I Extended FreeCAD MCP After 1.5 Hours of Assembling Through Chat. Then the Agents Built It Alone

Description and use

Automated agents assembled a pan‑tilt mechanism in 15–17 min but incorrectly swapped side plates; verification tools only confirmed metric precision, not semantic correctness.

Problem

Automated CAD assembly agents required extensive human guidance and produced incorrect part placements, revealing limitations in current tool checks.

Outcome

The extended MCP server enabled automated assembly in under 20 min, but the built‑in checks only verified metrics the agents declared correct, not the semantic correctness of part placement.

Workflow

• 1. Forked hram/freecad-mcp and added new alignment/verification tools.
• 2. Ran Claude to assemble the archive autonomously.
• 3. Ran Codex to assemble the archive autonomously.
• 4. Compared agent outputs to expected geometry and inspected check results.
• 5. Analyzed why checks failed to catch swapped side plates and added spacers.

Evidence

The agent executed CAD operations, but I was the one assembling, through a chat. It took 1 hour 37 minutes, and the base was still unassembled.

Source

Claude and Codex each assembled the same mechanism on their own, in about 15 and 17 minutes.

Source

Codex had swapped the two side plates.

Source