David Henshaw Whittemore (1832-1892) designed The Union Apple Parer to pare in the forward and reverse directions (Whittemore, 1866). The drive and intermediate gears have a series of cams along their inside. The drive gear has 4 cams that turn the intermediate gear. The intermediate gear has 10 cams that are so arranged as to rotate the paring knife segment gear clockwise to pare an apple from stem to calyx and then counterclockwise to pare a second apple from calyx to stem.
The drive gear has 36 teeth that engage with a pinion gear with 12 teeth. With each turn of the drive gear the pinion gear and fork rotate three times. Three turns of the drive gear rotate the apple nine times as it is pared.
The Union Apple Parer design evolved over time. The initial Union paring arm was designed with a one-inch shaft oriented at 90 degrees to push the paring arm into a position so that the pared apple could be removed (see third video on modified helical gears). This somewhat fragile design was replaced with a plate that not only provided a sturdy guide for the paring arm but also shielded the paring arm gear from juice and parings. The video above shows the first Union design to utilize the plate before the push-off was added.
The Union and Hersey's Double Action Apple Parer were the first parers designed to pare apples in both the forward and reverse directions.