Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Mismatched helix angle for gear ratio

Mismatched helix angle for gear ratio

Mismatched helix angle for gear ratio

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!

RE: Mismatched helix angle for gear ratio

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

RE: Mismatched helix angle for gear ratio

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close