Method of forming a brake drum

A method of forming a brake drum comprising the steps of:

• casting an iron cylindrical braking drum with a flange end and an opened end to include a plurality of generally axially extending fins around an exterior surface thereof, said casting including providing each of said fins with radially extending side walls which diverge along a length thereof from said opened end to a widest distance therebetween at a predetermined location from said opened end and converge along said length thereof from said predetermined location to said flange end, whereby adjacent said side walls of adjacent said fins define a space therebetween having its narrowest portion at said predetermined location;
• machining a braking surface about an interior of said cylindrical braking drum;
• machining the top of said fins on either side of said predetermined locations to form a shoulder extending around the drum and spaced inwardly of the opened end;
• forming a steel band;
• and
• securing said steel band to said braking drum at the machined top of said fins to encircle said braking drum and engage said shoulder to define, with adjacent sides of the fins, a plurality of venturi-shaped cooling channels at said predetermined locations.