CHAPTER XXV. CRANK-HAMMERS.

Power-hammers operated by crank motion, adapted to the lighter¹ kinds of work, are now commonly met with in the forging-shops of engineering establishments. They are usually of very simple construction, and I will mention only two points in regard to such hammers, which might be overlooked by an apprentice² in examining them.

The faces of the dies remain parallel, no matter how large the piece may be that is operated upon, while with a trip-hammer, the top die moves in an arc described from the trunnions of the helve, and the faces of the dies can only be parallel when in one position, or when operating on pieces of a certain depth. This feature of parallel movement with the dies of crank-hammers is of great importance on some kinds of work, and especially so for machine-forgings where the size or depth of the work is continually being varied³.

A second point to be noticed in hammers of this class is the nature of the connection with the driving power. In all cases there will be found an equivalent for the elastic⁴ helve of the trip-hammer—either air cylinders⁵, deflecting⁶ springs, or other yielding attachments,—interposed between the crank and the hammer-head, also a slipping frictional belt or frictional clutches for driving, as in the case of trip-hammers.

1 lighter   

n.打火机，点火器；驳船；v.用驳船运送；light的比较级

参考例句：

• The portrait was touched up so as to make it lighter.这张画经过润色，色调明朗了一些。
• The lighter works off the car battery.引燃器利用汽车蓄电池打火。

2 apprentice   

n.学徒，徒弟

参考例句：

• My son is an apprentice in a furniture maker's workshop.我的儿子在一家家具厂做学徒。
• The apprentice is not yet out of his time.这徒工还没有出徒。

3 varied   

adj.多样的，多变化的

参考例句：

• The forms of art are many and varied.艺术的形式是多种多样的。
• The hotel has a varied programme of nightly entertainment.宾馆有各种晚间娱乐活动。

4 elastic   

n.橡皮圈，松紧带；adj.有弹性的；灵活的

参考例句：

• Rubber is an elastic material.橡胶是一种弹性材料。
• These regulations are elastic.这些规定是有弹性的。

5 cylinders   

n.圆筒( cylinder的名词复数 )；圆柱；汽缸；（尤指用作容器的）圆筒状物

参考例句：

• They are working on all cylinders to get the job finished. 他们正在竭尽全力争取把这工作干完。 来自《简明英汉词典》
• That jeep has four cylinders. 那辆吉普车有4个汽缸。 来自《简明英汉词典》

6 deflecting   

（使）偏斜， （使）偏离， （使）转向( deflect的现在分词 )

参考例句：

• A variety of mechanical surfaces have been employed for deflecting the exhaust jets of solid-propellant rockets. 人们已经用过各种类型的机械控制面来偏转固体推进剂火箭的排气流。
• If she made a leading statement, he was expert deflecting her into more impersonal channels. 只要她一开口，他就会巧妙地把她的话题转到与个人无关的问题上去。