How do you smooth an inside radius?

[Truelove]

I'm making a knife with an index finger hole (think Busse's BARF or a karambit's pinkie hole). How can I smooth the inside of the hole so it is an even, gentle semi circle instead of the 90 degree wall made by the drill press? Please note my hand filing skills are not up to the challenge. Maybe a Flexshaft / dremel attachment?
Thanks, as always!

 

[kungfumo]

I have an oscillating drum sander. They run about $100. I am currently converting it to a horizontal 2x72, with the ability to turn it back into a drum sander. Should work very well,its a pain to get krambit holes straight.

 

[Carl_First_Timer]

It depends on what machinery you have at your disposal.

Round file, and sand finish.

Large C'snk and sand finish.

Inside radius bit.

 

[Frank Niro]

A round file and then sanpaper backed with a dowel. Frank

 

[SBuzek]

3/4"sanding drum in the drill press.
Stan

 

[H0tR0d]

a carbide countersink will work as well.

 

[oldschool45]

SBuzek+1, cost you a whole $8 at harbor freight http://www.harborfreight.com/20-piece-sanding-drum-kit-42006.html great for shaping handles too:thumbup: