How to plan and layout a new blacksmith's coal forge design
Under Construction. A very large rewrite is now in progress. Everything in the forge design page group will be changed and improved. This is a massive work spread out over 14 pages and will take a substantial amount of time and effort. I add these as I have time.
Understanding the blacksmith's fire is key to good forge design
All coal forges are designed around the 'heart' of the fire. The new forge builder must first posses a thorough knowledge of how a blacksmith uses a fire before he can build a serviceable coal forge of his own. If you don't know what is meant by 'heart' of the fire than stop right here and learn how the blacksmith's fire is used. Follow the link to Using the Fire linked at http://www.beautifuliron.com/thefire.htm.
Updated July 06, 2005. New page layout created. Updates now logged at bottom of this page similar to the Home page. This page group is under a large transformation to make it easier to read. What you find in this page group is a large work in progress, and you see it as I write it. Numerous computer crashes have resulted in loss of backed up work so I now save many updates and changes directly to this website as they are made. This website was begun 5 years ago and I had no idea when I started it, that there was so much knowledge that was put into the building of good blacksmiths forges. This is just the beginning.
All coal forges have several features in common
Coal forge design is based entirely on (#1. the position of the fire and (#2. location of the chimney. Design of the hearth and chimney must accommodate the use of the fire in a way that allows the smith to place the longest bars he is likely to heat, through the heart of the fire. The forge must be placed in a location that allows the smith easy access to the fire and convenient and unobstructed movement from the fire to the anvil or other tool or machine. Style and position of the chimney may possibly interfere with movement of work into and out of the fire so the smith must take care to locate the chimney out of the path of work flow.
First rule of forge design: The hearth or ducks nest, supports the fire in a position that places the 'heart of the fire' centered (half above and half below) at the same level as the hearth or side edges of the forge (whichever is taller) The iron that is to be heated, must pass through the center of the 'heart' of the fire when placed on the forge for heating. This rule applies to all forges whether they are side blast or bottom blast. The iron must be placed through the heart of the fire without being bent. There must never be a need to build a larger fire just to heat a bar that is held far above the heart of the fire because the sides of the forge are too tall or the fire too deep below the hearth. Larger fires consume tremendous amounts of fuel and require extra blast air. Again if you don't understand the use of the fire then see the link to the Fire page above.
Rule #2 - Chimney must not interfere with the work.
How tall should the forge be built?
Rule #3: Height of the forge hearth is important. Too high and the smith must reach over the hearth with his arms raised all the time. Working with the arms raised for any amount of time gives the smith a sore back just like working at a table that built at chest height. The best height of the forge is the same height as the anvil or maybe an inch taller. Measure this by standing straight and tall and with your arms at your sides relaxed, make a loose fist and measure from your second finger joint to the floor. This measurement would be a good approximate height for the center of the heart of the fire and the hearth of the forge.
Rule #4: Size of forge is important. This is influenced to a large extent by the style of forge.
Generally the small enclosed forges are somewhat uncomfortable to use compared with a good open style shop forge. Small enclosed forges are great for portability and practical use for say, shoeing horses. Some shop forges are built small and enclosed for short bar lengths used by farriers and knife makers and chain makers. At right is a photo of a small enclosed forge for making horseshoes. The small hood keeps fuel in the small hearth. But the small access opening in the front of the hood requires the smith to work from a small area in front of the fire.
A small forge with open sides would be terribly uncomfortable to work with because fire tools won't rest on the hearth of the forge without falling off, and fuel would constantly fall off the hearth while moving work in and out of the fire. On the other hand a small enclosed forge would work well for small items such as knives, chainmaking, and horseshoeing because the hood that encloses the hearth would hold the fire tools inside and also contain forge fuels within the area beneath the hood. In other words, if the forge is to be smallish say around 20 inches diameter or square, it will function well if it is enclosed, but if this small forge were to be open then it would be terribly uncomfortable and unpractical to use.
Shop forges Under Construction
By shop forges I am referring to those coal forges that will remain permanently set up in a shop.
Rule #?: Coal and coke forges are the same forges. I have been asked repeatedly about this. All coal forges use coke fires. But not all smiths buy coke. Many smiths buy coal. This has more to do with availability of fuels in a region. The smith that uses coal, makes his own coke as part of the ongoing process of maintaining his forge fire. The fire is the same. The forge is the same. The difference is in the method that the smith must handle his fuels while maintaining the fire. All firepots are coke pots.
Move the following-
Most of the
This does NOT preclude the use of the sideblast tuyere used by many smiths. This text is only meant to show that a good ready-made firepot is the best option if the smith chooses a bottom air blast design.
Forge height. The general purpose forge needs to be tall enough that the smith need not bend to reach into the fire. Neither should the forge be tall enough to require the smith to lift their arms to reach over it. Too short and the forge is awkward to work with, while too tall and the smith will develop a sore back during the days work.
Approximately same height as anvil the general-purpose forge hearth is level with the smiths knuckles or second finger joint. As an example, my forges are about 1/2 inch taller than my anvils with the actual measurement of height of hearth being about 31-1/2 tall above the floor.
To find the height suitable for your own general forge, stand straight and tall, form a loose fist, measure to a point from the floor to the second finger joint of your fist or to your knuckles. Record this measurement and plan for this dimension in your forge design so that the top surface of the hearth is level with your measurement. The height of any sides or edges around your forges hearth are not part of this measurement. At this time we are only measuring for the height of the hearth.
