Is the helical gear tooth profile in the transverse plane an involute?

[aujwc]

Colleagues
I have a helical gear. A helical gear has a normal pressure angle which is different to the transverse pressure angle. The tooth profile in the normal plane is an involute.
Question 1:- Is the tooth profile in the transverse plane also an involute?
Question 2:- Is the base diameter in the normal plane the same as the base diameter in the transverse plane?

JWC
Mechanical/Structural
Brisbane, Australia

 

[leisure17]

everything should be true in the transverse plane - I think. The normal plane is then slightly "corrupt" and you have to use the virtual diameters

 

[Occupant]

You can't have it both ways, but leisure17 is correct, the profile in the traverse plane is off.

 

[aujwc]

Colbourne, 1987: "all the geometric relations for a spur gear can be applied to the transverse section of a helical gear".

This is consistent with comment by leisure17.

We therefore calculate the "true" base diameter from the transverse geometry.

When rating the bending strength we use a "virtual" base diameter.



JWC
Mechanical/Structural
Brisbane, Australia

 

[geesamand]

Visually, I like to think of a helical gear as being made from a deck of cards, where each card matches the spur/involute form and the deck is twisted into the helix shape.

 

[mfgenggear]

helical gears are given in normal DP & PA, however all all calculations resultant in the transverse. profiles are mfg & Inspected in the transverse. That why the helix angle is an impotant factor in the calcs.

Mfgenggear