Many thanks to all who replied.

I didn't realise that you can get hole-saws that can be used on cast iron.
As they are available, I'm going to cut the hole directly into the cast
iron pipe.

Steve


"fred" wrote in message ...
In article , Steve stevescholnic
writes
Can anyone recommend a good way to cut the hole in the pipe, to connect a
boss ?
Not the cheapest, but suggest you cut a hole with a hole saw (57mm) and
use a strap on boss. The boss has a flange which fits inside the hole &
makes the whole thing a bit less hit & miss. Add sanitary silicone around
the flange before fixing. Boss will accept rubber or solvent adaptors.
Rubber adaptors look insecure, but solvent leaves you without an option to
dismantle. A solvent stub mated to a pushfit pipe makes the job a bit more
serviceable.

List of bits, prices and codes are for http://www.bes.ltd.uk

57mm hole saw code 7799 £6.11 + vat
Large Arbor code 7801 £8.40 + vat
Strap on boss 110mm grey code 13002 £1.61 + vat
Adaptor rubber 32mm code 11191 or 40mm code 11192 cost about 90p
Solvent & other adaptors on site, post is free

HTH
--
fred