A real three-handed job here. With 4 to build, I was relieved that they didn't all take as long as the first one or it would have taken most of a day to put them together !
First job is to make sure you have the correct stretchers - the kit is available for 14mm (representing a prototypically correct 2 foot guage) and 16.5mm modellers. For some reason I originally got the narrower version which confused me initially although replacements were quickly supplied.
Building started with drilling out the axleboxes to accept brass bearings, plain not top hat ones here so they slide into the hole. Then some dry fitting to ensure the stretchers mate with the sides properly. A locating peg is present but the hole for this has to be drilled out as it's not deep enough.
The one sideframe is soldered to the stretcher. And then adjusted to make sure it is at right angles to the side in all planes. While heating the parts have to be gripped between blocks of wood as the metal warms beyond finger point.
Then the tough stage - gripping the wheels, locating the peg and fixing the other side on. All the while keeping things flat. Much juggling of bits of wood and balancing the assembly on an old computer hard disk. Heating solder on one side for too long also weakens the solder on the other too which just makes the work even more "entertaining".
Any slight un-flatness can be twisted out gently with fingers although I found it easy to over do this and have to twist the chassis back. Frustrating.