Wednesday, October 1, 2014

Active Coupling Bore and Keyway Standards - What Are They & Where Can I Find Them?

The first thing to know about coupling bore and keyway standards is that there are quite a few currently active and available. Given your application and the origin of the product/shaft in question, you should be able to quickly determine what standard applies to you. (If not, call an application engineer at a coupling company you trust... and they will quickly point you in the right direction.) 

Active Standards include: 

In North America...

  • API STD 610 - Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries
  • API STD 671 - Special Purpose Couplings for Petroleum, Chemical and Gas Industry Services 

  • AIA/NAS NA0139 - Keyway and Key Slot Dimensions Metric (an Aerospace standard)


In Germany... 

  • DIN 6885-1 - Drive Type Fastenings without Taper Action; Parallel Keys, Keyways, Deep Pattern
  • DIN 7172 - Tolerances and limit deviations for sizes above 3150 mm up to 10000 mm; principles, standard tolerances and limit deviations (ISO 286 Addendum for larger sizes)


In Japan...


And Globally (ISO)...

  • ISO 286-2:2010 - Geometrical product specifications (GPS) -- ISO code system for tolerances on linear sizes (Part 1: Basis of tolerances, deviations and fits & Part 2: Tables of standard tolerance classes and limit deviations for holes and shafts)
  • ISO 3912:1977 - Woodruff keys and keyways
  • ISO 3117:1977 - Tangential keys and keyways

In addition to these active standards, the Mechanical Power Transmission Association's excellent (and free) 18 page "Frequently Asked Questions on Metric Bores and Keyways in Couplings" PDF can be used to discover a number of no longer active (expired or withdrawn) bore and keyway standards. (Note: Unfortunately, the MPTA document does not provide a route to secure these documents... but at least they can confirm the standard you seek did in fact exist at one time.) 

To broadly and briefly touch on bore and keyway standards, the North American (inch/imperial) standards tend to be more straight forward with limited variation (derived off the shaft)... while the metric options tend to be much more diverse (and were largely derived off the bore hole and were fragmented by various national approaches). Case in point, the metric standard (ISO 286), calls out over 100 different shaft and bore tolerances! Fortunately, great strides have been made to popularize a much smaller subset of these metric possibilities...  and, today, many coupling manufacturers default to using just a few metric tolerances as their standard (with Js9 keyways, and H7 clearance fit or P7 interference tolerances for the bore being a very popular default).
And as a final (also free) reference: Lovejoy's Engineering Data PDF catalog, which covers both inch and metric shaft tolerances in great detail on pages ED-10 through ED-20. 

(Bonus Hint: Lovejoy's Engineering Data catalog does comply with and specifically reference ANSI/AGMA 9002-B04 and ANSI/AMGA 9112-A04...and does use Js9 keyways as well as both H7 & P7 as default metric tolerances... so, if your need is narrow in scope, you might possibly consider saving a few bucks by pulling the data you seek directly from Lovejoy.)

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