We cut these holes on our Waterjet to make tapping easier. The laser would harden the material increasing the chances of the tapping tool breaking.
We provide a lot of parts for other fabrication and engineering companies and where holes are required to be tapped in thick steels we would always recommend waterjet cutting. Although the waterjet cutting process can be more costly than other cutting methods, it provides a higher level of positional accuracy than manually drilling, holes can be cut to size rather than having to use pilot holes and it reduces wear and tear on any tools used for completing the process.
M20 tapped holes in 20mm mild steel.
Nice M20 tapped holes in a flange.
