I'm on a Quest

[longnine009]

For the longest time now I have been trying to find the answer to one simple question: Why do spark erosion forgeries have "sharp" "knife-like" "proof-like" edges? Read anything about spark erosions and you will most likely see one or all of these descriptions. Sometimes it's even the very first thing stated. What they won't say is why? What makes spark erosion dies so special, so different from transfer dies or impact dies?

I'm guessing that a black cabinet collector knows this answer or perhaps collectors in other countries that depend more on their own abilities to detect forgeries than TPGs.

But it doesn't really matter who has the answer or why. I'd just like to know what it is.






"You fool Longnine, the Lady of the Lake has degreed  it so, that's why."

[Paint Your Wagon]

I saw a laser measuring devices at work in a carfactory producing motorblocks
The laser measures the XYZ coordinates to the micron  (like a gps tells you were you are)
and then can show you the motorblock threedimentionally on a computer screen

If you reverse the proces and make a computer tell your "cutter" wich XYZ coordinates to cut away with spark erosion the "cutter" will be as good as the positioning and feedback system is and exactly cut away what you ordered

The other two methods you mention are contact processes . Here the exactness of the tooling bench and the pressure of the transfer determine the sharpness.

Now I think the sharper the die the faster it will break or need maintenance

NO Contact is the key phrase in the tech description

http://www.metacrawler.com/info.metac/clickit/search?r_aid=10A11F71207448949A2AA135C69C9BB0&r_eop=2&r_sacop=3&r_spf=0&r_cop=main-title&r_snpp=2&r_spp=1&qqn=gsk5aR.y&r_coid=239138&rawto=http://en.wikipedia.org/wiki/Electrical_discharge_machining

[Paint Your Wagon]

Between 1973 and 1981  I was responsable for getting moulds for labo test machines ; the first mould cracked in two pieces during the deep hardening process in Holland .
So I went to high Brinell hardness materials and sputter cutting and only surface hardening . Solved that problem . Not the flow problems though since in those years the computer flow predictions of plastic matter were not very good . It was mostly trial and error and getting a robot to do 24 hours of polishing with diamond paste  to get the mirror finish ( deep ultra cameo 
The making of a die or mould can be the same . A die however stamps . A mould only has to remain closed with a few hundred tons of closing pressure . Allthough it is easy to make a fake coin by having a mould in dental plastic and clamping it between a vice to "strike" the coin
Will break though after only a few coins

[longnine009]

Allthough it is easy to make a fake coin by having a mould in dental plastic and clamping it between a vice to "strike" the coin
Will break though after only a few coins

I've seen some replicas on ebay that looked as though they had a plastic "sheen" to them. Maybe that comes from centrifugal casting in dental plastic?

The laser device you mentioned seems like something  that probably is being used to make  transfer dies.  They've  probably been doing it for 20 years, so, we'll probabaly get an "urgent report" on that any day now. 
But how about this: Why can't the laser/computer scan a coin and reverse that image  before cutting it into a die. Then you have the die exactly the way it has to be without losing as much-- or perhaps any-- detail. I think even I can reverse images in work shop pro. Why couldn't a real computer do that?

 

[Paint Your Wagon]

Why can't the laser/computer scan a coin and reverse that image  before cutting it into a die. Then you have the die exactly the way it has to be without losing as much-- or perhaps any-- detail. I think even I can reverse images in work shop pro. Why couldn't a real computer do that?

No problem but every coin would have the same defects as the original and each other and a laser coupled computer would see that immidiately

With the dental plastic I meant a mould out of two pieces on which you put pressure with a metal screw.
This will give  non poured non struck pressure produced coins and try and detect the missing strike flow lines 
The die is very cheap and will produce like a dozen coins

[longnine009]

Why can't the laser/computer scan a coin and reverse that image  before cutting it into a die. Then you have the die exactly the way it has to be without losing as much-- or perhaps any-- detail. I think even I can reverse images in work shop pro. Why couldn't a real computer do that?

No problem but every coin would have the same defects as the original and each other and a laser coupled computer would see that immidiately

That might not be much of a problem anymore for forgers. It used to be that the ANA Authentication Bureau cataloged  repeating depressions. They often publish photos of them each month in the NUMISMATIST. When another coin came along with the same depressions in the same spot they knew they had something.  With so many TPGs now, where's the  "central" data base? In fact where's the Authentication Bureau's old data base?

[/quote]
With the dental plastic I meant a mould out of two pieces on which you put pressure with a metal screw.
This will give  non poured non struck pressure produced coins and try and detect the missing strike flow lines 
The die is very cheap and will produce like a dozen coins
[/quote]

Is that also known as the Bulgarian Blast Cast? I've heard about a cast that can capture flow lines. But I can't find any details about the method.