Drilling a cast iron soil pipe

[denso13]

Fine on a downpipe which will also have water going through it I'd say. Just fit a cheap neutraliser if there are any concerns.

 

[dilalio]

I’ve done this dry; what exactly would you use for lubrication?

Drilling cast iron is self-lubricating.

 

[endecotp]

So.....

Buoyed by my success with the scrap bit of pipe (post #13), this afternoon I have attempted to drill into the real pipe.

The material seems to be massively harder. After maybe 30 minutes of drilling (with breaks), it has barely got below the tip of the drill. And the drill seems to have worn down significantly in the process. It hasn't got to the point where the hole saw is in contact with the metal.

I've actually changed the pilot drill for one from another hole saw, previously used only on wood I think so still quite sharp, with no improvement.

I think these pilot drills are just regular HSS. So I could get a 1/4" drill better suited to cast iron and use that to finish the hole. But then I still have the actual hole-sawing to do, and I imagine that the saw I have will be similarly useless.

Please share your advice. Especially if you've ever actually done this!

Thanks.

 

[trojanhawrs]

30 minutes rofl. Cast drills easy with a sharp drill and you should be through it in seconds if it's cutting. You'll have work hardened that spot now and it will likely be very difficult to drill. Try a brand new drill roughly the size of the pilot in another spot - slow speed setting and good pressure. Burst it a couple seconds at a time, make sure you can see swarf coming out - if its not discard and get a new drill immediately. Once youve proven you can get through give the hole saw a bash - if it struggles get a tungsten carbide one, they're not that dear

 

[Stuart981]

A consideration - an external condensate drain needs to be of a large enough diameter to avoid freezing in winter and when connecting such a drain to an external stink pipe be careful not create a choke point.

 

[endecotp]

30 minutes rofl. Cast drills easy with a sharp drill and you should be through it in seconds if it's cutting. You'll have work hardened that spot now and it will likely be very difficult to drill. Try a brand new drill roughly the size of the pilot in another spot - slow speed setting and good pressure. Burst it a couple seconds at a time, make sure you can see swarf coming out - if its not discard and get a new drill immediately. Once youve proven you can get through give the hole saw a bash - if it struggles get a tungsten carbide one, they're not that dear

Thanks for that! “Work hardening” sounds like a plausible and interesting possibility.

Regarding drills - some include cast iron in their “suitable for” and some don’t. I now wonder if I should take any notice of that. Tomorrow, I could get a pack of 5 “suitable for metal” Erbauer drills and/or one Bosch “suitable for steel and cast iron” drill.

 

[dilalio]

Cobalt pilot

 

[endecotp]

Cobalt pilot

Thanks.

At one point, I got the impression that cobalt drills might be less suitable for cast iron. Now why was that….

Ah yes:

Bi-Metal Hole Saws for Wood, Metal & Plastic | UK Drills

Bi metal hole saws for clean cuts in wood, plastics and metal using the correct arbor and speed. Fast UK dispatch from a specialist supplier.

ukdrills.com

Note that their “bi-metal” hole saw says “suitable for: … cast iron”. Now tap on the “cobalt” tab and it says “For wood, plastics, steel and stainless steel”.

But then look at drills, rather than hole saws:

Cobalt Drill Bits for Stainless Steel & Hard Metals | UK Drills

Shop M35 cobalt drill bits for stainless steel, harder metals and heat-resistant drilling. 5% cobalt alloy drill bits with fast UK dispatch.

ukdrills.com

and it’s the “cobalt 5%” drills that say “cast iron”.

 

[Razor900]

And you can't discharge condensate into a cast iron stack either!

Are you sure about that???

 

[endecotp]

Latest update:

Try a brand new drill roughly the size of the pilot in another spot - slow speed setting and good pressure. Burst it a couple seconds at a time, make sure you can see swarf coming out - if its not discard and get a new drill immediately.

Success, with a new Bosch HSS drill I was through in about a minute, using bursts as described. But:

Once youve proven you can get through give the hole saw a bash

Brand new hole saw, same one as before. It did the first couple of mm OK but then stopped making any progress.

I do wonder if it gave up when I first squirted it with water - might that cooling contribute to hardening? I wasn’t using any water when I did the experiments outside.

- if it struggles get a tungsten carbide one, they're not that dear

I guess that’s the next step then!

 

[dilalio]

Are you sure about that???

Well, I was!