GlossaryKind of term: Standard and conventionSTEP AP242
What is STEP AP242?
STEP AP242 is the ISO 10303 application protocol for 3D models that can carry dimensions, tolerances and datums alongside the shape.
STEP is the ISO 10303 series of standards for exchanging product data; an application protocol (AP) defines which data a file holds for a given purpose. AP242, ISO 10303-242, is the protocol for managed model-based 3D engineering. It brings together the older AP203 and AP214 and among other things extends support for PMI: dimensions, geometric tolerances and datums attached to the faces they apply to. An AP242 file can carry PMI but need not: that depends on the model and on the export settings of the CAD system.
What does the standard say about STEP AP242?
ISO 10303-242 was first published in 2014, and later editions have extended it. The file is usually a text file in the ISO 10303-21 format (.step or .stp) whose header names the protocol under FILE_SCHEMA. PMI can come in two forms: as presentation, lines and text you read on screen, or as semantic data that software can attach to a face and read. AP242 does not define what a tolerance means; the tolerancing standard the model refers to does, such as ISO 1101 with ISO 8015, or ASME Y14.5. How well PMI survives the exchange depends on support in both the sending and the receiving system.
How does STEP AP242 work in practice?
When an AP242 file with PMI arrives together with a PDF drawing, you have two sources for the same requirements. If they differ, for example a ⌀12 H7 that appears only on the drawing, ask which source is authoritative before you quote; that agreement belongs in the order or the purchasing terms. If a requirement is missing from the source you price from, the price may miss a finishing pass or an inspection step. Where only the shape matters, most CAM systems treat an AP242 file like any other STEP file; an older system that does not know the AP242 schema may reject the file or read only part of it.
What is STEP AP242 often confused with?
AP242 is not the same as STEP: STEP is the series of standards, AP242 one protocol within it, alongside AP203 and AP214. An AP242 file is not automatically a model with PMI either; without PMI it mainly carries the shape, much like an AP214 export. And AP242 is not MBD: it is a format that can carry the data, while MBD is the practice in which the model is the authority.
How does a STEP file get into Blake?
In Blake you upload the STEP file with the PDF drawing for each request. Model and drawing are paired per part by file name; where the name is ambiguous, you confirm the pairing yourself. Material, tolerances, roughness, finishing and threads are set out as proposals from the drawing, for you to confirm or correct. More on requests.
Frequently asked questions
How can I tell whether a STEP file is AP242?
Open it in a text editor and find the FILE_SCHEMA line near the top. A schema name starting with AP242 points to AP242. AUTOMOTIVE_DESIGN stands for AP214; CONFIG_CONTROL_DESIGN, or a name starting with AP203, for AP203.
Do I still need the PDF drawing with an AP242 model?
Usually, yes. You can do without it only if the customer records that the model is authoritative and its PMI is complete. Often the PMI is missing in whole or in part, and material, roughness and finishing appear only on the drawing.
What is the difference between AP214 and AP242?
AP214 came from the automotive industry and carries shape, structure, colours and layers. AP242 brings AP203 and AP214 together and can also attach dimensions, tolerances and datums to the geometry as semantic data. For shape alone, it makes little difference to most CAM systems.