View Full Version : Odd drill bit

08-16-2011, 10:57 AM
A friend gave some stuff that was mostly scrap iron but I saved this to see if anyone knows what it's for. It says, 3/8" Speed -Bit on one side. The sides are undercut for clearance and the tip end is rounded and the tips are a chisel form and the shank is tapered. Has anyone seen these before?


08-16-2011, 11:14 AM
Looks like an old carbide tipped drill.

08-16-2011, 11:22 AM
I've seen a couple of those before, but can't quite place the maker. Could it be for drilling glass?

08-16-2011, 11:35 AM
It's steel, not carbide. It doesn't look like it has been used or sharpened.

08-16-2011, 12:01 PM
If the other side is round, looks like a typical "1/2 round" or D bit. Hardwood, brass...

08-16-2011, 12:06 PM
Like a spade bit, no flutes, lots of room for chips.

08-16-2011, 12:12 PM
The old brass drills I have look like fluted drills that have no twist to the flutes,just straight flutes . They would also be good for drilling sheet metal or plastic,where you don't want the drill sucking through as it breaks through the other side,breaking the plastic,or causing the sheet metal to pull upwards and spin around if it is not well clamped down.

08-16-2011, 01:06 PM
The truly curious part to me is the taper shank. You imply it is not a standard taper such as a MT0, in which case the more compelling question is, "what does it fit?".

08-16-2011, 05:43 PM
It was for use with an air chisel type deal. The taper is not original.

08-16-2011, 08:35 PM
No, not a D bit, it's flat on both sides. The taper is original as far as I can tell and it has not been modified as far as I can tell. I have not measured what the taper is

doctor demo
08-16-2011, 08:52 PM
The taper looks to be close to the taper used in the older roto-hammers before spline and sds drive systems.


08-16-2011, 09:54 PM
I dont think its tapered, just an optical distortion from the lens. Probably was taken close up with wide angle.

Mike Burdick
08-16-2011, 10:02 PM
What is printed on it after the "SPEED-BIT"?

doctor demo
08-16-2011, 10:30 PM
I dont think its tapered, just an optical distortion from the lens. Probably was taken close up with wide angle.

The O.P. seems to think it is tapered, maybe He's only looking at it through the view finder of His camera:D


08-17-2011, 12:06 AM
Alas, the suspense is killing me. Isn't this fun?

I suppose I could tell you what it is but that would entail a half page write-up. Not sure if I'm into that; but, with a little coaxing I may if you have all given up.

08-17-2011, 03:48 AM
Its a masonry drill bit from before the days of carbide.
The shanks were tapered and were called "A" or "B" taper.
I never heard of a "C" shank.

I have many of these old bits and have actually used them several times with an old Syntron electric hammer.

Most of time they were used with a hand drilling tool, which is a short length of bar stock with a taper hole for the bit in one end and some knurling or other grip.
To use it you placed the bit in the taper hole and placed the point on the surface to be drilled and hit the other end with a drilling hammer, turned it slightly, hit again and repeat until deep enough.

The original cordless hammer drill. Coffee and doughnuts for recharge.

08-17-2011, 09:48 AM
Mike, it says United States of America and part of the lettering is missing which tells me the tip has been ground.

The shank is tapered, there is .045" difference between each end of the taper.

It is sharpened somewhat like a masonry drill but most masonry bits have four cutting edges. It probably is a masonry bit used in a drill of some type.

YF is probably right since he has some of them and has used them.

Mike Burdick
08-18-2011, 06:06 AM

Before hammer drills were readily available, holes in rock and concrete were drilled using a "star drill". One would strike the shank with a hammer and then rotate it about a fourth of a turn and strike it again, just like you said that one is. Star drills are still sold today. The early ones were made from hardened carbon steel; the ones now have carbide tipped edges.

It's hard to imagine that little bit standing up to the constant hammering required for hand drilling in concrete even if fitted into another handle. Machine drilling... I might be inclined to believe.


08-18-2011, 07:22 AM
Miners would use such a tool for blasting holes then a bronze ramrod for packing the powder. If you did a tour of the Llangollen slate works would get the story of a miner who was rushing to be home for a special occasion and used the steel drill to ram the powder and blew himself up.

A.K. Boomer
08-18-2011, 09:39 AM
The pic makes the tip look carbide, if it is carbide its simply an old style cement bit, if its not carbide then I really don't know what it's use is as typical HSS or anything else will be useless for drilling through cement.

08-18-2011, 11:14 AM
Looks like a task-specific hammer drill - clay or mortar, perhaps. The tapered shank in particular is used in some hammer drill motors.