Worm gear drawing - complete, or incomplete

[Tmoose]

A customer reports the steel worm wears at a rate of about 4-1, so we have sold them 4 worms that fit fine, but now need a replacement worm gear for their coal stoker drive.
The original drawing dates from 1922, so it seems likely we have supplied a successful worm gear or two over the years.

The new worm gear reportedly does not mesh with the worm we provided. I will find out more about exactly what that means.

As a start, Does the attached drawing contain all the info needed to make a worm gear?
I am questioning the lack of "helix angle," but am a complete novice in this gear stuff.

Also, the reading I have done suggests I need to ask the machine shop if the worm gear is crowned, and if they used a hob, what the diameter of the hob is, as a worm gear/wheel made with a hob with the identical pitch diameter as the working worm is crownless, and is very difficult to assemble.

thanks,

Dan T

 

[3DDave]

The helix angle doesn't seem as much a problem; I didn't see a pressure angle, but that file was too blurry to make out all the details. You know that the mating worm is 38 teeth over a certain pitch line; Pi*36.29 = 3 inch per revolution on a blurry pitch radius.

 

[spigor]

The most important parameters I didn't see on the drawing is number of starts of the worm and the pressure angle.
The hob diameter must be bigger than the worm by amount in which the desired bottom clearance plays the most important role, but not solely decisive. Typically the hob must be 3" TCP not 3"CP and you need to have a special designed hob for the worm gear unless you know ways to go about it. Also, the worm gear could be cut 14.5PA. Do you have a drawing of the worm?