drill all drill bits

on one of the shopping channels they were flogging sets of these drills,they used a grinding wheel to test a drill and it made no impression on the drill,then they used the sane drill to drill through concrete,brick and finally a car disc brake plate,anyone used these and what did you think as i have tins full of blunt drills and they are never the same re sharpened,tia
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sounds like a universal or multi-material bit with sharp TC tip. Masonry use will blunt the tip, leading to loss of function with wood, steel etc, but will still work fine on masonry. Useful for combination material workpieces, but regular or preferably titanium twist drills are best for metal, dowel bits or aggressively reground twist drils are best for wood, and standard masonry bits a fair bit better for masonry.
http://wiki.diyfaq.org.uk/index.php?title=Drill_bit and http://wiki.diyfaq.org.uk/index.php?title=Drill_bit#Steep_angle_twist_drills
NT
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On 22/11/2010 14:02, bob wrote:

According to the Ideal World web site, they are simply cobalt drills. Cobalt drills are intended for drilling hard and difficult maaterials, but are more brittle than HSS, so you could end up with a box of broken drills, rather than blunt ones.
Colin Bignell
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Nothing simple about cobalt drills.
If they're cheap (or on TV) and they're "cobalt", then they'll be a cobalt _coating_ and probably a bluish rainbow colour. These aren't worth having.
Decent ones are solid M42 alloy. These are good, but keep them in the workshop "for best". They also work in a drill press, but not well in a hand drill. Try Axminster for a supply.
It's also very easy to drill concrete, brick, brake disks and files. The concrete needs to be a mix with little, or a very soft aggregate in it. The bricks shouldn't be blue or over-fired. Brake disks are soft cast iron. Even files are only hard on their skins, even before you annealed them off-stage beforehand.
For a really good multi-material DIY drill, try the Bosch Constructor series. I've just built a fireproof workbench for the glass kiln, which involved a bunch of drilling through stacked asbestos cement board and Dexion. These are carbide tipped and don't bunt in an abrasive board, but they're ground sharp enough to drill steel with hand drill pressure. They're also efficient enough to work with the cordless drill and clear dust well enough to cope with cloying wet cement dust.
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On 22/11/2010 15:49, Andy Dingley wrote:

Well, I wouldn't consider them anything particularly special. They were my standard workshop drill when I was still making medical devices.
Colin Bignell
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On Mon, 22 Nov 2010 07:49:59 -0800 (PST), Andy Dingley

I think I saw this show as I was channel hopping. They were very, very shiny almost like chrome vanadium sockets but who knows, may be they had been polished and had several kilowatts of light shining at them. The presenter was hilarious: "the man who fitted our bathroom had his van broken into and his tools stolen. He had another job the next day and didn't want to let the customer down, so he asked if he could borrow my tools. I lent him these..."
Stephen.
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In article

Car discs aren't hard to drill.
Sharpening HSS drills just needs a decent grindstone and skill. A lot if they are small. ;-)
--
*Eagles may soar, but weasels don't get sucked into jet engines *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I saw a demonstration in Debenhams where a woman did much the same with an ever sharp carving knife (She didn't catch many takers though...)
S
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