AutoCAD solid modeling — combining primitives into one solid Which AutoCAD command combines two or more 3D solids into a single, complex solid model using a Boolean operation?

Introduction / Context:
Boolean operations are central to 3D solid modeling workflows. Being able to join solids, remove volumes, or compute intersections allows designers to build complex forms from simple primitives efficiently. AutoCAD and many other CAD tools provide standard commands for these tasks.

Given Data / Assumptions:

• We are working with 3D solid objects (not surfaces or meshes).
• AutoCAD naming conventions use specific command names for Boolean operations.

Concept / Approach:
AutoCAD uses the commands UNION (add volumes together), SUBTRACT (remove one solid's volume from another), and INTERSECT (keep only the overlapping volume). To “combine into a single complex 3D model,” the intended Boolean is UNION, which fuses the participating solids into a single body with combined volume.

Step-by-Step Solution:

Verification / Alternative check:
AutoCAD help and command reference list UNION for combining solids and distinguish it from JOIN (primarily for 2D polylines) and ATTACH (for references or external files).

Why Other Options Are Wrong:

• Add/form/merge2d: not standard AutoCAD solid Boolean commands for combining 3D solids.
• Attach: used to reference files (Xrefs), not to fuse geometry.

Common Pitfalls:

• Attempting to UNION non-solid entities (surfaces, regions, or meshes) without first converting them to solids.
• Forgetting that solids must overlap or touch appropriately; otherwise, union may fail.

Final Answer:
union