A useful machining brief includes a dimensioned drawing and, where appropriate, a 3D model. The two should agree on geometry and revision. Identify the part function so the review can focus on the surfaces that matter.
State the requested material, surface finish and critical dimensions. Apply tolerances deliberately rather than assuming every dimension needs the same level of control. Datum references help explain how the part will be inspected and assembled.
Provide the required quantity and expected schedule. Manufacturing feasibility, final tolerances and inspection methods need an engineering review; manufacturing capabilities require project-specific confirmation.