cutting a hole in a cast iron soil pipe

Hi
In order to plumb-in a washing machine, I need to connect to the old cast iron soil pipe to carry away the waste. (The pipe is just over 4 1/4" diameter.)
Can anyone recommend a good way to cut the hole in the pipe, to connect a boss ?
I've seen an old post where someone recommended drilling a ring of closely spaced holes and then joining the holes so the disc can be removed. But I don't see how you'd be able to drill the holes closest to the wall.
Whatever the method, I don't want to risk cracking the pipe - presumably old cast iron is fairly brittle.
Many thanks
Steve
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closely
old
have you considered just cutting out a section of the iron pipe (with an angle grinder) and slipping a length of plastic pipe in its place?
-- John Stumbles -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -+ Experiments to demonstrate the existence of Sod's Law by dropping slices of buttered toast all failed. That's Sod's Law.
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If you can't get hold of a suitable steel hole cutter, then cut the pipe and fit a plastic connector with the facility to fit a boss. Most manufactures make a connector/adaptor fitting
dg

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and
boss.
Thanks for the suggestions. But if I cut the soil pipe, it will mean the (not inconsiderable) weight of the upper part isn't supported by the lower part; this will put a lot of stress on the 2 higher supports and on the outlet from the upstairs toilet. Isn't this a problem ?
Steve

closely
old
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an
If it's as I imagine I think the outlet from the upstairs wc connection will help support the rest of the stack, but it should have proper supports anyway. You could always add some more if you think fit (using steel or iron brackets of course, not plastic).

old
It's brittle to the extent that if you wack it with a hammer it may crack. Sod's law dictates that it will resolutely refuse to do so if you want it to and do so too easily if you don't :-)
When I've cut a pipe that was in a corner, using a 4" grinder, I cut halfway through the pipe at 2 points about a foot apart and sliced lengthways to remove a sort of rectangular section, then I could get the grinder in to cut the rest of the way through to the back of the pipe. USE A MASK: the dust and other stuff that comes of grinding through a soil pipe is outlawed for use in combat under the Geneva Convention.
-- John Stumbles -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -+ No Rules, OK
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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

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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

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