Minimum Belt Wrap and Tooth Engagement

Did you know that synchronous belts need a minimum amount of wrap along with a minimum amount of teeth in mesh to transmit rated loads?  The minimum teeth required in mesh to achieve rated drive capacity is 6 teeth.  Anything less than 6 teeth reduces rated capacity significantly.  In fact, for each tooth less than 6, you lose 20% of the rated load!  This means at 4 teeth, you’re already down 40% of the rated load capacity!  And as mentioned above, this isn’t the whole story.  Even if you have 6 teeth in mesh, but you have less than 60 degrees of wrap, you may have belt problems.  This really only applies to drives with more than two shafts.  Idlers that do not transmit load do not have a minimum tooth engagement or degree of wrap required.

Minimum Belt Wrap and Tooth Engagement

Synchronous belt horsepower ratings listed in our catalogs are based on a minimum of six teeth in mesh between the belt and the sprocket. The ratings must be corrected for excessive tooth loading if there are less than six teeth in mesh. The number of teeth in mesh can either be calculated using Design IQ or the simple formula below

Where:                   D = pitch diameter, large sprocket, inches

d = pitch diameter, small sprocket, inches

C = center distance between shafts, inches

Ng = number of grooves in small sprocket

In cases where fewer than six teeth are in full contact, 20% of the horsepower rating must be subtracted for each tooth less than six not in full contact.
In addition to the number of teeth in mesh, some drives with more than two shafts may have a greater potential for the belts to ratchet where loaded sprockets have six teeth in mesh, but a small arc of contact. In order to minimize this condition, each loaded sprocket in the drive system should have an arc of contact, or belt wrap angle, of at least 60 degrees. Non-loaded idler sprockets do not have tooth meshing or wrap angle requirements.

Poly Chain GT2 Sprocket Specifications

Poly Chain GT2 sprockets are manufactured to close tolerances to ensure proper drive alignment, tooth engagement, and overall drive performance.  Modifications such as reboring may result in unsatisfactory results in the belt drive system.  Strict adherence to the standard tolerances outlined below is highly recommended.

For any additional questions feel free to look through our other blog topics or contact us at ptpasupport@gates.com or 303-744-5800.