The pom's ability to cut helical gears, let alone hypoid bevels or double helical gears has always been rather marginal, and in the mid-1930's --- effectively non-existent.
A little unkind I think
Leadie. The Napier Sabre powering the Typhoon and Tempest was the most powerful production engine built. While it had gestational problems it became an excellent reliable engine, but its reduction gearbox was never a problem. From "Allied Aircraft Piston Engines of WWII", Graham White.
The propeller reduction gearing exemplified the innovative design and engineering that characterized the Sabre. A compounded “back gear” drove the propeller through four pinions. When multiple pinions drive a single reduction gear, the problem of equal tooth loading becomes a major issue, particularly in a heavily loaded, high-speed application with high torsional vibration such as the Sabre reduction gear. The solution Napier devised was nothing short of inspirational. Each crankshaft drove a pair of straight-cut, first-stage pinion gears, which in turn were integral with a second-stage pinion, which drove the propeller reduction gear. The second-stage pinion gears featured a helix angle, which generated an end thrust as power was transmitted. Herein lay the secret to the Sabre’s tooth load balancing system. The upper and lower pairs of pinions were connected with a centrally pivoted balance beam. Preloaded volute springs acted on the ends of the beam against the pinions, thus ensuring that the helically cut pinions would float along their longitudinal axis as they transmitted the considerable power of the Sabre and guaranteeing equal tooth loading. Even though the Sabre was beset with numerous problems as will be related, reduction gear problems were non-existent thanks to this very innovative piece of engineering. Propeller shaft radial loads were handled by massive roller and ball thrust bearings mounted back to back, the latter also taking care of propeller thrust loads. In addition, a plain bearing was mounted at the rear of the propeller shaft that also transmitted oil to the de Havilland constant-speed propeller.