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CNC Machine Base

Reference

Standards That Govern a Machine Base

21 standards, grouped by what they control. Most machine base disputes come from citing one where another was meant, or from citing none at all and letting the fabricator assume. The notes say which is which.

The three most commonly confused: ISO 13920 governs how straight and square the finished weldment is. ISO 5817 governs how good the welds themselves are. ISO 3834 governs whether the shop has a welding quality system at all. A complete drawing cites all three and they do different jobs.

Dimensional and geometric tolerance

ISO 13920: General tolerances for welded constructions
Four graduated classes A to D for linear dimensions, angular dimensions and shape and position of a finished weldment. Permitted deviation widens with the size of the dimension. Class B is the usual choice for machine frames.
In practice: This is the one most often missing from a machine base drawing. If it is absent the fabricator assumes, and will reasonably assume a loose class.
ISO 1101: Geometrical product specifications: geometrical tolerancing
The ISO grammar for flatness, parallelism, perpendicularity, position and profile, and how datums are specified and simulated.
In practice: Reference it or ASME Y14.5 in the title block, once. A drawing mixing both gets interpreted twice.
ASME Y14.5: Dimensioning and tolerancing
The American equivalent of ISO 1101. Covers the same ground and differs in detail, notably around datum simulation and material condition modifiers.
In practice: Use whichever your organisation and supply base already work to.
ISO 2768: General tolerances for linear and angular dimensions
General tolerance classes for machined features not individually toleranced. Commonly cited as a default note on machined drawings.
In practice: Applies to the machined geometry, not to the weldment before machining. Those are separate requirements.

Welding and fabrication

ISO 3834: Quality requirements for fusion welding of metallic materials
The quality system a welding shop works to, in comprehensive, standard and elementary levels. Covers procedures, personnel qualification, equipment, inspection and records.
In practice: ISO 3834-2 is the comprehensive level and is what a serious heavy fabrication shop will hold.
ISO 5817: Fusion-welded joints in steel: quality levels for imperfections
Acceptance limits for weld imperfections at quality levels B, C and D. Governs porosity, undercut, penetration, cracks and bead profile.
In practice: Different from ISO 13920 and frequently confused with it. 13920 is how straight and square, 5817 is how good the weld itself is. You need both.
ISO 9606-1: Qualification testing of welders: fusion welding of steels
How a welder demonstrates they can produce a sound joint in a given process, position and material range.
In practice: Ask for current certificates covering the processes and positions your part actually needs.
ISO 15614-1: Specification and qualification of welding procedures
How a welding procedure is qualified by test. Produces the WPQR that supports a WPS.
In practice: A shop quoting heavy structural work should be able to hand you WPS and WPQR without hesitating.
EN 1090-2: Execution of steel structures: technical requirements
Execution classes EXC1 to EXC4 for structural steelwork, with tolerance requirements split into essential and functional.
In practice: Permits ISO 13920 as an alternative to its functional tolerances, which is usually the right route for a heavily welded machine base.

Castings and materials

EN 1561: Founding: grey cast irons
Grades EN-GJL-100 to EN-GJL-350 by minimum tensile strength in MPa, measured on a separately cast test bar.
In practice: The grade number is a test bar value. Strength in a thick section of your casting will be lower. Specify the grade and the governing section thickness together.
EN 1563: Founding: spheroidal graphite cast irons
Ductile iron grades such as EN-GJS-400-15, where the first number is minimum tensile strength in MPa and the second is minimum elongation as a percentage.
In practice: Tougher than grey iron and damps noticeably less. Substituting one for the other is a real engineering change.
EN 10025: Hot rolled products of structural steels
Structural steel grades including S235, S275 and S355, with sub-grades for impact toughness.
In practice: S355 is the common choice for heavy machine base weldments where strength matters more than formability.
EN 10204: Metallic products: types of inspection documents
Certificate types. 2.1 declaration of compliance, 2.2 test report, 3.1 certificate with specific test results validated by the manufacturer, 3.2 additionally validated by an independent party.
In practice: If you want traceable material, ask for 3.1 by name. "Material certificates" on its own means whatever the shop decides.

Inspection and non-destructive testing

ISO 17635: Non-destructive testing of welds: general rules
How to select an NDT method for a given material, thickness and joint type.
In practice: Useful when you know you want NDT but not which kind.
ISO 17637: Visual testing of fusion-welded joints
How visual weld inspection is performed and recorded.
In practice: The baseline. Every weld should get this; the question is what else.
ISO 9934: Magnetic particle testing
Surface and near-surface crack detection in ferromagnetic materials.
In practice: The usual choice for full-penetration welds on a machine base.
ISO 17640: Ultrasonic testing of welded joints
Volumetric inspection of welds, and the practical method for heavy sections.
In practice: Also the practical method for volumetric inspection of a thick iron casting.

Surface, packing and trade

ISO 8501-1: Preparation of steel substrates: visual assessment of surface cleanliness
Blast cleaning grades Sa 1 to Sa 3 and the rust grades they start from.
In practice: Specify the grade, or "shot blasted" means whatever the shop has time for.
ISO 12944: Corrosion protection of steel structures by protective paint systems
Corrosivity categories and paint system specifications matched to environment and required durability.
In practice: Lets you specify a paint system by result rather than by product name.
ISPM 15: Regulation of wood packaging material in international trade
Requires solid wood packaging in international trade to be heat treated or fumigated and marked accordingly.
In practice: Standard practice at any competent exporter. If you need fumigation-free specifically, say so: heat treatment and fumigation are different treatments.
Incoterms 2020: ICC rules for the use of domestic and international trade terms
EXW, FOB, CIF, DAP and the rest: who books carriage, who pays, and where risk transfers.
In practice: DAP normally does not include unloading. On a multi-tonne crate that matters.

This index tells you which standard applies. For what to put on the drawing, readthe ISO 13920 guide andGD&T for machine bases. To have a part quoted against them, send the drawing.