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Research & opinionFile Type · Production filesFor Creators & MakersA file unit is a production instruction
Why a maker cannot treat numeric coordinates as a product size until the unit, and the intended finished size, are explicit in the handoff.
The question
How can a creator and maker agree on the physical size encoded in a production file?
A file can contain precise numbers and still leave the product size unknown. Coordinates without a unit are not a size. They are a set of numbers waiting for someone to guess millimetres, inches, or another scale.
That guess is a production decision. It should not be hidden inside import software.
Make the unit part of the package
A useful size instruction has three parts:
- The unit used in the file, when the format can store one.
- The intended finished size of the product, in the same or a clearly converted unit.
- A way for the maker to verify that the imported geometry or artwork matches that size before production.
If the format cannot store a unit, the unit still belongs in the production package: a note, a drawing, a dimensioned screenshot, or a stated bounding size. “It should look about like this on screen” is not a size.
Use formats that can carry a unit when they fit the job
The 3MF Core Specification defines a model unit used to interpret all vertices, locations, or measurements. The default is millimetre. Allowed values include micron, millimetre, centimetre, inch, foot, and metre. That is a property of 3MF, and only when producer and consumer preserve it.
ISO/ASTM 52915:2020 specifies the Additive Manufacturing File Format (AMF). It allows the unit system to be specified as millimetre, inch, foot, metre, or micron, and says millimetres are assumed if no unit is specified. That default helps interoperability only when both sides know they are using AMF and that default.
A mesh or drawing format that does not carry a unit does not become millimetres by habit. The maker still needs an external size instruction.
Verify size before committing the process
Creators should export with a known unit, then state the intended finished size in the brief. If several files are included, they should share one size definition or clearly mark any exception.
Makers should check the imported bounding size against the brief before quoting a tight fit, nesting parts, or starting a long run. If the imported size and the stated size disagree, stop. Do not scale to “make it look right” without approval. Scaling can change wall thickness, hole size, artwork height, and whether a method can still meet the requirement.