Building a sdie draft coal forge

[petere76]

Coal forge 101. Invest some of your time in identifying your needs and the capabilities of your shop. Once you decide to go with coal, size the forge to both your intended function and your own (personal) working dimensions. Think in terms of the rough height of your anvil (s) and other working surfaces in your shop; save your back. Some of the older HD forge set-ups I have seen in railway yards were built close to the deck because the materials being worked were very heavy. The trade off on these arrangements favored the movement of the work piece rather than the backs of the workers. Be guided accordingly.

I decided on a side draft exhaust configuration, as the side draft appears to offer both the best use of the available materials and the space required. The side draft model, when and where properly designed and constructed, offers a very efficient and relatively low loss transition from horizontal to the vertical (smoke direction). To this end, I studied everything I could get my hands on including old New England Rumford Fireplaces and existing masonry working forges dating back to the early 1900s. The side draft was the choice of the pros then and now as well.

Other design considerations that are less apparent, include, portability. This consideration favors shops and business circumstances that can change. There is little advantage in building a large, expensive and permanent structure if you have “any” idea of ever moving it. Change being one of the few constants in life, I decided early on in this process to make my shop both modular and where possible as portable as practical. You can’t take it with you when you go… but at least you can move it around while you are still here.

The design process, in my particular situation, involved allocating space, sheathing the surrounding bulkheads (fire protection) with sheet steel and accommodating a 10 in through bulkhead insulated uptake system. The uptake and associated ducting is critical to the proper function of the forge and keeping you, your helpers and your building safe. Too small and you suffer the fate of a smoky shop. Too large and you are wasting your money because the material costs outweigh any realized benefits.

Materials required for this project were collected over a period of time after some study as to the effectiveness of the various components. The side draft forge design is proven and I went with a modified “super-sucker design as depicted by drawings on the Anvil Fire web site. Modify the opening of the hood face (inlet variable) to that of the uptake dimension inlet (fixed variable pipe size). The inlet to the hood is smaller (sq inches) than that of the uptake exhaust. The differential in area (proportion) supports the acceleration of the flu gasses and thus creates a negative pressure area into which the gases can be drawn. This is best described as a working venturi effect in a gas (mass) flow device. The rule here is (F=MA) force equals mass times acceleration.

Table size, 36 in x 48 in. .3125 plate (heavy) for the tabletop and 2.5 x.25 in angle for the frame. The plate was actually a drop acquired from a local steel supplier (Browns Metal) who very much supports our endeavors. Fire Pot is a NEBA 50 Lb casting made in Lewiston Maine for the NEBA. The table was cross supported for the fire pot by additional angle iron to avoid any possible heat distortion that might occur in way of the fire pot. I have seen several forges where the tabletops are heat distorted and the builders were not all that pleased.

Tuyer was fabricated by at Ball and Chain Forge in Portland Maine. The Blower is a 120V 60 hz , SC, producing 164 cfm at roughly 40 oz psi. Aluminum air gate and blower both supplied via Blacksmiths Depot. All air connections were machined from reclaimed soil and drain pipefittings and are designed to easily slip together, no fasteners required. The table incorporates various modular sockets around its perimeter to accommodate hangers and or auxiliary shelf mounts. All external mountings are removable to assure a clear path to the fire pot when using long or irregular stock pieces. Both sides of the table feature an extendable stock rack for long work pieces.

The side draft forge hood is made of .125 sheet steel plate and attaches to standard 10-inch stovepipe. The plating was CNC plasma cut and bent by a local fabrication shop to our specifications. The variable sliding inlet door was required to both keep the shop warm in the often times chilly Maine winters and still accommodate a reasonable range of fire loading while operational.

The project took a realistic 40 hours of shop time, spread over many months, and 1200.00 USD to complete. I did not estimate personal labor or travel time to collect parts. If you can locate the metal chimney sections used, you can do better on the bottom line as that represents a good portion of the cash outlay.

I took some photos of the construction process and the finished product. Photos attached for your review. I feel that the project was a success and thus far, the new forge performs very well. IFI in many ways supplied the motivation and the avenues for the research as well as great input from around the world on various designs. Thank you.

Peter

[petere76]

Gents,

Other photos of the forge building evolution.

[petere76]

Still trying to get IFI to accept the photos.

[Bill Roy]

Very nice forge. Would love to see pics of the whole shop.

Does the forward slant of the exhaust opening help? Or have you found it to get in the way at all?

[petere76]

Bill,

The forward rake of the face plate does not limit access to the fire pot. Unless your intention is to lower a 8 inch solid piece of iron into the fire I see little chance of any interference.
I was suprised at the suction lift on this unit, it is very is very efficent. I can close down the opening with a sliding gate that I use to secure the exhaust when the forge is not operational. At roughly 50 percent open, the hood will still draw a running fire with no smoke in the shop. The first test fire (no forced air) shot out of the fire pot and right into the hood. the side draft concept certainly works as advertised.

i'll try and get some pics of the shop.

Peter

[Tubbe]

Very nice Peter.

I'm also doing research for the "perfect" forge design... the side draft is indeed a strong candidate for the exhaust.

Maybe you could clarify this part:

Modify the opening of the hood face (inlet variable) to that of the uptake dimension inlet (fixed variable pipe size). The inlet to the hood is smaller (sq inches) than that of the uptake exhaust.

Do you mean that the front opening area should be equal or a bit smaller than the uptake pipe? If smaller, what percentage do you think is beneficial?

Also, is there a particular reason for your rather large front plate, compared with the "original" super sucker drawings?

[petere76]

Tubbe,

In regard your question about uptake vs opening dimension. Yes the open should be somewhat smaller for the ideal draft. However, I did make the forge opening adjustable with the sliding closure. Other than during the start-up sequence the volume of smoke produced is actually rather small. I am ver pleased with the draft characteristics through the full range of firing.

The face plate in my particular case is .25 in stock and I chose the heaver dimension to preclude any distortion caused by heat. Additionally, the welding process attaching the box (.125 in) to the plate is made easier because you don't have to worry about burn through on the thin parts or any associated distortion. The fabrication was done with a flux cored mig as opposed to a TIG.

Good luck with your own design process and production. Post a few pics if you get the chance.

Peter

[JDB]

I really like the looks of the side draft hood that you built. It looks similar to the hood that Lester Beckman posted on anvilfire .com. Compairng the tow, I looked at the photos and could not tell if the bottom inside the hood is angled 90degrees to the face plate or not. It does appear that you extended the top of the faceplate a bit. Do you have any sketches for the changes that you made? I need to put a hood up in my shop this winter and this one seems to work very well indeed.
JDB