I am a small scale bespoke frame builder, building frames from steel in Sheffield UK. I build using traditional methods, fillet brazing, silver brazed lugs etc etc. I use these traditional methods but always look for opportunities to build in technical and functional improvements in to the frames. Have a look at my web site for more of a picture www.fieldcycles.com 

Thanks for the reply, I wasn't sure if my ye olde  methods would appeal to people on here !! thanks for the tips, I think making a lug and bonding a tube in will be the way to go. I realise why the i.d of tubes are the specific measurement with the wrapping round a mandrel method to form a tube. Ideally I would like to just find the right sized o.d tube and not get too involved with the production of the tubes, just cut them and then bond in. Do you have any tips on the correct adhesive to use and what sort of glue gap I should leave ?