rail 18 by bracket 45 which is adjacent to the shell shaft 34 the idler arms push the idler 38 out so that the distance from the drive pulley 26 to the idler pulley 38 and the distance from the idler pulley 38 to the shell 32 remains the same regardless of the distance from the drive pulley 26 to the shell 32 this idler arm movement could be accomplished by having a spring biasing either of the arms outward however we prefer to move the idler pulley outward by pivoting the two idler arms 42 and 44 between the ring rail 18 and the spindle rail 14 with the arms so positioned it may be readily seen that the total distance from the drive shaft to the idler shaft and from the idler shaft to the shell is always the same also it may be seen for smooth operation it is necessary for the arms to extend outward slightly when the ring rail 18 is in the full top position therefore it is necessary that the length of the spindle idler arm 42 plus the length of the ring idler arm 44 be greater than the distance from the drive shaft 24 to the ring rail 18 the drive belt 36 is trained over the pulleys as seen particularly in fig2 it will also be understood from fig2 there would be one belt 36 for four or more rings 20 a ring drive belt 37 would be used for each of the rings 20 it should be understood that the idler arms 42 and 44 form a portion of compensating means on the frame for moving the idler pulleys responsive to movement of the ring rail so that the belt is.