London Obverse Sizes

markn · May 10, 2016, 09:44:15 AM

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.

trout · May 10, 2016, 10:10:23 AM

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:

Fulvio · May 10, 2016, 11:21:50 AM

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.

r9453 · May 10, 2016, 11:44:02 AM

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

Robster · May 10, 2016, 05:35:20 PM

Very cool pic! :good:

Fulvio · May 10, 2016, 05:52:38 PM

Quote from: 'Robster' pid='88463' dateline='1462867520'Very cool pic! :good:

Yeah, very cool. Any idea where this was?

r9453 · May 10, 2016, 06:09:17 PM

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

Mister T · May 10, 2016, 08:10:55 PM

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.

markn · May 12, 2016, 05:52:41 PM

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.

trout · May 12, 2016, 05:59:39 PM

Looking at that setup I imagine that it would take some degree of skill just to get the size close let alone perfect.

Mister T · May 12, 2016, 07:59:34 PM

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.

Fulvio · May 12, 2016, 11:11:49 PM

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:

r9453 · May 13, 2016, 04:54:04 AM

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.

markn · May 13, 2016, 08:51:29 AM

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.