core drills

[Stephen]

Hello,

I've used 4" core drills to make holes for fan ducting but I see you can get much smaller diameter cores: 22mm and 28mm, which are 300mm long. I think most guide bits are shorter than this. So when using these core bits, do you need to buy a rarer, longer, guide, or don't you need a guide/pilot bit when drilling narrower holes?

I notice that on ebay some chap is selling a 107x40 mm core bit for sinking sockets. Has anyone used one for this before? It's an interesting idea but since you don't go all the way through the wall, the core would need to be chiseled out. OTOH isn't that how these sds socket sinkers work: they drill a circle and then punch it into a square?

Thanks, Stephen

[Roger Mills]

As far as I am aware, drills used for sinking sockets are usually more like Forstner bits - which remove a circle of material, not just cut a ring. With most of the material out of the way, it's fairly easy for the box chisel to finish the job.

I wouldn't have thought that a core drill would be suitable.

[Tabby]

Perhaps the intended method is to drill a hole with a short core drill, then do the rest without a guide bit. I've done this but they do tend to wander in soft masonry.

easy enough for soft masonry

Not the ones I've seen.

NT

[Stephen]

Hello,

I've used 4" core drills to make holes for fan ducting but I see you can get much smaller diameter cores: 22mm and 28mm, which are 300mm long. I think most guide bits are shorter than this. So when using these core bits, do you need to buy a rarer, longer, guide, or don't you need a guide/pilot bit when drilling narrower holes?

I notice that on ebay some chap is selling a 107x40 mm core bit for sinking sockets. Has anyone used one for this before? It's an interesting idea but since you don't go all the way through the wall, the core would need to be chiseled out. OTOH isn't that how these sds socket sinkers work: they drill a circle and then punch it into a square?

Thanks, Stephen

I forgot to say that the reason I am asking is that when I try to drill a 22mm hole (to pass a 15mm pipe through, sleeved by a 20mm overflow pipe) the brick breaks in half. They are the bricks with three holes down the middle, so I don't know whether the sds is too violent for them. What should I do: turn off the hammer or use a core?

Thanks, Stephen.

[Tim Watts]

You can get a small core started without a pilot - can jump a bit and is easier to start on plaster vs brick. Once it is started it's fine.

I tried one that ground out the full circle - great on celcon blocks (at al) but very very messy and slow on brick. My solution is to drill loads of 10mm holes with a masonry bit to the depth required then take a chisle to it.

A core will give you a nice hole (subject to breakout risk on the back side).

[R D S]

Hello,

I am thinking about buying a set of core drills with sizes up to 4 inch (preferably 6), but concerned about either spending more than I need to, or spending little and buying a load of crap.

Looking across the net it would appear that I can get a set from £60 to £hundreds. I'd be happy spending as little as possible obviously.

Are there any particular things to look out for, brands to avoid or any brands people would recommend?

Ta, Rick

[Roger Mills]

They really need to be diamond tipped - which is more expensive than TCT.

[John Rumm]

Another trick to start a core without a pilot, is to cut a matching hole in a bit of ply, and temp fix that to the wall - use it to guide the core. Once started you can do away with the guide.

[YAPH]

No, you can start them guided by hand, with appropriate gloves - I use better quality soft-leather-faced gardening-type gloves.

[TheOldFellow]

Depends on the duty you are going to put them to. I bought a very cheap (Faithfull, I think) diamond 50mm core drill from Toolstation together with arbours and long extension to put in 40mm wastes, it is still going strong after maybe ten runs through cavity walls.

You need an no-hammer SDS+ to drive them, and it takes a while.

R.

[js.b1]

A large core drill bit with discrete sintered diamond tabs will tend to skate around without a pilot drill. Essentially you would have to turn the bit by hand to get a channel dug - adding time which somewhat defeats the objective. That core drill bit diameter is sufficiently large to use a conventional core drill arbor - which use a tapered drill bit (removed by knocking in a drift), there may be a stub drill bit available or you could cut one down with an angle grinder since it is only being used for core drill centring when starting.

I use core drill bits, but in a very different approach. If you search on Ebay UK you will find 20mm sintered diamond core bits available from Hong Kong for about =A38-10 delivered. Occasionally you get a duff one (diamond ring smaller than the body), but they refund quite happily with a photo. The sintered diamond edge is almost continuous so do not have to fight "tabs" chattering around on brickwork, the sintered diamonds are deep enough to last about 400 holes in typical non-sandy brick. Fit the drill in a cordless or mains drill, and simply stitch drill a backbox hole and break out the cores. Very quick, very neat in that you do not disturb existing decoration (useful for deepening boxes to

35mm or replacing wooden light boxes).

They are also useful in other applications - shaping brickwork by angle drilling etc. An SDS is more useful in many applications, but can disturb decor (crap plaster on semi-blown browning, get used to pipetting PVA down behind if afflicted to bond it back to the wall very effectively). However a really good powerful SDS (3.2J) is quite expensive, the weaker SDS (1.5J) are pretty junk if you have hard brick, the mid-range SDS (2.7J) are ok but topping =A3130-158 these days. So for a few backboxes or a great many an =A38-10 drill bit is quite useful. I have also used it for channelling on brickwork, really needs a cup of water to keep cooling it down (they cut dry BTW) and a mains drill or you will get bored. Overlap the holes and keep a wide bladed screwdriver ready to snap the cores out.

SDS is a very useful tool, so not a substitute - just a cheap less aggressive solution.