diagnostics for doubled die vs machine doubling

camcues

What are some diagnostics to see the difference between doubled die and Machine doubling. For the life of me, I can't SEE the difference.

ModernDollarNut

Camcues, in a nutshell, hub doubling (doubled die) shows as side-by-side images often separated by a "notch" at corners of serifs, sometimes just by a thin line (really a rounded partial separation with a furrow in between, though it can very shallow and very thin and transient) that typically runs parallel to long axis of a device segment ("high line"). Sometimes, devices are just thicker without other apparent cause.

MDD (machine doubling, shelf doubling) is caused by the die slipping sideways as it is retracting from the strike, thereby sliding some or all devices sideways off their bases. The bases remain in place continuous with the slid-over devices. Generally this does not cause notching or "high lines" and instead leaves a flat shelf to one side and integral to the device.

MDD has lots of variations: the sideways slippage can have chatter leading to a cascade of shelves at progressively higher relief. Sometimes a sharp shelf running from a sharp serif can look like its notched but generally the flatness of the shelf is a dead giveaway.

IMHO we do not understand the precise mechanics of all types of MDD but with patience and practice it can be identified firmly as MDD 99% of the time.

You might want to use the search engine on this forum and google: there are several excellent summaries published though none are perfect and we all have a tendency to want to separate Doubled dies into the 8 classes laid out by Alan Herbert. The problem is many DD's are downline from doubled master dies: this leaves minor doubling from master die to working hub and minor doubling from working hub to working die to complicate matters, to say nothing of the changes in doubled die patters as individual dies age AND, the common and underappreciated compounding influence of machine doubling. . . Many DD coins can not be categorized, or it's guesswork to do so, just too many variables in play.

For this reason, it is the well recognized naked eye massively doubled dies that have by far the greatest notariety and value, deservedly so.

Hope this helps, I am by no means a DD expert, LOL. Rob

kranky

Adding to MDN's comments, there is a great explanation of this in the Cherrypicker's guide which also includes a quiz with photos to test your skill.

charley

Welcome. You may want to activate your pm function-or not. Respectfully, John Curlis FLG

ricko

Good explanation MDN..... can be a tough area as you stated... Cheers, RickO

MikeInFL

MDN, How sure are you of this?


<< <i>MDD (machine doubling, shelf doubling) is caused by the die slipping sideways as it is retracting from the strike, thereby sliding some or all devices sideways off their bases. >>


To wit, I always thought the slipping was during the strike, not the retraction -- but like you, I'm anything but an expert.

Thanks in advance...Mike

tahoe98

<< <i>What are some diagnostics to see the difference between doubled die and Machine doubling. For the life of me, I can't SEE the difference. >>




hope this helps.

http://www.geocities.com/NCADD/educational1.html

TAClough

Link

Try this link

ModernDollarNut

Mike! Don't get me going! (I already have the record here for most verbiage per post.)

Alan Herbert did extensive research to establish that shelf doubling occurs after the strike, the reason MDD is officially spurned by the DD crowd since anything that occurs after the strike is damage and not error.

I know he is 95-99% correct but have some fantasies that there is a component of MDD that occurs during the strike, based on the simple logic that irregular, random MDD ("chaotic" MDD) can not occur out of the blue (in contrst to a repetitive MDD image from one coin to the next (ie, found in a bag or roll) which is likely due to a parasytic oscillation of the hammer die).

Newton's laws would suggest that there is a force set up during the strike that is released as the die withdraws. Otherwise why would the withdrawing die have enough lateral force (or rotational) to shear sometimes heavy devices close to the field?

My fantasy is there is slippage as the dies sink into the planchet, slippage between die face and planchet or slippage between die faces or even slippage that's highly localized on/in the planchet due to some planchet irregularity such as a localized non-uniformity in the planchet metal.

The slippage, like sliding on a slippery surface only to have one's shoe grab hold, is held fast during the high compression part of the strike but as the dies withdraw nothing is held fast and the stored force is released as lateral or rotational movement of the die(s) back toward neutral position.

