Different solder melting points - Model Railroader Magazine

I use wet tissue or paper towels as heat sinks.   Usually, a wad of wet material can be moulded to stick in place, but I also use alligator clips, clamps, or locking tweezers to hold the wet tissue where it does the most good.
I rebuilt this old Akane brass steamer into a model of a particular prototype for a friend.

I used a propane torch to assemble and install the Kemtron (PSC) cast brass cab, then various soldering irons to add the details.  These included, where appropriate, 25 and 45 watt pencil irons, and a larger 85 watt model and a 200 watt model for the bigger stuff.

The rear ladder on the tender was built on a homemade jig, and is pinned in place on the plastic tender, as are the footboards.

The front ladder on the tender is also pinned in place, but because the rungs are curved, it had to be assemble in-place.  The two ladder stiles, with holes pre-drilled and mounting pins soldered in place, were first installed on the plastic tender shell, then wet tissue was applied to all points where the ladder contacted the plastic.  The pre-cleaned  and pre-bent rungs were then installed and individually soldered in place.  As each was finished, it got an application of wet tissue, to prevent further movement while the next one was being soldered.  No damage at all to the plastic. 

The plastic turret cover (just ahead of the cab, atop the boiler) did get damaged by a soldering iron, but only because I accidentally touched the iron to it while soldering nearby.    Easily repaired with a little body filler.

With the range of soldering irons used and the seemingly random order in which detail parts needed to be applied, the use of heat sinks was much easier than trying to use solder of different melting points.

Wayne