< Brake System 4 >
The brake cylinder is made of gunmetal casting ordered with a pattern by MODELA.
After cleaning the bottom face, the bore is finished in a desired diameter on the face plate. At once, a section for cylinder cover is finished. After that, the casting is reversed and another section is finished.
The cylinder covers are made from brass round bar. The under cover has projection supporting the piston rod.
To save material and cutting effort, the under cover blank is silver soldered from different brass rods. Projection profile is turned and parted off without center hole. The center hole is drilled and reamed when the inner fit is finished.
Bolting holes are positioned by X-Y stage of the milling machine. The drill goes through the cover and countersinks the body. After that the cover is removed and the body is drilled and tapped.
The piston is made from gunmetal round bar, and the piston rod is made of free-cutting stainless steel bar. The rod is press fit into the piston. The top half of the fit is threaded so as to pull the rod into the piston. The photo shows pulling the rod by rotating the head by hand.
After the press fit, the piston is finished to a desired diameter. The rod is exactly centered in four-jaw with a dial gauge. Finally a groove for O-ring is cut.
A coil spring is inserted between the piston and the under cover, and a cross head is screwed into the piston rod. The crosshead is bent from a steel bar and secured by a lock nut. The O-ring pressure should be enough small to allow the piston move by the coil spring. The coil spring is made from 0.9mm stainless steel hard wire. The coil's O.D. is 10mm.
The parts to connect the crosshead to the brake arms are made from laser-cut thick plates. The center hole of the equalizing arm is cut tapered from both sides.
The photo shows assembled brake cylinder with the brake arms. The cylinder is mounted onto one of the chassis stretcher. Steam inlet will be prepared at the side of the cylinder. Right now I cannot optimize the inlet because I have not finished design of the boiler.
The brake system is attached into the chassis. In the photo the chassis is on a sharp bend track of 7.5 meter radius. The brake shoes follow the curve very well but I found the second brake shoes tend to drop out from the wheel frange.
I had no choice but add support plates on the back faces of the brake shoes. They hold the wheel franges firmly.
The whole brake system is completed.