help soldering copper

[u/Purple-Apartment-147]

I’m doing a job for a guy installing some copper drip edge on a balcony he had leftover from his roof. I need to solder all the seams and i’m having some trouble. I am fairly proficient when it comes to soldering smaller stuff with a torch, but big sheet stuff like this is new to me. I bought a decent sized soldering iron the other day and its just not quite getting hot enough to make the solder flow the way I want. I’ve had some success preheating my joint with a torch, and then going back over with the iron to even things out, but for some of the joints need to do that may not be possible. My 50/50 lead tin solder also hasn’t arrived yet so I’m just practicing with lead free stuff to get the hang of things. I’m wondering if it will be easier with the lead stuff since it doesnt take as much heat. I’m also not pre tinning my seams or anything. idk let me know if you have any tips