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I rented a drill and bit I think for around 50 quid for a day from Speedy. The drill needs to be serious for a bit that size including having a means not to rip your arm off if it gets jammed, which it will. Have someone with you especially if you're up a ladder. It is a crap, crap job and depending on the type of wall you're going through I cannot see chisels ever working without hammering at it for a week. The surround on the inside is large but the outside vent is typically not much bigger than the hole, so won't mask major changes in direction in case a chisel goes awry. If you've got anything like render on the outside it's another opportunity to flake a big chunk off with a chisel compared to neatly sawing through with a drill. If you're feeding a solid pipe through you can't have any snags. If you're feeding one of those tinfoil pipes through I still wouldn't want any snags.
CYOA-
Yeah I'm not really looking forward to it. I have one of Screwfix's finest SDS drills which has a safety clutch, so should be ok on horsepower. Thanks for the suggestion on hiring, but I can't find anywhere that will hire the actual core bit (excepting HSS, but that seems to have a a proprietary Hilti drive interface 🤑).
hamrack
I have a large hole to put through our kitchen wall for the extractor hood. Nobody happens to have bitten the bullet on a 150mm core drill have they?
Likewise, because I don't fancy cutting mitres by hand, is anybody looking to sell on a mitre saw?
I'm keep an eye on eBay of course, but thought the internet's friendliest forum might be able to help too...