A Master Hub Mystery The Case Of The Missing Master Hub Some Answers

A Master Hub Mystery
The Case Of The Missing Master Hub
Some Answers​

I express my gratitude to all who have contributed to a discussion about this topic! I find dialogue about the issues involved truly educational and I am deeply appreciative to all who have served as my teachers!

This is one of the topics I have unearthed in my review of DIE CURVATURE HISTORY and I am reporting what I have learned. The topic will be included, along with others, in a paper I am preparing. I imagine there is more to be said and I would welcome further feedback.

There is a distinct probability that Master Hubs are no longer used in the die making process.

Consider the following:

It is reported that:

All coin designs are modeled and digitized or produced digitally. Master dies are prepared on digitally controlled milling machines at the Philadelphia facility. Master dies are distributed to the Denver facility, which produces its own working hubs and dies. Despite using the same masters, the crown heights of dies and design heights of relief produced at the two facilities differ, which has a measurable effect on coin fill. (ALTERNATIVE METALS STUDY, Contract Number: TM-HQ-11-C-0049, FINAL REPORT, August 31, 2012, Submitted to: United States Mint, Page 301)

This would mean that Master Hubs are no longer a part of the die making sequence.

HOWEVER, it is stated elsewhere that the die making process involves “machining the master hub” (ALTERNATIVE METALS STUDY, 2012 op. cit., Page 300) {This Study issued a voluminous report, most likely with numerous authors. This internal discrepancy was obviously overlooked.} Also, “A CNC machine engraves the design onto the master hub.” (Die Making at the U.S. Mint, by Stephanie Meredith with help from the staff of the Denver and Philadelphia Mints, April 2021. https://www.usmint.gov/learn/production-process/die-making#) (CNC = Computer Numerical Control)

In an excellent article on the die making process (coinworld.com | August 2021 “Before a coin can be struck, the U.S. Mint needs to make dies” by Paul Gilkes, Pages 18,20), Paul Gilkes also indicates the process begins with a computerized numerically controlled machine cutting a master hub. HOWEVER, his primary source for his information is a mint website!

Because of these conflicting statements, I was uncertain about an interpretation indicating the obsoleteness of Master Hubs, so I made further inquiries. Reports from individuals involved in the testing of Martha Washington Nonsense Dies in 2012 and also from those involved in mint operations indicate, with a high degree of certainty (but not 100%), that current die making starts with the Master Die made via the CNC 3D technology, and that Working Hubs are still hubbing all dies, that there is 100% single hubbing, and that this process also applies to the Martha Washington nonsense dies. If I am understanding these findings correctly, they mean that Master Hubs are now obsolete in the die making process at the US Mint.

I also find it interesting that, in discussing hubbing technology in the 2024 Biennial Report by the Mint, Master Hubs are no longer mentioned, but only working hubs. (2024 Biennial Report to Congress as Required by the Coin Modernization, Oversight, and Continuity Act of 2010, (Public Law 111-302), United States Mint, Department of the Treasury 2024, Pages 8 & 28.)

I have a growing suspicion that sources asserting the use of Master Hubs are simply relying on “Mint lore” for the die making story without verifying that the story is currently in practice! I find it easy to envision mint media folks, who have limited understanding of processes, repeating the same story year after year.

Since the mint began using CNC, there have been a limited number of instances of Master Die Doubling (MDD) being authenticated. The existence of MDD might suggest that a Master Hub was involved – or does it?

• We know that, in the past, there have been instances of Master Hub Doubling (e.g. Right top of W in WE on a Wheat Cent) created by the movement of the stylus needle on a pantograph machine. Is a similar event possible on a CNC machine during the cutting of a Master Die? I have found no discussion of that question.

• There are only a few examples (2019, 2022 and 2023) of attributed MDD since the beginning of CNC technology, and there are lingering questions concerning whether the 2022/23 examples are instead examples of Working Hub Doubling (WHD), or even examples of die dents or similar. (Examples: 2019 1¢ WMDO-001 https://doubleddie.com/2474337.html; 2022-P 25¢ MA WMDO-001 & 2022-P 25¢ MA WMDR-001, https://www.doubleddie.com/2680879.html? And Nickel 2023 Doubled Master Die https://www2.briansvarietycoins.com/listings/view/1869?) WHAT HAPPENED IN 2022?

• Experts disagree about properly attributing whether an example is MDD or WHD.

• Methods of attribution differ among the major attributors:

1. Look primarily for doubling that affects all dies. The more dies found dictates an elevation in status from DD to WHD to MDD. Some of these attributors are aware of the inexactness of this method.
2. Look primarily for appearance, then numbers of dies found. As far as appearance, WHD looks like Strike Doubling and MDD looks like Hub Doubling. (That the appearance resembling strike doubling being diagnostic for WHD is not commonly known, recognized, or accepted as being diagnostic for WHD). ​

With the advent of CNC, the mint set about in earnest to pursue optimization of coin design to prolong die life utilizing failure mapping, characterization, and design modification techniques, with a large portion of these adjustments applied by CNC programming. Elements of the process included in this effort were die shape and stamping force, level of detail, sharpness of transitions, relief height in the coin’s design, overall curvature of the coins’ faces, and the upsetting process (which deforms the blank’s material to the planchet’s rim). While it is unclear just how many of these efforts were applied to circulating coinage in 2022, the appearance of the microscopic features attributed as Master Die Doubling during this time suggests some adjustments to the die making/coinage process were being made. (Page 12, 2022 Biennial Report) An explosion of hub doubling varieties in 2022 has been noted as possibly being related to experimentation with die curvature affecting how a die slips and creates doubled dies. (American Women Quarters Doubling Study by Tanner Scott, (http://crdievarieties.com/doku.php?id=awqstudy)

For the most part, we know that controlled stamping trials were underway and if successful, production trials were to start culminating in a shift to circulation production in 2024. We do know that exponential die curvature for circulating nickels was implemented at both Denver and Philadelphia in 2021 with little impact on die life and that further design optimization was called for.

It is quite possible that the incremental design optimization efforts being applied through adjustments to CNC programming could be influential in the appearance of those features being attributed as Master Die Doubling.

I note with interest:

· that the doubling seen on the 2019 Cent is of complete digits, in contrast to the doubling seen on the Quarter series. The 2019 Cent has not been questioned regarding it resulting from hubbing a Master Die by a Master Hub.

· That while some of the features of 2022 Quarters appear to be more expressive of Working Hub Doubling in appearance (Strike Doubling), others resemble Master Hub Doubling (Hub Doubling).



I have come to the realization that eliminating a Master Hub from the die making process would make economic sense. Since a CNC milling machine can fulfill the role of a Master Hub by cutting a Master Die instead, the expense of an entire stage of the process can be eliminated.

I would CONCLUDE that we are witnessing:

· EITHER a shift away from Master Hubs initiating the die making process with only quarters (discounting the one nickel example as questionable) still involving Master Hubs in 2022,

· OR that Master Hubs have been eliminated from the process, at least since 2019, if not before, with any possible examples of MDD not originating during hubbing, but resulting from design optimization effects such as die curvature modification, or from vibration or misalignment (or some other minute malfunction) of a CNC controlled milling machine during the cutting of a Master Die.

· Ultimately, because of confusion and inconsistencies in the attribution process making attributions unreliable, a study of Master Die Doubling simply provides inadequate information to contribute to a definitive answer as to how that doubling originates.

 

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Sorry I can't add anything to the discussion but I very much enjoyed the information you've shared with us. Thank you.

Bruce

 

Thanks for the read Pete. That's some interesting info.