< Brake System 3 >
The brake rods are pulled by a brake cylinder through cast iron brake arms. The photo shows the cast arms after cutting outside faces. The arms convert the movement from vertical to horizontal and increase the force. So the casting is comparatively big and solid.
Backside profile of the casting consists of two parallel faces at both ends and one slant between the ends. The photo shows cutting the slant.
The large axle hole is opened by drill and end mill.
Connecting holes at both ends are also opened. Parallel ribs and a slit are cut by end mill.
Connecting pin at the shorter arm is secured by a screw and a nut. Note the screw is offset from center of the pin.
Two brake arms are bound in a brake shaft. And the shaft is fixed in cast iron brackets. The shaft also secured by crossing screws. Hole for the screw is opened in both the bracket and the shaft at a time.
The bracket hole is parted in two halves by 0.3mm slitting saw. It is because the shaft has to be mounted from underneath.
The shaft is locked in the brackets and the both arms rotate independently around the shaft.
The arms are secured at both ends of the shaft with screw flange sets, same as the driving wheels' crank pins.
The brackets are mounted under one of the chassis stretchers. Rear ends of the brake rods are connected to the arms with gunmetal die blocks. The die blocks are push from back by adjusting bolts. After adjustment, the bolts are secured with lock nuts.
I modified the brake shaft securing screws and holes so as to do away with the nuts. The new screw was cut from a larger size screw. (Compare with the forth photo before it)
Vertical linkage of the brake system caused drooping of the parts. So the prototype employs many kinds of hooks. The photo shows L-shape hooks to keep the first and second brake beams horizontal.
The hook is made from rectangle section steel bar, annealed and bent as the photo.
The photo shows studs to hold the L-shape hooks. They are screwed into the main frames from inside. And the hooks are held at opposite ends with cotter pins.
The third brake beam is hung by triangle rings. The rings are made from stainless steel wire, bent and silver-soldered at the bottom. The J-shape hooks hang the triangle rings. The hooks go through the main frame and secured with cotter pins.
These are hooks for the brake rods. They are also made from rectangle section steel bar.
The whole brake system is assembled tentatively without driving wheels. Every connecting pins and holes has suitable play, in order to allow the second brake shoes move just 2mm left and right from the center.
The remaining job of the brake system is the steam brake cylinder.