CNC cutting — documentation, tolerances and order preparation
In CNC cutting, the contour of the part alone is not enough. Correct order preparation requires consistent documentation: the geometry used to prepare the toolpath and a drawing that defines the requirements for the finished part. Features that affect assembly need the most attention — hole spacing, datums, mating edges and the surfaces on which the later fit of the part depends.
The scope of a CNC order starts with documentation
We assess whether a part can be made on the basis of its material, thickness and geometry and the requirements for its edges and tolerances. This information affects the choice of process, the preparation of the program and the scope of any operations after cutting.
In an enquiry, it is worth separating two levels of requirements: the contour to be cut and the expected condition of the finished part. If the part is to go straight to assembly after cutting, the requirements for burrs, edges, holes or further machining should be included in the documentation as early as the quotation stage.
The drawing and the contour file must describe the same version of the part
The technical drawing defines the function of the part in terms of dimensions, tolerances, material and revision. The contour file, on the other hand, is the source of the geometry used to prepare the cutting process. Both files must refer to the same version of the part — even when a change concerns only one hole, an undercut or a section of the outline.
Before sending the contour, remove duplicate lines and separate the actual part profile from frames, notes and dimensions. Overlapping profiles can cause the same path to be cut a second time. An export to DXF alone does not replace the drawing: the file format does not define the tolerances, the material or the acceptance criteria for the part.
Tolerances follow from the function of the part
Not every feature of a part requires the same accuracy. For a component bolted to an existing machine, the spacing of the holes relative to the mounting datums may matter more than the accuracy of the whole outline. The documentation should indicate precisely those relationships that determine the fit and function of the part.
The required tolerance has to be linked to the material, thickness, geometry and the chosen technology. If the edge condition, the absence of burrs or a machining allowance left for further processing is important, these requirements should also be recorded on the drawing or in the order specification.
Documentation for quotation and order preparation
The more complete the set of data we receive at the start, the easier it is to agree clearly on the scope of work and the way the part will be accepted.
| Data | What to provide | Why |
|---|---|---|
| Material | Grade, thickness and information on who supplies the stock material. | Assessing the process and the scope of supply. |
| Geometry | The current contour, the overall dimensions and a drawing with its revision number. | Preparing the correct version of the part. |
| Critical features | Dimensions, datums and tolerances that determine assembly. | Assessing feasibility and planning inspection. |
| Edge | Requirements for burrs, finish and further machining. | Defining the condition of the part after production. |
| Batch | The number of parts and the part markings. | Defining the scope of the order. |
| Acceptance | Features to be checked and the required documents. | Agreeing the conformity criteria. |
Agreeing production and acceptance
Before an order is started, the applicable documentation revision, the scope of work and the method of checking the critical features must be clearly specified. This ensures that the production program, the part and later measurements all refer to the same version of the part.
For a new part, a design change or particularly important assembly requirements, a first-article inspection can be agreed before the rest of the batch is produced. The scope of such an inspection should cover specific features, acceptance criteria and the way the result is reported.
The most common problems in CNC cutting documentation
- the contour files and the drawing come from different revisions;
- the contour contains duplicate lines, notes or elements that are not part of the component;
- the drawing does not indicate the datums and features that actually determine assembly;
- tolerances are given without reference to the function of the part;
- information on the required edge condition or further machining is missing;
- it has not been specified which dimensions are to be checked at acceptance.
Questions about documentation
Does a contour change require a new drawing revision?
A change in geometry should be linked to the current version of the documentation. In the revision designation or in the agreement, it is worth indicating the changed features and the point from which the new version applies. This is particularly important when older parts are still in use. Consistent designations make it possible to assign the production program and the measurement results to the correct part.
When is it worth agreeing a first-article inspection?
For a new part, a design change or assembly requirements that should be confirmed before the whole batch is produced. We agree the scope of the inspection before work begins: we specify the features to be measured, the acceptance criteria and the way the result is reported.
Is a DXF file alone enough for a quotation?
A contour file shows the geometry, but it does not replace information on the material, thickness, tolerances, edge condition or acceptance requirements. If the part is to work with an existing machine or another component, the technical drawing is the basis for defining the critical features.
Feasibility enquiry
Send us the current drawing, the contour file and information on the material, the number of parts and the critical features. On this basis, we can agree on whether the part can be made, the scope of the order and the way the documentation will be delivered. Contact.