SDS Drill Bit Life

Any thoughts about the relative quality of SDS Drill Bits?
Living in a house built from 750mm solid stone walls and fitting a new bathroom (an indoor one!) I've found myself needing to drill quite a lot of holes. A 1000mm long 16mm bit from Screwfix lasts me about 3 holes before going blunt. Actually not so much blunt, more that the tip has just worn away. Cost per hole, about 6 quid! Are these 'cheap' drill bits or will they all last like this. Just ordered a couple of Bosch bits, to see if they're any better.
Also is there a correct way to drill? Should I be putting a lot of weight behind the drill, or letting it do it's own thing. I think the speed is constant on my GBH2-24 so I can't vary that even if I wanted to.
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On Mon, 21 Jul 2003 11:02:43 +0100, Rob wrote:

Any idea what sort of stone? Granite is tougher than limestone or sandstone...

Shouldn't need to lean on an SDS just hold it in so it doesn't bounce about and let it do it's own thing. You do have the "hammer" action switched on don't you? An SDS drill with "hammer" on is more akin to a rotating cold chisel than a normal drill.
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Dave Liquorice wrote:

Well it's not sandstone, but I wouldn't have thought granite. A regular masonry bit in a hammer action drill barely marks it though.

:-) Yep! That much I can manage.

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Rob wrote:

Wow! Our house has 600mm stone walls (granite), and my 600mm 25mm SDS bit is still going strong after at least a dozen holes. It cost me around 25.
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Grunff wrote:

Do you happen to recall where you got that? The longest 25mm SDS bits I've seen are only 450mm long and more like 35 a go.
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Rob wrote:

It was about 18 months ago, and from one of three local hardware shops - but I can't tell you which one.
Screwfix do an SDS 1000x16mm for 20: http://www.screwfix.com/app/sfd/cat/pro.jsp?ts 403&id150
Or a 1000x22mm for 39: http://www.screwfix.com/app/sfd/cat/pro.jsp?ts 403&id252
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Sorry if I'm stating the obvious, but you do withdraw the bit regularly to let it cool don't you? I find when drilling old concrete posts etc (70+ yrs) that the bit will get red hot on the tip and melt if it's not withdrawn often. It's almost like the concrete melts in there too, no idea what's actually going on though!
The biggest drill I have is 16mm x 450mm but this has been used for perhaps 100 maybe 200 holes in concrete or similar? Yes the end is a little worn down, but it still drills fine. And yes it's a Screwfix bit, on a 2kg Makita.
Alex
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I can remember a job I was on where that was happening. The foreman was very angry with us, suspecting theft but even he was only getting one or (occasionally) two holes drilled. We were drilling through concrete just deep enough for brown plugs. It was a mystery that never got solved.
I suspect there was steel in it and we were hitting that each time.
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The best drill bits I have ever used came from a hardware store in France, they're designed for stone walls.

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Can't you resharpen the drill bits? I think you would cover the cost of a bench grinder quite soon. I hired a concrete breaker (SDS drill on testosterone) and was charged for resharpening of the bits. Bloke told me it wasn't just sharpening, the ends had to be re-hardened as well. Don't know if he was having me on, however. I have a cheapo SDS drill from Homebase and I have sharpened the drill a couple of times on my bench grinder, and this does seem to improve things. Main problem will be the drill bit getting shorter and shorter. These are the breaker bits, which bang in and out and don't rotate.
On the other hand, are you talking masonry drills (like hammer drill bits but with a different shaft)? Again you can sharpen the bit using a bench grinder or a drill bit sharpener such as the Martek one (on my wish list). If the hardened insert in the end is wearing away very quickly then you have a cheap bit OR your walls are made out of finest quality gritstone and are acting like a bench grinder :-)
Cheers Dave R
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