Very rare, and aimed at what must have been very much a niche market, the Boley 4BK was a heavy-duty, plain-turning lathe (that is, without power feeds to the carriage or backgear) fitted to a large cast-iron stand complete with a rugged, built-in drive system. The motor, fitted with a 3-step V-pulley, sat above and drove down to a splash-lubricated gearbox equipped with a combined multi-disc clutch and brake assembly. The mechanism was designed  to absorb the punishment created in a production process were it was necessary to start and stop the machine several times a minute. The whole of the countershaft unit was carried on a large casting that could be adjusted vertically to tension the final-drive belt with the gearbox was carried on its own pivoting plate to set the V-belt. Drive to the bronze bearing supported spindle was by a suitably wide, smooth-running flat belt, the 3-step pulley running in its own bearings (to absorb the belt pull) with drive to the spindle by a peg. For production work a lever-action collet closer was fitted as part of the standard equipment.
Allowing the operator to sit, the front of the stand was recessed, in typical Boley fashion, and reminiscent of those used on other production models such as the 4H, 4E, 4P and RD-25 - and even some versions of the conventional screwcutting toolroom lathe, the 5LZ.
Clamped to the flat-topped, bevelled edged bed by a through bolt, the compound slide assembly had (instead of the traditional "open" variety) a top slide of the ordinary covered type, obviously to protect the ways and screws from wear.
If any reader has a 4BK, or any literature concerning the model, the writer would be interested to hear from you..

The whole of the countershaft unit was carried on a large casting that could be adjusted to tension the final-drive belt; in addition, in order to adjust the V-belt, the gearbox was carried on its own pivoting plate. Final drive to the spindle was by a suitably wide, smooth-running flat belt.