, and the model usually follows in one to two weeks.

Sources

• Creaform, HandySCAN 3D SILVER series brochure (2024): laser lines, accuracy, part size range.
• Trimble X7 3D laser scanning system datasheet: 3D point accuracy, registration report.
• ISO 10303 (STEP), list of parts: Part 21, clear text encoding of the exchange structure