Creating a medieval dropforge

Question

Glornakan the blacksmith is looking for a way to mass produce plate armor with medieval technology.

More specifically with a creation requiring nothing beyond what existed in our medieval history. This question on history SE gives what appear to be good estimates on how long it takes to craft various types of armor ( handy :D )

Glornakan's kingdom has need of vast quantities of breastplates and only limited resources in the form of skilled blacksmiths, though the smiths they have are very skilled. To that end Glornakan called together his fellow smiths in a Smithmoot to help him come up with a plan.

The plan is very detailed and creative, they plan to drop heavy things on top of the glowing hot metal in order to reduce the time it takes to forge.

What they essentially want to design is a power hammer or drop forge. Not that they know how...

As the greatest scholars and scientists of the land the Smithmoot is calling on you to aid the kingdom in this time of need to help design the aptly named: super heavy smasher

Details:

• You have access to inconsistent wind power
• You have access to a mountain stream
• You have access to many unskilled laborers (and no you can't teach the unskilled laborers how to work metal)

The goal is to create a machine that will allow quickly repeating strikes from a hammer that can be adjusted to use 25, 50 and 100 lb hammer strikes. The hammer should be able to strike at a minimum, 15 - 20 times per minute, though faster is better. This is to limit how often the metal must be re-heated.

Additionally the process should include a die that limits how much manual manipulation of the billet is necessary.

Answer 1

According to Wiki, water driven hammer forges have been around since Ancient China, the Greco-Roman era, and Medieval Europe.

One or more trip hammers were set up in a forge, also known variously as a hammer mill, hammer forge or hammer works. The hammers were usually raised by a cam and then released to fall under the force of gravity. Historically, trip hammers were often powered by a water wheel, and are known to have been used in China as long ago as 40 BC or maybe even as far back as the Zhou Dynasty (1050 BC–221 BC)1 and in medieval Europe by the 12th century. During the Industrial Revolution the trip hammer fell out of favor and was replaced with the power hammer. Often multiple hammers were powered via a set of line shafts, pulleys and belts from a centrally located power supply.

There is also a video of a Water Powered Hammer on YouTube that shows, what they call, the last fully functional water hammer forge.

Answer 2

The goal is to create a machine that will allow quickly repeating strikes from a hammer that can be adjusted to use 25, 50 and 100 lb hammer strikes. The hammer should be able to strike at a minimum, 15 - 20 times per minute, though faster is better.

That's not particularly heavy, or exceptionally fast. As noted in ShadoCat's answer, such machines have been around for a very long time; the Wikipedia article on Trip Hammers describes significantly heavier hammers, and the YouTube video he linked demonstrates a quite sufficient strike rate.

So, if you really want to justify the name super heavy smasher, we'll need to think about how to turn this up to 11, in a way that could be done by medieval craftsmen if they only had the idea--i.e., no new materials, no new construction methods, just mechanisms they could already know about, put together in a novel way.

For a given amount of power, you can use wooden cogwheels or leather belts and pulleys to adjust gear ratios to either lift a light hammer quickly, for lots of strikes per minute, or lift a heavier hammer more slowly. If we want to lift heavier hammers, lift them higher, lift them more frequently, or just lift more hammers (so more smiths can work simultaneously), we need more power. So, how do we get the most power possible?

If you want to be able to operate on a regular schedule, you certainly won't want to use inconsistent wind power as your primary source. If the geography is right, however, you may be able to take advantage of wind as an auxiliary source (described in more detail below).

The simplest arrangement, which you could turn on and off at will, is to use all of that unskilled labor to run treadwheels to power the hammers. More treadwheels with more laborers running in them gives you more power for more, and heavier, hammers.

However, you can also multiply the water power available with the use of a dam. If the stream isn't big enough to run all the hammers, or the size of hammer, that you want just by sticking a water-wheel in it, you can construct a dam to store up the stream's energy, and then release it on-demand. Over a long period of time, your average power use will be restricted by the stream's natural flow rate, but if you aren't working 24/7, a dam will allow you to capture the energy of the falling water during off-periods (nights and weekends, so to speak), and add it to what's available during the workday. A system of sluice gates could also be used to divert water to multiple wheels, so as to control multiple hammers independently without complicated gearing or clutch systems, and to control the flow of water to adjust the wheel speed.

Now, if you have a convenient pond or lake below the hammermill, you can augment your water-power system with wind power, via pumped water storage. A flat lake is no good for water wheels, but it serves a recyclable water source for increasing the power of the stream; a windmill, located by the lake or up by the dam, can be used to pump water from the lake up into the dam, via an Archimedes screw or other pumping mechanism, thus converting inconsistent wind power into controllable, stored hydropower.

