Mismatched helix angle for gear ratio

[E_Beccles]

I have a gear ratio, 21/50, 2.5 module, 30 degree helix, 35mm wide gears.

When I model these in 3D and align the teeth on one side of the gear, they are then mismatched on the other side. Both gears are the same width and same helix angle. Do I need to adjust the helix angle when I have addendum modifications?

The spreadsheet I am using states the helix angle is 30 degrees, it then also states that the 'base helix angle' is 28.0243 degrees. I can't find any additional description on what this parameter is or how it is calculated. When I use this value on the gear, (with pinion at 30 degrees helix) the gears 'appear' to line up.

Can anyone please shed some light on this situation? Cheers!

 

[mfgenggear]

OK I am forgetting some of my math in formula's with gears , but I believe the lack of response is due to the lack of data given.

Give the #teeth, Diametral Pitch Normal (DPn)= 10.16 or module =2.5 , pressure angle (PAn), Helix Angle = 30 deg.
Major diameter. minor diameter. of both details. I know on external mating parts one has to be Right Hand Helix, the Other L.H. helix in order to mate.

now to focus your question. what are you trying to achieve? design a set of gears with cad?
similar to this

https://www.youtube.com/watch?v=3h8EvOXtziA

 

[mfgenggear]

here is some good info

https://www.bostongear.com/pdf/gear_theory.pdf

 

[tbuelna]

E Beccles-

First, I am assuming these are both external gears with parallel axes. Second, both gears should have the same helix angle, which in your example is 30.0 deg. Third, as mfgenggear noted the mating gears should have opposite helix directions (ie. left hand and right hand).

I'm not clear about what you mean by the teeth of your gear CAD model(s) being "mismatched" on one end.

Are you asking about the 21T pinion and 50T gear in a mated condition, with the end faces aligned and the tooth edge profiles at one end face accurately timed at the mesh location? If so, the pinion/gear tooth edge profiles at the opposite end face will be rotated in opposite directions due to the LH/RH helix lead. However, the timing between the mating gear teeth should still be correct.

If you are asking about an (unintentional) deviation of the tooth profile along the face width of your gear CAD model, then it is most likely a problem with how the CAD model was constructed. Check to make sure the geometry you are using is correct. Are you using the correct tooth profile (normal or transverse)? Also the 30 deg helical curve is defined at the PD cylinder.