I wrote the original program in the second half of the 1980s on an Enterprise 128 home computer for my father, a mechanical engineer who designed V-belt drives in his daily work. The program, EKSZIJ.BAS, was written in IS-BASIC, the Enterprise’s structured BASIC dialect, and worked entirely from data typed in from the Hungarian engineering handbooks of the time: Gépipari táblázatok (1970) and the Pattantyús mechanical engineering handbook (1969). It contained the eight V-belt sections then standard in Hungary, their inside belt lengths, and power-rating tables by belt speed. From the power, the shaft speeds and the centre distance, it listed the belt sections suitable for the drive and the permissible range of pulley diameters, interpolating between table values. Its most useful feature was that it did not simply calculate pulley diameters from the speed ratio. Using the exact belt-length formula and a bisection search, it found the pulley diameters for which the belt length at the given centre distance came out exactly at a standard belt length. The user could choose between a shorter belt with smaller pulleys or a longer belt with larger ones. This calculator is a modernised version of that program. It keeps the original method, but works with today’s European classical and narrow V-belts (DIN 2215, DIN 7753-1, ISO 4184), adds a second design method based on standard pulley diameters, and runs in any web browser in four languages.