If the mountain stream is particularly long, it may be desirable to build multiple water-wheel powered hammermills in stages going down the slope, and possibly multiple control dams as well. Building multiple small dams would also be simpler than building one huge one--and if one fails, it doesn't shut down your whole industry. Cascading millworks of this sort, while not common, have been around since antiquity.

Including a die is no problem. In a pinch, you can make them out of cast iron in a sand or ceramic mold. That won't produce the hardest or most durable dies, and they may require periodic replacement, but it'd work. Just don't drop a cast iron die onto a cold workpiece by accident.

For smaller hammers (such as specified in the question), it would also be a relatively simple matter to swap out heads of various weights on a single hammer, possibly held in place with a peg system. These could be lifted with a tilt-hammer (or tail-helve, as described in the Wikipedia article) cam-and-lever system (cam pushing down on the opposite side of a lever from the hammer head). For heavier hammers (e.g., quarter-tonners), you probably wouldn't want to go to the trouble of trying to swap them out on a regular basis, but that shouldn't be a problem since the bigger hammers are a bonus feature anyway. Those heavier hammers would use a nose-helve cam-and-lever system (a cam lifting the end of the hammer shaft beyond the head, on the same side as the fulcrum) to get better leverage with less strain on the wooden beams. Again as described in the Wikipedia article, belly-helve hammers (with the cams acting between the pivot and hammer head) could be used for intermediate-weight hammers, but they don't need to be, and if you have any super-heavy smashers, it makes sense to minimize the number of different kinds of mechanisms that need to be built, and just stick with the nose-helve design for anything too heavy to use a tail-helve.

Answer 3

Alternate solution

I don't know if you are dead set on a drop forge, but there are alternate solutions available for even higher quality and faster steel forging. I just did the research on this for this answer so I'll summarize how that is relevant here.

The 19th century open hearth process is replicable with Medieval technology

The heart of the matter is that the processes that allowed fast, cheap, high quality steel to be made after the Industrial Revolution were in fact available to the Medievals. If Glornakan was the Isaac Newton of blacksmithing and had been born in the Middle Ages, it is plausible that he could have developed the entire process in a few decades of experimentation; and a a bit of luck.

Basically, the difference between steel after ~1850 versus before was the use of hot blast to push pre-heated the air going into the furnace through the molten steel itself to remove impurities. This combined the smelting and forging steps into one, and allowed you to do it to large batches at once, within hours. Without this process, you had to smelt separately, and then pound it out with power hammers (or regular hammers) to work the impurities out.

In Europe, hot blast couldn't be invented until there was a powerful enough heat source, like coke furnaces, introduced in 1709. By 1740 Europeans could melt steel to form crucible steel in small batches. But the Chinese had been melting iron with coke in puddling furnaces since maybe the 1st century AD.

The technology for a pre-heating furnace is not complicated either. The first ones in the 1850s were simply brick lined pits where exhaust air, forced through the furnace with a water powered bellows, would be gathered. A heat exchanger, made of clay pipes, then passed through the brick lined chambers and heated the air being forced in with the bellows.

So, had Glornakan actually been the Shen Kuo of blacksmithing, he had all the technology needed to operate this process before the Middle Ages even started.

What do you do with the molten steel?

So now you can make steel that has three big advantages over any process that existed in the middle ages:

• Large batches can be produced at once (up to several tons), so you economize on fuel usage
• The 'blow' that removes impurities for a while batch takes less than an hour, compared to days of pounding from your drop hammmers
• The ingredients are much easier to measure consistently when you make big patches. That way you can make the best quality steel every time.

At this point you have to form the steel into something usable, so you will need to roll the steel into plates. As far as I can tell, hot rolling iron was first done in Europe in 1697 but didn't really take off until the 1800s.

The way to do it with medieval technology would be to pour molten steel out onto a plate, then pass it between sets of rollers to flatten it into a sheet. This equipment would obviously have to be made from stone or ceramic to handle the heat, and would be able to benefit from waterpower as well.

Once steel plate are being made in industrial quantities, the Glornakan and his fellow Smiths of the Moot could fashion the sheets into fitted armor.

The next big technological advancement would be stamping to form the sheets into standardized armor pieces, but I think that might be a bridge too far for Medieval technology.

Conclusion

With a Bessemer type process, the cost of making the steel itself can be greatly reduced, and the quantity of high quality steel made is increased. With a ceramic rolling mill, this cheap steel can be converted to thin sheets. The raw materials for armor production have now been provided, and you just need enough armorers to assemble the finished product.

Not sure if this answers your question or not, but if you are really after the best way to make lots of plate mail, the Smithmoot can do even better than the Super Heavy Smasher!