Worm tooth angle

[Trukker]

We use a worm and worm gear on a brake adjuster essentially as static load members. I am working on a modified design of worm with buttress thread. I tried to verify my calculation method using the existing drawing. I calculated the pitch from the worm gear Pitch dia & no of teeth. Using this as axial pitch for the worm I calculated the "tooth angle" ( lead angle) as Pitch/(Pi x Worm pitch dia). I got a higher value than in the drawing.
I would appreciate any suggestions

 

[Matt51]

The lead angle is the arc tangent of of what you calculated. If you meant arctan, then there might be an error on your drawing. Or, if your worm has two threads, then you would add a two to the numerator.

 

[Trukker]

Hi Matt51
Yes, I used arctan - just missed that in the post. I went back and checked the numbers - it works out OK now. I must have used the root dia instead of pitch dia.
Thank you for your help