Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height, and
about as far left as I can possibly have the new hole if I'm having a
chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.

Ben

"Ben Blaukopf" wrote in message
...
Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height, and
about as far left as I can possibly have the new hole if I'm having a
chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.


You probably want to fill the hole so the pilot stays inline.

Failing that you may getaway with mounting a thickish board over the hole
and drilling through it so it stays in line.

dennis@home wrote:
"Ben Blaukopf" wrote in message
...
Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height, and
about as far left as I can possibly have the new hole if I'm having a
chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.


You probably want to fill the hole so the pilot stays inline.

That was my initial thought, but it's a cavity wall, so a bit of a pain
to fill.


Failing that you may getaway with mounting a thickish board over the hole
and drilling through it so it stays in line.

Makes sense...

Ben

Ben Blaukopf wrote:
Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height,
and about as far left as I can possibly have the new hole if I'm
having a chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same
time, so that the left edge of the hole didn't move any further left.


This is impossible with a core drill.

Never used a core drill, no idea if this is going to work or not. The

I have and it won't.

alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.


Or make the hole larger with a hammer and chisel, like in the days before
core drills - it's only the exterior brickwork that matters anyway as inside
can be plastered up easily enough, and outside, the fitting on the extractor
is often 2 or 3 inches larger than the diameter of the liner, and if it's
not, you can patch it up with mortar and/or pieces of brick you
remove....this is assuming the house is less than 10 years old, if it's any
older, the chances are that it's been patched up in places anyway by now.

Almost impossible with a core drill ,it needs a pilot hole to guide the
core,use a sds drill with a 5mm to stitch drill the new side of the hole and
chisel out the remains,it was the common approach before diamond core drills

Ben Blaukopf wrote:
Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height, and
about as far left as I can possibly have the new hole if I'm having a
chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.

Ben
Yes, easily done with a core drill & pilot. I usually do it by hot melt glueing
a sheet of plywood over the existing hole, then use the core drill on that. The
thickness of the ply is more than adequate to stabilise the core drill once the
core is out of the ply.

Use a thickness of ply to suit the job, access & your strength. In a door, you
can get away with 3 ply, in a ceiling you need much thicker.

--
Karen

If you can't be a good example, then you'll just have to be a horrible warning.'
Catherine Aird

On Sun, 15 Apr 2007 22:43:53 +0100, Ben Blaukopf
wrote:

|!Lots of questions tonight...
|!
|!The old cooker hood in my kitchen has a 4" hole at the right height, and
|! about as far left as I can possibly have the new hole if I'm having a
|!chimney hood.
|!
|!Modern cooker hoods appears to want 5", or more usually, 6" holes.

Get a 5 inch to 4 inch adaptor, that is what our local Builders merchant
offered me.
--
Dave Fawthrop sf hyphenologist.co.uk 165 *Free* SF ebooks.
165 Sci Fi books on CDROM, from Project Gutenberg
http://www.gutenberg.org/wiki/Main_Page Completely Free to any
address in the UK. Contact me on the *above* email address.

On Mon, 16 Apr 2007 13:18:48 +1000, Duracell Bunny
mused:

Ben Blaukopf wrote:
Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height, and
about as far left as I can possibly have the new hole if I'm having a
chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.

Ben
Yes, easily done with a core drill & pilot. I usually do it by hot melt glueing
a sheet of plywood over the existing hole, then use the core drill on that. The
thickness of the ply is more than adequate to stabilise the core drill once the
core is out of the ply.

Use a thickness of ply to suit the job, access & your strength. In a door, you
can get away with 3 ply, in a ceiling you need much thicker.

Are you on about a normal holesaw for plasterboard and the like and
not a dry diamond core? I have never seen a dry diamond core drill
used in a door or ceiling before.
--
Regards,
Stuart.

On Mon, 16 Apr 2007 06:57:14 +0100, Dave Fawthrop
mused:

On Sun, 15 Apr 2007 22:43:53 +0100, Ben Blaukopf
wrote:

|!Lots of questions tonight...
|!
|!The old cooker hood in my kitchen has a 4" hole at the right height, and
|! about as far left as I can possibly have the new hole if I'm having a
|!chimney hood.
|!
|!Modern cooker hoods appears to want 5", or more usually, 6" holes.

Get a 5 inch to 4 inch adaptor, that is what our local Builders merchant
offered me.

