A good many electrical concerns mount some of their styles of dynamos and motors (especially the light duty, small size) upon two _V_-shaped rails, Fig. 21 (the bottom of the motor or dynamo base being V-grooved for the purpose). The machine's weight and the screws _A_ are counted on to keep it in place. If the machine be properly mounted on these rails, as regards screws _A_ in relation to its drive, the screws reinforce the machine's weight in holding it down and also permit a surer adjustment through this steady holding of the machine.
Fig. 22 shows the machine properly mounted. The belt tension and pull tend to draw _B_ corner of the machine toward the shaft _C_; and screw _B_^1 is there to resist this pull. Owing to this resistance and the pull along line _D_, _E_ tends to lift and slew around in _E_^1 direction; screw _E_^2 is, however, in a position to overcome both these tendencies. If the screws are both in front, there is nothing but the machine's weight to keep the back of it from tilting up. The absurdity of placing the screws at _F_ and _G_, though even this is thoughtlessly done, needs no demonstration.
When putting a new belt on a motor or dynamo, both the driver and the driven are often needlessly strained by the use of belt-clamps, in the attempt to take as much stretch out of the belt as possible. On being loosely endlessed it soon requires taking up; and if only laced, when the time for endlessing comes the belt is botched by the splicing in of the piece which, owing to the insufficiency of the original belt length, must now be added to supply enough belt to go around, plus the splice.
The proper mode of procedure is: Place the motor on its rails or slides 5 inches away from its nearest possible approach to the driven shaft or machine and wire-lace it (wire-lacing is a very close second to an endless belt). Let it run for a few days, moving the motor back from the driven shaft as the belt stretches. When all reasonable stretch is out, move the motor back as close to the driven shaft as possible.
The 5 inches forward motion will give 10 inches of belting, which will be amply sufficient for a good splice; and, further, the machine will be in position to allow of tightening the belt up, by simply forcing the motor back, for probably the belt's lifetime.