The Home Machinist!

I agree with the Uni-bit / stepped bit suggestion.

That's the solid state electronics switching on and off. If you have an incandescent light on a dimmer you can hear the element vibrating while it's dimmed down, which is from the SCR switching on and off, chopping bigger and bigger sections off the sine wave of the AC voltage as you continue dimmin...

spro wrote:Well I bit after investigated. I saved it. When I tried to open it, it says corrupted file. so it's probably just me.

spro,
You had a problem with the Excel file I have in my dropbox account or the OPs Excel file?

Here's a collection of charts and calculators I've put together over the years for use in fabrication shop work.
I love this kind of stuff.

https://www.dropbox.com/s/is60q91gcll12 ... Calcs.xlsx

I would go with the thickest boring bar you can fit in the bore.

Some common fixes:
Sharp tool
Slower speed
faster feed
Clamp some dead weight to the bar to give it more mass

Hope some of this helps,
Mike

You may could drill it with a ball nose end mill, this can get you close if you don't have one with the correct radius and save a bunch of hogging with the radius tool.