I wanted to exchange some opinions about worm gear enveloping. I am designing a worm gear 3d model and, putting the appropriate amount of thought in it, some interesting points arise. One may either: 1) Envelop (is that right?) the worm gear helix, so that its radius increases from the gear's centre and outward, in a way that matches the perimeter of the spur gear 2) Envelop the spur gear teeth, so that thir angle/helix matches the one of the worm gear 3) Both 4) None (doh!) The question arises when both are done, and it regards the spur gear. Let me call the point at which the spur gear is closest at the worm gear's shaft as "centre". As stated, as much as one goes far away from centre, the worm's helix must reach further from its shaft to touch the spur gear. With a constant circular pitch, that means that the helix angle of the worm is changing (declining as we go centre->edge). So...what is the point to envelop the worm gear too? There is not a helix angle for the spur's teeth that will serve more than a single point (distance from centre). And an infinitesmall angle is enough to reduce tooth touching, from a whole line segment, to a single point, much like it would be if there were no spur gear enveloping at all!