1552

THEORY AND PRACTICE OF ENGINEERING.

Book II.

them is 2 cwt. lqr. 14 lbs. and that of the wheel and pinion, 3 cwt. Oqrs,ring is shown in the lower figure, with its footsteps or gudgeon, round

The capstan works the chains, whichlead to the middle of the head-post oneither side, and is admirably well adaptedfor its purpose.

The covering plate of the capstan-holeis made very solid, and prevented fromturning round by six projections on itsouter edge.

The bridge and conical roller whichturn the capstan is also of iron, theweight of the former being 2 cwt. 6 lbs.

The pivot working in a recess is some-times so arranged that the cup whichreceives it is let into the stone sill,and prevented from turning by two

Fig. 2881.

26 lbs.

the bottom

which it

works.

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Fig. 2884 pivot.

Fig. 2885. profile.

dovetail pieces at the sides; to attach thepivot to the turning-post, four verticalprojections or dovetails are placed at equaldistances round its upper edge, as shown inthe figure.

The collars to the turning-posts are usuallyof iron, the interior radius of which is shownby the dotted line, and its elevation at theside. The iron rollers under the other postof the gate, which runs on an iron plate, areso fixed that they clear themselves in thegrooves cut to receive them ; they are usuallyfrom 5 to 6 inches in diameter, and run onan iron axle fixed into a frame that receivesthe end of the gate. Where the wheels runupon timbers, the sill is formed of severalpieces, altogether 4 inches in width : theradius of the gates determines their curve,and they are secured by iron cramps to theground timbers or stone sills. Around theheel-posts of some gates is a collar, to whicha rod of iron is attached that passes throughthe entire width of the lock-walls, where it issecured in blocks of masonry, or by formingan eye it may be linked on to another joint,and made fast to an upright post.

In attaching the iron-work to lock-gateswe must be cautious not to weaken theframing, or in any way to obstruct theirmotion; for as they are of course very heavy,

and the lower rails nearly in contact with the bottom or floor of thelock, should they lose their form, the mitre posts by sinking wouldimpede their opening and shutting : as the gates are sometimes' coveredby water and at others left dry, the material of which they are formedshould be carefully selected, and all the metal work applied to them 2890 '

protected from the effects of these alternate changes. To balance the gates and supportthem properly is the best method of preventing their tendency to sink and drag; and ifevery precaution is not taken to make them move easily and readily, they will be a constanttrouble and expense, which can only be remedied by their total removal.

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