picks 50742 = 12·07
For the lower number of picks the motion does fairly well, but for the higher numbers of picks the changes cannot be made with sufficient exactitude by changing a single wheel. Even in the lower picks it is now required to make the smallest fractional changes.
An improved arrangement of wheels is now largely adopted. This is Pickles’ motion. [Fig. 72] shows the train of wheels. The change wheel B is in this case a driven wheel, and therefore if a larger wheel is used it will give a larger number of picks in the cloth, and if a smaller wheel is used it will give a smaller number of picks; so that if the wheels are so proportioned that the change wheel B has the same number of teeth that there are picks per quarter-inch, it will always remain so, whatever size the wheel is. If a 20 driven wheel gives 20 picks, a 30 will give 30 picks, and so on.
The wheel A is also changed, and this is usually called the “standard” wheel. This is a driver wheel, and therefore a smaller wheel gives more picks, and vice versâ. The wheels are so proportioned that if A, the standard wheel, has nine teeth, each tooth in B, the change wheel, represents one pick, and therefore, this wheel being a driven, the number of teeth in it will also represent the number of picks per quarter-inch. If an 18 standard wheel is used, it is obvious that the emery beam will be driven twice as fast, therefore each tooth in the change wheel B will then represent half a pick per quarter-inch. With a 27 standard each tooth in the change wheel B will represent one-third of a pick. With a 36 standard each tooth in B will represent a quarter of a pick per inch.
FIG. 72.
The wheels mostly used are those in the diagram, and supposing we have a 36 standard and a 45 change wheel, and taking the emery beam as 15·05 inches in circumference, we get—
| B | |
| 24 × 45 × 89 × 90 | = 11·088 |
| 36 × 24 × 15 × 60·20 | |
| A | ·166 = 1½ per cent. for shrinkage |
| 11·254 picks per quarter-inch. |
Thus with a 36 standard a 45 change wheel, B, gives 11¼ picks per quarter-inch, or each tooth in the change wheel gives a quarter of a pick per quarter-inch.