Зображення сторінки
PDF
ePub

CHAPTER V

DROP-HAMMERS: THEIR DEVELOPMENT, WEIGHTS, FOUNDATIONS,

AND DIES

The Development of the Drop-Hammer

FROM 1847 to 1862, among the green hills of the State of Vermont, there was located one of the best equipped plants for the manufacture of machine-tools in this country. It was there, in the years 1854 and 1855, that most of the machinery was built for the manufacture of the then celebrated Enfield rifle for the English Government, on the interchangeable system. Previous to that time they made their fire-arms on the "cut and try" plan, or by what we would term in this country hand-work. The parts were made in different shops; for instance, one manufacturer was skilled in making the barrel; another, the stock; another, part of the lock, and so on through the list. The various parts were assembled at the Tower of London, and it was there that the "cut and try" plan commenced, filing a little here, clipping off a little there, with several trials before the parts would go together satisfactorily.

On the introduction of American machinery all this was changed, for it was found possible to machine the pieces of the arms so that the same kind would be exact duplicates of each other; consequently the cost of production was reduced and the quantities in a given time increased over the old method.

To America is due the credit of introducing the interchangeable system in the manufacture of firearms, sewingmachines, watches, etc.

It was necessary to have uniform forgings, so that they could be handled in special fixtures adapted to the different

parts. The art of forging in dies at that date was the weak point. Drop-hammers had not come into use, and all the forgings were made by the old hand swedging processes, represented by Fig. 1. A base of cast iron, with suitable opening in the top for keying the guide-stock and lower die was set up, the upper die being made to work freely up and down in the guide-stock. In the faces of the two dies were cut the forms of the parts to be forged. The power used was hammer and sledge, wielded by the smith and helper.

So far as can be learned, drop-hammers were first used by Colonel Samuel Colt, about the year 1853, in the manufacture of the celebrated revolving firearm that bears his name.

The hammer of the Colt drop was raised by a vertical revolving screw. In the first year of the Civil War, Golding & Cheney obtained a United States patent on a drop-hammer, the principal feature of which was raising the hammer by a leather belt between friction-rolls. These friction-rolls are in use to-day on what are considered the best hammers for dropforging. In other respects there have been great improvements. Some of the latest of these improvements are explained in the following.

Counterbalanced Treadle

This treadle is made from one piece of steel-forging. The advantage of this construction is that it does not become "shackly" from wear, and when the pressure is put on one side the opposite side acts simultaneously, and the mechanism on either side of the machine does its work as it was designed to do. Instead of springs to hold the treadle in a raised position, counterbalance is provided which runs across the back of base and is attached at either end to levers whose fulcrums are pine-driven into the sides of the base, the short ends of the levers having projecting points extending underneath the sides of the treadle and holding it in the raised position desired.

The improvements claimed for the counterbalancing treadle are that the pressure required is the same at the start as

at the finish of the movement of the treadle, and that the construction is such that repairs are not frequently needed, as in the cases where the springs or pulleys and chains are used.

Compound Lever Device for Operating the Lifting or Head Mechanism

This device was designed with a view to lessen the shock of the blow given to the friction-bar by the hammer when in operation. It consists of a clamp on the friction-bar, having a projection on the inner side, which acts as the fulcrum of the lever, whose short end is a fork which engages with pins projecting from the left hand upright, and whose long end is actuated by a pin in the hammer, which pin is placed as near the right hand side of the hammer as is practicable, in order to enable the long arm of the lever to be made as great a length as possible, thereby reducing the speed of the movement given to the friction-bar, and incidentally the shock of the blow.

All this tends to obviate the necessity of repairs, as it reduces the tendency of the friction-bar to become crystallized, and it imparts to all the friction mechanism a moderate, easy movement, which is conducive to the durability of that part of the machine.

Another feature of this device is the ease with which it is adjusted for the different heights from which the hammer falls. There is only one nut to turn, and when this is loosened the clamp is perfectly free upon the bar and will drop from its own weight, or can be raised with one hand. This one nut is sufficient to hold the clamp in place, as the latter is not subjected to the sharp blow as in the old method.

Jointed Swinghead Construction

The main idea of this construction is to lessen the expense of repairs. The two sides of the head are connected by a heavy web at the bottom edges, through which there is a rectangular hole to accommodate the board. The upper halves of the two sides are fastened to the main head-casting

by a hinge-joint at the rear, and are primarily held in place by the small swivel bolts, the same as used on a lathe center-rest, and incidentally by two of the head-bolts which pass through the upper and lower parts as well of the head and through the top of the uprights.

On both sides of the machine, running horizontally through the upper part of the uprights, through the web of the lower part of the head and into the rectangular hole in the latter, good stout bolts are used which hold the upper part of the machine rigidly together, and relieve the head-bolts proper

[graphic][merged small]

FIG. 170.-The first "interchangeable" blacksmith.

from all shearing strain and also obviate the elongation by wear of the holes in the uprights. The eccentrics are made of steel-castings, which are stronger and more durable than bronze or gun metal. These are chambered and babbitt-lined, this lining being easily replaced when worn out. The sliding rear boxes for adjusting the friction are operated in the usual

way.

Paper Pulleys

Experience has shown that iron pulleys are not reliable for drop-hammers. They become crystallized and break, and some one is likely to get hurt. Wood pulleys with iron hubs.

[graphic][merged small]

FIGS. 171 and 172.-Sectional views of drop-hammer.

« НазадПродовжити »