A shallower angle, such as 150 degrees, is suited for drilling steels and other tougher materials.
2.
:: : I would suggest an electric drill with a bit suitable for drilling steel and that is a few millimetres smaller than the lock barrel.
3.
They were built with a technique which involved drilling steel pipes into the riverbed, then surrounding them with concrete and steel, instead of installing cofferdams, which would be more costly and would disrupt the river.
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