Worm gears

[Google Feedfetcher]

Yes the helix angle of the pinion, lets just call it a wheel, is equal to the helix angle of the worm.
If you get a worm, or piece of all thread and offer it up to a spur gear it will sit canted to one side because of the helix angle.
To sit at 90 degrees [ normal setup for worm and wheel l the wheel will have to carry the same angle.



I think this picture off Google images shows it well.

[ArtF]

John:

  Thank you, I handn't looked into them deep enough to realize all that,
the helix is obvious once you consider it , I guess I hadnt till now.

Art

[Nate]

When I tried to generate worm gears for 3D printing, I found that the tooth form changed from the top to the bottom of the gear, though probably not enough to matter much with real world gears.

http://www.thingiverse.com/thing:270309/

I imagine nobody is silly enough to try to produce the pointy bits at the top and bottom on a working part.

[ArtF]

Hi Nate:

  Those look like the pressure angle is way too high, .. or is that on purpose I wonder?

Art

[Nate]

Hi Nate:

  Those look like the pressure angle is way too high, .. or is that on purpose I wonder?

They're designed to mesh with acme screws, so the pressure angle is - nominally - 14.5 degrees.  The thing is that the screw is really only a trapezoidal rack on the plane that contains its axis, and does more interesting things as you move away from that plane.  I think I also profile shifted aggressively so that the gear could 'grab' more of the screw thread.

[ArtF]

>>profile shifted aggressiv ely so that t

Ahh, that would explain it..

Art

[Barbudania]

Oh well, accept my vote for worms also