what arbor for TCt core drill with no thread?

[RobertL]

Can somone advise me please? I have used core drills only a couple of times and they used an arbor that screwed into the drill.

I have just bought a 40mm core drill and I find it has a smooth 20mm diameter tapered hole for the arbor (no threads).

All the arbors I have seen before have threads. Do I need a smooth "shank"? Is it just held there by friction?

thanks for any guidance,

Robert

[A.Lee]

Yes to both queries.

20mm hole for the arbor? That seems really large, my core drill pilot is a 8mm drill bit with a tapered end.

[John Rumm]

Are you two perhaps talking at cross purposes? I was under the impression the OP was talking about the connection between core and arbour that attaches it to the electric drill, and not the connection to the pilot drill?

My diamond cores have a 8mm taper fitting for the pilot drill, but fitting on the back of the core takes a threaded attachment on the end of the arbour. e.g.

[A.Lee]

Yes, you may be right, my pilot drill is an arbor fitting, which is a term we used in engineering - any drill with a taper fitting was an arbor drill, which is what my core drill uses for its pilot, with the main core bit screwed onto a separate 'arbor'.

Alan.