Friday, July 23, 2010

Belt Profiling

If you know anything about synchronous belts you'll know that belts come in different sizes. This can mean different widths, lengths, and pitches (spacing between teeth). So if you know these three dimensions of a belt it means you can go to the store and pick up a new one right? Wrong. One other important characteristic you need to know about a synchronous belt is the tooth profile.

The tooth profile is going to identify the shape of the tooth whether it's flat, round, or a combination of both. Industry profile standards were created for belt manufacturers to simplify the process of designating a belt type. For example "Timing belts" have flat or trapezoidal teeth where "HTD belts" have round teeth. As technology has advanced, so too has the synchronous belt tooth profile. Multiple variations of tooth profiles have emerged from different manufacturers such as GT, RPP, HTD, and STPD profiles, as seen below.

Because of the difference in shape amongst the profiles, not all belt tooth profiles work in each others sprocket grooves. This is one very common mistake made with synchronous belt drives. A belt is replaced with another one that has a different tooth profile and it fails much faster than the previous belt. This is because the tooth is not sitting into the sprocket grooves properly so it's not transmitting the load as it was designed to.

Now this doesn't mean that two different belts are never compatible with each other. There are actually quite a few that you can use as drop in replacements for one another, but you need to know which ones will work and which ones wont. Gates has published a catalog just for this problem called the Belt/Sprocket Interchange Guide. In the guide you can look up which belts will work in different sprocket configurations and which ones will not with a description of why or why not. Of course its always recommended to use the belt that matches the sprocket grooves, but sometimes this will not be an option. The Gates Belt/Sprocket Interchange Guide can be found online at

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