GlossaryKind of term: Manufacturing termDrawing requirements
What are drawing requirements?
Drawing requirements are what a drawing demands of the part, such as size, form and location, roughness, material and finish.
They apply to the part as delivered, and they can be recorded in the model as well as on the drawing. They cover dimensions with their tolerances, geometric tolerances with any datums they call for, roughness and other surface requirements, threads, edges, material and condition, finish, hardness, and whatever else the notes demand, such as marking or cleanliness. A requirement states what the part must be, not how to make it.
What do drawing requirements depend on?
Where the requirements sit depends on how the customer documents the product. In a conventional request the STEP model carries only the shape, and the requirements sit on the drawing, in its notes and in the standards or customer specifications it refers to. In a model-based definition, a STEP AP242 file can carry tolerances and annotations as PMI. A requirement is only unambiguous with its conditions: which standard the drawing invokes, ISO or ASME, which principle links size and form, and which general tolerance covers the rest. Which document governs when they disagree follows from the agreement with the customer, not from the file type.
How do drawing requirements work in practice?
Drawing requirements shape which operations, setups, inspections and subcontracted steps a part needs. A tight dimension may be held in a pass you make anyway, or it may call for a finishing operation; features with a tight location tolerance between them are best made in one setup; a finish such as anodising often goes to a subcontractor. What a requirement costs depends on process, machine, material, quantity and measuring equipment. A requirement missed in the estimate tends to return later as hours or rejects. One you cannot meet, or one that clashes with another, is best raised with the customer before you quote.
What are drawing requirements often confused with?
A drawing requirement is not a feature: the hole is geometry, the H7 tolerance class on it is the requirement. Nor is it an operation: tapping or thread milling is how you meet the requirement M6. And a requirement is not an assumption: anything not stated on the drawing, the model or the order is something to ask, not assume.
How do you see drawing requirements in Blake?
In Blake, what the drawing asks for in material, tolerances, roughness, finish and threads is attached to the part as proposals. Each value is yours to confirm or correct, and every change shows who made it and when, with a note if you leave one. More on requests.
Frequently asked questions
Which requirements are missing from the STEP model?
That depends on the file. A plain STEP model carries the shape only; tolerances, roughness, material and finish then sit on the drawing. A STEP AP242 file with PMI can carry them. Which document governs follows from the agreement with the customer.
What do I do with a requirement I cannot meet?
Raise it with the customer before you quote. There is often room: a different tolerance, a different finish or a deviation permit. Handle a conflict between drawing and model the same way.