What kind of coin press was used at the Bombay Mint in 1895?

Discussion in 'World Coins' started by Insider, Nov 9, 2019 at 3:52 PM.

  1. Insider

    Insider Talent on loan from...

    When we look at many of our AU/MS coins, especially the large ones, we can see radial flow lines. They are best seen near the coin's rims. The flow lines become longer, deeper, and more noticeable on coins as the die is used.

    I have a "dollar sized" silver British trade dollar struck at the Bombay Mint. The lines on this coin are not in the usual radial direction! They are curved away from the center. I'm trying to understand why.

    I was told its because the coins were struck using old screw presses sent from the Royal Mint. I'll post an image.

    [​IMG]
     
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  3. ldhair

    ldhair Clean Supporter

    I have never seen flow lines that look like that. Could this just be a die that had a lot of work done on it and not polished out properly?
     
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  4. Coinsandmedals

    Coinsandmedals Active Member

    I seem to recall that Boulton supplied the Bombay Mint with presses (I think the number was eight, but I’d have to look it up). I’m not sure if these same machines would have been in service in 1895, but it could prove to be an interesting area to explore. If I recall, the Boulton presses were used at the Royal Mint until the 1880s, so It is entirely possible that the Bombay Mint kept them in commission longer.
     
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  5. ldhair

    ldhair Clean Supporter

  6. GDJMSP

    GDJMSP Numismatist Moderator

    At this point so am I.

    I don't think this explanation really holds water. I say that because the direction of force being applied to the coin by the dies in the press does not change, no matter what kind of press is used. Hammered, screw press, steam press, hydraulic press - the direction of force is always the same - it's vertical, or horizontal, which is dictated by the press design. So that simply cannot be the explanation for the change (from normal) in the direction of the lines.

    Next I would say that the directional aspect of flow lines is always dictated by the design of the dies/coin. Metal is always going to flow, from the fields, towards the recesses in the dies. And wherever the deepest recesses are in the design is where the majority of the metal is going to end up. This is a given and not debatable.

    So to see where the metal is going to flow from and to, and thus the direction it's going to take, all one has to do is look at the coin. And given this design -

    [​IMG]

    [​IMG]


    - it's pretty obvious where the majority of the metal from the planchet is going to end up - the center of the coin's obverse.

    So, to me, the question then becomes are these lines on the coin flow lines, or some other kind of lines ? Well, from the part of the coin we can see they have the same basic characteristics of flow lines. They are all running in the same basic direction, we can see where die wear from repeated metal flow has occurred at the edges of the devices, and we can see that some are indeed taller. and or deeper, than others just like they always are on any coin struck with worn dies. So I'd have to say that yes it does appear that they are indeed flow lines. That said, the variation in their direction is puzzling.

    I think to see the answer we have to look at the very outer edge of the coin, on the inner edge of the rim just beyond the denticles.

    [​IMG]


    See what looks like gouges leaning to the right on the inside edge of the rim, and how the upper end of the denticles looks to be pushed a little bit to the right ? And, how this leaning to the right of the gouges matches the direction of the lines ?

    And if we look at this other coin, same date mint -

    https://images.pcgs.com/TrueView/34744473_Large.jpg

    [​IMG]


    - you can see the same thing happening almost all around the coin. But if you look closely (using the link so you can see the blowups) you can see that not all the denticles on both obv and rev lean to the right - some are straight and vertical like they should be.

    This indicates to me that at the moment of strike, that the dies twisted in the press, turned slightly in other words, to the left.

    So, how could this happen ? It happens because of the way the dies are set into the press. For one reason or another the dies are not held securely and they twist slightly at the moment of maximum pressure. And it is this twisting that imparts this unusual angle to the top of the denticles and the lines on the coin.

    Now maybe this particular press was worn out, or maybe the stem of the dies used for this date mint had a flaw of some kind causing the dies to be unable to be locked securely into place. Or maybe the locking mechanism just wasn't tightened enough. Either way, the same kind of thing could happen to any kind of press, screw press, steam press, hydraulic press, it wouldn't matter.

    I looked up several coins, same date mint, and they all have this characteristic to one degree or another at the denticles. And this indicates to me that that's indeed what the problem was - the dies simply weren't locked in securely.

    But Mike, if you got some other explanation, I'm willing to listen.
     
  7. Coinsandmedals

    Coinsandmedals Active Member

  8. Coinsandmedals

    Coinsandmedals Active Member

    Unrelated to the original topic, but I noted that the thread posted by @ldhair mentioned that machinery sold to the Royal Mint by Boulton was replaced in the 1870s. Peck notes on page 218 (2nd edition) that the machinery remained in use at the facility until 1882. I wonder where the discrepancy arises. I knew I read this somewhere, but I couldn't remember where.
     
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  9. Insider

    Insider Talent on loan from...

    Apparently at least one old screw press remained in use at the Royal Mint until that date or 1881.
     
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  10. Coinsandmedals

    Coinsandmedals Active Member

    I don’t know enough about the history of the Royal Mint to suggest otherwise. I also wonder if Peck was referring not only to the presses but also to other equipment supplied by Boulton. I will try to explore this more when I get the time.
     
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