Fig. 2492.
It is obvious that if the joint faces of the brasses are left open and oil be supplied to one brass only, a great part of the oil supplied will pass out between the joint faces before reaching the other brass, and one brass will therefore be better lubricated than the other, unless each brass be lubricated independently. Even in this event, however, a great part of the lubricating material will be lost from finding rapid egress through the opening of the brasses. This may be to some extent prevented in brasses whose joint faces lie horizontally by chamfering the edges of the bore so as to form a trough extending nearly to the ends of the brass, as shown in [Fig. 2492]. Now it is obvious that the oil hole must always be above the journal or bearing bore; hence when the joint faces stand horizontal, the oil hole should come through the crown of the brass, and oil grooves are necessary to convey and distribute the oil along the bore. A single groove, as in [Fig. 2490], is sufficient for light duty, but for heavy duty a double groove, such as shown in [Fig. 2491], is necessary.
Fig. 2493.
When, however, the joint faces stand vertically and come brass and brass, the oil hole may be filed half in the joint face of each brass, and the edges chamfered off as in [Figs. 2492] and [2493], a b representing the chamfers and c the oil hole, the two brasses put together appearing as shown in section in [Fig. 2493].
This plan has the advantage that the oil is confined within the journal, except in so far as it may in time work through the ends of the journal bore, while there are two oil grooves provided without reducing the bearing or bedding area of the brass. When the oil grooves run diagonally, as in [Fig. 2491], there is the advantage that the length is greater, and lying nearer to the plane of rotation the oil flows along the grooves easier, being assisted by its frictional contact with the journal, but on the other hand the bearing area of the brass on the journal is so much the more reduced.
Oil holes that are not provided with oil cups should be provided with small wooden plugs, which will serve to keep the dirt and dust out; they should be made of as small diameter as the quantity and nature of the lubricant to pass through them will admit of, and should be left plain at the top and not countersunk, because the countersinking simply forms a dish that will collect dust, &c., which the oil applied will carry down into the bearing.