When you assemble plural parts sequentially, you will face trouble very easy - the part which you assembled earlier comes off because of the heat.
If you are used to soldering, you will be able to assemble a part with shortest heating time and do most things without trouble.
But until you will be used to it you better take this measure.
To avoid overheating aluminum clips are sold but you do not need to spend extra money.
Just cut a thin stripe of tissue, dip it into the water and cover the part to intercept heat with it.
With this method you only have to be careful with the size of the tissue and the position to cover.
If you cover too close to the new to solder place the temperature of the place does not rise enough and it will be hard to assemble that part.
2. Accumulate solder
Generally, putty is uncongenial to metal. So It is useful for you to know the “accumulating solder” method when you add an arc welding line on brass and thickness to an etching part, fill the gap of parts and so on.
This method is very simple too since you should do reverse of good soldering.
For the good soldering you must heat the part enough and let little solder flow thinly.
But for accumulating solder you do not need to worry neither about heating the part nor to the quantity of solder.
1.) Cleaning the oxidation surface
With this method you have to clean the oxidation surface with liquid flux like with general soldering.
If want to control a place where to accumulate, you should apply flux to only the part which you want to build up solder or you can control it with masking tape!
2.) Quantity of solder
In general soldering the quantity of solder should be a minimum.
But with this technique you should catch solder about as much as in the reference photo.
3.) Accumulating the solder
In general soldering, you heat parts and let flow the melted solder between the parts.
But with this method you should not heat a part that much. You should only ride the soldering iron over the part where the melted solder shall settle.
4.) Incising texture
Here is an explanation of adding an arc welding line.
If you build up too much solder, you should scrape off the surplus solder and incise the welding mold with chisels!
5.) The finishing step
As the last step, you should round the edge with a wire brush.
Well, with this method white metal can also be used as a substitute to the putty.
In this picture I used spare Friul Models tracks.
Since white metal is easy to be unified and is suitable to serve by small quantity you can make a rough shape easily.