Tuning pin drilling?

[Ron Nossaman]

> There must be something subtle happening right at the cutting edge of 
> the drill where tiny variations in sharpening / grinding make noticeable 
> differences in hole size, or maybe surface texture inside the hole.  
> I've been using a Woodcraft fast spiral brad point 17/64 in delignit.  
> The first one I bought gave me 120 in-lb with 1/0 pins.  Thinking I'd 
> discovered the holy grail, I went out and bought a half-dozen more 
> bits.  They all mic the same (.267) but each gives a different pin 
> torque.  Except for that first bit, none have given me a tight enough 
> fit on a 1/0 pin.  Is a puzzlement.
> 
> Mike

I've always freehand sharpened jobber bits when I managed to 
damage the cutting edges. I've learned from this that it 
doesn't take much of an off center point to make the hole 
oversized.  I've also learned that double drilling brings 
final size accuracy back into range when you need close 
tolerance accuracy, even with hand ground angles and 
centering. Trying to drill 0.009" undersize in one pass in 
Delignit with a brad point bit and getting a uniform (much 
less a medium torque level) fit strikes me as wildly optimistic.

Ron N