Engineering article
One hole can change the way the tube fails
How does a cross hole affect a 20x18x1000mm tube and why the cutout position, layup pattern and fasteners need to be determined before ordering the blank.
The hole doesn't just remove a small area
The cross hole cuts some of the continuous fibers and creates a stress concentration around the edge. The remaining sections of the wall must redirect the load, and the thin tubular geometry adds local deformation. Therefore, the influence of the cutout is determined not only by the diameter. The distance to the end, the direction of the main load, the clamping method and the presence of internal support are important. The same hole can be insignificant for an unloaded fastener and critical in a load-bearing joint.
The laying pattern changes the failure mode
A study of rectangular CFRP tubes with circular cutouts under axial compression shows that the hole changes the energy absorption and failure mechanism, and the result depends on the orientation of the layers. This is not a ready-made calculation for a 20x18 mm round tube, but a clear confirmation of the general risk of geometric fiber rupture. A specific assembly requires wall architecture or tested product data; A catalog diameter alone does not justify a connection without engineering verification.
What can be decided before drilling
Sometimes the hole can be replaced with a glue-in, an external clamp or a tip that introduces a load over a greater length. If a hole is necessary, you can pre-select its position, support the wall with a bushing, and determine the machining method without impact loading. These solutions depend on the function of the fastening and are not a one-size-fits-all recipe. The main thing is to include the hole in the design before purchasing, and not add it to the finished tube without analyzing the distance to the edge, the direction of the fibers and subsequent assembly.
What data is needed for the quotation and engineering response?
For factory tube, specify quantity, length, surface requirements, cutting tolerance and lead time. If a prefabricated assembly is required, please attach a STEP or sketch showing hole diameter and position, fastener type, internals and load. Separately indicate whether the supplier must perform the machining. The price is provided on quotation, since it depends on the design and batch. Documents and photographs are requested for a specific offer; Their availability cannot be promised only by the general name of the size. It is useful to agree on a trial sample of the machined assembly prior to series production.