Bert Coules wrote:
Thanks Dave and everyone else who responded. I've done this now: the
drilling went OK, and if there was any breakout under the panel it must
at least have been contained with nowhere to go: there's no sign of any
loose chips or other damage either inside or out, and the holes weren't
impeded in any way.

The hardest part of the job was driving home the fixing bolts -
Multi-Mondi hex heads from Screwfix. I had to use a small
socket-and-ratchet tool and the last few turns needed quite an effort.
Indeed, the last few turns on the first bolt proved impossible until I
realised that I hadn't drilled the hole deep enough...

Bert




next time you could try drilling the smallest size possible then drill
from both sides with the bigger drill.