Q. David Bowers
The Milling Machine
If you examine a double eagle, or lacking one, a quarter of a dollar, a slight rim will be noticed around the edge, raised a little higher than the device. It is done to prevent the device being worn by rubbing on counters, etc., and also that the coins may be piled one on another steadily. This edge is raised by a very beautiful piece of mechanism called a milling machine, the invention of Mr. Peale; and vastly superior to any other in use.
Some 20 or 30 planchets are placed in one of the brass vertical tubes, of which there are three, for different sized coins. At the bottom of the tube the lowest planchet is struck by a revolving feeder, which drives it horizontally between the revolving steel wheel one side, and the fixed segment on the other. The segment is on the same curve as the wheel, though' somewhat nearer to it at the further end. The planchet is caught in a narrow groove cut in the wheel and segment, and the space being somewhat less than the diameter of the planchet the edge is crowded up about the 32nd part of an inch.
The planchet makes four revolutions when it reaches the end of the segment, and being released from the grooves falls into a box below. The edge is perfectly smooth, the fluting or "reeding," as it is termed, being put on in the process of coining; The work is so nimbly performed that about 120 double eagles, or 560 half dimes, can be milled in one minute. This is a vast improvement on the English milling machine, worked by hand, and operating on but two planchets at a time. (Footnote: A full description of the English process of coining, with engravings of the machinery, can be found in Encyclopcedia Britannica, article "Coinage.")
The planchets being milled are called blanks. They are very dirty and discolored by the processes they have undergone, requiring to be polished before coining. This is done in the Whitening Room, and an exceedingly hot place it is. Sometimes in summer the thermometer will indicate 120 degrees, though the tall man by the furnace declares that it is often at 175 degrees. The room is too small and poorly ventilated for the use to which it is put.
There are two furnaces for annealing the blanks, they being placed in a copper box, with a cover sealed on airtight with clay. Boxes and blanks are heated red-hot, and the blanks tipped into a vat containing a weak solution of sulphuric acid and water, to cleanse them. The stream of water in the other "at is hot, in which the blanks are washed free from the acid, leaving them a beautiful white color, almost like silver.
The curious copper machine, looking like a large revolving squirrel-cage, is the drying drum. Almost half of it is a tight copper drum, into which the blanks from the hot water are placed with a quantity of basswood sawdust. Steam is introduced through the axis to heat the interior, and the drum made to revolve, causing the blanks to roll among the heated sawdust and dry themselves. Basswood dust is used because of its freedom from sap, pitch, or gum of any kind. It is extremely pure. In the language of one of the men, "It ain't got nothing about it but just wood."
When the blankets are dry a door in the end of the drum is opened, allowing them to fall into the sieve, where they tumble about, the dust gradually sifting out, leaving the coin clean. To brighten them they are kept revolving for an hour, and the friction of one upon another gives them a beautiful lustre. It is in this way that pins, brass buttons, and the like are polished.
They are taken from the drying-drum, and heated in a large warming-pan, with steam pipes running under it, until Jessie would hardly hold a handful for the gift of them, though they are all double eagles. They are now ready for coinage, and that prettily painted truck is taking a couple hundred thousand dollars to the other room for the purpose.
How Dies Are Made
Before examining the coining we must visit the Die Room, to learn how the dies are made. A coin has an impression on both sides, requiring, of course, a die for each. These are to be made with extreme care, to be of the finest workmanship, and all exactly alike. Their manufacture is one of the most important operations in the Mint.
Look at the bas-relief of Liberty on one side of a coin. It would be exceedingly difficult to design this in hard steel and of so small a size; so they first make the design in wax, probably six times as large as the coin, by which means the beautiful proportions can. be obtained .. From this a brass cast is taken, and reduced on steel to the size of the coin by a transfer or reducing lathe. This ingenious instrument was introduced from France by Mr. Peale, who also operated it for some time.
The brass cast is fastened to the large wheel at the right hand side of the lathe. On the small wheel to the left of the cast is fastened a piece of soft steel, on which the design is to be engraved. Both of these wheels revolve in the same .way and at the same speed. There is a long iron bar or lever fastened by a joint to an iron support at the extreme left, which runs in front of the two wheels. A spring at the upper end draws it in toward the wheels. Fastened to the lever is a pointed steel stub, which touches the cast.
A very sharp "graver" is fastened to the lever below, which touches the steel. The wheels revolve, and the stub, when it is pushed back by the heavy relief of the cast, forces back the lever, which draws back the graver, and prevents it cutting the steel. So where there is a raised place in the cast the graver is prevented from cutting into the steel, but where there is a depression in. the cast the graver cuts the same in steel. As the lever is jointed at the left, the nearer the graver is placed to that end the less motion it will have. So that the distance of the steel from the joint regulates the proportion of the reduction from the cast.
After the graver has cut one small shaving around the steel a screw is turned, which lowers the right end of the lever slightly, just enough to allow the graver to cut another shaving; and the stub to touch the cast a very little further from the centre. Thus the graver cuts a very little at a time; but the work is cut over several times, until the design is sufficiently blocked out. This machine will not finish off the die perfect enough to use; but it reduces the design in perfect proportion; and performs most of the rough work. The original dies for coins being now all made, the lathe is used mostly for medals, of which a great many are struck, by order of Congress, for various purposes. A very fine one was presented in the Japanese while they were in this country. There is now in the machine a cast of Washington's bust, merely to show how the cast is placed.