I was thinking about getting some spare tips - but do I need to? How long do they last / how often do you need to change them? How do yo know when they need changing?
Difficult to give a time scale really but it's something that you should always have spares of; most common cause for needing to replace one is the wire welding itself to the tip (through getting too close or a blocked torch lining) but they do need replacing fairly regularly, as they get spattered up & deform with heat.
weldequip
How long is a piece of string! I have had tips last for weeks and other times got through 6 in a afternoon! They need changing when wire stops feeding properly(juddery) or as said before when welded up.
I've spent time cleaning them up. With the little files you use for gas welding nozzles, or whatever, remember ox/acet gas welding?
Logical thing, I once filed out a 0.6 tip to take 0.8 wire, in desperation.
I made a 15M barge last year from Alloy with a Rilon push pull Mig, I was going through alot of tips and found it best to stop and change it as it started to stick, it was easy to drill them out alot cheaper than buying more, the ones that had melted to the end I cut end off with the airg rinder weld chaser then drilled them out, for Alloy its worth it soft to drill, the wire and tip size was 1.2mm Alumium and the drill size to suit this was 1.7mm .5mm clearance,