# How to add rotate pdf page without turning the material

This article how to add rotate pdf page without turning the material about mechanical gears. Two meshing gears transmitting rotational motion. Note that the smaller gear is rotating faster.

Since the larger gear is rotating less quickly, its torque is proportionally greater. One subtlety of this particular arrangement is that the linear speed at the pitch diameter is the same on both gears. The teeth on the two meshing gears all have the same shape. An advantage of gears is that the teeth of a gear prevent slippage. In transmissions with multiple gear ratios—such as bicycles, motorcycles, and cars—the term “gear” as in “first gear” refers to a gear ratio rather than an actual physical gear.

Its time of construction is now estimated between 150 and 100 BC. Internal gears do not cause output shaft direction reversal. They consist of a cylinder or disk with teeth projecting radially. These gears mesh together correctly only if fitted to parallel shafts. No axial thrust is created by the tooth loads. Spur gears are excellent at moderate speeds but tend to be noisy at high speeds.

The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. In the latter, the shafts are non-parallel, and in this configuration the gears are sometimes known as “skew gears”. The angled teeth engage more gradually than do spur gear teeth, causing them to run more smoothly and quietly. In spur gears, teeth suddenly meet at a line contact across their entire width, causing stress and noise. Spur gears make a characteristic whine at high speeds. The crossed configuration is less mechanically sound because there is only a point contact between the gears, whereas in the parallel configuration there is a line contact. This is the case with the gears in the illustration above: they mesh correctly in the crossed configuration: for the parallel configuration, one of the helix angles should be reversed.

The gears illustrated cannot mesh with the shafts parallel. Double helical gears and herringbone gears are similar, but the difference is that herringbone gears do not have a groove in the middle like double helical gears do. Double helical gears overcome the problem of axial thrust presented by single helical gears by using two sets of teeth that are set in a V shape. A double helical gear can be thought of as two mirrored helical gears joined together. This arrangement cancels out the net axial thrust, since each half of the gear thrusts in the opposite direction, resulting in a net axial force of zero. This arrangement can remove the need for thrust bearings.