Expanding hole in masonry

[Mike Barnes]

I have a hole about 15mm diameter going through about 1m of stone wall. It's for audio/network wiring and I now need to put through more cables than will fit.

I'd like to expand the hole and ideally line it with some 32mm waste pipe. So I need a roughly 35mm hole with a strong preference for it being exactly along the line of the existing hole.

I've heard that core drills are great for this sort of thing but I've never used one.

I have a cheap SDS drill. What more do I need? Can the core drill be guided along the existing hole? Do I buy cheap stuff or hire good stuff? (I'm unlikely to be doing much like this in future.)

[The Natural Philosopher]

shotgun and deer shot has been known..

[polygonum]

Is that solid masonry - does it have a random rubble core? Might affect the answer significantly.

[Mike Barnes]

polygonum :

Ah. OK. It's not a simple one metre wall, it's two houses built next to each other with 50 cm walls. I remember some jamming problems when drilling the original hole so rubble infill is a distinct possibility.

[Moonraker]

I cannot see how a core drill will work, though someone may have a good idea. Core drills require a solid material to drill into as they have a smallish drill which leads the way thus keeping the core drill steady, at least that is how the ones I have work.

[fred]

In article , Moonraker writes

I think there is some potential for cleverness here, take a dowel of the same size as the existing hole, drill a hole in the centre of it the same size as the centre hole of the guide drill, fit dowel over centre drill and use this as the guide for the core drill. Clear core regularly and (well tightened) core drill extension shafts will be required.

The dowel doesn't need to be long enough to pass all the way through the existing hole but it could help in pushing the core drill back out in case of difficulty.

[ARWadsworth]

Cleverness my arse. This is the job for a 32mm masonry bit.

[John Rumm]

You only need the pilot drill to get them started - once you are in enough to centre the core you can take the pilot out. See the recent thread on starting cores without a pilot bit.

However the difficulty will be following the existing hole exactly if not using the pilot. (and often the pilot bit will shake loose from the arbour if its not actually drilling and just rattling about in an existing hole - meaning you can't always use it). You might manage by withdrawing the core often and checking your heading, and drilling in from both sides.

Personally I thin using a f'off big SDS bit would be easier and quicker.

[Andrew Gabriel]

That's what I did when I needed a hole for a 28mm gas pipe and sleeve. I hired an SDS-max bit (can't recall if it was 35 or 40mm), and a thinner one, and drilled through many times starting with a thin bit, opening the hole out wider each time.

I used my SDS-plus drill with an SDS-max adaptor, but it was probably a mistake not to hire an SDS-max drill too. If you use an adaptor, you will probably need one per bit, as you likely won't be able to get the bits out of the adaptor (hire shop has a tool for separating them afterwards).

Note all the usual warnings about SDS drills, e.g. they don't stop just because the bit jams - the drill will spin round and do you a nasty injury unless you have a tight grip on it and it has a safety clutch.

[Mike Barnes]

I've just found this which looks as if it might do the job:

(I'm amused by the price clarification "£0.72 / oz". )

I could drill from each end. Hopefully the existing hole will ensure that the two ends meet. They might not line up well enough to get the liner all the way through, but if they were close, two 500mm pipes would be good enough.

[Newshound]

[Dave Liquorice]

A core drill won't like really loose bits, indeed an SDS drill might not like loose bits either if a lump drops down into the flutes and jams. BTDTGTTS...

I can see clearing the core and then threading the the core drill back into a loose bit 50cm away with no access being "fun".

Think I'd go for the BFO SDS and take it steady, assuming you can get a 1m long 35mm SDS bit or even 60cm one come to that. At least you have a 15mm+ pilot hole. B-) I'd also not remove the drill until I was ready to push the liner through and use that to push the drill out. Less (note less not no) chance of a bit of rubble fill dropping down if the drill is there.

[Mike Barnes]

Dave Liquorice :

I'll do exactly that.

Thanks to you and to everyone who responded. I don't know how I'd manage without this group.

[ARWadsworth]

You still have a good change of hammering a waste pipe though a bit of rubble drop.

Of course saying such a thing means a very large piece of rubble will fall into the hole:-)

[Lee]

Even if it means hiring it. If the bit jams you *will* be appreciative of the safety clutch.

Lee

[John Rumm]

Indeed. I have never yet had a standard SDS bit jam though (and never yet *not* had a core bit snag and slip the clutch at least once!)

[Andrew Gabriel]

I've had an 8mm bit jam, but that just twisted off. Looked like a sausage of plasticene after someone twisted it in half. More annoying was that one of the mounting holes for something heavy was unusable due to 3/4 of the bit being jammed in it.

Had core drills jam too, but mine has a clutch, although that's only any use if you're holding it firmly.

A friend had two accidents. First was a core drill which jammed, and the drill spun round, but only a little way before it hit a wall, and then it put a bend in the [rented] core arbor, making it useless.

Second time I don't know what he was drilling, but the drill spun round and whacked him on the chin, which required stiching in A&E.

I believe twisted wrist injuries are also a possibility. ISTR someone here having done that in the past.

[John Rumm]

Yup, I can see that being irritating on so many levels!

The clutch on my SDS is relatively tame with a 107mm core. As long as you are holding both handles it gives without too much twist.

In tricky walls it actually lets go too easily. I have got a Sparky core drill, but in reality that let's go almost as easily, so it not actually that much more useful even though in theory it has a few hundred watt more power. I think one day I will ebay that and get a proper one!

I remember walking through a a multi story car park once and there were a couple of blokes installing some new fire alarm wiring. They were core drilling close to the ground - almost sat astride the side handle of the drill. I thought to myself at the time, if that snags you are going to be using your nuts as an end stop!