earthtojake--text-to-cad/benchmarks/04-stepped-shaft-keyway.md

4. Stepped Shaft With Keyway

Prompt

Create a single solid stepped shaft STEP model in millimeters.

The shaft axis runs along X. The total length is 120 mm. The left end center is at X = 0, Y = 0, Z = 0.

From X = 0 to X = 30, the shaft diameter is 20 mm. From X = 30 to X = 90, the shaft diameter is 30 mm. From X = 90 to X = 120, the shaft diameter is 20 mm.

Add a 1 mm chamfer to both end edges.

Add a rectangular keyway slot on the top of the 30 mm diameter middle section. The keyway is 6 mm wide in Y, 3 mm deep in Z, and runs from X = 40 to X = 80.

Export as a STEP file.

Test Cases

Test	Expected result
STEP import	File imports successfully
Solid count	Exactly one watertight solid
Shaft axis	Along X, not Z
Total length	120 mm
Left section	Diameter 20 mm, length 30 mm
Middle section	Diameter 30 mm, length 60 mm
Right section	Diameter 20 mm, length 30 mm
Coaxiality	All three cylindrical sections share same X-axis
End chamfers	1 mm chamfer at both ends
Keyway location	On top of middle section
Keyway length	From X = 40 to X = 80
Keyway width	6 mm in Y
Keyway depth	3 mm downward into shaft
Negative check	Keyway should not pass through the shaft; shaft should not be vertical