To be able to guide the belt effectively and safely, the drums should have a certain profile. Generally, the drum width should be narrower than the belt, the central portion cylindrical and the edges somewhat tapered. Tolerance of the drums cylindrical portion is very important for proper guide.
Generally the drums are made of fabricated carbon steel.
The drum face should have a smooth surface ( surface roughness Ra 1,6 micron ).
The tolerance of the drum should be measured as a peak-to-valley measurement while rotating the
drum on a shaft. This is usually done with a dial indicator which is moved transversely across the cylindrical face of the rotating drum. The peak-to-valley reading, should not exceed 1.25 x 10-4 x cylindrical width.