Question about Blakesley Effect

Discussion in 'Error Coins' started by moneycostingmemoney, Aug 10, 2017.

  1. moneycostingmemoney

    moneycostingmemoney Yukon Coriolis

    Im really enjoying learning about the different varieties of errors and am really glad that I found the CT community as a resource to learn more about all aspects of collection and the minting process.

    I've noticed the mention of Blakesley effect and how it validates a clipped planchet error over PMD (although it's not a must have in order for it to be so from what I've gathered) enough to want to read further into it. I've seen plenty of examples of it and feel confident now with what I'm looking at, but being a mechanical thinker I was also looking for the explanation behind when and how...

    Does it happen because when the planchet is cut the punch fairs towards the side of least resistance and cuts the planchet oddly?

    Or is it when the coin is struck and the die meets the surface of the planchet if fairs towards the side of least resistance, causing the impact to be less opposite of the clip?
     
  2. Avatar

    Guest User Guest



    to hide this ad.
  3. moneycostingmemoney

    moneycostingmemoney Yukon Coriolis

    Or am I off altogether?
     
  4. cpm9ball

    cpm9ball CANNOT RE-MEMBER

    Clips occur during the process of cutting the blanks from the sheet of coin metal. Sometimes the clip happens to be from the very end of the sheet and other times there is slippage while advancing the sheet into the cutting position. There are other types, but I think @paddyman98 would be more informed to explain these to you than me.

    Chris
     
  5. Michael K

    Michael K Well-Known Member

    I assume some of these errors must be handpicked out and discarded.
    So even less actually make it to circulation.
     
  6. SuperDave

    SuperDave Free the Cartwheels!

    A planchet is punched under circumstances which don't allow much metal movement - if you visualize it, you'll see that pressure is essentially equal across all points of the blank being punched whether the punch is a hollow cylinder or the solid cylinder actually used.

    At the moment of strike, though, one must contemplate the planchet metal more in terms of fluid dynamics than solid. Dies are not consistent in relief and a lot of planchet metal needs to move relatively significant distances to fill the "voids" in the die deeper than the original planchet thickness. The Mint leverages these concepts of liquid dynamics to make it possible.

    I've always thought that your second idea is the basic explanation for Blakesley Effect - metal is moving, like a liquid, towards the path of least resistance (in this case the blank space left by the clip) and the planned migration of planchet metal towards the opposite side lessens, leading to a weaker strike opposite the void.

    It's intuitive, however, that slight differences in die alignment and clip location relative to the die (is there in the design more need, or less, for metal to flow in that specific direction?) can have a bearing on how pronounced the Blakesley Effect is, or even if it appears at all.
     
    dchjr and moneycostingmemoney like this.
  7. Oldhoopster

    Oldhoopster Member of the ANA since 1982

    The planchets move along a vibrating table that has holes slightly smaller than the diameter. Anything smaller (clipped planchets) fall through and are discarded. It is a large volume, production process, so sometimes undersized planchets make it through. The mint makes about 9 billion cents per year so even if the defect rate is 0.001% (10 ppm) that is the potential for 90,000 clips/year just for cent coins
     
  8. moneycostingmemoney

    moneycostingmemoney Yukon Coriolis

    @SuperDave I wasn't thinking fluid dynamics, but your points make sense. In my minds eye I saw the die "tilting" as it mated the surface of the planchet causing the weakened strike opposite the clip. But imagining the surface of the planchet being displaced until enough resistance causes the movement to stop- I see that pretty easily. Thank you for the explanation.
     
  9. Oldhoopster

    Oldhoopster Member of the ANA since 1982

    The die is also basined (slight curvature) to help push the metal outward equally in all directions, more or less.

    As Dave posted, there is less resistance for the metal to flow into the big, gaping area left by the clip, than there is to flow up into the rim, and devise on the opposite side.

    This also helps explain why the letters and rim right at the edge of the clip are weak. If you see a fully formed rim and letters at the clip edge, then it's a good idea to check for evidence of post mint grinding.
     
    moneycostingmemoney likes this.
  10. moneycostingmemoney

    moneycostingmemoney Yukon Coriolis

    That makes a lot of sense as well. I've seen a couple images of coins that were slabbed (by top tier) with "clipped planchet error" and the devices, lettering and rim were clean up to the clip. I thought it odd at first but just wrote it off thinking that the TPG would know better if there was foul play. Are clean devices at the clip more rare of an instance?
     
