In computer aided manufacturing, how is the coordinate system for describing a workpiece defined in practice?

Introduction / Context:
Correctly defining coordinate systems is essential for machining accuracy, probing, and repeatable setups. This question focuses on how work coordinates are established relative to a machine reference rather than being arbitrary or always planar.

Given Data / Assumptions:

• Workpieces are mounted on machines or fixtures.
• CNC systems support machine coordinates and work offsets.
• Dimensional control is three dimensional for most operations.

Concept / Approach:

In practice, a work coordinate system is tied to a datum such as a vise corner, a fixture pin, or a touch probe measurement relative to machine zeros. This ensures the program’s coordinates map predictably to physical positions and compensations like G54 through G59 in standard CNC practice.

Step-by-Step Solution:

Verification / Alternative check:

Shop procedures show consistent part alignment when datums and work offsets are used. Dimensional inspections validate that machine referenced systems yield predictable results.

Why Other Options Are Wrong:

Option a is wrong because many operations require three dimensions. Option b is misleading since while parts vary, coordinates are still defined relative to machine references for repeatability. Option d cannot be right because a is false. Option e is unnecessary as c is correct.

Common Pitfalls:

Relying on arbitrary screen based coordinates rather than physical datums, and forgetting to re probe after fixture changes.

Final Answer:

It is defined with respect to a reference point on the machine or fixture