. The Locomotive. vere enough to wreck the best of designs. The illustration shows acrosshead that was broken by an improperly fitted key. There are a few points regarding this fitting of the key in the cross-head that require particular care. If a rectangular key is used thecorners should be relieved because it is difficult to obtain a perfectlysquare cornered hole in the crosshead. A key with square cornerswill almost certainly produce the effect shown in Fig. 5, which condi-tion cannot help but set up stresses tending to shorten the life ofthe crosshead. An excellent way to avoid any such t
. The Locomotive. vere enough to wreck the best of designs. The illustration shows acrosshead that was broken by an improperly fitted key. There are a few points regarding this fitting of the key in the cross-head that require particular care. If a rectangular key is used thecorners should be relieved because it is difficult to obtain a perfectlysquare cornered hole in the crosshead. A key with square cornerswill almost certainly produce the effect shown in Fig. 5, which condi-tion cannot help but set up stresses tending to shorten the life ofthe crosshead. An excellent way to avoid any such trouble is tomake the key with full rounded edges as shown in Fig. 6. Of coursethis requires possibly more time to fit than a rectangular key but thestresses are more equally distributed. If a rectangular key cannot beavoided it should have the corners relieved. It is not always easy to separate a rod and crosshead when theyhave been drawn firmly together on a taper joint. For such work a 40 THE LOCOMOTIVE. [April,. driving out set of keys is very helpful. This set is composed ofthree specially formed pieces which are shown in Fig. 7 on Page 40assembled in place and ready for use. By striking on the centerwedge, B, the joint may very readily be eased up. Some mentionmight also be madeof the keying ofwheels and pulleysto shafts. The func-tion of a key usedfor this purpose isto prevent turningbetween the wheeland the shaft, end-wise motion or slid-ing usually beingprevented by setscrews or by thecompressing of asplit hub on theshaft. For this rea-son the key should be a close fit on the sides but should have a clear-ance at the top. If this clearance is not provided, the load, whenthe hub bolts are tightened up, will be concentrated over the key,and the stresses tending to break the hub will be very much greater than if the load wereequally distributed overthe shaft. The illustra-tion herewith shows aflywheel hub that wasbroken in this key had first beendriven into plac
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