anti-wander drill grind

[TRX]

So, I'm looking at an old magazine with a too-blurry-to-be-useful picture of a long drill. The caption reads,

"As an illustration of how special bits are available if required, here's a 1/4 in. diameter one over 12 inches long. Wandering off line is almost inevitable during the making of a long hole with a normally ground drill. To obviate this, this one has a specially designed double angled cutting edge which acts as both a centre and a cutter and keeps the drill in line over long distances."

Oooo-kaay, that's a new one on me. I've seen drills with clipped corners and split points, but I've never seen claims that such things made them track straighter.

Deep hole drilling is a bane of my life. Anyone know what one of these drills might be called, or who might make them? If there's a tip geometry that can let me drill a straighter hole, I want it...

[GlennW]

Deep hole drilling is a bane of my life. If there's a tip geometry that can let me drill a straighter hole, I want it...

It sounds like you may be applying too much pressure when drilling.

I use a bed turret on my lathe and can exert a considerable amount of pressure on a drill and the result is a deflected drill and an off center hole.

Using only enough pressure to keep a properly sharpened drill cutting yields straight holes.

[John Hasler]

You may be looking at a D bit http://www.stubmandrel.co.uk/workshop/29-d-bits
Or a gun drill https://en.wikipedia.org/wiki/Gun_drill#Types

[TRX]

It definitely wasn't a D-bit or gun drill. It looked like an ordinary twist drill in the blurry picture.

[BadDog]

Was it just talking about a faceted or "web thinned", or maybe split point? Those things are better than a typical plain ground point, but no recipe for guaranteed straight holes, particularly not with a 12" long 1/4" drill.

But it kinda sounds like it's talking about something like a cutting edge ground partially ground at 2 different angles. Like if you had the inner part near the web at 135, and the outer part near the margin at 118? Never seen such a thing. The only reference I've got for double angle edge is like you put on a working knife edge, but that clearly doesn't match the rest of the description.

[jscarmozza]

If you can find a copy of the Sept/Oct 2007 edition of The Home Shop Machinist, there's an article about sharpening drill bits that may be what you are looking for. I made the sharpening jig and sharpened some of my bits to the new form, the tip form is similar to an end mill and it works very well. The only draw back that I found is the jig has limited size range. John

[Mr Ron]

Sounds like the profile is similar to a center drill, but longer.