104 TECHNOLOGY. 
ance of the rim of the coin, the edges are polished by passing them through 
a machine, seen in jigs. 17 and 18, similar to the milling machine, the 
edge of the disk, w, and the corresponding concave being smooth, so that 
the edges of the coins, as they are carried through by the revolution of the 
disk, w, are polished and compressed. 
5. Srampine. The coins are now to be stamped with their appropriate 
devices upon both surfaces. P/. 20, fig. 34, is a section of the principal 
parts of a stamping machine constructed by Gengembre in Paris. A reci- 
procating rotary motion is communicated to the triple-threaded screw a, 
within the female screw n, secured to the frame of the machinev ; beneath the 
screw are the dies c and Pp, between which the blanks are placed, and as 
the screw a is turned, it descends upon the upper die and presses it down 
upon the blank, which is thus stamped upon both sides. That the coin 
may not lose its circular form, the lower die is surrounded by a steel 
ring which just incloses the coin at the moment it is stamped, and 
retires again that the coin may be withdrawn. That no damage may 
arise to the machine should the coin fail to enter the ring, the latter is 
placed upon springs that it may be forced down, and only the blank be 
injured. Sometimes the coin is surrounded by a ring made in sections, 
which are brought together at the instant the coin is stamped, and thus 
the inscription upon the rim of the coin is formed at the same time (pl. 20, 
Jigs. 82 and 33). 
After the stamping-screw a (jig. 84) rises, the upper die and the parts 
connected with it are raised by the spiral springs ss, to make room for the 
next blank. In many of the common stamping machines, the blanks are 
placed upon the lower die, and removed again after they are stamped by 
hand. In the better machines, however, this is all done by machinery. 
The apparatus which effects this is called the carrier, and is operated by the 
vertical motion of the screw-stamp. ‘This carrier first moves backwards to 
take up the blanks, then forward, gliding across the ring round the lower 
die, into which it lets the blank fall; after the coin has been stamped, the 
carrier strikes it and casts it out of the machine. This is effected by a con- 
trivance (fig. 27) called the conductor, on the front edge of the carrier. 
Fig. 21 is Boulton’s stamping mill in the London Mint, which will not 
require a detailed description; jig. 22 is the guide ring and set screws for 
the top boxes of the stamping screw; jig. 23 is the box for the upper die; 
jig. 24 the box which encircles the upper die; jigs. 25, 25 a, 256, 25 c, are 
the details of the stamping ring; jig. 26 is the box for the lower die; jig. 27 
the crescent-shaped conductor on the carrier, which has charge of the pre- 
pared coin ; figs. 28, 29, and 30, show the details of the carrier ; jig. 31 is the 
lower box for stamping with a divided ring; jig. 32 is a section of the 
divided stamping ring; fig. 33, bottom view of the stamping ring ; jig. 35 is 
a view of a stamping machine in which the die is worked by the crank e, 
and levers @’, c, and which operates without the violent shaking produced 
by the machines worked by levers. 
In the principal mints the machinery is driven by steam, the pressure of 
the air being very ingeniously employed to transfer the effective power of 
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