GlossaryKind of term: Manufacturing termDrawing reading
What is drawing reading?
Drawing reading is the interpretation of a technical drawing: the dimensions, tolerances, roughness, material and finishing that define the part.
The aim is a set of unambiguous requirements for the part. The work covers the views and sections, the dimensions with their tolerances, the geometrical tolerances for form, orientation, location and runout with their datums where they apply, the surface texture indications, the threads, the general notes and the title block: material, general tolerance, finishing, revision and projection method. An example: EN AW-6082 T6, ISO 2768-mK, Ra 3.2 µm overall with Ra 1.6 µm on a bearing seat, black anodising and eight M6-6H threads. A person can read the drawing, or software can extract values from it; either way the result is an interpretation to be checked against the drawing.
Which standards decide how a drawing is read?
A drawing can only be read unambiguously together with the standards it refers to, usually named in or near the title block. For ISO drawings these include ISO 128 for presentation, ISO 129-1 for dimensioning, ISO 1101 for geometrical tolerancing, ISO 2768 for general tolerances and ISO 5456-2 for the projection method. A callout such as ISO 2768-mK combines the class for linear and angular dimensions (part 1) with the class for geometrical tolerances (part 2). Under ISO 8015:2011 the independency principle applies as soon as a drawing invokes an ISO GPS standard, unless the drawing states otherwise, for example with the envelope requirement Ⓔ or an -E suffix after the ISO 2768 class. On an older drawing without a reference to ISO 8015, a national envelope rule may be intended. A drawing to ASME Y14.5 applies the envelope rule (Rule #1) by default, so the same dimension can mean a different requirement under each standard.
How does drawing reading work in practice?
For a request, reading the drawing establishes which requirements drive the route. Material and condition set the stock and, together with tooling and machine, the cutting data. Tight size and geometrical tolerances can call for an extra finishing pass, a different setup sequence or a check on a coordinate measuring machine. Whether a low roughness value is reachable in the last pass or needs grinding or polishing depends on process, machine, tooling and material. A finish is often a subcontracted step with its own lead time. A thread can be tapped, milled, turned or rolled. The 3D model gives the shape; unless it carries PMI, the requirements are on the drawing and in the documents it refers to, such as a customer standard or purchase specification.
What is drawing reading often confused with?
Drawing reading is not feature recognition: it finds features such as holes, pockets and slots in the geometry of the 3D model, while the drawing sets the requirements on those features. Nor is it OCR: OCR turns characters into text, whereas reading interprets that text in context, so that ⌀12 H7 is a hole with a tolerance class rather than a string of characters.
How do you see drawing reading in Blake?
In Blake the material, tolerances, roughness, finishing and threads from the drawing sit with the part as proposals. You confirm or correct each value against the drawing; who did so and when stays visible, with a note if you add one. More on requests.
Frequently asked questions
What if the drawing is a scan or hard to read?
Then a reading error is more likely, for a person and for software alike. Check the values with extra care, especially decimals, tolerances and thread callouts, and ask for a better copy or the native file when in doubt.
Do I need the 3D model as well as the drawing?
Usually, yes. The model gives the shape and often dimensions the drawing leaves out; the drawing gives tolerances, roughness, material and finishing. Which of the two governs when they disagree should be settled in the request or the purchasing terms.
Why are extracted values put forward as proposals first?
Because reading is interpretation, and an error in a requirement carries through to the route and the price. A proposal shows what was extracted and waits for a person to confirm or correct it against the drawing.