< Rear Side Frames >
The rear side frames were laser-cut and bent from 6 mm steel plate, by a local factory. To attach them onto the main frames precisely, I employed milling machine's stage as a flat surface. The main frames are bolted down onto the stage. Front ends of the rear side frames are fixed to the main frames with two screws. Back ends of them are combined each other with a round brass bar. Suitable packing under the bar holds the rear side frames in a desired height. Then main and rear side frames are clamped firmly.
Drill the main frames through holes of the rear side frames. For this operation, I used small milling machine. Such a tiny machine is sometimes more useful for huge job.
A recess of 1.5 mm depth was cut from inside face of the each frame. It is a trick to increase swinging degree of the trailing truck, so as to clear 7.5 meter radius track layout.
Two castings, front expansion bracket and trailing truck pivot pin bracket, are mounted. All of side faces are milled as same as the other castings.
Here I adjusted the broadening degree of the rear side frames to be symmetric. The photo shows how to do this with milling machine's stage as a flat surface and a height gauge.
The picture shows frame reinforcement castings. They have two side faces broadened along the rear side frames. These faces have to be machined precisely.
I made a jig from steel bars that can trace the taper of the rear side frames. After cutting one side of a casting, the jig is applied to align another side perpendicular to the stage.
Align and clamp the castings, countersink in the castings through the holes in the frames, disassemble, drill and tap at the countersinks.
The rear expansion bracket consists of three castings, two side castings and one center casting. First the side castings are machined and bolted onto the frame, and then the center casting is aligned and bolted.
The photos show how to machine the side castings. It has three flat faces perpendicular to each other. The left hand photo shows cutting two faces at a time. The right hand photo shows cutting the last face. Note the tricky clamping because the castings have complicated shape.
Two kinds of laser-cut parts are bolted onto the main frames.
Assembled chassis. It is two times longer than the William. Moreover the tender will follow it.