Hello

I am installing plumbing and heating to a new house in Sussex, the client is keen to avoid pipes on view, the house is timber framed and the walls are stud partition approx 50mm at the point I need to drill and sometimes there is a double timber, I always insulate all my pipework, I need to drill holes in the stud work and need the hole to be 40mm to allow the pipe and insulation to pass easily through, what is the best drill bit to use, flat bits seem to take a long time to drill through and start to get very hot, the same for hole saws, I was hoping to get a 40mm Auger bit but the biggest I have found is 32mm any ideas

Thanks for your help

Forsner bits s/f pt. no 83345 or an expansive bit 17377 (I havn't used the latter) the forstner bits are very good

Am i stupid   or am i reading you are planning to drill a 40mm hole through a 50mm stud so therefore leaving 5mm either side?
If you need to you can call me stupid,its the way i read the question

Could you not just insulate up to and beyond the studwork?

I never have any problems just using a hole saw, I do a lot of large holes through joists for waste pipes and they go through ok with a right angle drill

I do not like the pipework to touch the wood  at all, there is no chance of any creaking noises if the pipe is not in direct contact with the timber.

[quote author=woodsmith  link=1106056328/0#1 date=1106067396]My first thought was a Forstner bit but these may not have the depth you need. Axminster Power tools sell sawtooth cutters they are about 130mm long and you can get them up to 50mm diameter.
http://www.axminster.co.uk/product.asp?pf_id=22801&recno=8
[/quote]
Woodsmith, what's the difference between a Forstener bit and a Saw Tooth bit?  They look the same to me.

Jerry the Forstner bits have 2 cutting edges wheras the sawtooth cutters have a sawtooth edge, basically it allows you to drill into end grain which Forstner bits won't.