Hi,

I noticed on Toolstation's web site that they sell a small guide bit
for use with TCT core drills and a long guide bit for use with diamond
core drills. Why is there a difference in length?

I bought a TCT core from them (I couldn't afford a diamond core nor
the drill to spin it LOL!) but I would like to use a longer guide bit
so that it goes through the brick and marks the centre, allowing me to
drill from both sides. Is there any reason I cannot use the longer
guide bit?

TIA

Fred wrote:
Hi,

I noticed on Toolstation's web site that they sell a small guide bit
for use with TCT core drills and a long guide bit for use with diamond
core drills. Why is there a difference in length?


I would say the answer is because the length of the guide drill bit is
related to the length of the core and the TCT cores tend to be shallow
(for cutting holes in tiles and cutting shallow holes in brickwork for
electrical accessories, etc), whereas the diamond core drill bits tend
to be long (for cutting holes all the way through masonry).


I bought a TCT core from them (I couldn't afford a diamond core nor
the drill to spin it LOL!) but I would like to use a longer guide bit
so that it goes through the brick and marks the centre, allowing me to
drill from both sides. Is there any reason I cannot use the longer
guide bit?

TIA

There's no need to buy a special long guide bit, just use an ordinary
SDS drill bit to drill the entire guide hole before you even get the
Core drill out of it's box. Just make sure your pilot hole is the same
diameter as the guide drill that comes with the core drill.

On Wed, 02 Jun 2010 15:56:19 +0100, Dave Osborne
wrote:

I would say the answer is because the length of the guide drill bit is
related to the length of the core and the TCT cores tend to be shallow
(for cutting holes in tiles and cutting shallow holes in brickwork for
electrical accessories, etc), whereas the diamond core drill bits tend
to be long (for cutting holes all the way through masonry).

Thanks. I didn't know TCT was for tiles. I thought it was for people
like me who couldn't afford the diamond ones! BTW, what is special
about diamond drills, other than the safety clutch? Why do diamond
cores need their own special drill?

There's no need to buy a special long guide bit, just use an ordinary
SDS drill bit to drill the entire guide hole before you even get the
Core drill out of it's box. Just make sure your pilot hole is the same
diameter as the guide drill that comes with the core drill.

I thought of that after I posted. OTOH if you are lazy, having a long
guide bit, would save you having to swap bits

On 03/06/10 01:14, John Rumm wrote:
On 02/06/2010 22:42, Fred wrote:
On Wed, 02 Jun 2010 15:56:19 +0100, Dave Osborne
wrote:

I would say the answer is because the length of the guide drill bit is
related to the length of the core and the TCT cores tend to be shallow
(for cutting holes in tiles and cutting shallow holes in brickwork for
electrical accessories, etc), whereas the diamond core drill bits tend
to be long (for cutting holes all the way through masonry).

Thanks. I didn't know TCT was for tiles. I thought it was for people
like me who couldn't afford the diamond ones! BTW, what is special

TCT will do softer bricks and blocks etc, but probably won't last long
an something very hard.

Yes. I've bashed a 70mm wide one through a concrete floor on hammer. Got
2" in, then had to SDS a load of small holes round the circumfernece.
Then finished the next 2" with the core again. That took about 30
minutes. Did it nicely (for a new mains water pipe) but the TCT was a
little the worse for wear.

about diamond drills, other than the safety clutch? Why do diamond
cores need their own special drill?

Depends on the size of the core. My 720W Makita SDS is just on the limit
with a 107mm core if you take it gently and get the hole nice and
straight. Push it too hard and the clutch lets go.

You want one of these:

http://www.youtube.com/watch?v=En78Wor26WI



--
Tim Watts

Hung parliament? Rather have a hanged parliament.

On Thu, 03 Jun 2010 01:14:49 +0100, John Rumm
wrote:

TCT will do softer bricks and blocks etc, but probably won't last long
an something very hard.

Yes, I think I had read that before but for one or two holes, I think
TCT is the cheaper option for the occasional DIYer.

My 720W Makita SDS is just on the limit with a 107mm core if you take it gently

I bought a 110mm TCT core and have used it twice to drill for 4" fan
ducting. It went through breeze block inner and brick outer, though
obviously you have to stop now and again to clear the core.

