The chance to burn through is much greater on a butt weld.. the heat has nowhere to go when starting at the bitter end of the metal.
Plus warpage is more pronounced with butt welds. If you are not sure of your welding skills lap welds (and a pair of flange pliers) would be a much better route. If you can talk about heat zones, penetration and wire speeds you should be able to pull of butt welds.
If you do butt weld set up the machine on scrap first!
