"Bill Woods" wrote in message
...
Do drill bits for use in ordinary "home use" drills get blunt with
the result that they work less well?
Absolutely.
I ask this because I recently used my hammer drill to make some 6mm
holes in masonry in the concrete ceiling above me and it seemed like
very slow work. When I used a smaller drill bit of about 4 to 5 mm
in the same masonry material then it was much, much easier to make
the hole. I used a vaccum cleaner to suck up particles and to
prevent the bit clogging with concrete dust.
Sometimes you will hit rebar or aggregate. Go slow so you can stop before
you smoke a bit. For a piece of aggregate, I use a round pin that comes in
a wrought iron gate spring kit. It is cold rolled steel, and won't bend. I
grind a point on it, and stick it in the hole to break the piece of
aggregate. If it is rebar, you will know it by the feel when you hit it.
BTW, pulling the drill out occasionally, and letting the cuttings fly away
is a good idea.
Of course the smaller bit makes a hole with a smaller area but the
difference seemed far greater than this. I wonder if my 6mm drill
bit (and maybe others) need replacing?
Unless you do this for a living, just buy run of the mill bits, and visually
check them during use. Hold a new good one next to a questionable one. If
it is shredded, you will SEE the problem. If it looks much like the new
one, you are hitting something in the hole. Masonry bits are more forgiving
than regular bits, and sharpening them isn't as exacting. I have a Drill
Doctor, but as yet haven't sharpened one bit on it, masonry or regular.
This is the type of drill bit I used:
http://www.tool-up.co.uk/tooldev/images/items/24343.jpg
http://www.tool-up.co.uk/tooldev/images/items/9487.jpg
Like I say, if you are going to be doing this a lot, you might want to spend
the $200 US for a rotohammer and some bits. If only a weekend warrior, any
old hammer drill and bit will do it, just not as fast. The larger drill
bits may take longer depending on the sack mix of your original concrete.