Question about Poland 20 zlotych 1990 Y#153.2

[bart]

Since many years I own the following coin, which I received from someone who got it as change. It comes out of circulation.
The special thing about this coin is that the edge is plain instead of reeded, but it is also about 1 mm smaller in diameter.
Does somebody know about these coins struck on a wrong planchet, or was it altered?
And if it was altered, how could it have been done, as the planchet is perfectly round.
Look at the pictures: the coin on the right is a "normal" 20 zlotych, the coin on the left is the coin with the plain edge.

diameter normal coin: 24.0 mm
diameter plain edge coin: 23.2 mm
thickness normal coin: 1.7 mm
thickness plain edge coin: 1.7 mm

Bart

[bart]

I tryed to scan the edge; I hope the difference is clear.

[RHM22]

Do you have an accurate with which to weight it?

[chrisild]

The 2009 Schön lists two types of that coin: Riffelrand (milled edge) 1989, 1990 / Rand glatt (plain or smooth edge) 1990. But since it simply says "Ø 24 mm", I guess that should be the proper diameter for both ...

Christian

[translateltd]

I tryed to scan the edge; I hope the difference is clear.

Is it just me, or did anyone else see a pair of knees above a pair of long white socks in that photo before their eyes adjusted correctly?

[Figleaf]

A milled edge is normally made in a milling machine, before the actual striking takes place. Milling reduces the diameter of the planchet slightly. If a planchet somehow escapes the milling machine, it can still be struck, but it wil have a smooth edge and it will be slightly larger.

Since your piece is slightly smaller, it was made of a milled piece, probably by someone who had access to industrial metal working equipment.

Peter

[Abhay]

A milled edge is normally made in a milling machine, before the actual striking takes place. Milling reduces the diameter of the planchet slightly. If a planchet somehow escapes the milling machine, it can still be struck, but it wil have a smooth edge and it will be slightly larger.

Since your piece is slightly smaller, it was made of a milled piece, probably by someone who had access to industrial metal working equipment.

Peter

Yes, Theoretically, it is possible to make this Plain coin using a Precision Lathe machine. All you need is just to turn down the Reeded coin by just 0.4 mm, to bring down the dia from 24.00 to 23.2 mm.

Abhay

[translateltd]

If the smaller coin had been turned down using a lathe, I would have expected a mark or two on the face where it was clamped for the process, all the same.

[chrisild]

But why would one do that? If the smooth edge version was considerably more expensive, one might be tempted to turn a milled edge into a smooth one this way, and then sell it to people who are not aware of the difference in size. However, it seems that both are pretty inexpensive ...

Christian

[RHM22]

The reeding on a coin is imparted during the striking and not the milling of the planchet, so it would be impossible to have a coin without reeding unless at least one of the things occurred: a broken collar (but that would cause a broadstrike, which this is not), a severely undersized planchet (which this is not) or an intentional minting variety. Of course, all this is assuming that Polish minting practices are/were close to those of the U.S.

[Figleaf]

But why would one do that? If the smooth edge version was considerably more expensive, one might be tempted to turn a milled edge into a smooth one this way, and then sell it to people who are not aware of the difference in size. However, it seems that both are pretty inexpensive ...

To demonstrate a new machine to a client. To demonstrate the technique to a class. Out of boredom. To fool a collecting colleague ...

Peter

[RHM22]

To demonstrate a new machine to a client. To demonstrate the technique to a class. Out of boredom. To fool a collecting colleague ...

Peter

Quite! It's very easy to underestimate the power of a bored numismatist with power tools.

[bart]

Thanks for all the reflections. I am unable at the moment to weigh the coin, but if the weight of the plain-edge is a bit lighter than the reeded-edge version, I can conclude the reeding was removed and so the coin was altered.

On the other hand: chrisild made me aware a plain-edge variety of this coin exists, as it doesn't appear in Krause.

Bart