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360-degree rotation

Q: Why do some stringing machines have the tension head so high that it’s in the way, so you can’t rotate the racquet 360 degrees?

A: When you pull tension on the string with the tension head at the same level as the stringbed, you don’t have the friction of the string rubbing against the grommet. The lower the friction, the more accurately the string can be tensioned. This is why on some of the more expensive electronic machines, the tension head actually rises up to the level of the stringbed during the tensioning process, lowering again after tensioning to allow racquet rotation.

If you want to get really technical, you also get some tension loss due to the “cosine effect,” which comes from the difference in angle between the string and the angle at which you pull the string, which is whatever angle there is between the edge of the frame and the tension head. Stringing machines with the tension head at stringbed level, and those with tension heads that rise up during tensioning, pull with less angle between the stringbed and the tension head, reducing both the friction and the cosine effect, for greater accuracy.

From the January 2006 issue
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