• TOPICS
    • Design
    • Manufacturing
    • Inspection
    • Heat Treating
    • Lubrication
    • Materials
    • The Gear Industry
    • Gears by Type
  • MAGAZINE
    • Current Issue
    • Departments
    • Archives
    • Subscribe
    • Advertise
  • NEWSLETTER
    • Subscribe
  • VIDEO
    • Gear Technology TV
      • Ask the Expert Live
      • Revolutions
    • Industry Videos
  • BLOGS
  • BUYER'S GUIDE
  • NEWS and EVENTS
    • Product News
    • Industry News
    • Events
  • ADVERTISING
    • Brand Awareness
      • Print: Display Advertising
      • Online: Web Banners & Keyword Banners
      • Online: Native Advertising (Sponsored Content)
      • E-mail: Custom, White Papers & Webinars
      • E-mail: Newsletter Sponsored Content (Native Advertising)
    • Response & Lead Generation
      • Online: Sponsored Content (Native Advertising)
      • E-mail: Newsletters
      • E-mail: Newsletter Sponsored Content (Native Advertising)
      • E-mail: Custom, White Papers & Webinars
      • Online: Buyers Guide
    • Print Advertising
      • Print: Display Advertising
      • Print: MPT Expo Showstoppers
      • Print: Buyers Guide
      • Print: Manufacturing sMart
      • Print: Specifications
      • MPT Expo Show Guide Advertising
    • Online Advertising
      • Online: Web Banners & Keyword Banners
      • Online: Native Advertising (Sponsored Content)
      • Online: Buyers Guide
      • Online: Specifications
    • E-mail Advertising
      • E-mail: E-Newsletters
      • E-mail: Newsletter Sponsored Content (Native Advertising)
      • E-mail: AGMA Industry News
      • E-mail: Custom, White Papers & Webinars
      • E-mail: Specifications
    • Special Promotions
      • Print: MPT Expo Showstoppers
      • Print: Buyers Guide
      • Print: Manufacturing sMart
      • MPT Expo Show Guide Advertising
  • CONTACT US
  • AGMA
    • Membership
    • Events
    • Education
    • Emerging Technology
    • AGMA Media
    • Standards
Subscribe
  • Sign In
  • Create Account
  • Sign Out
  • My Account
Home » Blogs » Gear Talk With Chuck » Facing Down Contact Ratio

Gear Talk With Chuck
Gear Talk With Chuck RSS FeedRSS

Design / Manufacturing / Inspection / Materials / The Gear Industry / Bending Stress / Contact Ratio / Crowning / Helix / Lead / Mesh / Strength / Stress / Tooth Load / Processes / Chamfering / Shaping / Testing / Pitting / AGMA / Standards
Charles schultz
Chuck Schultz is a licensed engineer, Gear Technology Technical Editor, and Chief Engineer for Beyta Gear Service. He has written the "Gear Talk with Chuck" blog for Gear Technology since 2014.

Facing Down Contact Ratio

November 4, 2020
Charles D. Schultz
No Comments
Before we move on from helix angle restrictions, I want to say a few things about face contact ratio. Soon after the appearance of the first helical gear, designers and engineers found an entirely new topic to argue about, i.e. — how many teeth were sharing the load across the face of the gear mesh. With a spur gear, the face contact ratio is clearly zero. If you lay a straight edge on top of a spur gear, you quickly see that the load shifts from one tooth to another rather abruptly. In actuality, there are portions of the cycle where two teeth are in contact, but most of the time a conventional spur gear puts the entire load on one tooth and this “single tooth loading” is the basis of our strength rating formulas. [I have blogged before about my role in destroying the giant strain gauged tooth that was used in the late 1930s to validate AGMA’s understanding of bending stresses. It is one of the biggest regrets of my professional life.] If you repeat that exercise with a helical gear, you can count the number of tooth tips that intersect the straight line and get a good approximation of the face contact ratio. Some gears will not even get to “two” — reflecting a face contact ratio of less than one. Rating standards penalize the designer for this “error” because “true helical action” never occurs; at some point there is a dramatic change in the number of teeth sharing the load. It is “better” than a spur but not truly helical, either. Once you have a face contact ratio of 1.0 or more, the standards for a “helical” gear are applied. So why would you want more face contact ratio? When I started out in 1971, our “family recipe” required a face contact ration of 2.0 or more. Some “experts” thought there was some magic in integral face contact ratio and we put lots of effort into getting as close to 2.0 as possible. Hours of fun were enjoyed debating whether the “magic” would still happen at 1.95, or if the 2.00 had to consider tooth chamfering. You can speculate plenty when there is no funding for research or testing, and no one actually has methods developed for either. What “evidence” we did have was from noise checks and field reports. Keep in mind that gear quality was lower and most U.S.-produced machinery used through hardened gears. We honestly believed that “initial pitting” was beneficial because it “spread the load out” and would eventually quiet them down. You might laugh now, but our servicemen and sales engineers were trained to repeat the “singing gears are happy gears” mantra. All of that predates the first issue of Gear Technology, of course, so you would have to really do some old fashioned library time to find out the reasoning behind the change in design philosophy. Suffice it to say, we did not know what we didn’t know and had no reason to change — until “hard gears” completely turned the gear world upside down.  

Recent Comments

Thank you for this - Happy Saint Patrick's...

Post a comment to this article

Report Abusive Comment

Free Gear Technology Subscriptions
Subscribe
Free Gear Technology Subscriptions
Subscribe
FEATURED VIDEO
  • Marposs
    Marposs OptoCloud EDU
December 15, 2022
RECOMMENDED
  • Precision Equals Performance at ZPE GripTec

    October 12, 2022
    gt0922_Page_28_Image_0003.jpg
  • State of the Powder Metal Industry

    October 12, 2022
    gt0922_Page_30_Image_0001.jpg
  • The Afterglow of Furnaces North America 2022

    October 12, 2022
    gt0922_Page_20_Image_0001.jpg
  • Reigniting the Educational Infrastructure

    December 5, 2022
    gt1122_Page_20_Image_0001.jpg
  • Profile: Continuing Education and Training with the AGMA

    December 5, 2022
    gt1122_Page_26_Image_0001.jpg
  • Reigniting the Educational Infrastructure

    December 5, 2022
    gt1122_Page_20_Image_0001.jpg
  • Profile: Continuing Education and Training with the AGMA

    December 5, 2022
    gt1122_Page_26_Image_0001.jpg
  • Precision Equals Performance at ZPE GripTec

    October 12, 2022
    gt0922_Page_28_Image_0003.jpg
  • Subscribe
  • Advertise
  • Contribute
  • AGMA
Powered byAGMA
Copyright © 2023 Gear Technology
  • Privacy Policy
  • Contact