Boring Bar

[TomG]

If you are boring a 1/2" hole with those boring bars, they are likely rubbing below the cutting edge. Sharpen them up and add a secondary clearance angle so the area under the cutting edge doesn't rub on the bore. For most jobs you would be better off with high speed steel bars instead of carbide. They are easier to sharpen and much more forgiving.

Another option I've used in a pinch is to substitute an end mill as a boring bar. You just have to orient it so a cutting edge is horizontal and on the center of the part.

Tom