Abstract: A driving gear assembly for a double helix extruder. The assembly includes a multiple power path from a transmission gear to produce synchronism in the extruder helix shafts. The structure of the gearing enables a simple adjustment of the proper mesh of the extruder helices when mounting the gearing by mere disengagement and re-engagement of a (normally not disengageable) tooth coupling.

Abstract: A driving and a driven spur gear, lying in a common plane, are operatively coupled with each other through the intermediary of an idler gear in mesh therewith, the idler gear being radially shiftable against a resilient force in the common plane of rotation. The tangent to any tooth flank of both the driving and the driven gear at its point of contact with a tooth of the idler gear includes a pressure angle .alpha. with the common diameter of the meshing gears; the angle .delta. between the two common diameters should be so chosen that the two tangents are substantially perpendicular to each other, with .delta. - 2.alpha. = 90.degree. for rotation in one direction and .delta. +2.alpha. =90.degree. for rotation in the opposite direction.