how many teeth per inch do i want again?

how thick's the thing you're cutting?

coarse is always good for aluminium to stop the blade clogging, but not too coarse.

for steel i think the rule's something like 3 teeth + on the workpiece
tom

ah, right its 1.6mm tube, so probably want quite a few teeth then? stop it snagging?

18TPI for tube, 14 for thicker plate otherwise they just clog up.

You should have more to have 3 teeth in contact, but there we go

A good trick when filing aliminium is to rub talcum powder on the file before filing. When the teeth get clogged full of the ali just give it a tap and all the ali falls out

Or rub a stick of chalk along the file - same effect.

If you're not going to paint the piece (or are prepared to do some clean-up afterwards) then a squirt of wd40 is very helpful.