246

MODERN STEAM PRACTICE.

wrought-iron straps and jibs and keys for adjusting the brassbushes; suitable lubricating cups are fitted to the straps.

The main cranks are of cast iron, but most engineers wouldprefer them of wrought iron, as they are much stronger and betteradapted for engines subjected to severe shocks. They are usuallybored out and shrunk on the shafts hot; but when they are forcedon cold with an hydraulic ram the material is not so much strained,while the holding power is equally good. The cranks are furthersecured with a single key, fitting into a recess planed in the shaftand slotted out in the crank eye. The crank pin is slightly taperedin that part fitting into the hole in the crank, and is forced on andthen rivetted at the end, a part being turned out for this purpose;this makes very secure work. In some recent examples the cranksare formed of discs of cast iron, with a side flange on the circum-ference of the disc, strongly ribbed to the boss at the centre. Thisplan balances the engine better than the single crank arm. Thecrank pin is secured by means of a nut and feather or key on thepin.

The main pillow blocks are separate castings, fitted with brasses,and caps arranged at an angle, so that the brasses are adjusted inthe direction of the greatest strain. The bottom of the blocks areplaned, as also the fitting strips on the bed plate, which has extrastrong joggles cast on it for driving in wedges, thus taking theshearing stress off the pillow block holding-down bolts.

The bed plate is a strong frame of a box section, open at thebottom; it is tied at the ends and at the middle in the casting, andshould be strengthened with cross feathers between the sides, havingall the necessary joggles and fitting strips for the cylinder, pillowblock, pumps, and other minor fittings. There should be at leastfour large holding-down bolts on each side of the frame, passing downthrough holes left in the foundation, and secured on the under sidewith a plate and key for each bolt. The foundations should con-tain suitable man-holes, so that these bolts can be adjusted at anytime. In some instances the plates at the bottom of the foundationare carried across, embracing two bolts; by this means a foundationof brickwork laid in cement is firmly bound from top to bottom.When brick is used for the foundation it is preferable that a layerof stone-work or balks of wood be placed on the top, for the mainbed plate to rest on.

The main shaft of the engine should be of wrought iron, and all