Alan understandably gets quite perturbed when I prattle on about this MDD theory as I have only the slightest support in some uncommon MDD images, one of which being the "ghost" doubled image on many Ike proof mintmarks with MDD: the ghost is nearly always on the opposite side of the direction of the MDD.

A leading numismatist thinks this is more likely a die bounce phenomonon but I can't quite buy that explanation.

I think a reasonable possibility is that the ghost is the remnant of the original position of the die at first contact with the planchet before the slippage occurs. Then slippage occurs during the earliest phase of the strike. The tension created by the slipping is released as the dies withdraw leading to a shelf being formed on the opposite side of the "ghost" image.

Rob

(edited for language)

WoodenJefferson

ModernDollarNut, that's a mouthful! I was thinking about this particular line in your analysis:

~Newton's laws would suggest that there is a force set up during the strike that is released as the die withdraws. Otherwise why would the withdrawing die have enough lateral force (or rotational) to shear sometimes heavy devices close to the field?~


Could it be possible that the surface metal has not yet completely solidified, then the forces required to rotate the design elements a few 1/1000ths of an inch would not have to be as great as one would think?

ModernDollarNut

Good question. Tried to work it through with Andy Oscam, the metallurgical member of the group and I think the concensus is planchet metal, when struck, moves as a plastic, not from heating per se but simply in response to the enormous pressure.

Thus, struck coins are just pleasantly warm to touch immediately after being struck.

The plastic state is an instantaneous response to the super pressure and exists only as long as the pressure exists.

The struck coin, therefore, is probably solid with normal metal properties even as the dies are withdrawing to the point of shearing devices.

I'm not putting this forth as fact or with any kind of certainty. . . it's just as close as I can come to the mechanics at this point.

Would love to hear what others have to say. Rob

BECOKA

OK, how does a hub get doubled?

ModernDollarNut

from misaligned repeat slow hubbings? What am I missing? We could get into "wavy steps" and other single hub "doubling" that is faintly similar, maybe, to my fantasy mechanism of MDD?

I gotta run, sorry. Rob

BECOKA

Sorry, guess I was looking at how does the hubbing process happen and then why does it happen again to get miss aligned.

howards

See:

JT Stanton article

ModernDollarNut

BECOKA, the quick answer to your question, at least before the era of single-squeeze hubbings:
- Master die, working hub and working die all needed two to four hubbings to bring up the design. If done in one squeeze the hub or die being created (blank)would be so work-hardened in the process that it would be damaged as the squeeze continued. Each squeeze therefore had to be much gentler than what would be required to raise a hub or sink a die in one squeeze.
- After each squeeze, the "blank" would have to be annealed (softened) in preparation for the next squeeze, a several-day process.
- In the Ike era there were no fail-proof keys for automatic perfect realignment for the second and subsequent squeezes so one has all sorts of rotational and off-center DDs.
- Because even tool steel is not perfectly homogenous, there is always the possibility that part volume of the "blank" would react differently to the annealing process resulting in highly localized doubling.
- Sometimes the entire blank would expand or contract a bit during an anealling, possibly the cause of Class VI doubling in which the letters at the rim simply look broader than normal, not rare at all.
- You can imagine that with dozens if not hundreds of master dies, working hubs and dies going through this process at any one time, the possibility of misplacing a blank or losing track of its specific "hubber" could lead to different designs being superimposed. OOPS!

So, lots of possibiities for doubling, all complicated by compounded doubling and sometimes by different forms of doubling in the same hubbing operation.

Again, I am far from an expert in this field, just had to dabble to begin to get a handle on my Ike DD's. Rob

TheRegulator

For your classic doubled dies, the secondary image is the same as the primary image. Think of your 1955 Lincoln Cent. Both images are the same.

On machine doubling, the secondary image tends to have a fat, smeared look to it, and is usally "larger" looking. It does not quite look like the primary image.