Thread: Hubs
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Old 02-10-2007, 11:34 PM
toyhatsu toyhatsu is offline
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Join Date: Dec 2006
Location: Colorado Springs, CO
Posts: 63
Default Hubs

I am sure that there are much more qualified people to do a write up on this subject. So please feel free to correct me for something that is wrong.

Small hubs and dies are for producing coins, medallions, jewelry as well as pieces for inlay work. A hub and a die together will produce what I call ( I don't have a technical term) a shell stamping. It is a hollow piece usually made from much thinner material but looks to be solid and much thicker. More on that later.

The late Carl Mcdougal called them hobs and he is the person who I first learned of this process. Hobs and hubs are the same thing. A hub is a read right positive, convex image used to sink dies. Mr. Lindsay's engraved medallion for his fancier AirGraver handles was cut as a hub. This hub was hardened and used to sink a die. From the die the multiple pieces are produced (struck, pressed) then trimmed and finished for the final piece. You can go from die to hub or hub to die. I am used to sinking (cutting) the die in reverse though it is much more natural to engrave or carve a hub. You don't have to think backwards. So most anything small that you engrave or sculpt can be used to produce a die to make multiple copies. This needs to be done on tool steel so that it can be heat treated to Rockwell 65-67. It is then drawn down to about Rockwell 57-60 for a working die for gold, silver, copper, brass etc...or to sink another hub.

The most common use of the hub is in coining. The U.S. Mint's pieces and commerative medallions are sculpted on and rather large (20-24" diameter X 2" thick) plaster basin with a rim. This is where the curved background field comes from. On this basin wax is applied (sheets and blobs by hand) and the sculpting is built up in wax using dental like (and larger) wax and plaster sculpting tools. Some parts are easier to cut in the negative like lettering rather than trying to sculpt them in the positive. A negative plaster is cast from the positive. Then the lettering can be cut into the plaster before it hardens. Then another plaster casting is made to get a positive again. This goes back and forth till the final design is reached. After this (I hope that I get this right) the basin is dipped or painted with beeswax. Copper powder is sifted over the basin to get a thin even layer. The whole thing is then nickel plated to a substantial thickness. This nickel shell is then popped off the basin and placed on a (Victor) Janvier machine which is a very detail oriented reduction pantograph. The cutting of the die takes several days if I remember correctly as the machine goes very slow. The stylus is placed on the periphery of the nickel shell and the cutter on the periphery of the die blank. It slowly spins and each revolution moves closer towards the center. These machines are very accurate and little if any touch up work is needed for the finished die. The die is then heat treated and drawn down to a working Rockwell. From this master die five master hubs are created. I can't remember how many secondary master dies and secondary master hubs are created. The original tooling is put away in storage. From these secondary masters production tooling is produced always making back ups for the future. Dies wear and crack and have to be replaced periodically.

Here is my collection of hubs. Some of them I made and some were salvaged from the scrap metal pile. The dragon hubs and dies were given to me by an fellow employee and were made in Viet Nam. I gave him my tattered copy of Meeks The Art of Engraving as he was interested in engraving and monograms being a jewler. He said that people sit in the dirt on mats all day and cut these hubs by hand, I assume with a hammer and chisel. Then a die is sunk. He no longer works with me or I would get some more information.

There are eight different sets of these dragons.
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Last edited by toyhatsu; 02-10-2007 at 11:50 PM.
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