T i m wrote:
On Sat, 15 May 2004 20:35:34 GMT, Ian Stirling
wrote:

T i m wrote:
Hi folks,

I'm trying to make a special drill for drilling out the stump of a 9"
sq wooden gate post but want to leave the surrounding concrete intact.
snip
(Someone kindly suggested 'sharpening' a masonry bit but looking at
it's design I'm not sure it would work very well through 4.5m (9 holes
x .5m deep) of 'good' wood?)


Why not?
Looking at one, if you take a fair bit off the top, to leave a
90 degree cutting edge, with some relief, then it will cut fine,
though perhaps not as fast as a proper bit.

That was my thought Ian .. ;-(

Cutting away a large portion of the bit support that the carbide is
soldered into to enhance chip removal would be a good idea.

I *do* have a 1m long 25mm SDS bit but I didn't really want to muller
it just for this job when for similar money I could (possibly) make
something more suitable?

Maybe.
I too have a 1m long 25mm SDS bit, but probably don't treasure it as much,
as it only cost me ten quid.


Alternatively, a simple auger worked very well for this sort of thing.
If I could have welded it on a long shaft, it'd have been ideal.
(it was around 1")

Are you talking 'hand brace' here Ian? Well that *is* a thought, would
be easy to extend and would be quiet in use but I don't fancy plugging
through 4.5m of even softish tannalised timber by hand if I can help
it?

Actually, not.

Mains 600W drill, worked fine.
If it was longer, it'd have been a lot easier, as I ran into problems
with it hitting the sides of the hole.
An adaptor for the much slower turning more rugged SDS drill would be
just about ideal.
You do of course have to beware of hitting the concrete at an oblique angle.
Hitting a flat end, or hitting a side at a very shallow angle doesn't do
too much damage.

Maybe I'll get one of those wood chewing things for the angle grinder,
lock it on, throw it into the hole and run away! ;-)

Those are fun.
I needed to abrade off the gel-coat from a fiberglass pond, and it
made the job almost trivial, providing a really nice key all over.
(the existing gel-coat was flaking)
At least a hundred times faster than a wire brush in a drill.