Interesting thing about the HO Cal Scale AB brake set. Like many styrene parts, the C.S. brake set was a flat casting, and each side of the part sprue was derived from the engraved detail on that half of the mold. When being cast in the injection molding machine, the mold's two halves were clamped together and the high pressure molten styrene would be injected into the cavity. As this mold was made decades ago, and many 1000s of shots were made, the mold would eventually start having plastic escaping the cavity at the interface of the clamped together mold halves. This is where "Flash" comes from. The mold machine operator could tighten down the clamping pressure up to a certain point, but the abrasive wear from this constantly squirting out of the molten styrene made the flashing problem even more severe. The solution was to machine the facing portions of these mold halves to restore the tight fit. Unfortunately for the Cal Scale mold, this was done enough times that the mold's cavity got thinner until the air resevoir  portion lost its cylindrical shape and started imitating a football in shape. I suppose a die maker could add some grinding into the mold cavity to restore the proper cylindrical shape, though I don't think that this has ever been done.

-Andy Carlson

Ojai CA