ScanRuler: Free Tool Turns 3D Scans Into Parametric CAD

Plenty of 3D scanners end up as expensive paperweights, CNC Kitchen argues, and not because they scan badly. The software that ships with them captures a part and little else, the free version of GOM Inspect now needs a company email since Zeiss bought GOM, and the alternatives are expensive. His answer is ScanRuler, a free, open-source tool that runs locally, and its most ambitious feature hands reverse engineering to an AI agent. For makers who print replacement parts, it covers the gap between a mesh and a model you can edit.

The Framework

CNC Kitchen’s write-up, based on a video sponsored by Elegoo, walks through ScanRuler with scans from Elegoo’s new M1 Ultra scanner, which starts at $1,599. It needs no installation, has no tracking, and runs on your own machine. Its workspaces suggest four ways a scanner earns its place in a print shop.

1. Measure What Calipers Can’t

You fit features such as spheres and planes to a scan, then measure between them. Across nine scans of a precision ball bar, every result was within the M1 Ultra’s specified 0.035 mm, with the largest deviation three hundredths of a millimeter over 257 mm. The same method measures draft angles, fillet radii, and a car wheel’s offset and bolt pitch circle, which came out close to spec. Fitted features export as STEP geometry.

2. See Where a Print Warped

The deviation workspace compares a scan with the original model. CNC Kitchen printed the same ABS case twice, once with the door open and heater off, once in a 65°C chamber. Both averaged around 0.3 mm of deviation, but the cold print warped, with flat areas bowing inward, while the hot print stayed mostly flat and shrank evenly. After adjusting the scaling factor, a rescan almost perfectly matched the reference. A wall thickness map of a vacuum-formed hood showed the lower bends at less than half the original stock.

3. Repair Broken Parts With Trim to Scan

For a broken engine housing, the author sketched the missing wall with some overlap, extruded it, then used a mesh tool the author calls virtual kintsugi. Trim to Scan finds the fracture surface, extends it and trims the new wall to match, with an optional gap for glue. The printed piece fits into place.

4. Let an Agent Rebuild the CAD

ScanRuler includes a manual reverse-engineering workspace with sketches, a feature timeline and parametric dimensions. It also has an MCP server, so Claude, Codex or a local model can drive its tools. Instead of turning every triangle into a CAD surface, the agent aligns the scan, fits features and rebuilds the part’s design intent as clean, editable geometry, then runs a deviation check. Simpler parts take a few minutes to an hour. Notes pinned to the part steer it: a note asking it to recreate a broken bridge on a fridge bracket produced a repaired model about a minute later.

Where It Doesn’t Apply

CNC Kitchen is open about limits. Complex parts, freeform surfaces and very rough castings often turn out poorly. The author has had the best results with Opus 5.5, and less capable models sometimes do a terrible job. The agent is optional, and ScanRuler is vibe-coded, which the author acknowledges not everyone likes. Stack Archive covered Backflip AI’s scan-to-CAD generator, a commercial take on the same mesh-to-model problem.

Source: CNC Kitchen

Content created with AI assistance and reviewed for accuracy.