Engineering article
Why the perfect hole is not the only quality criterion
Why is the quality of a hole in a 3 mm sheet assessed together with the geometry of the connection, and the technological file is supplemented with a control drawing.
The photo of the hole doesn't show the whole picture.
When machining carbon fiber, attention is naturally drawn to chips and delamination at the entry or exit of the tool. But a defect of the same type can have different meanings in two parts. Its effect depends on the diameter of the fastener, the presence of a washer, the distance to the edge, the direction of the layers and how much of the hole actually transfers the load. The NASA study looks at hole quality in conjunction with geometry and joint conditions. This is a more useful approach than trying to evaluate a part from just a photo of the edge.
The hole changes the load path in the laminate
The round cut breaks the continuous fibers and forces the force to bend around it. A non-uniform stress field appears near the edge, and the contact of the fastener adds local crushing. If a hole is located close to an edge or multiple holes are close together, the zones of influence may interact. Therefore, drilling parameters are only one part of quality. The designer sets the diameter, position and tolerance, the technologist chooses the machining method, and control must take into account the function of the unit: basing, free passage or force transmission through the fastener.
Why add readable PDF to DXF?
DXF conveys contours well, but does not always clearly communicate the purpose of dimensions, the presentation face and the priority of tolerances. The reference PDF links geometry to engineering meaning by showing datums, critical holes, threaded features, mating areas and edge requirements. For 3 mm sheet, this is especially important if the part is part of an assembly and must maintain the exact relative position of the holes. The file for the machine and the drawing for acceptance solve different problems; a valid order includes both views.
What to agree on before producing a series
Before starting, confirm the material and thickness, the orientation of the face design, the format of the original sheet and the position of the parts on it. Separately list the critical holes and the acceptable type of tool exit. If the connection carries a load, provide the fastening diagram and distances to the edges; production control does not replace the calculation of the unit. For a repeat batch, it is prudent to retain an approved sample or measurement report. This way, the “clean hole” requirement turns into a verifiable set of characteristics, rather than remaining a subjective assessment.