Blacksmith basics – the forge
This post will cover more specific details on the forge a blacksmith uses in their craft than our previous post “absolute basics” did. This resource will cover mostly coal forges, with gas forges covered in a later article. I will be leaving out the exotic and semi-exotic heating sources here, such as electric resistance heating systems and solar forges. These other systems are more specialized in their application and generally financially out of the reach for the average hobbyist smith. In later articles we will cover some simple variations of the modern and historical forges that can be built very inexpensively and in short order.
The forge is a place that the smith can contain and control a fire to heat metal up to working range, which is usually hotter than a normal camp fire. The term also often means the building the forge is located inside of, and the term “forging” is something made in a forge. Forgery is not the correct term for making something in a forge though... that would be smithing, which comes from smite; to strike something. You know... blacksmith, a smith who strikes iron, which comes from the ground and fire black, as opposed to gold or silver.
The history of metal smithing is a long and varied one, and forges have undergone many variations and changes over the passage of time. Originally, the forge was a simple hole dug into the ground, and a blowpipe was used to increase the heat of the fire. As time passed, the smiths decided that standing up was a lot more comfortable than crouching down to work in a ground forge, but a few clever smiths dug holes to stand in next to their ground forges, and in a few parts of the world these ground forges are still used today.
The next evolution was to make the forge a roughly waist high table, either of laid stone or brick. This allowed the air-blast to come into the forge from under the fire, instead of from the side or above, which increased efficiency and allowed the smith to get even greater temperatures from his fuel. There are variations during this long age, including forge tables built of wood and covered in clay, side blast forges and long trough forges. For simplicity sake, we will only cover the generic, basic forge here for now though and save the unusual ones for later.
In modern times, the forge is often built as a steel table with a heavy walled cast iron firebowl or firepot at the center of the table to contain the fire. This forge bowl is usually several inches deep and a bit more than a handspan across. This allows a decent amount of fuel to be used, yet is not wasteful. It also allows the solid sides to absorb and reflect some of the infrared heat back into the center of the fire, increasing efficiency.
In all ages, the area around the forge bowl is often used to hold extra fuel and lay out work pieces and tools. Careful fire management will keep the fire contained in the smaller, central pot so as to not waste fuel. Many smiths build special fittings into the table to aid their work. These can be tool racks, special dies for forming or bending, or workpiece supports for long rods of steel.
So why build a large, heavy table for a forge in this day and age? Forges are an efficient means of heating steel compared to other options, such as a simple torch with either a fuel air mix or a fuel-oxidizer mix. The fuel air torches are things like a propane plumbers torch which have only a single gas cylinder. A fuel-oxidizer system like a oxy-acetylene cutting torch, will have a pair of tanks. The problem with using either style of torch is the amount of lost heat that is simply blown into the room and not absorbed by the work piece. The amount of fuel used by either of these torches in medium to heavy blacksmith work will make them prohibitively expensive in short order.
That about covers the basics of the forge, now we need to look at the fuel, air input assembly and the hood or draft system to remove smoke and heat.
Historically, forges burned coal, charcoal or in some rare cases peat moss as fuel. Raw wood is generally not clean burning enough to be used as is, so it was usually rendered down into charcoal, which gave a better heat and was less troublesome. Today, coal is probably the most common, as the amount of charcoal one uses for even simple projects makes it somewhat cost prohibitive in comparison to a coal forge. Coal is somewhat uncommon these days, but not terribly hard to find, and we will cover resources for finding it later on in our article about fire building and management.
For a moment I would like to diverge here to discuss gas forges in passing, just so the reader will have a bit of familiarity with them until we reach that chapter.
Most modern gas forges are a box like object with a pipe or set of pipes on top, so they can easily be put in a number of places like the tail gate of a pickup truck for field work. A gas forge can be built into a table like a coal forge, or sit on a stand or mount at any convenient height for work in a shop. The forge box is lined with a fireproof refractory material, much more resistant to heat than common brick, and this makes these forges rather heavy for their size. The pipes that enter the top of the forge are gas jets, and have a system to mix fuel and air from the room together to produce a clean burning flame inside the forge box. Most gas forges are set up to run on propane, but any flammable gas that can be pressurized can be used (such as hydrogen, methane or natural gas). More on gas forges later though...
Once we have a forge and something to burn in it, we need to consider how to get that fire hotter than normal. This was originally done with a blowpipe. It works, but is pretty tedious and can make you quite light headed very quickly. So some clever smith came up with a way to build an automatic lung, which we today know of as a set of bellows. There were a number of improvements in bellows tech over the years, but in this modern age most smiths use a much smaller mechanical fan system. Heck, you can even use the output from a vacuum cleaner or a hair dryer, but both of these have interesting problems we wont cover here yet. Most of these systems have some way to control either how fast the fan turns or how much air it is allowed to push into the fire to better control the heat in the forge. Too hot can burn the steel and too cold will make many jobs much harder if not impossible.
This air system is connected to the underside of the forge with a section of fireproof pipe, and enters the bottom of the firepot through a specialized part of the bowl, usually called a tuyeer. (There are some variant spellings of this word.) Usually this section of the bowl also has a gate or some kind of door to allow the ash that falls out the bottom of the bowl to be cleared out.
Now that we have air in our forge, we have to do something with the smoke... that's where a stack and hood or some other system comes into play. Now if you are just outside, you can let the smoke drift away, but I have done this a lot, and I can tell you it will often drift right toward you (there really is a scientific reason too – you create turbulence in the air stream passing you, and the smoke can be pulled right to you even if you are up wind of the forge). Building a stack (or chimney) is a more complex process than it may at first look, but I will cover it in great detail later on, so do not fret. Connected to the stack is some kind of metal hood that collects and funnels the smoke, allowing it to leave the building through the stack. There are optimal ratios for the intake area vs the pipe size and stack height, and I will cover them in that article I just mentioned. For now, I just want you to be aware that most smiths use a steel hood over their forge, though some use what is called a sidedraft hood system. This is the system I prefer, and I will have a full article including pictures and plans up here soon as part of the aforementioned article.
That wraps up our lesson for today, and once we get past these most basic lessons we will begin to get into the real meat of it.
Until then, stay out of trouble.
The podcast for this will also be up at http://alonetone.com/ironangel under "albums and playlists - Blacksmith lessons".
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