There are many metal working processes including shearing, piercing, rolling and notching. The tubing is held rigidly in a clamping device, a multi-toothed hole saw or boring tool is used to slowly cut a circular hole in the tubing; although it is a circular hole the effect is a notch that allows the tube in question to butt nicely with another tube of equal or larger diameter in preparation for welding.
Examples of tube notching:
There are many examples of metal assemblies where two light gauge tubes need to be joined together. The joint is often a “T” but the tubing notcher can be set up to cut the notch in such a way that any angle is attainable. A perfect example of tube notching is a typical bicycle frame. With a bicycle frame, every joint is a little different angle, furthermore different size tubing is used for different purposes. The cross bar is usually light weight, reasonably small diameter tubing while the tube that runs from the pedal bearing area to the fork tube is considerable larger and heavier.
How is circular tube notched?
It is simple to notch a flat bar, because it is solid it can be notched in a press. This is not the case with tubing. Tubing is hollow and even thin wall tubing has very high strength to weight ratio, the problem is, being hollow it would crush if the operation were to be done with a punch.
A typical tubing notcher uses a rotating hole saw. If the saw that used for the operation is the same diameter as the tube, the resulting notch is semi-circular. If the piece of tubing that is subject to notching is smaller in diameter than the tube it will be welded to, a larger diameter hole saw will be use, one that will match the arc of the larger tube.