I hadn't realised that a diamond core of that size could be used in a
sds drill, I thought a special drill was essential. I think Aldi do
diamond cores; are they any good? For one or two 4" holes they may be
worth a go as branded cores that size cost a fortune. I wonder if they
also sell a drill to spin them

BTW, I left the core attached to the arbor for months between uses and
really fought to take it off. What do you use as a tommy bar to fir
through the core? The only bit of metal I could find long enough to go
through the 100mm core was a bit of earth rod. It did manage to loosen
the core but the rod was bent useless in the process!

TIA

On Thu, 03 Jun 2010 01:26:42 +0100, Tim Watts wrote:

You want one of these:

http://www.youtube.com/watch?v=En78Wor26WI

Looks impressive!

BTW, what do diamond drills have at the end? Do they have a
traditional chuck that takes a hex shank? I see that the catalogues
offer an sds or hex arbour, so I am guessing the hex is for diamond
drills? Surely it can't be for "traditional" drills, as I didn't think
these had a clutch?

Google found some old posts from this very group on one of those web
sites that "borrows" content from usenet. Someone suggested blue spot
cores from Amazon as a cheap source of cores. Are they any good?

I see that "traditional" drills are still being sold. Why would anyone
want one when there is sds? Woodworking?

TIA

Oops, forgot to ask: are the arbours all standard diameters or do you
need different arbours for different makes of core? Thanks again.

Small diamond such as 20-22-28mm have a hex end usually, they can have
an enlarged end to take an arbor though. Larger diamond such as
38-152mm have an arbor end, with push-fit pilot drill (use the drift
to remove it).

Amazon do Blue Spot diamond core bits cheaply, and they resell ok too.
They can be "extremely good" or "just good" depending on the luck of
the draw, and at the price (£28 for 152mm?) are very good value.

A diamond core drill has a reduction gearbox to give the huge starting
torque - note that the "start" tends to be "instant quick" so make
sure you go very gently on uneven brick surfaces because you do not
want to shear a tab off. This is one reason to buy a core drill bit
rather than hire - breaking the tab off a 152mm Hilti bit is likely to
be very expensive and is chargeable.

You can pick used diamond core drill up on Ebay, 110V & 240V, but they
seem to look rather the worse for wear. If you have a lot to do
(bathroom shower toilet 107mm, dryer 107mm, kitchen extractor 152mm,
kitchen fan 152mm, wall mounted HVAC 70mm) it can work out ok. A note
re kitchen extractor, go for 152mm because you can sleeve down. BES do
a brown gravity flap for 125mm & 150mm which has the same 200mm
outside "form-factor-n-holes" so you can just fit a 5" tube through to
spigot & wall plate on the inside, if you later go to a bigger cooker
hood it is easy to upgrade as needed. Do sleeve the cavity properly, a
relative had a slip tube since 1996 and it never sealed properly on a
dryer - duct tape unwinds even amalgamating didn't bond fully, going
to be a long weekend or two sorting that mess out when we go cool
weather again.

Most fun of all, if you have not met diamond dust, you will soon - it
makes a mockery of IP66 due to particle size :-) 110V TX vary from pig
heavy (1.5kVA) to plain misery (3.3kVA) so you may want a 110V
extension if doing a lot of stuff.

A pity no-one has done a "hybrid" SDS drill with 2:1 gearbox or
similar. Diamond core drills are rather expensive for what they are -
unremarkable motor rating, just a reduction gearbox and heavier duty
clutch assembly, £300 for a Makita. I believe some are 2 speed and
some a re 1 speed (all those I have hired are 1 speed which is rather
inappropriate). Big core means very slow & small core means somewhat
quicker but not quick. Let the bit do the cutting and keep it straight
because they do like to wander if one brick is hard and another very
soft. True engineering takes... time to drill thro and cheap core bits
will just spark due to "too much glass and too little diamond",
screeching is the first indicator.

A final comment is "getting started" with small diameter but very long
bits (22x350mm), these lack a guide drill and can wander particularly
on textured brickwork. It can be worth having a short small diamond
bit to machine a "pocket starter", Ebay do 20mm from Hong Kong (7-8
working days) which are fine for this in a cordless drill. I used a
stub 20mm core drill one today to start off a very long 22mm bit
(sleeving through a cavity) and again to enlarge the 22mm ends to take
20mm conduit bell-bush (silicone flex to halogen does not like sharp
edges). I also used a stub 20mm core drill to create a cutout
perimeter for a 152mm bit which was "skipping around" despite pilot
drill due to one very hard & uneven brick surface, the 1-speed makita
core drill would not soft or slow start enough with such a huge
"barrel of a core drill bit".

