• 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 » Unreasonable Backlash

Gear Talk With Chuck
Gear Talk With Chuck RSS FeedRSS

Design / Inspection / Heat Treating / The Gear Industry / Accuracy / Backlash / Center Distance / Mesh / Temperature / Tooth Thickness / Runout / Carburizing / AGMA / Sectors / Mining / Bevel Gears
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.

Unreasonable Backlash

February 21, 2017
Charles D. Schultz
No Comments
Not to worry — no politics here. The “backlash” I want to talk about is the “lost motion” in gear systems. It sometimes seems to rile people up almost as much as politics and I have long been puzzled about the misunderstandings that persist. At one time, AGMA actually included “backlash grades” in the quality standard, and this may be the root cause for confusing “low backlash” with “precision.” While a clock or other timing mechanism needs a minimum of lost motion, the amount of backlash in a power transmission gear is not a reflection of its precision. It is entirely possible for a very high-quality-ground tooth gear to have a wide variation in tooth thickness — a key variable in set backlash. For unidirectional service, where rotation and power flow do not change, backlash is only “active” upon start-up. As long as the teeth are still thick enough to carry the load and the spacing accuracy meets specification, “extra backlash” is not going to cause a failure. Absence of sufficient backlash, on the other hand, can destroy a gearbox in very short order. The forces generated in a tight mesh, or a mesh with debris going through it, are incredibly high. There has to be enough “open space” to account for runout, spacing errors, center distance tolerance, and temperature changes. So how much backlash is enough and how much is too much? It depends on tooth size and application. Process capability will determine the range of tooth thickness for a particular part, but the designer has to establish a lower limit. You can calculate all the variables that could be involved in determining the actual operating center distance. Or, you could work from a “rule of thumb” and vary it with tooth size. I use .030 inches divided by the normal diametrial pitch and have yet to encounter a “tight mesh.” For an upper limit I specify 1.5 times the lower limit. No matter how small the teeth get, I do not go lower than .0015" for minimum backlash. I do not remember ever seeing this information in a magazine article, but you could easily check in the Gear Technology archives.

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