[Aussie Mike]

Don't grind the electrode for aluminium. Just put it in straight out of the packet. It will melt itself into a rounded end if it's all set up right. You should also be using a straight tungsten electrode (Grey or white painted end from memory). The Zirconated (spelling?) electrodes with the red painted end are for steel and shouldn't be used on ally.

When welding steel or stainless grind the tip to a sharp point tapering over about 1/2" Make sure you grind in line with the electrode rather than side on as it effects the shape of the flame. You should also wear a respirator when grinding electodes as some of them are mildly radioactive.

Wire brush the work piece just before welding and you might also want to look at your clean width setting on your welder. I've only just recently started getting good results on aluminium and all I can say is practice and more practice.

There's also a formula for tip size vs welding current vs nozel size. Most of the time I use a #6 nozel with a 2.3mm electrode (from memory. I'll check tonight)

Cheers