Wonderful tools with no breakout compared to SDS (you can screw a
plank the other side and stitch drill, it needs care to avoid a bell-
mouth effect with the middle too small and outer too large). Wear
goggles & mask or you will need a JCB to clear your nasal passages out.

On Jun 4, 5:06*pm, John Rumm wrote:
I think with hindsight, buying cheap cores is ok,
but its worth spending more on the drill.

Very much so unless you are a hire firm :-)
With even a cheap diamond core drill it takes a very long time to wear
the tabs off, but just a mistake to break one. Generic are about 60%
of the speed of Marcrist & Hilti, but it can take a bit to wear in and
take the glaze off.

And the worst job is holding one overhead to cut a boiler flue exit hole
near a ceiling...!

That does not bear thinking about.

I think the best solution for mains diamond tools is plastic sheet the
floor, walls, ceiling - and yourself. Use the tool, slip out of the
bagged room, use a vacuum not to pick up the dust, but compress the
bag down to something small and bin :-)

On Fri, 04 Jun 2010 23:39:32 +0100, Tim Watts wrote:

Well, drill dust is large particulate and tends to fall IME close to the
drilling. Same with holesaw in plasterboard. Bit messy but doesn't hang
in the air.

Angle grinder and sanding output is far worse - finer particles which
tend to float in the air for ages.

I can see diamond grinding could produce an even finer dust, so I would
expect much evil.

Think I'll stick to TCT cores - bit messy, but the crap is similar to
drill dust and tends to fall fairly quickly into a pile on the floor.
Certainly doesn't fill the room.

Thanks. My (limited) experience has been with TCT cores, so that was
really the question I was asking: is the dust from a diamond core
really much worse than from a TCT one? I thought the dust would be the
same because they are both cores rotating at the same speed through
the same brick, but it seems I am wrong to think that. Thanks for
putting the record straight. Too late now, I've ordered a 107mm
diamond core to try. Perhaps I should have saved my money and stuck
with the 110mm TCT one I already have!

I have angle grinded and wall chased with diamond discs before, so I
certainly know about the dust! One day I intend to buy a Dyson DC04 or
07 from ebay to use as a dust extractor. I'm still not sure whether
it's worth paying the extra for the 07 over the 04?

Since diamond discs in grinders do wear down over time, is the same
true of diamond cores? OTOH I suppose TCT cores wear too, and faster,
so I guess there's no getting away from having to replace them.

Thanks.

On Sat, 05 Jun 2010 12:27:31 +0100, John Rumm
wrote:

You can (if you don't mind creating all the dust inside!) - generally if
you take it easy on exit you usually get a clean hole.

[...]
Pilot drill through and drilling from both sides will guarantee clean
holes, although at the slight risk of a minor mis-alignment or bend in
the hole.

I did the drilling all from the inside because drilling from the
outside would have involved working off a ladder and I wasn't keen on
being up a ladder if the clutch failed and the core jammed. It seems
that either way has its disadvantages: drilling from both sides might
have slight misalignment and drilling outside in may damage the
bricks.

On Sat, 05 Jun 2010 12:21:23 +0100, John Rumm
wrote:

One thing to watch is that you don't
overheat a DIY class drill - it needs lots of airflow through it, so
keeping the revs up is important.

How many revs do you need? I thought you had to go slow, especially
with large cores. Would the drill set to its lowest speed generate
enough airflow, or would you suggest removing the core from the wall
and spinning it faster in the air to cool it every now and again?
Thanks.

On Sat, 05 Jun 2010 12:52:36 +0100, John Rumm
wrote:

A search for "diamond core" brought them all up for me first time.
Remeber not to just look at the top five matches - but expand the Core
Drill Bits section out below.

I was about to buy the Bluespot cores from Amazon when you gave me
that link. Thank you very much. I think I ordered the last 107mm core.
They also had a 152mm core for 6" ducting. I bet that is interesting
to use!

I see what you meant about the guide bits: the long guide bit in the
diamond core and the short bit in the TCT core both protrude by about
the same amount once inserted. They supplied a bluespot bit BTW.

I'm not sure about all this talk about using drifts to remove the
guide bits as my experience in both the TCT and diamond core is that
the bit falls out the arbor too easily: I hear a metallic ringing and
remove the core from the wall to find the guide is stuck in the wall,
detached from the arbor.