If the extractor wants a 5" hole then reducing it to 4" will impair
the performance. I did the same thing on one job and I had complaints
the cooker hood wasn't too great. Whether that was because it was just
crap (doubtful as it was some huge AEG thing that was as big as the
range cooker) or because of the vent diameter I don't know.
--
Regards,
Stuart.

Lurch wrote:
On Mon, 16 Apr 2007 06:57:14 +0100, Dave Fawthrop
mused:

On Sun, 15 Apr 2007 22:43:53 +0100, Ben Blaukopf
wrote:

|!Lots of questions tonight...
|!
|!The old cooker hood in my kitchen has a 4" hole at the right height, and
|! about as far left as I can possibly have the new hole if I'm having a
|!chimney hood.
|!
|!Modern cooker hoods appears to want 5", or more usually, 6" holes.

Get a 5 inch to 4 inch adaptor, that is what our local Builders merchant
offered me.

If the extractor wants a 5" hole then reducing it to 4" will impair
the performance. I did the same thing on one job and I had complaints
the cooker hood wasn't too great. Whether that was because it was just
crap (doubtful as it was some huge AEG thing that was as big as the
range cooker) or because of the vent diameter I don't know.

Presumably if it wants a 5" hole, sticking a 4" in will reduce the flow
by at least 36%. In practice, the flow reduction will be greater,
because flow speed varies according to distance from the edge of the
pipe. Possiby not much greater though - I've no particular inclination
to work it out.

It's pretty academic, because the vast majority of hoods want a 6" hole.

Lurch wrote:
On Mon, 16 Apr 2007 13:18:48 +1000, Duracell Bunny
mused:

Ben Blaukopf wrote:
Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height, and
about as far left as I can possibly have the new hole if I'm having a
chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.

Ben
Yes, easily done with a core drill & pilot. I usually do it by hot melt glueing
a sheet of plywood over the existing hole, then use the core drill on that. The
thickness of the ply is more than adequate to stabilise the core drill once the
core is out of the ply.

Use a thickness of ply to suit the job, access & your strength. In a door, you
can get away with 3 ply, in a ceiling you need much thicker.

Are you on about a normal holesaw for plasterboard and the like and
not a dry diamond core? I have never seen a dry diamond core drill
used in a door or ceiling before.

Doesn't matter, the principle is the same ... you use a new surface to guide the
core drill.

--
Karen

If you can't be a good example, then you'll just have to be a horrible warning.'
Catherine Aird

On Mon, 16 Apr 2007 13:05:29 +0100, Ben Blaukopf
wrote:

Lurch wrote:
On Mon, 16 Apr 2007 06:57:14 +0100, Dave Fawthrop
mused:

On Sun, 15 Apr 2007 22:43:53 +0100, Ben Blaukopf
wrote:

|!Lots of questions tonight...
|!
|!The old cooker hood in my kitchen has a 4" hole at the right height, and
|! about as far left as I can possibly have the new hole if I'm having a
|!chimney hood.
|!
|!Modern cooker hoods appears to want 5", or more usually, 6" holes.

Get a 5 inch to 4 inch adaptor, that is what our local Builders merchant
offered me.

If the extractor wants a 5" hole then reducing it to 4" will impair
the performance. I did the same thing on one job and I had complaints
the cooker hood wasn't too great. Whether that was because it was just
crap (doubtful as it was some huge AEG thing that was as big as the
range cooker) or because of the vent diameter I don't know.

Presumably if it wants a 5" hole, sticking a 4" in will reduce the flow
by at least 36%. In practice, the flow reduction will be greater,
because flow speed varies according to distance from the edge of the
pipe. Possiby not much greater though - I've no particular inclination
to work it out.

It's pretty academic, because the vast majority of hoods want a 6" hole.

I hired a 6 inch core driller but ended up stich drilling the
circumference because the core was taking ages and almost killing me
up that ladder. My SDS drill took a couple of minutes and the
untidyness is hidden by the grill thingy.

On Sun, 15 Apr 2007 22:43:53 +0100, Ben Blaukopf wrote:

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.


With a good drilling machine with a mechanical gear box for low revs and
electronic variable speed control, and thick leather gloves to guide
the core by hand you may be able to start it in the right place to drill a
concentric hole over the existing one. The trick is to angle it so you're
only trying to start at one point otherwise it jumps around horribly.
Otherwise some sort of mechanical support to guide the core may be worth
while. A couple of battens banged in by masonry pins to make a V-shaped
guide would probably do (again you need to start the core on the angle) or
to be really posh a bit of 18mm board with a hole cut to the new size,
fixed over the existing hole, would be the biz.

