ON

THE SHAFTS OF MILLS.

INTRODUCTION.

To proportion the diameters of axles to the stress they have to bear, is in millwork of great practical importance. On the one hand, if the shafts be made too weak, it is evident they must soon give way; and on the other hand, if made too strong, they occasion not only unnecessary expense in the construction of the machinery, but what is in most cases still worse, a waste of power from unnecessary friction. It is therefore desirable, that the millwright should have some rules to guide him in this very important part of his business; a part which, I believe, has

hitherto in most cases been conducted entirely at random.

I shall endeavour, therefore, in this Essay, to give such a practical view of the subject as shall enable the millwright to proceed with greater certainty.

Until of late years most of the shafts used in millwork were constructed of timber. The use of cast-iron in this and other parts of millwork, however, has now become almost universal. For this improvement we are perhaps indebted to those who are engaged in the cotton manufacture. After Arkwright's invention, it became a great object with them to save time in the erection of machinery, and to render it as durable as possible; for every stoppage was attended with great loss, by throwing idle the numbers of people necessary in cotton mills.

Besides the expense attending the repair, what had perhaps still more weight

with them was, that the profits at that period on cotton spinning, were almost unparalleled in any other branch of manufacture.

Another circumstance which tended very much to the advancement of millwork, arose from Mr. Watt's improvement of the steam engine. This enabled cotton-spinners and other manufacturers who required power to work their machinery to carry on their business in towns. Hence power and people might, without trouble, be concentrated on the most eligible spot, and the great expense and disadvantages avoided which are attendant on colonizing the remote situations in which powerful falls of water are commonly found. I shall not here enter into the question of health and morals; but certainly the unprecarious supply and steady exertion of such numerous hands, not only rendered the people more expert in all their operations, but tended very much to the improvement of. their machinery.

The introduction of cast iron then may be considered as a kind of new era in the history of mills. Without the use of this material, it would not have been possible with the same number of operative mechanics to have constructed one tenth of the machinery which has of late years been erected in Great Britain.

CHAP. I.

SECTION I.

General Description of Shafts.

129. The axles used in millwork are commonly denominated, when of a large size, shafts; those which are smaller, are usually called spindles. Thus, for example, we say the shaft of a water-wheel; the spindle which carries the millstone of a corn-mill.

130. When shafts lie in a horizontal direction, they are called lying or horizontal shafts; when vertical, they are termed upright, or vertical shafts.

131. Shafts are usually made of wood, or of iron. Large wooden shafts are generally made either of solid oak, or are built of fir-logs. The scarcity of large oak occasioned the built shafts of fir to come