I couldn't get the diamond core to get started in my [brick] wall. I
think the guide bit issue didn't help, so I reused my TCT core to cut
an inch or two into the wall and then carried on with the diamond core
from there.

[about tct core and arbor sticking]
Stick the core in a wood working vice (wrapped in a cloth) and use the
flats on the arbour then...

I'm not sure my vice would open wide enough to take a 107mm core. I
did manage to free it using a 22mm spanner on the arbor and an earth
spike through the holes in core to hold it in place. The spike got
bent in the process though.

On Sat, 05 Jun 2010 12:31:05 +0100, John Rumm
wrote:

Most of the dust from core drilling is better contained than with a AG.
You get some fine floating stuff toward the front of the hole, but once
in the wall this is controlled reasonably well.

I did find that the dust was very soft as described earlier in the
thread but you are quite right, it was nothing like an angle grinder.
I could always see the whole of the room I was in Of course, I've
only drilled the one hole but I would say to anyone in my position not
to worry about the dust, it really wasn't that bad but: in my limited
experience, YMMV, etc.

Thanks for all your replies John, they've been very helpful.

The 152mm bits are heavy and quite difficult to get started, patience
required.

Dust is very much contained to the area being drilled - some "smoke"
wanders, but nothing like with an angle grinder.
#1 do not obscure the drill's fan outlet in such a way as to direct a
blast of air into the dust stream, generally the air stream is too hot
but if it does happen you will soon know when you look around after
drilling :-)
#2 the 152mm bits have side slots obviously some inches from the
centre which throws dust out radially, screwing a height cut-down
bucket with a hole in the bottom to the wall with a vacuum duct taped
to the bottom might prove useful.

Wonderful tools, the small 22x350mm & 28x350mm are great for round
conduit through cavity walls.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Fred
saying something like:

I'm not sure about all this talk about using drifts to remove the
guide bits as my experience in both the TCT and diamond core is that
the bit falls out the arbor too easily: I hear a metallic ringing and
remove the core from the wall to find the guide is stuck in the wall,
detached from the arbor.

Or fallen down the cavity.

On Wed, 09 Jun 2010 01:21:57 +0100, John Rumm
wrote:

For the typical core sizes (i.e. up to 150mm) they usually recommend 900
- 1300 rpm. That's usually max speed on a SDS,

I had my 107mm core on a Screwfix Titan sds drill. It has a speed
setting from 1 to 6, so I had it set on number one. Perhaps this was
too slow for adequate cooling? It seems that some Titan drills mention
a clutch in their description and others do not. My model was one that
did advertise a clutch and it appears to work! Once or twice the core
stopped turning and the drill "buzzed" but it didn't kick and my
wrists are intact.

On Wed, 09 Jun 2010 01:30:19 +0100, John Rumm
wrote:

Not done a 6" personally - but I expect 'kin heavy would be the word. As
JS said - I can well imaging getting one started is a pig as well.

Is that the largest core in normal use? I can't think of a reason to
go wider domestically but does ducting in commercial situations
require bigger holes?

Getting the 107 core started was a pig but perhaps that was because of
my inexperience? As I said, I had to start the cut with the tct and
once there was a slight circle scribed into the brick to guide the
diamond core it worked well. Without the slight groove to guide the
diamond core, it just bounced all over the place. I hope with practice
my technique will improve. Using tct to start a diamond core rather
defeats the point of buying diamond over tct!

I tend to put a bit of wood on the end of the bit and clomp it home with
a hammer. That usually sets it in there for long enough.

I tapped it against the wall to get it stuck but it soon came loose
again

The trick is to get it spinning and then offer it to the wall gently...

Hopefully I will improve with experience then. I resorted to the TCT
because I was cutting from outside and didn't want to risk the diamond
core dancing all over the brick face and ruining my wall.

A mechanics vice would have to be quite large, but wood working ones
usually open that wide. You could just stick a bit of plate in a vice
and engage the lugs over it - however that would risk breaking a lug!

I think I bought the 4" vice rather than the 6" to save money. IIRC I
paid for the Irwin which was twice the price. Perhaps I should have
bought a bigger version in a cheaper brand for half the price?

Thanks.

On Tue, 8 Jun 2010 13:34:31 -0700 (PDT), "js.b1"
wrote:

Wonderful tools, the small 22x350mm & 28x350mm are great for round
conduit through cavity walls.

