Transverse Pressure Angle

[gearcutter]

I need to cut some helicals to an old British system; "Sykes". The specs call for 4 DP "Real", 15 deg Helix angle, 20 deg Pressure angle. This works out to 4.141 Normal DP. As there is no chance of getting hold of a hob to do this I'm thinking of roughing out with a 6 module 20 deg hob and finishing the blanks on a gear grinder. The question I have is; Is the Pressure angle for this system in the normal or transverse plane? The drawing doesn't specify which. I'm assuming it's in the tranverse plane but thought I'd better check. Does any one know where I can get more information?

 

[Carburize]

Not an answer to your question but a comment. Are these true Sykes helical gears? - if so they have no apex groove but come together as a pure herringbone. You cannot hob and grind without having some central space for the hob cutter and grinding wheel to exit.

 

[gearcutter]

Carburize,
From what I understand Sykes have several of their own systems. Their Helical and Herringbone systems are seperate from each other. Their Helical system uses around 6 different helix angles rather than just the 2 helix angles that they use for the herringbones. I've also been told that the Helical system is based on a standard British system which quotes the pitch as being in the transverse plane. Please, any one correct me if this is incorect.

 

[diamondjim]

Since they are defining the 4 dp as
real, I would assume the pressure angle
applies in that plane as well.