Sheev

I don't think that there can be any objection to using an eccentric shaft to contribute to the screen out of balance (quite a lot of reputable manufacturers do this) but usually it is not practicable to be able to achieve the full moment required.

For example if your screen weighs 5000 kg and you want to operate at 8mm stroke (0.4cm radius), then the static moment required (from either counterweights or shaft) must be equal to 5000 x 0.4 = 2000 kg.cm.

This could be achieved by either:

(1) an eccentric shaft with say 2.5cm radius where the eccentric mass would need to be 2000 kg.cm/2.5cm = 800 kg.

or

(2) a set of counterweights at say 25cm radius where the eccentric mass would only need to be 2000 kg.cm/25cm = 80 kg. (40 kg per side)

In summary

if you can achieve the required static moment by means of an eccentric shaft without adding much extra weight to the screen - then it is a sensible solution.

However if you have to add significant extra weight to the shaft, then it is not usually economic and the extra weight means shorter bearing life or larger bearing size. ■