I need to make a 2' 6" x 1' hole in a lightly reinforced 8" deep concrete
floor. There is already a 12" diameter hole in the middle but it ain't big
enough. I was thinking of using a 4 1/2" diamond core drill that I already
have to cut out the corners, a 9" angle grinder to join the corners up and
then hammer in steel wedges to try to crack the concrete out cleanly.

If I can get beneath any rebars with the angle grinder I reckon that I've got
a chance to do it, however I've got one concern...

The diamond core drills that I have are general purpose, light weight dry
cutting ones. To cut this sort of depth in concrete and through any rebars
that I find, I suspect that I would do better with vacuum or water cooling and
dust removal for the drill. Vacuum would be difficult and the core drill and
arbour aren't really designed for water injection.

I can make a shroud to go over the top of the drill, drill some holes in its
top face and introduce water that way, hoping that the zero-pressure water
will find its way down the inside face of the drill and up the outside face.

I could drill a small hole across the path of the big drill with a 1 1/2" core
drill pecking to remove the dust and cool the drill. I could then get a
sufficient supply of water to the big drill to stop it from overheating or
clogging.

In either case I plan to use an old (late 40's) bench drill anchored to the
floor, with its head back-to-front to avoid the base for driving the drill.
This should keep the drill straight and help to avoid the muscle spasms that
would result from trying to do 24" of hole with a hand held drill motor

Anyone got better ideas, other than hiring it out?


Mark Rand
RTFM

here in nashville , having a guy come out and cut that would be about
200 , or you can rent the stuff at sunbelt for about 1oo for a half day
and do it yourself ,

as to using water with a dry bit , it is perfectly acceptable , we use a
five gallon bucket with a couple of drops of joy detergent in the water
and use a small cup to pour down the side of the core bit , pulling the
bit and flushing with water and air every couple of inches ,


if you think it cuts well dry , try it wet you would be amazed

On Tue, 16 May 2006 19:27:23 -0500, "c.henry"
wrote:

here in nashville , having a guy come out and cut that would be about
200 , or you can rent the stuff at sunbelt for about 1oo for a half day
and do it yourself ,

as to using water with a dry bit , it is perfectly acceptable , we use a
five gallon bucket with a couple of drops of joy detergent in the water
and use a small cup to pour down the side of the core bit , pulling the
bit and flushing with water and air every couple of inches ,


if you think it cuts well dry , try it wet you would be amazed


Thanks for the encouragement. I hope to set up for it tomorrow. Water won't be
a problem since the job is to make a drainage sump in a pit bigger. Some ****
(guess who) didn't make the sump big enough to hold two pumps and float
switches :-(


Regards
Mark Rand
RTFM

Are you sure you cant put one pump on top of the other with the outlets
offset and use the existing hole?
One pump runs but if the water is fast rising and overwhelms it or if
it fails the other kicks in.

On 18 May 2006 15:21:34 -0700, wrote:

Are you sure you cant put one pump on top of the other with the outlets
offset and use the existing hole?
One pump runs but if the water is fast rising and overwhelms it or if
it fails the other kicks in.


Unfortunately the sump isn't deep enough for that either. The replacement sump
is going to be deeper, wider and longer than the one I made originally. I was
tempted to just fill the whole lot up with concrete, but since the floor is
18" below the local water table in summer I would rather not take the risk...
don't live or build a workshop with a cellar halfway down a hill on a clay
soil with bands of gravel in it :-(

Mark Rand
RTFM

On Thu, 18 May 2006 23:47:50 +0100, Mark Rand
wrote:

On 18 May 2006 15:21:34 -0700, wrote:

Are you sure you cant put one pump on top of the other with the outlets
offset and use the existing hole?
One pump runs but if the water is fast rising and overwhelms it or if
it fails the other kicks in.


Unfortunately the sump isn't deep enough for that either. The replacement sump
is going to be deeper, wider and longer than the one I made originally. I was
tempted to just fill the whole lot up with concrete, but since the floor is
18" below the local water table in summer I would rather not take the risk...
don't live or build a workshop with a cellar halfway down a hill on a clay
soil with bands of gravel in it :-(

Mark Rand
RTFM

When you use the term 'halfway down a hill', how much more
'downhill' do you have before you run out of your lot?

It's easy to get a backhoe and dig a long trench that starts below
basement level and ends at ground level downhill, and drop some
plastic DWV pipe in. Then the water drains out of the basement on
it's own using nothing more than good ol' reliable Gravity - and I
haven't met anyone that's either smart enough or stupid enough to
break that law yet... ;-)

You *are* pumping this free ground water out of your basement and
into a storage tank or a small pond, and using it for non-potable
things like washing the cars and watering the lawn, right?

Just do it, don't go bragging. If you don't own the water rights
to the property (as in they were sold off to a regional water board or
utility district when the property was subdivided) they might get
annoyed if they think you are stealing "their water"...

(Don't try using logic in a situation like that, they'd rather you
dump it in the sewer than do something useful with it.)

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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