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Forward
Hello to everyone once again! I'm
still in school, by the skin of my teeth as it were. Well,
so far I have appreciated this joint learning experience however, it
appears a bit one sided. I have appreciated the opportunity
to share with you and I have been looking in vain for any written response. I
haven't seen one. However, a big coinmonger “MONGER”
goes out to Bill J. for his continued support and lively discussions.
It is certainly sad that there appears to be
no interest especially since this month prize was a certified double
die Stone Mountain. Don't get me wrong, I can't be at the
meetings for a while so I had thought that this would be a great way
to keep up with all my numismatic friends. In any event,
writing a news article is a lot of work, and if there is not much interest
I could sure use the study time somewhere else if you know what I mean
Introduction
Last month we covered the introduction of the
galvano. This month we will look at the die making process,
specifically at the very first stage. We will be looking
at the process of cutting an impression into a piece of tool steel. Anyone
know what we will be making? (Homework question one.)
Okay, once the epoxy shell has been made (the
galvano as it used to be called) we note that its size is much too large
to simply make a die from. How large is the epoxy shell? (Homework
question two, hint; it is in last month's newsletter.) Besides,
one of the things the Mint is big on is originality. So,
the next step is to reduce the image, but how do we do it? (Homework
question three.)
The Master Hub
Understanding the design process is the key. Do you remember
Alan Herbert's PDS System and the three production areas in the mint,
planchets, die manufacture and striking? Which would you
place this process in? If you said die making, then you are
correct! The plaster disc is placed in a Janvier reducing
lathe. These are very special German designed lathes that
incorporate the use of a fulcrum to trace and cut a pattern. Did
you ever see a tracing arm in school? on the one end was
a tracing stylist that you traced the picture with and the other was
a pencil that made an etching exactly like the photo. You
could increase or reduce the size of the picture by moving the pencil
along the etching arm either up or down. This simplified
description will help explain the Janvier reducing lathe.
Instead of a pencil the Janvier reducing lathe
uses a cutting bit that cuts an exact image in relief on a piece of
tool steel. Remember relief means that the image is raised
just like on a coin. The piece of tool steel is the exact
same size as the coin it represents. The Mint named the process
of cutting the steel the reducing stage. Remember that the
lathes that are being used are still of the old mechanical type. Some
improvements have been added but they are not fully automated like modern
production lathes. So cutting the tool steel is still basically
a mechanical process and the actual process of transferring an image
can take days. Yes, that's not a typographical error, it
can take days for the lathe to complete the reduction transfer of the
plaster model to a piece of tool steel. Once cut the piece
of tool steel is then referred to as a Master Hub. This hub
is then extremely heated and quickly quenched in oil to temper it. Tempering
the hub is what brings the steel's hardness to a usable Rockwell that
will allow it to be used in a high-pressure hubbing press.
The Master Hub is inserted into the hubbing
press opposite a piece of 4" tool steel and hydraulic pressure
is slowly applied to bring both pieces together. This transfers
the image from the Master Hub in an incused image. Incused
means the image is impressed into the steel opposite of what a coin
looks like. This finished piece of steel now with the incused
image is the Master Die.
The process of hubbing requires the use of very
high pressures. These pressures cause the Rockwell of the
die to rise as the image is being pressed. When the Rockwell
rises greater than the ability of the press to overcome the die is removed
and annealed (softened) in an oven. The die is then returned
to the hubbing press for another strike. Sometimes a die
would require three or more hubbings.
Ok, now when a die was taken from the press,
the Master Hub was left in place, and when the Master Die was returned
it had to be aligned in the exact position it was before. Here
is where some of the difficulties arise that cause varieties (Double
Dies.) In the interest of space and time I won't go any further
than this for now. But, please remember the following facts,
which you may find helpful.
1. Double dies are not
strikes.
2. Double dies are repeating
varieties and the dies used have a workable life and therefore each
coin struck by such a die will be a double die.
3. Double dies generally
originate from working dies not Masters. However there are
a few documented cases.
4. Machine doubling
is nit a double die.
5. There are a number
of types of double dies, you should learn to recognize the different
ones. Machine doubling fools many collectors.
6. Remember this one
for sure. The Mint has improved the presses that are used
to create dies and need to anneal has been virtually eliminated. This
means that a single squeeze technique is being used which has for all
practical purposes eliminated the double die.
Homework
Well, this time I'm going to try an inexpensive
prize. I have two type I planchets for the first two correct
responses. Remember the third question requires a little
explanation. I sold last month's coin on E-Bay for around
$100. This month's coin I'll add to my collection. I'll
keep the planchets too if you wish. Surely there is a junior
member out there that would like to earn a few coins. I hated
to sell that coin, but hey, books are expensive. I'll have
another nice coin coming up soon, you will never know if you don't participate. Dealers
can't play so you collectors are missing out. Well, in the
famous words of one of my favorite voices, adi, adi, adi, that's ah
that's all folks! God Bless each of you.
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