thanks for all of the replies.
The problem with grinding is that the metal is very thin, (old roofing tin) and I'm afraid I can easily take off more metal then I can afford.
This is for a sculpture I'm working on. I'm planning on cutting out the shapes, shaping them on the english wheel, then attaching them together. I'd love to completely weld every seam, but it'll more likely be several tacks.
if it matters, I'm using oxy / acet for the work.