I need a 12mm shank indexable boring bar for my lathe, I've had a look on Ebay etc but there's so many to choose from I don't no what to get! I have small one (8mm?) but it's no good as I can't get it to centre height, the tungsten one I have was cutting ok but screeching badly until I tried sharpening it and now it's quite but don't work anymore So I think to save me from myself I need one with replaceable tips. Any suggestions on makes or type? I've got a Sandvik tool for normal turning jobs and it's very good but they are expensive, are the RDG tools ones any good? Thanks.