Tuning pin drilling?

[Mike Spalding]

You're probably right about the optimism thing.  I've never been accused 
of being either wildly or blindly optimistic, so I'll probably have to 
consider two-step in-the-piano drilling.  Dang.

Ron Nossaman wrote:
>
>> 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
>