What lathe lines look like on a die.

Hey gang!

Have you ever seen a coin with lathe lines?

A lathe line is a series of circular marks that are made when a die is made. They are usually eliminated when the die is finished (or polished) for use.

You can visit this site and see examples: http://www.errorvariety.com/Lathe-lines/index.html

Or see this coin:


Here is an unfinished NORFED Ron Paul obverse die I purchased recently. It has been properly canceled... but you can clearly see the lathe lines on the surface of the unpolished die. The finishing process usually eliminates these lines... but sometimes if the are not finished properly before use the lines will appear on the coins.

 

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Like finger prints, or the trade-winds of the far east. Sweet.

 

Ron Paul coin? Damn I would pay a lot for one of those!

Sweet pictures of the lathe lines.

 

Most people wouldn't know what they were if they saw them. Now hopefully they might.

 

Sometimes you will see a very small dot on the surface of a coin in a out of the way spot. This could be the point test mark for the tensile strength test of the die's metal. So, keep looking for the unusual.

 

I recently saw a video on how dies were created with a lathe. Very cool.

 

Matt,

When are the lathe lines added to the die? Before hubbing or after hubbing?

 

I assume they come from the preparation of the dies before hubbing. This Ron Paul die looks to be a laser cut die... Which is a little different then how the US mint does it... But the lathe lines are the same.

 

The reason I asked is before hubbing the face of a die is not flat - it is conical.

 

Very neat. Thanks for sharing LD! :thumb:

 

There are two possible sources for lathe lines. They could be created when the lathe is used to make the shallow cone on the die blank, or they could be left on the master hub from the reducing lathe. Since the lines are on the field they can be polished off the fields of a die. But polishing them off the fields of a hub, and removing them all the way to the edge of the devices, without polishing details off the hub would be very difficult. Lathe lines from the master hub could be polished off the master die and not progress to the working hubs and working dies. The chances that the lines would survive the polishing of both the Master die and the working die would be slight. Lines left from the machining of the die blank is much more likely.

 

I am a machinist by day and i will tell you what, whoever is making them dies needs to slow the feedrate. I run a two spindle lathe all day. Im guessing they would be turned to diameter and faced (do not know if they are concaved or convexed or just flat surfaced). The faster the feedrate, the more spreadout the lines will be, slow the feedrate down and the lines will be much finer and less noticeable.

 

Conder,

Thanks for reminding me of that possibility. Don't know why I didn't think of it. But now the Mint uses a computer-aided machine to cut the Master Hub rather than the Janvier reducing machine. That should mean that lathe lines would not be part of the Master Hub any longer. I don't know what year the Mint stopped using the Janvier reducing machine but has anyone confirmed coins with lathe lines that were struck from Working Dies derived from a Master Hub produce by the computer-aided machine rather than the Janvier reducing machine?

 

Here is another coin, a Wisconsin commemorative that has very fine lathe lines present.

 

Interesting post LD thanks.

If anyone is curious, these are also found on ancients, but most of the time on the flans not from the die. They are very common on Ptolemaic bronzes and other bronzes of the near east, usually with centration dimples where the machine attached to the flan.

 

Late 1800's South African coins with Kruger on them are notorious for circular lathe marks.

 

Here is a coin that I was just photographing that made me think of this thread.

 

Wow highly educational thread, thank you very much matt because if i had seen these lines on a coin i would think its pmd or something....:thumb: