Reply To: 1890 QDO-001–detailed pictures

Reply To: 1890 QDO-001–detailed pictures 2015-02-22T15:25:52+00:00

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DVCollectorDVCollector
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The heavy degree of die deterioration suggests there are plenty of them out there to collect.

You could be right–although it’s sorta tough to find for such a common date (and an est. ~250K pieces/die) I’ve been looking for years. I suspect the die was improperly hardened, which might also explain the process of how the QDO came to be. Evidence of this might be seen in the heavy deterioration in certain parts of the die, and not others. So it could also be due to uneven hardening after removing that 0/0 RPD.

Now for a pretty technical discussion to explain this QDO…
There are several theories on class VI doubling in various sources, but the explanations strike me as rather vague. For doubling that exhibits radial stepping from the center of the die, it might be easily explained by the process of thermal expansion. All materials expand when heated, and this coefficient has been carefully measured, as it’s so critical for engineering things that don’t fail under thermal stress. And given that dies are annealed in an oven between hubbings, it is very plausible that a heat differential may be the culprit here. So let’s do a few calculations. Bear with all these details—it does have a point, eventually. 😉

As I’m familiar with measuring objects in microscopy, I did a few calculations to arrive at the distance of an individual (but larger) step pictured above. The result is a figure of roughly 25 microns or 25/1000 a millimeter.
For the sake of easy calculation, let’s say the die radius is 10mm or (10,000 microns) and calculate expansion from the center outwards.

The total thermal expansion coefficient would be 25/10000 or 0.0025.
The expansion coefficient for steel, probably very similar in 1890, is 7.2×10^-6 (0.0000072).
So the temperature change would be = 0.0025/0.0000072 or 347°F. Note: this is for a large step.

If we consider the strong possibility that more hubbings were made, and a couple steps may have merged into one, the temperature differential might be only ~175°F. Let’s say there was a problem with the annealing oven, or the die blank was hubbed at different temperatures. Given the calculations above, it may be plausible that distortion is introduced into the hubbing—or the die was improperly hardened, resulting in the deterioration seen, and possibly shorter die life.


  • This reply was modified 2 years, 9 months ago by DVCollector DVCollector.