If you need to grind and shape a stainless steel mig weld with a 330mm air file then you will need to remove a lot of metal. For this reason we have selected our most aggressive FX87 Cibo Ceramic abrasive belts.
This is one of the few powerfile applications where we would recommend a 40 grit abrasive as the first choice. But this does depend on what you need to do afterwards.
n.b. Both a 40 and 60 grit belts will leave burrs. If you need an entrapment free finish then we would recommend following up with the FX87 80 grit and a coarse or medium conditioning belt.