You must play Onslaught for the Blast Furnace (and we used to be able to attune but no more) and I'm not gonna lie.. I've been playing every week (like 3-5 runs).. and maybe 1 Blast Furnace in all that time in TFS... Now the system may recognize that I have 9 Blast Furni' in my inventory including my absolutely adored Kinetic Tremors + Frenzy roll (3500+ kills on it already it shreds PVE). A tip for Onslaught (I actually think this is an awesome new activity we can run) ...you suit up as best you can with alternatives if you find its not working out with your team but most important: >>> you inspect your teammates.. and I'm sorry to say if you see a guardian without exotic armor and an exotic weapon (some exceptions could be there) you need to leave immediately.. that guardian has lost the plot.. or is a blube flying too close to the sun icarus style.. a troll.. you gotta get out.. you need good random teammates.. they do exist and its an awesome experience when that team gels. >>> I recently completed an Onslaught with a sword even.. as one random teammate brought that healing auto-rifle.. lots of builds and weapons are effective here and thats important to keep it fresh.. just be prepared to swap in-game if you are not helping your team. GL getting your roll