Cycloidal Backgear B2 only

The Pittler B2 differs once again from the normal type of backgear, it is not actually backgear in the recognised sense but performs the same function, it is actually rather cleverly hidden inside the drum next to the pulley shaft. Although von Pittler patented the idea of epicyclic back gear, which in later years was adopted by a number of other manufacturers worldwide inc the Swiss Micron and American Craftsman lathes, it didn't stand the test of time and was eventually discontinued in favour of the more conventional back gearing we still see today.

The drum contains a Sun & Planet system via a fixed annular gear of 66 teeth, two planet wheels and a centre gear of 22 teeth each. Normally the entire drum turns with the cone pulley, by raising a lever on the head-stock it pushes in a catch which locates in the drum which then releases the cone pulley and locks the rim of the drum from turning. The side plate will continue to turn at a slower speed than the cone pulley, the Sun gear being driven by the pulley cone, this revolves the two planet gears around the annular gear on the rim. For one complete turn of the cone pulley the planet teeth will walk round the 66 teeth of the fixed ring, this give it three revolutions on it's axle. In doing so it makes itself a fourth revolution in relation to the centre (sun) gear and therefore giving a total reduction of 4 to 1

The cone pulley is not permanently fixed to the mandrel but is attached only to the centre (sun) pinion of 22 teeth, this therefore powers the two 22 teeth planet gears which revolve on axles fixed to the side plate of the drum , the latter of which is permanently locked on to the mandrel via a lug located in a keyway.

The interior of the B2 back gear drum, the side plate fits and rotates inside the rim.

The belt pulley is held in place solely by the sun gear, the latter of which is not fixed to the drum or mandrel. The annular gear is made of Gunmetal.

On the left shows the interior of the drum and it's side plate, the latter has two axles upon which the two planet gears rotate. The photo below shows the oil screw and the channel to lead oil down to the centre gear.

The locking catch is out for normal use, the pulley is now locked to the drum

Above centre: shows the catch has been pushed in by the lever which is now upright and the outer drum casing now cannot move. The adjoining pulley wheel is free to turn the sun gear which passes into the drum and thus reduces the speed by 4 to1 via the planet gears

Above shows the catch is still locked in but the locking lever is now down. A few turns of the pulley, or by restarting the machine, and via centrifugal force the catch will spring back out and release the backgear and lock the pulley for normal use.