Gear Tooth Profile: One of the fundamental s of gear design is the profile of the gear tooth. Gears generally have an involute curve tooth profile. The tangent line of the base circle of the gear and the base circle of the pinion form the line of action for the gear set.
The relationship of the two meshing gears does not change. Their teeth keep them rotating together in the same relative numbers of rotations. The 15-tooth gear always rotates 3 times for every 1 rotation of the 45-tooth gear.
Interference can be avoided by using a higher pressure angle. As higher pressure angle results in smaller base circle and in turn allows more of the tooth profile to be made of involute curve. Another practical way of avoiding interference is by making the tooth of the driven gear as stub.
Drawing meshing gears
- Step 1: Start by drawing a horizontal centre line for both gears.
- Step 2: Draw a vertical centre line for the driver gear on the left.
- Step 3: Calculate the pitch centre distance.
- Step 4: Measure the centre of the driven gear from the centre of the driver gear.
The diametral pitch of a gear is the number of teeth per inch of pitch diameter. Pitch diameter is the pitch circle below. It specifies the tooth spacing along the pitch circle of each gear, which must be the same for the gears to work together. It's used to know that two gears will mesh.
The pressure angle of a spline is the angle between where the pitch diameter meets the involute curve and a tangent point on the base diameter (fig. 4). There are three major pressure angles used in the spline rolling industry today. These angles are 30, 37.5 and 45 degrees.
DIN 5480 was structured to permit easy slip-fitting of components such as, for instance, ball or roller bearings. This condition is met by making the reference diameter equal to the bore of the bearing and then modifying the profiles of the teeth of the hub and the shaft accordingly.
If v = k w /a where a is the distance between the line along which P travels and O, the trajectory of P is given by . Therefore, it is an involute of a circle when k = 1.
In mathematics, an involute (also known as an evolvent) is a particular type of curve that is dependent on another shape or curve. An involute of a curve is the locus of a point on a piece of taut string as the string is either unwrapped from or wrapped around the curve.
INVOLUTE SPLINES. Diametral Pitch (P) is the number of spline teeth per inch of pitch diameter. The diame- tral pitch determines the circular pitch and the basic space width or tooth thickness. In con- junction with the number of teeth, it also determines the pitch diameter. (See also Pitch.)
Module: is the unit of size that indicates how big or small a gear is. It is the ratio of the reference diameter of the gear divided by the number of teeth.
Spur Gear Conversion. (Units in inches)
| Diametral Pitch (inch) | Circular Pitch (inch) | Module |
|---|
| 3.1416 | 1 | 7.58 |
| 3.175 | 0.9895 | 8 |
| 3.351 | 0.9375 | 7.257 |
| 3.5 | 0.8976 | 7.257 |
Involute spline. where the sides of the equally spaced grooves are involute, as with an involute gear, but not as tall. The curves increase strength by decreasing stress concentrations.
