Friction drive pulleys are generally flat faced with no timing element. Crowning pulley faces is not generally recommended. To discuss the reasons why, please contact a Belt Technologies engineer who is familiar with metal belt dynamics. When crowning is appropriate, two geometries may be used: full radius and trapezoidal. A full radius crown is less stressful on the belt, but is more difficult to machine and, therefore, more costly. The trapezoidal crown is more cost effective and works well, but it should be avoided in applications having high belt tensile loads due to stress risers at the crown’s transition points between angled flats. Blending these points can be helpful but does not eliminate the high stress risers.
NOTE: Friction drive pulleys can be designed as narrow bodied rolls. Essentially, the narrow bodied roll is a pulley whose width is narrower than the belt that is running on it. They can make belt tracking easier and reduce total pulley weight as well as cost. The pulley face is typically not less than 1/2 the width of the belt.