On 15 Apr, 22:43, Ben Blaukopf wrote:
Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height, and
about as far left as I can possibly have the new hole if I'm having a
chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.

Ben

In my experience a core drill need a pilot drill only to start it off
and keep it in place. After that the pilot becomes useless - and if in
a morse taper it can keep coming loose, or wander off.
Once the core drill has cut a reasonable slot it should stay roughly
on line. So start through a board perhaps, as has been suggested. Also
you need a very big drill with an effective clutch or torque limiter
or you risk breaking your wrists.

cheers
Jacob

"normanwisdom" wrote in message
oups.com...
On 15 Apr, 22:43, Ben Blaukopf wrote:
Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height, and
about as far left as I can possibly have the new hole if I'm having a
chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.

Ben

In my experience a core drill need a pilot drill only to start it off
and keep it in place.

Same in my experience.

After that the pilot becomes useless - and if in
a morse taper it can keep coming loose, or wander off.

Usually down the cavity

Once the core drill has cut a reasonable slot it should stay roughly
on line. So start through a board perhaps, as has been suggested. Also
you need a very big drill with an effective clutch or torque limiter
or you risk breaking your wrists.

Also true in my experience. Also my apprentice has informed me that since he
started courting the core drilling is getting harder as he no longer has the
same strength in his right arm.

Adam

On Tue, 17 Apr 2007 18:20:03 +1000, Duracell Bunny
mused:

Lurch wrote:
On Mon, 16 Apr 2007 13:18:48 +1000, Duracell Bunny
mused:

Ben Blaukopf wrote:
Lots of questions tonight...

The old cooker hood in my kitchen has a 4" hole at the right height, and
about as far left as I can possibly have the new hole if I'm having a
chimney hood.

Modern cooker hoods appears to want 5", or more usually, 6" holes.

Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.

Never used a core drill, no idea if this is going to work or not. The
alternative is to find a hood that takes a 5" hole and use the 5"-4"
reducer I have hanging around in the garage.

Ben
Yes, easily done with a core drill & pilot. I usually do it by hot melt glueing
a sheet of plywood over the existing hole, then use the core drill on that. The
thickness of the ply is more than adequate to stabilise the core drill once the
core is out of the ply.

Use a thickness of ply to suit the job, access & your strength. In a door, you
can get away with 3 ply, in a ceiling you need much thicker.

Are you on about a normal holesaw for plasterboard and the like and
not a dry diamond core? I have never seen a dry diamond core drill
used in a door or ceiling before.

Doesn't matter, the principle is the same ... you use a new surface to guide the
core drill.

Yes, but you would really want a decent thinckness guide for a core
drill though. Depends on what your wall is made from and how well the
core drill will stay in it with minimal guidance.
--
Regards,
Stuart.

Lurch wrote:
On Tue, 17 Apr 2007 18:20:03 +1000, Duracell Bunny
Lurch wrote:
On Mon, 16 Apr 2007 13:18:48 +1000, Duracell Bunny
Ben Blaukopf wrote:
Is it possible, using a core drill, to drill over the the top of an
existing hole? Or is it going to wander so far that I end up with a
complete mess? Obviously I'd need to offset the centre at the same time,
so that the left edge of the hole didn't move any further left.
Yes, easily done with a core drill & pilot. I usually do it by hot melt glueing
a sheet of plywood over the existing hole, then use the core drill on that. The
thickness of the ply is more than adequate to stabilise the core drill once the
core is out of the ply.

Use a thickness of ply to suit the job, access & your strength. In a door, you
can get away with 3 ply, in a ceiling you need much thicker.
Are you on about a normal holesaw for plasterboard and the like and
not a dry diamond core? I have never seen a dry diamond core drill
used in a door or ceiling before.
Doesn't matter, the principle is the same ... you use a new surface to guide the
core drill.

Yes, but you would really want a decent thinckness guide for a core
drill though. Depends on what your wall is made from and how well the
core drill will stay in it with minimal guidance.

Well the guy who put the boiler in was moaning how hard my bricks were.

So I reckon I'll stitch drill it. It'll be cheaper that way anyway, as I
won't need to hire anything.

Ben