VARIOUS ROLLER-CHAINS.
The twin roller has entirely displaced the single. The value of the roller depends upon the difference in diameter between the roller itself and the axis on which it turns, the theory being that although there is a rubbing friction on the axis, the motion there is so slight as to be insignificant as respects wear. The smaller the roller the less this theory applies and the less the practical effect in reducing friction. Rollers in a chain are necessarily small; yet when the roller pulls off the sprocket tooth under pressure it is free to turn, and so there must be some lessening of friction—at least, the rollers cannot wear into flat spots as the blocks usually do. The twin-roller was hailed with satisfaction in England, a year ago, the chief mechanical authority in the trade press saying that “after using it for weeks in all sorts of weather we are firmly convinced that it is the chain of the future; in a gear-case it runs as smooth as oil, and even when unprotected and smothered in mud, dirt and grit seem to have little effect on it.” Since then some doubtful or dissentient opinions have been expressed, perhaps because some makers cut up this chain into a shorter pitch, and therefore get it slighter and more exposed to clogging. Without having practical experience of the twin-roller as yet, we strongly incline to agree with the opinion of it just quoted, and all theory is certainly in its favor. It has been regularly used on the Keating during 1897, and seems to be coming on.
BALDWIN
DETACHABLE.
The Thames chain, which is called a “[roller block]” instead of a twin-roller, has the peculiarity of a fixed cross-bar (very poorly shown in the cut) between each pair of rollers constituting a “block.” Thus the “centre block” is claimed to be rigid and the rollers to be kept more free to work; it seems to us, however, that the roller is slightly too small to be in the best proportion to the side plates.