I use a specific cutting oil for tapping aluminum & chuck the tap in a cordeless drill too... depending of the thickness of the piece you're tapping, you'll likely have to back the tap out several times, clean off the filings (I use a brass bristle brush) & relube before you tap all the way through... the cordless drill makes fast work of that.
I chuck the tap gripping the smooth round, instead of the squared end, so the tap slips easily when the cutting threads get too full of chips.
That's pretty trick welding Reg to fish the broken tap out!
I'm looking forward to getting my own tig welder here shortly & learning the craft.
