Rather than hijack a current thread i'll ask this here. Is the squared rim on a proof coin produced mainly by the die, the collar or the planchet? If a proof die was used on a business strike planchet in a business press, would the rim be squared or rounded?
I BELEIVE the squared off rims come from a) striking the coin twice and, b) striking it more slowly and at higher pressure. To answer your specific question, I think it's enhanced coin to collar contact. We already know what happens when proof dies are used to strike business coins. The wide AM and narrow AM cents show us this clearly - not a whole lot.
The rim of a coin is part of the die. It does not come in contact with the collar. Since the coin is struck twice that probably helps accentuate it. It is supposed to be flat. Take a look at a mint state Washington Quarter with the Type B reverse. This reverse was used to strike Proofs. The rims are flat.
The answer to the first part of your question has already been given, it's 2 strikes, (or more because some are struck more than twice) at higher pressure that produce the squared on edges (or corners if you will) of the rim. The answer to the second part is the rim would have rounded edges/corners. This is why. The rim of both a Proof and business strike die is shaped or formed exactly the same. One is not squarely cut and one rounded off - they are both squarely cut. But what I think some folks don't realize or seem to understand is that the rim is the lowest part of the die. Now think about that for a second. And when ya do, think about this. When one examines coins and they look at the highest points of the devices, sometimes the details of the high points are not as sharply or fully formed as they could be. And when we see this we say it is due to a weak strike. Well, it's the same kind of thing with the edges/corners of the rim on business strike coins because the rims are - the lowest part of the die, highest part of the coin. And the edge/corner of the rim is rounded off because it has not been fully struck. There just wasn't enough pressure to push the metal into the deepest recess of the corner of the die and create that sharp squared off edge. Just like sometimes there isn't enough pressure to fully form the devices. With a Proof, there is enough pressure the fill the very edge of the corner because it higher to begin with, and it is struck twice or more times. As for the part played by the collar in all this, it is the collar that contains that higher pressure and allows the sharp, squared of corners of the rim to fully form. Of course the collar does exactly the same thing on business strikes, it contains the pressure. But on business strikes there just isn't enough pressure to fully fill that corner.
Proofs are struck on hydraulic presses. This is what provides the extra striking pressure. They are not struck on ordinary circulation strike presses.
True, but the so-called "circulation quality" San Francisco mint ATB quarters are ALSO struck on a press that strikes proofs. Look at an S-mint ATB next to a D or P edge-on; they're just different.
In particular, 1972 business strike cents seem to almost always have wide, flat, squared rims. Has anyone else ever noticed this? With my eyesight these days, I have to examine the dates with magnification to look for doubled dies and such but can identify a 1972 cent from a distance just because of this. Is it possible that they increased striking pressure for some reason that year? What say you?
I'm not disputing that the rim is part of the die but, that being the case, how can a misaligned die make a strong strike on the planchet without smashing into the collar or anvil die?
The coins you've posted pictures of are what are commonly referred to as a railroad rim, and they occur because of a partial collar strike. And there are several different things that can happen (different outcomes) as a result of a partial collar strike and a railroad rim is but one of them. This is true because there different causes for a partial collar strike. But to answer you question, I think this picture will do a better job of explaining it than just words. This is what those coins would look like if viewed from the proper angle. The picture comes from this thread - https://www.cointalk.com/threads/is-this-a-railroad-rim.127503/ Now if you look at that picture you can see where the collar actually was (around the edge). And you can see that part of the coin (the part that is protruding beyond the edge) was outside the collar when it was struck. The picture also shows you that the hammer die did not, could not, come into contact with the collar or the anvil die. And that explains how a strong strike can occur without the 3 (hammer die, anvil die, collar) coming into contact with each other.
If the hammer die is far enough misaligned that part of the lettering is off the planchet, it DOES smash into the collar. And if left to continue doing that long enough the collar wears down the edge of the die. And if it is that far off, and smashing into the collar, the strike usually is weaker because part of the energy is being used to force down the collar.
