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

On 02/05/2011 16:49, Stephen wrote:
Hello,

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

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.
--
Cheers,
Roger
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On May 2, 4:49*pm, Stephen wrote:
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?

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.


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.

easy enough for soft masonry


OTOH isn't that how these sds
socket sinkers work: they drill a circle and then punch it into a
square?

Thanks,
Stephen

Not the ones I've seen.


NT

On Mon, 02 May 2011 16:49:44 +0100, Stephen wrote:

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?

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






--
John Stumbles -- http://yaph.co.uk

If we'd known how much fun grandchildren are
we'd have had them first

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 £8-10 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 £130-158 these
days. So for a few backboxes or a great many an £8-10 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.