Re: [sca_moneyer] Digest Number 396
- ----- Original Message -----From: dwills1@...Sent: Friday, May 27, 2005 4:11 PMSubject: Re: [sca_moneyer] Digest Number 396Thanks, that's good advice, the mirror.As I've said in postings here in the past, the pre-industrial safety mechanism is paying attention.And the "never getting tired" part is what we had in mind for the drop hammer.Well, that depends on how you hoist the hammer. Industrial drop hammers (or 'drop stamps' as they're apparently more commonly called in the UK) use an electric motor power assist to raise the hammer. Industrial drop hammers are fast and efficient, extremely powerful - and extremely heavy, and not cheap. They're not a project to throw together in your garage. 'RenFaire' drop hammers use a small winch to hoist the hammer, which is why they're very slow (they're designed for doing demos rather than 'production'); if you tried to max out production with one, cranking the winch would get very tiring pretty quickly. The only illustration of a 'period' drop hammer I've seen (attributed to St. Petersburg, 1704) shows three men hauling on the halyard to raise the hammer - safe bet they got tired.We're borrowing ideas for that from lots of sources, but have pretty well settled on two parallel rods that allow two fairly close fitting pipes (welded to the weight) to fall directly down onto the striker, which holds the upper die. The lower die is held in place below the coin blank, between the same two rods, in a (I don't know what to call it) holder-that-the-lower-die-goes-into. Lift the hammer into position, latch...Industrial drop hammers have a 'parking' lever a short way up the vertical guides; they're weighted and balanced so that they drop away when the hammer is lifted above them....slide the upper die holder up enough to get the coin blank in, lower top holder to contact the coin, trip the latch, bam! Repeat until the neighbors call the police for the bashing sound at 2AM. You know.Is this a design that you know somebody is actually using successfully and practically - or just an idea that looks like it should work? If it's the former, I expect that several people on this list would probably like a source for design details and specifications. If it's the latter, well, we'll enjoy hearing your reports of your experimentation, but I've got to warn you that simple does not equal easy. What usually happens is that people see a drop hammer in in operation at a Renaissance Faire and think, 'that's so stoned simple I can throw one together out of scrap lumber or spare plumbing parts'.I've talked shop with the guys running the RenFaire drop hammers (they've set up at SCA events such as West/ An Tir War and Estrella War). They're not as simple as they look. If there's any friction or misalignment of the vertical guides at all, they simply don't work. They have to be built and set up very precisely. I was told that to build one of the standard RenFaire drop hammers costs $12k. An old industrial drop hammer I've experimented with (we didn't get its electrical motor working) has a 100# hammer (140# with its nested collets); I estimated its anvil at ~888#. Its vertical guides, probably ~100# each and ~6' tall, are cast iron with a finely and precisely machined V shaped groove the 'ears' of the hammer slide in. The vertical guides have massive adjusting screws for making the relatively tiny adjustments to perfect their verticality after the anvil is mounted perfectly level on a rubber pad on a very solid foundation (without the pad, the hammer can break the anvil). That machine (built in 1918) is certainly far more powerful than what you need for the project described, but without a lot of experience with drop hammers, it's hard to say what smaller scale of machine will do the job.If you're still planning to try building a drop hammer, something you'll have to deal with is that, with a solid hammer and a solid anvil, the hammer will bounce, the struck coin goes flying, and you have to 'catch' the hammer to keep it from clashing and destroying your dies. Catching the hammer is a learned skill (a drop hammer operator I've corresponded with tells me that he's so consistent that the flying coins stack themselves in a corner of a cardboard box set up around the dies), but apparently not too strenuous with the electric motor power assist. The RenFaire drop hammers do not bounce because the hammer is a tube filled with shot rather than a solid hammer, and the anvil is set in a box containing a few hundred pounds of sand.At a reenaction, we don't propose to get much work done for talking about what we're doing. There will be a little bag of coins there already made for sale or whatever distribution is needful. We'll probably ping a few while people watch. Hopefully, we won't flatten too many thumbs (well, we can't, we only have four between us, heh)My experience is that, doing demos, there's about five minutes of talking for each strike. However, what excites people is seeing the coin they buy being struck (with the RenFaire drop hammers, often the customer is allowed to pull the release lanyard themself). Two man striking with a long handled hammer is very authentic and makes a very dramatic demo.IanD the BI use a 1500gram clubing hammer on silver just under the size of a mundane dime.
From that experience I think you'll have to hit a blank the size of a quarter pretty hard.
I agree that a drop hammer will be slower, BUT it never gets tired, and allways gives strikes of the same force, and if designed correctly no mis-strikes that send the top die into the furthers corner of the shop where it takes you 3/4s of an hour to find............(actualy I found it in ten minutes, the rest of the time was spent moving the junk, er I mean stockpile to get at it..............)
I never studyed it in depth because my persona wouldn't have used anything but a hammer to strike coins but I think a lot of coins were struck (so to speak) under a screw press.
A screw press was first used to strike coins in 1530, but they were generally used for punching out blanks rather than striking the coins for most of the 16th century. Screw presses were generally used for striking relatively small coins until the 18th century because it took until then for the technology to catch up to be able to cast multi-ton iron press frames. Small modern screw presses (e.g. 2 ton capacity) can be found on eBay for under $1k (although shipping can be pretty steep). However, to strike something quarter/shilling size would take a rather larger, heavier, more expensive press (e.g. 40 ton). I've been told that if you try to strike too large a coin with too small a press, there is a danger of breaking the press frame casting, in which case you've just created a very expensive piece of scrap iron.Ian