Start of Active profile on Internal Spur and Helical Gears 1

[Spurs]

Can anyone point me to a reference on how to calculate Start of Active Profile on Internal Spur and Helical Gear Meshes?

 

[L17Aurora]

email me mikebull@blueyonder.co.uk

 

[tbuelna]

Spurs,

The active profile of a high-performance involute geometry external gear tooth (spur or helical) is commonly modified at the tip to reduce dynamic meshing loads. Internal gear tooth profiles are also commonly modified to produce a full recess action meshing contact for improved efficiency. So the start and end of active profile can vary, depending upon how much the tooth profile has been modified from standard.

The active profile is the tooth flank surface that starts below the tip break or tip mod, and ends at the root fillet transition point. Or in other words, the surface of the tooth that starts where it picks up the contact load, and ends where the contact load is relieved.

The start and end of active profiles are normally defined by profile tolerance charts shown on your gear drawings. Tip relief and root fillet dimensions can vary, depending upon the tooth bending stresses (high root stresses require a full fillet radius) or type of heat treatment (carburizing requires rounded corners to prevent through hardening fractures) the gear requires.

Hope that helps.
Terry

 

[mfgenggear]

Nice book

Spurs & Helical gear Problems
Copy right by Invo Spline Inc
written by Walter E Dalby

 

[Spurs]

Terry

What I am asking for is a method to calculate the start of active profile given the outside diamters of both gears in the mesh, their tip raddi (ir chamfer) size, and their operating center distance.

The intent of this calculation is to in fact ensure during design that the SAP is always inside the involute form limits of the gear, unless extra tip relief is added for other reasons lke you describe.


mfgengear
I will try to find that book - thanks for the tip

 

[dinjin]

You might check some of the standard gear books by
Dudley and Buckingham and look at True Involute Form
Diameter and Lowest Point of Single Tooth Contact or simply Form Diameter. The SAP and Lowest Point of Single Tooth Contact should be in the Machinery's Handbook. These terms mean the same thing.

 

[L17Aurora]

Spurs, did you get my program?

 

[tbuelna]

Spurs,

Sorry for the tardy response. I understood your question, but the point of my post was that with high performance gears, the SAP and EAP points are where you specify them to be. If you are designing to AGMA standards, AGMA 917-B97 will give you the equations for SAP and EAP on a standard profile involute fine pitch cylindrical gear. Internal gears are covered specifically in section 6.7.2. I'd post the equations, but they would be meaningless to you without an explanation of the many variables involved. You can buy the document from AGMA for $40 if you're a member, or $80 if you're not.

But having said that, most gear tooth profiles employ profile mods like profile shift and tip relief, in order to balance sliding and reduce dynamic meshing loads. Using profile shift to balance sliding is particularly effective with a small diameter pinion driving a large diameter internal ring, as noted in your original inquiry. Dudley's 1994 edition handbook gives a basic approach to profile mods starting on page 3.130.

Good luck to you.
Terry