core drills (again)

[Stephen]

Hello,

I wondered what were the most useful sizes of core drills to have?

I'm guessing something slightly bigger than 32mm, something slightly bigger than 40mm, and something about 110mm? For both sizes of waste pipe and 4" fan ducting, respectively.

Is that about right? What about any others?

Are 22mm and 28mm any use? Perhaps the22mm one for 15mm pipe sleeved in conduit or overflow flow pipe and the 28mm one for 22mm pipe sleeved in something (though I can't think what).

I'm wondering whether to return the silverline 22mm one I bought from toolstation's clearance section. It fits the drill via a hex shaft rather than an arbour, so you cannot use a pilot bit, which I think reduces how useful it is.

Thanks, Stephen.

[Steve Walker]

I've used a 50mm for both 32mm and 40mm waste, you're going to have to fill the gap anyway, so an extra few mm around the pipe make little difference.

I've used a conventional bit for 15mm pipe.

SteveW