The Hakko 936 is an excellent IRON.

You need to turn the temp up almost all the way to get good results on the heavier gauge wire and posts (they tend to be good heat sinks). Especially when using the small tip.

A larger chisel tip would help immensely to transfer the heat rather than the smallish chisel tip that came with the iron. However, if you tin the tip and keep it clean it should work well. Also use good quality 60/40 solder intended for use with electronics and have some soldering flux to keep oxidation to a minimum.

I know because that is the set up I use.