Brian Sharrock wrote:

Genuine question; when 'producing' a wide hole through a cavity wall (
plaster, brick, cavity, brick, rendering) should one drill a (narrow) pilot
hole all the way through -then, and only then, widen the hole using the
'big' bit with its 'guide bit' fitted centrally.?

If you want to be able to drill from both sides then that is the way to
go. Alternatively you can just drill from one side, either using the
pilot bit all the way through, or just to get you started after which
you remove the pilot altogether and rely on the already cut section to
guide you. (the inner leaf acting as a guide for the outer leaf etc)

--
Cheers,

John.

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