Drilling cast iron soil pipe

[Marineboy]

I’m redoing the bathroom and have decided the most elegant route for the waste is straight through the wall and into the adjacent soil pipe. I have the plastic boss which fits into a 57mm hole in the pipe and looks very neat.

However, the challenge is drilling the hole. I’ve watched a YouTube vid and saw a bloke using a Starrett bi metal hole saw to do just what I want, so I bought the very same tool. Tried this pm to cut the hole. Drilling the central hole with the bit was ok but slow, but when it came to the actual hole... I was on ages and have made barely a mark. Am I doing something wrong, or is there a better tool out there?

 

[SammyQ]

Bonded-diamond holesaw? Cast iron should cut 'like butta' with a good HSS saw though...

Sam

 

[Marineboy]

Thanks Sammy, but it certainly ain’t cutting like butter - unless it’s straight out of the freezer.

 

[kevinlightfoot]

Sam is right cast iron should cut easily,is the hole saw a good make or a cheap Chinese cheese metal one.Starret are usually good tools perhaps you have a duff one.

 

[Marineboy]

It’s a Starrett, not noted for producing rubbish. And although I’ve been on ages with it the the teeth still feel sharp.

 

[sunnybob]

Speed is important. most hand power drill speeds are too slow, or too fast, for hole cutters.
try 2nd speed, but keep the trigger half compressed.

 

[Trevanion]

As already said, old cast iron should cut fairly easily... Unless it's more modern ductile iron piping which can be a pain. Slow speed, heavy pressure and a bit of oil helps.

If all else fails, drill small holes around the diameter of what you want and punch it in with a hammer.

 

[Marineboy]

Thanks Trevanion, there seems to be a consensus that cast iron cuts easily so I’m wondering if in fact it might be this ductile iron stuff. The bit I’ve cut looks bright and silvery - can this be a clue as to the metal?

 

[Trevanion]

Cast iron tends to be less shiny and darker from experience and the chips created are more like black dust and it's very dirty.

Ductile Iron as far as I'm aware creates a chip like steel would but I've never actually worked with enough of the stuff to give any real advice.

 

[SammyQ]

Just a casual thought: the drill rotation is clockwise as you view it? You haven't - by accident - got it in reverse?

Sam

 

[Trevanion]

Just a casual thought: the drill rotation is clockwise as you view it? You haven't - by accident - got it in reverse?

Sam

I unknowingly had a left-handed drill bit once :lol: Took me a good while to figure out why it wasn't cutting at all.

 

[Marineboy]

Sam - I’m certainly capable of that kind of idiocy but not in this case. I’ll have another go tomorrow, keeping it slow, putting oil on it, and applying as much pressure as I can, which is not easy 6 foot up a ladder.

 

[Racers]

I though that left handed bits where for filling in holes...


Pete

 

[julianf]

As mentioned above, cut it with (probably) the slowest setting on your drill.

For example, my mains drill has no speed control and I wouldn't even bother trying with it - I'd buy/borrow a slow speed battery drill and do it with that.

 

[MusicMan]

There are many variations of cast iron. I agree the type used for machinery beds (grey cast iron) usually machines well. Some
cuts easily but can still have a very hard skin at the surface. White cast iron is extremely hard all through.

A simple test is to see if you can file it fairly easily or whether the file just skates off.

 

[Lons]

Just a thought.

If you do manage to drill it be very careful the cut piece doesn't drop into the soil stack as it will lodge itself in the first bend and over time cause a blockage which will be very expensive to clear.
Not easy to stop but there are ways.
First check if there is a bolt on access panel below where you're cutting in which case it's easy to block it there and catch the cut out.
If the open outlet of the stack is straight above gutter height then it can be possible to lower as securely tied circle of wood ideally with a magnet attached to below where you're cutting and pull it up afterwards or alternatively stop just short of drilling right through, secure the piece you're cutting with bent stiff wire through the centre hole and finish the cut with small drill holes before knocking it out.

As an aside, regularly check the chuck on your drill is tight. My brother was drilling through a stack on one of our jobs, the hole cutter came out of the chuck as it broke through( plastic pipe ) and dropped a metre down and round a bend which was inaccessible under a concrete garage floor. I hell of a lot of verbal abuse followed and we lost 2 hours fishing it out with a very strong magnet as it was heavy. The alternative was unthinkable and I never let him near a stack again. :roll:

 

[SammyQ]

Thanks Musicman, I was unaware of different grades of cast iron.

Marineboy, another casual (read: slow and dopey) thought: if Musicman is right, whole different kettle of fish compared to the cast I'm used to, but...in model engineering, it is not unusual to encounter a harder 'crust' on castings. This has to be aggressively machined away to reach the softer 'cast proper' underneath.
So...if you managed a centre hole successfully, what say you to drilling a circle of shallow holes with that same drill, getting through the 'skin', then retrying with your hole saw?

Good luck. Sam.

 

[Marineboy]

Thanks for all those replies fellas, I’ve had a long hard think and I’m throwing in the towel. I’m still not sure I can actually drill through the sodding thing and even if I do the nightmare scenarios described by Lons are truly terrifying. I’m going to get some longer pipe and connect via a tee to the shower waste - it means routing the waste round the soil pipe with some elbows which is not very pretty but it’s at the back of the house and we can’t really see it. Importantly, resident chief of design has no objection to this workaround.

 

[Lons]

I didn't mean to put you off Marineboy just trying tell you to make provisions to prevent problems. If if was my house I'd be drilling the stack.

 

[sunnybob]

If its any easier, theres no need for 4" pipe once youve gone higher than the toilet pan. Its simple to fit a reducer and run any sink waste in smaller diameter, 3 or even 2" all the way up to the roof vent.