  11. Conder101

    Conder101 Numismatist

    When blanks are punched from the strip they have flat surfaces. If they were struck that way the centers would be strong and the coins would be weak around the rims and often not fully struck (the dies are slightly convex so the meet the planchet first near the centers and then working outward.) To counter this the edges of the blank are "upset". This is done by running them through a mill that applies pressure against the edges toward the center. As the blank goes through the mill the diameter decreases and the edge thickens. This allows the rim and periphry to form better during the strike.

    If the planchet has a clip, as it rotates through the mill, when it reaches that spot it is suddenly smaller in diameter than it is supposed to be and the pressure drops. With no pressure the upset rim doesn't form opposite the clip. Then when the coin is struck that missing upset results in weakness on the finished coin 180 degrees opposite the clip. (Blakely effect) The reason why it is not always present is because if the strike is strong there is enough force and metal movement to fill the rim in that location anyway.
     
  12. steve.e

    steve.e Cherry picker

    The blakesley effect occurs during the upset mill process. No pressure is applied opposite the clip causing flat spot in the rim.
     
    moneycostingmemoney likes this.
  13. Fred Weinberg

    Fred Weinberg Well-Known Member

    All I can add to this part of the discussion
    (because you guys got the Blakesley Effect
    right) is that I'm one of the very very few
    still alive that knew Mr. Blakesley

    He would attend the Error Club of Hollywood
    meetings (which started in the fall of 1967)

    He was just developing his theory of clips,
    and the effect that bears his name, at that
    time. He explained to me, and other club
    members, the three ways to authenticate
    a (curved) clip.

    1. Metal Flow towards the void/clipped area

    2. The weak rim area opposite the clip -
    which we now call the Blakesley Effect

    3. The "Cut & Tear" mark area INSIDE the
    clip itself, from when the Punch came
    down on the planchet strip - the punch
    only had to go thru 51% of the strip to
    punch out the blank - so all Type 1 Blanks
    of any denomination, and curved clips,
    have it - there is a band of smooth area
    inside the clip from the 'punch', and a
    rough area inside the clip (picture it horizontally)
    from the 'tearing' of the blank down thru the
    planchet strip - i.e.; Punch and Tear Mark.

    He was a great person - tall, lanky, an avid runner,
    very soft spoken, and very intelligent.

    Hope this background info helps a bit.
     
    -jeffB, paddyman98, gronnh20 and 8 others like this.
  14. moneycostingmemoney

    moneycostingmemoney Yukon Coriolis

    I'm really glad I asked this because even with the reading I've done on the minting process there were a few grey areas that you all have colored in for me. Thank you for that. I feel privileged to be wading in this very knowledgeable pool of specialists.

    I have a Jefferson nickel that I set aside the other night while CRH and something told me not to pitch it as just PMD. I haven't looked at it since the reading about the Blakesley effect and I think I'm going to give it another look now. If it is a clip it's not a strong example of one, but it would be my first clip find from the wild. I'll post some pictures when I have it in hand and if you guys could let me know what you think I'd greatly appreciate it.
     
  15. Fred Weinberg

    Fred Weinberg Well-Known Member

    Start another thread when you have the photos.
     
    Kentucky and moneycostingmemoney like this.
  16. moneycostingmemoney

    moneycostingmemoney Yukon Coriolis

  17. paddyman98

    paddyman98 Let me burst your bubble! Supporter

    Sorry.. I spent the last 12 hours preparing for my wedding this coming Saturday ;)

    Looks Like Fred Wienberg gave some answers on a post and he knows better than most of us.
     
    Last edited: Aug 10, 2017
    moneycostingmemoney likes this.
  18. Kentucky

    Kentucky Supporter! Supporter

    Spend more time than that...
     
  19. moneycostingmemoney

    moneycostingmemoney Yukon Coriolis

    It's starting already...:(:yawn:
     
    paddyman98 likes this.
Draft saved Draft deleted

Share This Page