''Iron Dwarf, Medium Rare'' is really the bane of existence to solo it for me. I'm 13 out of 25, so I tried to do it yesterday again, but alas, I haven't managed to get more kills.
At least I got ''Disarmed'', that achievement was annoying for me.
You have 12-13 minutes to spawn adds, once the enrage timer hits, just reset. Im not sure what class you play, but it was super easy at 100, just very very time consuming. I did it as a Demo lock. I was dot wardens and sentries since they don't need to be alive, but I don't want them attacking the engineers. I then used syphon life tag the guardians and lower their health. My damage was too much for 3 ticks, so I took off 2 pieces of gear. The 3 ticks when then bring them down to 7-12% depending on multistrike hits. I did this for every spawn wave til the turrets were ready. I hit the 4 turrets and the ones under 10% got killed, the ones over went down to 1-3% and would get killed the next wave.
The biggest problem for me was that only 1/3 or 1/4 of the kills registered, so I ended up having to kill over 75 of the bastards. It took me as long to do that one acheiv as it did to clear the rest of the place, at least it felt like it.
edit: don't attack razor scale at all. Once she perma lands under 50%, no more adds spawn.