What a useful thread. I always thought I couldn't use diamond because
I didn't have a special drill and now I know better. Why do they
bother painting diamond cores since the paint is rubbed off as soon as
they are used?

On the subject of using drill bits for smaller "copper pipe" sizes,
can you get short 22+ mm bits? All the ones I have seen are 600mm.
Great if you have to go through a cavity wall but impossible if you
are in a confined space. At the other extreme, I wanted a long 8mm bit
but could only find them in short lengths. B&Q did have a wide
selection of lengths made by Bosch but at £60 each, I walked by.

Thanks.

One last question: I know about the rules regarding notching joists,
and that you are only supposed to chase 1/3rd the depth of a wall but
are there any rules about punching holes all the way through a wall,
e.g. by using a core? I can imagine that kitchens may require a number
of holes to pass ducting from a cooker hood and other extractor fans,
plus a boiler flue. Is there a limit how many of these you can have in
one wall or how far apart they should be? I am guessing smaller holes,
e.g. 40mm waste, are less significant?

Thanks again.

On Thu, 10 Jun 2010 20:43:25 +0100, Fred
wibbled:

One last question: I know about the rules regarding notching joists, and
that you are only supposed to chase 1/3rd the depth of a wall but are
there any rules about punching holes all the way through a wall, e.g. by
using a core? I can imagine that kitchens may require a number of holes
to pass ducting from a cooker hood and other extractor fans, plus a
boiler flue. Is there a limit how many of these you can have in one wall
or how far apart they should be? I am guessing smaller holes, e.g. 40mm
waste, are less significant?

Thanks again.

Re large holes - not usually a problem unless you stuck several next to
each other. The circular hole transmits the stresses quite nicely anyway.

40mm waste - absolutely a non problem unless you are planning to put 1/2
dozen in a tightly spaced row Even then, if they were at 50% density,
the wall would probably survive.



--
Tim Watts

Managers, politicians and environmentalists: Nature's carbon buffer.

On Thu, 10 Jun 2010 20:19:10 +0000, Tim Watts wibbled:

On Thu, 10 Jun 2010 20:43:25 +0100, Fred
wibbled:

One last question: I know about the rules regarding notching joists,
and that you are only supposed to chase 1/3rd the depth of a wall but
are there any rules about punching holes all the way through a wall,
e.g. by using a core? I can imagine that kitchens may require a number
of holes to pass ducting from a cooker hood and other extractor fans,
plus a boiler flue. Is there a limit how many of these you can have in
one wall or how far apart they should be? I am guessing smaller holes,
e.g. 40mm waste, are less significant?

Thanks again.

Re large holes - not usually a problem unless you stuck several next to
each other. The circular hole transmits the stresses quite nicely
anyway.

Or stuck it a high stress part of the wall like right under a lintel
bearing.





--
Tim Watts

Managers, politicians and environmentalists: Nature's carbon buffer.

On Thu, 10 Jun 2010 21:55:14 +0100, John Rumm
wrote:

400 is easy enoough to find.

I was hoping for something slightly smaller still (for use in the
cramped conditions under the stairs)

On Thu, 10 Jun 2010 21:53:55 +0100, John Rumm
wrote:

Depends on how it slows - gearbox slowing being better than electronic
in this case. I would try it at the top speed. (helps if you have an
accelerating trigger to get it up to speed a little less violently)

I don't know how the Titan works but it is a (relatively) cheap 6kg
lump that Screwfix (I presume) import, so I doubt it uses an expensive
or complicated method. It certainly doesn't have a fancy trigger; it's
either on or off. I had it set to slow because I thought big holes
required slow speeds.

Daft question: why don't sds drills have a reverse like "ordinary"
drills do? TIA

On Thu, 10 Jun 2010 20:22:08 +0000 (UTC), Tim Watts
wrote:

Re large holes - not usually a problem unless you stuck several next to
each other. The circular hole transmits the stresses quite nicely
anyway.

Or stuck it a high stress part of the wall like right under a lintel
bearing.

Thanks. Is there a rule of thumb: keep x cm away from lintels or space
holes three diameters apart?

On Sat, 12 Jun 2010 03:17:15 +0100, John Rumm
wrote:

Unless its a mechanical feeling slider, or knob of some sort (and then
only offereing two or at most three speeds) you can be fairly sure its
electronic. That means at slow speed the motor is turning slowly and is
less able to get rid of heat (fan performance increases non linearly
with speed). So I would tend to go full speed or close to it (which will
be 900 - 1100 rpm probably)

Thanks. Is 1100rpm ok for big cores such as 107mm? I always thought
big holes needed a slow speed? In a way it's a design flaw that the
fan doesn't go fast enough to cool at low speeds.

