The standards carrying the cross slide are segments of a circle struck from the centre of the driving drum, which is necessary to enable the raising and lowering of the cross slide, and maintain a uniform tension on the belt driving the emery wheel without employing an idler wheel or belt Tightener.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose
It is obvious that in this case the driving belt must be made long enough to embrace the pulley when expanded to its maximum diameter, the slack of the belt due to reduction of diameter being taken up by a belt Tightener.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose
A belt Tightener should whenever practicable be placed on the slack side of the belt.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose