So, its come to my attention that the London 1966 20¢ Obverse dies were cut at a different reduction and produced noticeably smaller obverses (yeah, only too me 60 years to find this out.. der).
My question is, did this happen with other coins, or was it a one-off?
There are large and small versions of the 2004 obverse on the 20c.
Or did you mean on other 1966 coins?
Quote from: 'Fulvio' pid='88374' dateline='1462670785'So, its come to my attention that the London 1966 20¢ Obverse dies were cut at a different reduction and produced noticeably smaller obverses (yeah, only too me 60 years to find this out.. der).
My question is, did this happen with other coins, or was it a one-off?
50 years. Not sure but I think the Royal Mint-produced coins of 1981 aren't as easy to tell.
Quote from: 'Triggersmob' pid='88385' dateline='1462694256'Or did you mean on other 1966 coins?
Well, I meant London dies, as a way of telling them apart where there wasn't a deliberate mintmark. Two different dies from the same mint isn't really significant unless one has relatively tiny mintages.
And yes, I do realise that most years everything comes out of Canberra. Also, if I'm not mistaken, all predecimals had mintmarks, yeah?
Quote from: 'Mister T' pid='88388' dateline='1462699484'I think the Royal Mint-produced coins of 1981 aren't as easy to tell.
I wasn't aware of any way to tell them apart. Canada's easily distinguishable, but London (or was it Wales by then?)?
I have no recollection where I got this image but I have it labelled as London:
(http://www.australian-coins.net/gallery/albums/userpics/11093/1966_20Cent_London_xx28Unc29_23.jpg)
Quote from: 'r9453' pid='88395' dateline='1462707579'I have no recollection where I got this image but I have it labelled as London:
Heh, shoulda known Mark would have it covered....
http://www.australian-coins.com/australian-decimal-changeover/australian-1966-20c-obverse-die-differences/
Thanks for bringing this up Fulvio.
I learnt something new today :good:
I didn't realise you mean the gap
I thought you meant that the obverse die image was actually smaller
I assume that if the image is smaller then the gap must be larger.
I assumed that he meant that the obverse was smaller like the 2000 $1 coin that is considered a 'mule' due to a 10c obverse die being used except that the 20c die was engraved smaller to denote the mint
:)
Quote from: 'robbiegal' pid='88407' dateline='1462747131'obverse was smaller like the 2000 $1 coin
Well, no... more like the 2001 and others with different size obverses. And I really doubt they would do this as a deliberate mintmark. Rather it would be accidental, presumably an operator error when producing the master.
What I was getting at is whether this has occurred with any other coins produced at multiple mints, such that we could use it as a reliable indicator for coins where a deliberate mintmark wasn't applied.
BTW, I notice the US now uses laser-engraved dies. Presumably this would eliminate accidental varieties?
not at all
Quote from: 'robbiegal' pid='88428' dateline='1462772761'not at all
No? How so, when every die would be identical?
the laser is only as good as the programmer
Quote from: 'robbiegal' pid='88446' dateline='1462791958'the laser is only as good as the programmer
Yes, but replication is a no-brainer. Once you set up a task, one or a million, all will be identical.
Quote from: 'Fulvio' pid='88399' dateline='1462718159'Quote from: 'r9453' pid='88395' dateline='1462707579'I have no recollection where I got this image but I have it labelled as London:
Heh, shoulda known Mark would have it covered....
http://www.australian-coins.com/australian-decimal-changeover/australian-1966-20c-obverse-die-differences/
I'd forgotten that I wrote that. I often wonder if the reduction machines (Janvier reducing machines) are setup with different gear sets to produce the required reduction ratio. Or perhaps they have some sort of infinitely variable reducing gear like a cone/belt system. Either way there's going to be some sort of operator choice to setup the machine to reduce to the correct size to produce the master matrices.
So what if an operator chooses the 165 tooth gear set (for arguments sake) instead of the 166 tooth gear set? Or sets the reduction to 2.99 instead of 3.00 using some sort of dial? Or what if the London Mint 3x reduction set uses a 165 tooth gear set and the RAM's uses 166? That sort of situation would certainly explain how dies can vary a little between mints.
Pure conjecture of course. I've love to get a close look at a reducing machine and have it's operation explained to me by someone competent.
QuotePure conjecture of course. I've love to get a close look at a reducing machine and have it's operation explained to me by someone competent.
Maybe this bloke could help you out Mark :laugh2:
(http://www.australian-coins.net/gallery/albums/userpics/10019/i_shrunk_the_kids.jpg)
Quote from: 'markn' pid='88450' dateline='1462839255'I've love to get a close look at a reducing machine and have it's operation explained to me by someone competent.
I had the opportunity many years ago during a tour, and fluffed it. I was too keen to get to the presses and ignored the chance to learn something useful.
But yeah, there's clearly an operator choice in whatever machinery they use, and given that varieties exist, they occasionally choose differently.
One thing that has me perplexed, or perhaps its just my ignorance, is why the reduction process would occur more than once. As I understood it, that first step from the plaster produced a master die from which impressions were then taken and used to ultimately produce working dies. Why would there be a need for more than one master?
Presumably once we go all-digital (if we haven't already), this will all be a thing of the past.
Maybe when there is more than one mint involved (as with the OP) each one gets a puncheon?
EDIT: http://www.royalmintmuseum.org.uk/Blog/collection-in-context
(http://www.royalmintmuseum.org.uk/responsive/images/blog/cc1.jpg)
Very cool pic! :good:
Quote from: 'Robster' pid='88463' dateline='1462867520'Very cool pic! :good:
Yeah, very cool. Any idea where this was?
Quote from: 'Fulvio' pid='88464' dateline='1462868558'Yeah, very cool. Any idea where this was?
Lots of fascinating stuff here:
http://www.royalmintmuseum.org.uk/Blog/collection-in-context
Quote from: 'Fulvio' pid='88413' dateline='1462760726'Rather it would be accidental, presumably an operator error when producing the master.
My assumption was that it was to better suit their own machinery but maybe it was just a case of slightly different reduction settings or whatever.
PPH found this picture of a reducing lathe at the RAM in the 1960's. Notice at the bottom the twin set of conical gears with a belt running between them. That sort of gear set has infinite variability and I could easily see the situation where one mint has a 11.999:1 reduction ratio set while another has 12.001:1 ratio using the same type of machine. Which leads to different master matrices sizes.
(http://www.australian-coins.com/wp-content/uploads/2016/05/ram-janvier-lathe.jpg)
Looking at that setup I imagine that it would take some degree of skill just to get the size close let alone perfect.
Quote from: 'Fulvio' pid='88392' dateline='1462705334'I wasn't aware of any way to tell them apart. Canada's easily distinguishable, but London (or was it Wales by then?)?
I think there are some marginal differences, possibly strike characteristics.
Quote from: 'markn' pid='88556' dateline='1463041361'PPH found this picture of a reducing lathe at the RAM in the 1960's.
That's awesome! Thanks, PPH.. this answers a lot. Yes, I can see such an error creeping in. Still not sure why they wouldn't simply cut two identical masters at the same time, but hey, its the mint, right? Anything could happen!
Maybe even the tea lady knocking it and changing the setting while nobody was looking. :diablo:
It might not be possible to make identical masters. Even if two were cut with the same settings consecutively they might have slight differences due to temperature, wear on the cutting tools etc. Also, I read that it takes a long time to make one, more than a day. The machine is left to run overnight, its not a five minute job.
Quote from: 'Fulvio' pid='88581' dateline='1463060509'Quote from: 'markn' pid='88556' dateline='1463041361'PPH found this picture of a reducing lathe at the RAM in the 1960's.
That's awesome! Thanks, PPH.. this answers a lot. Yes, I can see such an error creeping in. Still not sure why they wouldn't simply cut two identical masters at the same time, but hey, its the mint, right? Anything could happen!
Maybe even the tea lady knocking it and changing the setting while nobody was looking. :diablo:
It's easy to imagine that they could have used a different type of press at each mint to hob out the production dies, even something as simple as the master die needing a different shaft size. Or a particular metal composition. Or a different OD. Any number of things could have resulted in the Royal Mint London making their own master die. They did the same thing for the 1951 strikes.