spur gear assembly 420 with a leftward slot 430 that exposes a top portion of the large bevel gear 412 and distally open left and right vertical slots 432 434 that expose top surfaces of a left and right spur gear 436 438 of the dual spur gear assembly 420 in fig1 18 a central beam 440 defined between the left and right vertical slots 432 434 has a t shaped hold down spring 442 mounted on top with its narrow end 444 mounted to a proximal end of the central beam 440 a laterally wider end 446 extends overtop of both vertical slots 432 434 a cyclic spring gate 448 extends laterally to the left and right from a proximal end of the t shaped hold down spring 442 and ramps downwardly and proximally with particular reference to fig1 each side of the central beam 440 has a respective left and right lower pin guides 462 formed as an upper surface of a wider lower portion an upper pin guide 449 extends laterally out from the central beam 440 on each side and is spaced respectively above the lower pin guides 462 470 to form a lower pin channel 451 although only the left upper pin guide 449 is depicted it should be appreciated that the right side includes a mirror image upper pin guide a rear ramped portion 453 of the upper pin guide 449 underlies and supports the cyclic spring gate 448 left and right cyclic arms 450 452 have distal ends mounted on respective ends of a transverse cyclic axle 454 whose central portion passes through a top end 456 of the index.