Peck drilling with a D bit

I was just reading about D-bits in a lathe turning book from about

Sadly they don't answer the question you raise, but if these D-bits are so good, why can't I buy a set ? Or can I ? They seem easy enough to make on demand if you have a complete set of silver steel in imperial and metric sizes, and you are prepared to reduce the shank, heat treat, and then grind the tip. You would think you should be able to buy a set like twist drills.

Steve

They are slow! The combination drill bit and reamer is much more efficient. But D-bits still are used for deep hole drilling, esp. gun drilling (we call them "cannon drill" (Kanonenbohrer)). For one (few) offs, conical bores or bores with odd shapes, they are unbeatable for the HSM.

Nick

Nick,

I have spotted that Reeves list D-bits in imperial sizes as 'milling tools', though there are no pictures.

Steve

Boo, Quite a bit( pun not intended) is in Ian Bradley's The Grinding Machine. It is doubtful whether this MAP book is available now but it describes making D bits from silver steel and the 'D' left after grinding is half the diameter plud 5 thous. This is tempered to suit the material to be bored. The cutting edge s are 10 degrees and 10 degrees.

Surprisingly, this format is still adopted for boring Northumbrian BagPipes in such as Lignum and Blackwood. Very long and very narrow bores are done this way. My experiences are there fore in wood but removing the wood bored is fairly hot on respective pecks and I knock the swarf(?) off the top of the flat with a thumbnail. It sticks and trying to keep things cool is a nightmare! As the boring gets deeper the heat gets greater from the friction.

Some time back you raised the question of cheap tool and cutter grinders and whether these could be got in the UK. Bradley, in the same book goes into making his own tooling for grinding D bits and quite a few fancier applications. Maybe, you could get a copy of this from E-Bay or a secondhand outlet.

I hope, however, that the foregoing is of some use.

Cheers

Norm

Ah, yes. but these are really for milling. To be precise, for engraving. They do have a relief on the radius, but not the D-bit. Also, the D is exactly 50% and not a tad more like with the real D-bit.

Here is a link with the geometry (text is in German, but the picture is quite self-explaining).

Nick

Now for a peck of Thanks. That's the drill or has the World changed to 'tec all and say nowt?

Norman Atkinson

Sounds like a better plan anyway.

Thanks,

Thanks

But well hidden under Various -> Always Available -> Page 4, imperial sizes 1/16 inch to 1/2 inch. No picture unfortunately.

Steve

On or around 8 Jan 2007 15:04:37 -0800, "Cheshire Steve" enlightened us thusly:

that's a point, they probably LH dies. I need an LH M8x1.25... which I couldn't find in J&L's catalog, somewhat to my surprise.