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Old 03-25-2008, 08:02 PM
Tom Maringer's Avatar
Tom Maringer Tom Maringer is offline
Steel
 
Join Date: Mar 2008
Location: Springdale Arkansas
Posts: 48
Default Re: Engraving coining dies

Quote:
Originally Posted by llott
Count me in. I definitely want to learn more about engraving coin dies. Want to learn all aspects from die material selection, to engraving techniques to heat treating the die to stand up to coining. Larry
Hi Larry:
The best place to start is the book I just referenced. It's a good general intro but does not get into some of the nitty-gritty like steel selection etc.

The best steel is D-2. Coin dies is what it was designed for, and it's still the steel that the US mint uses for all their dies. The downside is that it's expensive and rather a pain to heat-treat. A-2 is a good intermediate... O-1 is the next on the scale, and then finally the W-1.

Frankly, for most of what I do I use plain old water hardening tool steel. The main reason is because it's cheap and you can get a good hardening without messing up the engraving... because of course you do all the engraving and other die work before heat-treating. I only use the higher grade steels for critical dies that have to last a long time or which have some sort of unusual features that require extra strength.

The second thing is to choose the diameter of the steel. You will need die-holders that mount to your press to align the dies for striking... if you make your dies random sizes you'll need lots of holders. You can't buy them and they are a pain to make... so you standardize. I have settled on two sizes... 2.00" round stock for the bigger coins (quarter size to dollar size) and 1.25" round for smaller coins (dime to penny size). Those are standard sizes available as precision-ground stock from many dealers.

When I job out die engraving I will usually supply the die blank, which is turned on a lathe with a flat base and flat top, sometimes necked down, sometimes with a hobbed image in the center, and sometime already rimmed on the lathe. That leaves the "field" for the engraver to work with.

Hobbing is perhaps the most misunderstood aspect of traditional diesinking. For that reason it has been my especial study, even moreso than engraving. (because I know there are lots of people who know engraving and I can learn it whenever I want, but the number of people who know hobbing is fewer every day).

The idea is that, counter to intuition, annealed tool will flow like soft copper IF YOU PUSH ON IT HARD ENOUGH. So you can make a design in the positive, and PRESS it into the annealed tool steel blank to make and impression. Then you turn down the face, bring the (now distorted) die blank back to cylindrical, and add other design features. The detail that is possible is really quite incredible with this techique. It is safe to say that the majority of old-time die engravers spent much more time working on master hubs (which would then be used to press out dies) than they did working directly on the dies in the negative.
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