worm gear, helix angle

[spears]

Does a worm gear have to be helical? Or can it be a spur gear?

My output shaft angle is 58 degrees instead of the common 90 degrees. I have read from several sources to treat this as a crossed axis helical gear configuration. Crossed axis helical gears with opposite hands, require that

(worm,helix-angle) + (gear,helix-angle) = output shaft angle

According to this equation a spur gear with a helix of 0 degrees and a worm with a helix of, say, 15 degrees would have a output angle of 15. Thus, for a 90 degree angle the worm gear must be helical to compensate for the worm helix angle.

If anyone has information on this subject I would greatly appreciate it.

Thanks
Spears

 

[Philrock]

It is true that you are talking about a kind of crossed helical arrangement. All crossed helical arrangements suffer from point contact, as opposed to the much more desirable line contact of parallel shaft spur or helical arrangments. Neither a helical gear nor a spur gear can serve as a proper worm gear. A true worm gear has curvature across the face width, which makes for line contact with the worm.