T–58 When identifying a shaft center location, each X-Y coordinate is specified with a measurement in the "X" as well as the "Y" direction.  This requires a horizontal and vertical measurement for each shaft center in order to establish a complete coordinate.  Either English or Metric units of measurement may be used. A complete coordinate is specified as follows: (X, Y)      (13-1) where:    X  =  measurement along X-axis (horizontal) Y  =  measurement along Y-axis (vertical) In  specifying  X  and  Y  coordinates  for  each  shaft  center,  the  origin  (zero  point)  must  first  be chosen as a reference.  The driver shaft most often serves this purpose, but any shaft center can be used.  Measurements for all remaining shaft centers must be taken from this origin or reference point.  The origin is specified as (0, 0). An  example  layout  of  a  5-point drive system is illustrated in Figure 28. Here, each of the five shaft centers are located   and   identified   on   the   X-Y coordinate grid. When specifying parameters for the movable  or  adjustable  shaft  (for  belt installation and tensioning), the following approaches are generally used: Fixed  Location:      Specify   the nominal shaft location coordinate with a movement direction. Slotted  Location:      Specify   a location coordinate for the beginning of the  slot,  and  a  location  coordinate  for the end of the slot along its path of linear movement. Pivoted  Location:    Specify  the initial shaft location coordinate along with a pivot point location coordinate and the pivot radius. Performing  belt  length  and  idler movement/positioning  calculations  by hand  can  be  quite  difficult  and  time consuming.          With     a     complete geometrical  drive  description,  we  can make  the  drive  design  and  layout process quite simple for you. SECTION 14    BELT PULL AND BEARING LOADS Synchronous belt drives are capable of exerting lower shaft loads than V-belt drives in some circumstances.    If  pre-tensioned  according  to  SDP/SI  recommendations  for  a  fully  loaded  steady Fig.  28    Example of 5-Point Drive System (-4,7) (8,0) (3,-1) (2,2) (0,0) -2 2 4 6 8 10 -2 2 4 6 8 10 -4 -6 -8 -10 -4 -6 -8 -10 Y X