Blower height. If the forge uses a hand cranked blower, the blower is mounted in a way that allows the crank handle to come no lower (while revolving in its circular travel path) than the inside of the smith's fist when he is standing straight and tall next to the forge. In other words the smith should never need to bend at any time while cranking the blower handle around its entire circular path.
Never mind the final height of the forge. What is important in mounting a blower is that the smith need not reach too high or too low while cranking the blower. Reaching too low is worse than reaching a bit high so we calculate height of crank handle from its lowest position.
Measuring for blower height. Cut off a piece of broom handle or obtain a short piece of hammer handle to use as a reference for measuring your height of grip. Grasp the temporary handle with your left hand (it doesn't matter if you are left or right handed at this point in time) and stand straight and tall with your arm relaxed and straight down by your side. Measure from the floor to the center of the piece of handle in your left hand. Record this dimension. This is the lowest point through which the blower crank handle will be allowed to pass as it is rotated to operate the blower. All methods of mounting or positioning the forge blower must allow for the center of the crank handle to reach this height dimension as it rotates through its lowest point of travel.
Lateral positioning of blower. The blacksmith needs room to work between the blower crank handle and any long bars of iron extending out of the forge. If the blower is placed too close to the fire laterally then there is no room to stand between the blower and any long bars of iron that are extending over the side of the forge as they are being heated, and the smith would then be forced to reach over the iron bars to crank the handle of the blower.
Hand-cranked blowers are heavy. Blowers are usually made of cast iron and are heavy enough to cause many small forges to overbalance and tip over when the blower is mounted far from the fire. That is the reason the blowers on most ready-made cast iron forges are mounted close to the hearths. The new smith often uses the ready-made manufactured forge as his example of construction technique and places his own blower too near the forge hearth. I am cautioning the new forge builder to avoid mounting the blower so close to the forge as it causes problems later during use. However the new smith will need to consider how the weight of good cast iron blower may overbalance his forge and cause it to tip over under certain circumstances.
There are a number of solutions to overbalancing problems for blower mounting.
The smith needs room to stand either between the blower and any long bars extending out of the fire, or in front of the blower and next to any long bars in the fire. In determining placement of the blower, the smith always assumes there will be a hood or chimney on the forge at some time. The two best positions to mount the blower are as follows:
Special purpose forges are of many different heights depending on the work they perform and methods of using them. I have seen examples of an anvil forging shop from Germany in which the forge hearths were about 9 inches above the floor and very large to accommodate the large amounts of fuel to heat the parts of anvils for forging. But cranes and other lifting devices were used to move the parts in and out of the fire and it is easier to shift large shovels full of coal onto a low platform than a high one. The height should best suit the work and the methods of using and servicing the fire.
Plotting Chimney Position
A plumb bob is used to find the ideal position for both the chimney base at floor level and also the position in the roof where the chimney must exit. The plumb bob string is held against the roof or ceiling at each point or corner of the area on the roof that the smith thinks he will cutout for the chimney. Moving the plumb bob string around until the best area is located both at floor and ceiling level. Mark both the floor and roof at these points so the chimney can be constructed on this location. Tack nails at each corner of the proposed cutout in the roof to tie the string of the plumb bob onto before making marks on the floor.
Chimney position dictates position of the forge! Understand this point before making any alterations to the shop. The physical area or 'footprint' of the lower chimney structure directly influences where and how the forge hearth is built The chimney flue should be built as straight as possible from bottom to top. This is especially important if the chimney is made of brick or stone because a tilted or bent masonry chimney will eventually break or fall down. To take this a step further we find that when we follow a masonry flue structure down from roof level to the forge, we find the lower structure of the chimney always occupies the area directly underneath the flue. Obviously the base of the chimney and the forge itself take up more area on the floor level but keep in mind that the flue structure is straight and will take up area directly beneath the chimney for a base to support the weight of the chimney flue.
Since the chimney is often larger and of much larger shape at floor level compared with the shape of the chimney where is exits the roof, the blacksmith must be careful to note the exact location of the plumb bob string at floor level and compare with his/her final forge plan to determine if the full chimney base will fit in the location marked out with the plumb bob. The position of the base of the chimney may not be compatible with the position of the flue structure as originally marked out on the floor, so be ready to adjust or move the forge plan around until it fits. Also keep in mind that the forge plan can still be changed at this point too. When the smith is satisfied that the final forge plan fits the location and that there is enough room for a chimney flue to pass through the roof, then final marks are made on the floor for construction.
Things that effect the position of the forge
Hood and chimney supports, air blast pipes, bellows and pull ropes, blowers and blower mounts or stands, draft breakers, cleanout holes in the proposed forge, and anything else mounted between the forge and any nearby walls or walkways or tool racks may force the smith to either modify his/her forge plan or build it farther out into the workshop area then originally anticipated.
What is work to be done
How many fires?
Chimney materials (brick or stone, steel pipe)?
Side draft or overhead hood?
Type of hearth (steel-welded angle plate and pipe, steel bolted or riveted, angles, plate or sheet iron, wood and cinder, concrete, masonry or stone, refractory brick)?
Here we break the discussion into four categories, the brick side-draft forge, large overhead hood, the half hood, and the conventional large hood. And the retrofit hoods such as my steel sidedraft hood and large conventional hood.
Updated on July 06, 2005.
This page under construction and lots more to be added.
The author can be emailed at address in picture below:
Page created on October 15th, 2001.