Cheers many thanks I took a look at the thread. The burrs I have seam pretty well balanced there's certainly no noticeable vibrations and cut well at around 6-7000rpm I think the way to start is going to be getting a collet extender which luckily come in er 20 1/2" and relatively cheap and will allow me to use the burrs I have all be it having to do a few more passes and get me going then try a few other cheaper bits and and hopefully in the mean time save up for something a bit more specific when I know what works best.