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 Replies: 10 / Views: 1,290 |
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Pillar of the Community
United States
1247 Posts |
Die steel is machined into a cone shape and then polished to mirror finish before that steel is hubbed into a working die. Why is it polished? If it's going to be hubbed into a die won't that polished finished be ground away? This isn't a trick question or anything. I really am curious about this as I was re-reading the Plaid Book last night.
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Pillar of the Community
United States
2724 Posts |
Polishing is done for multiple reasons, but the main reason is for detail. This process is repeated on all working hubs also.
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Pillar of the Community
 United States
1247 Posts |
ND I'm referring to blank steel (or what is referred to in the book as bar steel) that is about to be hubbed. It is first machined into a cone shape. This too is a mystery, although I suspect it is done that way to allow metal to escape. If the hub is sitting on the point of the blank steel then metal being cut or gouged out of the blank has a way of escaping...I guess.
But polishing blank steel doesn't make any sense to me. If you have the 3rd edition of the Plaid book look on page 75. It shows a photo at the bottom of two pieces of blank steel. One dull finish, (apparently not yet polished) and one polished. and the following text: "A machinist buffs and polishes the cone shape until it has a mirror finish and is flawless..." This is the same steel that is going to be hubbed into a working die. Isn't that polish going to be ground away from the hubbing?
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Valued Member
United States
160 Posts |
Possibly to aid in inspection , the sentence you have quoted seems to imply that "flawless"
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Pillar of the Community
United States
2724 Posts |
quote:
Originally posted by longnine009
"A machinist buffs and polishes the cone shape until it has a mirror finish and is flawless..." This is the same steel that is going to be hubbed into a working die. Isn't that polish going to be ground away from the hubbing?
Let me do a better job of explaining. Polishing the steel is for multiple reasons. However, when a metal worker is trying to create a detailed work of art, they need nice smooth sufaces to work with. Polishing will remove small imperfections in the metal and leave behind a very smooth mirrored finish. With every etching that the machines make, the metal is again polished. The polish is ground away, also acting as a lubrication. A flawless surface is needed to ensure that there are no cracks, no weakness, no abrasions. The process of creating working dies is very time consuming. Every detailed must be as close to perfect as possible. If you are working with a "flawless" piece of material, it makes your job easier than trying to work with "rough" or "raw" material. Does that make any more sense? Here is a quote from Q. David Bowers. Some excellent resources are named. Especially, the subjects of how dies were made and how coins were struck have been addressed by several scholars, a short list including Craig Sholley (who has made good use of Mint archives), Thomas K. DeLorey (whose observations of die idiosyncrasies I have long admired), the team of Bill Fivaz and J.T. Stanton, David W. Akers (such as in his die descriptions in the Pittman I and II catalogues), Dr. John W. McCloskey's observations of date logotypes (published in The Gobrecht Journal), and various students of specific denominations and series, ranging from Half Cents upward. I fully expect that more good information will reach print in the next decade than at any other time in the history of our hobby-and this is with full realization that there is already a lot of excellent material available. |
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Pillar of the Community
United States
1247 Posts |
ND and Daveyn thanks for the replies. I'm not trying to be combative with this. I do agree that the blank die would be inspected for defects before spending alot of time hubbing and annealing it. But I still don't see why the steel must have a mirrored flawless surface to be inspected for cracks or flaws. If the surface is clean cracks or defects in the steel should be observable. Here's another crazy question. After the first impression won't the blank steel that is being hubbed now be flat instead of cone shaped? So if another impression is needed to bring up detail you have two flat objects pressed against each other in a hydraulic press under tons of pressure. They would even be locked together with the hub in positive and the die in negative. So how does this new metal being ground away excavate? I know I'm a cynic.  Speaking of which, has anyone actually witnessed the mint's "single-squeeze" hubbing? That is, from start to finish? I have a lot of doubts that this process even exists. And it's not like the Mint hasn't blown smoke up our butts before.  Edited by longnine009
07/30/2005 6:45 pm
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Pillar of the Community
United States
2724 Posts |
I will forward this question over to the mint and see what answer they can give.
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Pillar of the Community
United States
7123 Posts |
The polishing of metal has several effects on metal not the least of which is a semi harding of the outer surface, this may be necessisary to keep the metal from flakeing and chipping during the milling process.
One other after thought, the metal being pre polished allows for a more accurate relief depth to be achieved without having to figure for the fractional removal of metal if polished after machining.IE full relief first run coins before the die would have to be re-polished.
Rick
Edited by Metalman
07/30/2005 10:28 pm
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Pillar of the Community
United States
2724 Posts |
I have forwarded this thread and question to Micheal White of the U.S. Mint. I will post his answer as soon as it is received.
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Pillar of the Community
United States
1247 Posts |
Cool. Is this guy associated with the die shop?
There must be a logical reason they do this. The mint is producing something like 20-30 billion coins a year? We might not think much of the designs, but as production goes it's a lot and they seem to be *acceptable* quality as far everyday use goes. Could they really be that efficient if they were taking wasted steps in their production? There has to be a reason they do this.
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Pillar of the Community
United States
2724 Posts |
Mr. White is the public relations guy at the mint.
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Replies: 10 / Views: 1,290 |
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Posted 07/29/2005 6:05 pm