On Sat, 12 Jun 2010 03:21:55 +0100, John Rumm
wrote:


The only thing I can suggest is get a 12mm 160 or 200mm SDS bit to make
the initial hole, and then a conventional masonry 22mm short bit to open
it up without hammer action in a normal chuck.

It is strange that there aren't any 200mm long, 22mm wide sds bits. It
is just breeze block to go through though, so an "old fashioned"
masonry bit would probably be more than enough to do the job. Thanks
very much for the idea.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Fred
saying something like:

It is strange that there aren't any 200mm long, 22mm wide sds bits.

I've had a 25mm, 200mm long SDS bit for years, so look around.

In article , Grimly
Curmudgeon scribeth thus
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Fred
saying something like:

It is strange that there aren't any 200mm long, 22mm wide sds bits.

I've had a 25mm, 200mm long SDS bit for years, so look around.

Seems that you need a decent hardware outlet. I've seen some a matter of
feet long in Mackays in Cambridge!...

--
Tony Sayer

Fred wrote:
On Sat, 12 Jun 2010 03:21:55 +0100, John Rumm
wrote:

The only thing I can suggest is get a 12mm 160 or 200mm SDS bit to make
the initial hole, and then a conventional masonry 22mm short bit to open
it up without hammer action in a normal chuck.

It is strange that there aren't any 200mm long, 22mm wide sds bits. It
is just breeze block to go through though, so an "old fashioned"
masonry bit would probably be more than enough to do the job. Thanks
very much for the idea.

http://www.lawson-his.co.uk/scripts/...Above%2014m m

22mm x 250 if that's any use.

On Sun, 13 Jun 2010 17:04:03 +0100, Dave Osborne
wrote:

http://www.lawson-his.co.uk/scripts/...Above%2014m m

22mm x 250 if that's any use.

Yes, thanks and a sensible price too. BTW who are heller, is it a good
brand. I think I have seen the name before in the tool station
catalogue (but not those bits at those sizes).

On Sun, 13 Jun 2010 12:57:04 +0100, John Rumm
wrote:

Yup, I would think so. 11k rpm is slow in drill terms (i.e. similar to a
conventional drill in low gear)

[...]
To be fair its not often you use a hand held drill with a high
continuous load at low speed.

Thanks. Until this thread I hadn't appreciated that an sds drill was
much slower than a conventional drill, thanks for pointing that out.
So to sum up: you do need a low speed for a large core but the top
speed on an sds still counts as slow, so it's safe to do so. Thanks
again.

On Fri, 18 Jun 2010 21:37:30 +0100, John Rumm
wrote:
[about sds drills]
Oops typo - make that 1k rp, is slow (11k would be 'kin fast!)
[...]
Yup, a conventional drill will often be 2000 - 3000 rpm at full speed.

Ah, so that might answer my earlier question about why people buy
conventional drills: they are faster. Whilst looking through the cpc
catalogue for something else, I did spot a blue bosch conventional
drill that mentioned having a two speed gearbox and clutch for cores
but on closer inspection was only for cores up to 68mm but rated 1100W
IIRC. What a shame it wouldn't do 107mm cores, I might have treated
myself otherwise

Thanks for all your help on this subject, I have learnt a lot.

On Tue, 22 Jun 2010 22:31:03 +0100, John Rumm
wrote:

Well my 720W Makita in theory only does cores to that size or possibly a
little smaller. However it has drilled many 107mm cores in its time. So
I expect the Bosch would do as well or better as long as the clutch is
not set to disengage at too lower a torque.

Perhaps with it being a blue bosch, it is rated to 68mm cores in
regular, daily, use by a tradesman. Perhaps for once a year DIY
drilling the drill would cope with a big core now and again?

If you are drilling "conventional" brick an old 480W non-SDS drill
will do 107mm, gets hot, but just about does it. Will not even get a
152mm going re torque of course (tried, it died, hireshop visited).

So a 850W SDS run in non-SDS mode with lower RPM and potentially
higher torque should do 107mm without much difficulty in
"conventional" brick.

Conversely if you have hard engineering brick, which will take hours,
forget it - and you need a better bit than the generics if it does
more sparking than drilling.