Not as common on other makes as one might expect, given the transformation it made to the lathe's capabilities, the compact epicyclic (or planetary) backgear assembly gave a range of slow speeds that allowed screwcutting and the facing of large diameters to be undertaken with a greater chance of success.  The mechanism used on the AA-manufactured Craftsman 109 range consisted of three elements: a gear attached to a 3-step pulley, a carrier with 3 planet pinions and an annulus gear.
The 3-step pulley together with its attached "sun" gear was free to rotate on the headstock spindle. Opposite was a large gear cut on the inside surface of a short cylinder so that its teeth faced inwards (an annulus gear): this assembly was also free to rotate on the spindle. The "sun" gear on the 3-step pulley engaged simultaneously with 3 "planet" gears (called pinions because they meshed with a larger gear) mounted on studs attached to a carrier plate that was both keyed (permanently) to the spindle and locked (temporarily, by a sliding block) to the annulus gear. Because the carrier was both keyed to the shaft and locked to the annulus gear non of the gears could rotate and turning the pulley caused the spindle to rotate giving a direct drive. For any epicyclic gearing to work one of the three gears sets has to be held stationary so that one of the other gear sets can act independently as an input and the third set independently as an output. In the case of the 109 lathe it was the annulus gear that was prevented from rotating (by a 2-position indented pin passing through the front face of the headstock into its face) and the carrier assembly that had to be released so that it could turn independently. The carrier had six slots cut in its periphery into which a block, sliding in a slot cut in the face of the annulus gear, could engaged and so lock them together. The block was clamped in place by a bolt and slackening this let the block slide out of engagement and allowed the carrier and its planet pinions to rotate. With this new arrangement set up turning the pulley caused  the "sun" drive gear to rotate the planet pinions, mesh with the annulus gear and so reduce the drive ratio.
Another AA epicyclic backgear assembly, with the annulus gear held stationary by a clamp, can be seen  in pictures of the company's last lathe, the 109.21290.