I use coke only, it's the best way to go if you can afford it . Its the cleanest, hottest , most ash free fire you can burn your job with. somewhere here I posted pics. of welds, all welded in a coke fire from 7/16, to 7/8. my guess is you aren't getting hot enough , burn two pieces together, meaning heat them on top of each other until you see sparks, then wait until the sparks get to going then you know what the fire looks like when you ruin your job, do this and you get to know when its time, by the way, pull those burning pieces out and just tap them together with your hammer with increasingly heavy blows I think you will be pleasantly surprised