Questions on ground forge design, materials.

[TimeToWaste]

First thing first, sorry for the long post and pile of questions. I appreciate everyones time and consideration.

After disappointing results with brake drum forges I've taken the advice of some IFI members and have built a "prototype" charcoal ground forge. Poor design caused a fire on the floor of my 2'×2', 8" box. All in all it performed well but I need to fix it and would like to get it right this time. I've spent more time tinkering with forges than forging anything.

I back filled the box with sand, formed the fire pot(about 5" deep,1' across) with a large kitchen bowl using(oh no, here it comes) the dreaded plaster (dangerous, ineffective, temporary, free) of paris/sand mix. Three heavy coats of 2700° stove type(non castable but available and very cheap) refractory cement on top of that. 1 1/4" floor flange heavily cemented to the 1/2" ply floor, bottom of pot about 2" above(all cement between).Fire started there. I thought cement would protect floor, with blower off tuyere got very hot then fire escalated. My questions are;

Could I use cement board like dura rock to replace floor?(I plan on raising the pot a few inches) If not, what would work? 

Replace plaster mix with kastolite30, then coat with mizzou instead of cheap paste type? Any suggestions on kastolite thickness? Or...?

Before the fire, the forge easily achieved welding temps, should I protect walls from flux (20mule borax) from what I gather it destroys liners and don't want to damage it right away as I'm trying to learn to weld and will be using a lot of flux.

What is an appropriate backfill, vermiculite, clay...?

Any suggestions on tuyere design to prevent future issues with heat?

Sorry again for so many questions.Feedback would be greatly appreciated. Thanks again for your time and experience.

 

 

 

 

 

[Charles R. Stevens]

Over thinking it, first, 2" flore is min. Fire brick or soft red brick is idea as it keeps us from digging down to deep when clearng out the forge.  One inch to the bottom of the tuyere. Charcoal only makes about. A 6" fire ball on a one inch tuyere so 1 foot is a waist of fuel. 

Clay rich subsoil is all you need, or sand or sand and ash, nothing fancy. 

Newest rendition of my dirt bag forge, 7 1/2" deep. 

 

[Frosty]

Ditto Charles WAY overthought. Ram damp clayey soil till it's hard, mixing it 1pt clay to 2pt sand will help prevent it heat checking. No, don't go buy "clay" just find some clayey soil. I suppose if you want to get fancy toss ONE CUP of cement or PoP per 5gl bucket in the clayey soil / sand mix. It WILL help it to stick together and that's little enough any bad characteristics of overheating it are negligible.

There is ZERO need or reason to use refractories at all, if the clayey soil burns out so what it's just garden soil dig some more or dig an extra bucket for patches. Same for worrying about flux damage, it's garden soil, see above.

This is just a hole in dirt on a table so you don't have to bend over, NOT a Sistine Chapel fresco. A duck's nest the size of one of those soup mugs is plenty large enough. Fire bricks are how I enlarge or shape a fire on a duck's nest.

Getting fancy or trying to make the perfect tool has a consequence as you have noted you're spending more time trying to make a forge than you are forging. Once you've been smithing for a while you'll begin to know what you need or want from the fire. Better still you'll be learning enough about how fires work to be able to get it to do what you want.

Frosty The Lucky.

 

 

[TimeToWaste]

 Thanks for taking time out of your holidays to respond. I had a feeling I was overdoing it, just didn't think by so much(I was moments from installing the spoiler and neon under lights). So quit the cement, it was easier to find than any type of clay here outside of expensive artist supply. I thought the cement would hold up till spring. The soil around here is mostly forest soil, gravel or hay/corn fields and the ground is also starting to freeze. If I'm forced to buy is there a specific clay to use? I read about some here on IFI but can't find the post again. I get it, it all just clicked. Need a big fire, build up and out with firebrick not oversized for the rare occasion, save fuel. Consumables get consumed, replace as needed, castable cement is for more permanent applications. Firebrick under firepot should prevent floor from burning. I was looking at the whole thing wrong. 

Is there an advantage to running the tuyere in horizontally? Could I build a smaller box because of the smaller firepot? It really does take a couple guys to move. 

Thanks again for the advice, and patience with another newb. Happy Holidays.

[Glenn]

Search for the 55 Forge. Horizontal side blast is the easiest to build. If it is to large use brick to reshape or reduce the inside to what ever you want.  As Frosty said, play in the fire to learn what shape works best for you and they type work you want to do.

When in doubt take a shovel and dig a small hole in the ground, add a horizontal air pipe, and be happy. Today's forges have been made more convenient by raising the hole in the ground to waist level so you do not have to bend over. Do not overthink simple.

[Charles R. Stevens]

Just buy play sand, if you really think you need clay mix it 2 to one with cheep cat littler. 

Or ask the building supply for "fire clay" and mix it 1 part clay, 2 parts sand. Or a poetry place.  But plane sand and ash works fine. 

[TimeToWaste]

I really was over thinking. Its in my nature. Would have repeated the same problems and only solved the fire issue. Weeks or months of kicking myself avoided. The 55 forge seems simple and foolproof...avoids a couple irritating problems with brake drum forges. The hole in the ground was the first one I tried and all the bending over alone made it nearly impossible. 

Thanks again to All.

Charles, thanks for clarification on clay.

[House of D]

Dick Nietfeld's website, Shady Grove Blacksmith, also has alot of terrific information on the building of forges, firepot design, managing fires and everything you can imagine for blacksmithing. It is truly an exceptional resource and Dick is a stellar dude....not to mention he sells and imports some superb anvils! Great guy.

D

[Charles R. Stevens]

The pictures I posted are the local subsoil. 

I like the "55 side blast" I built one using 3 legs from 1" c 1/4" with scrolled ends and a drum clamp for a stiffener at the bottom. Got fancy and went with a pancake bellows. 

Anyway don't overthink it. It's millinia old tech. 

Side blast forges (tuyere from the side) is easer to build and more versatile to fuel. Being that the box is filled with dirt the fire bowl can be reshaped for different applications. A simple manifold can be made to make trench fires, or larger fires (charcoal is limited to about a 6" hotspot otherwise)

4 hours from first board cut to first fire...

note the bottom edge of the fire brick glows hot as it's dang close to the hot spot...

[TimeToWaste]

House of D, thank you for the response and the resource, its difficult to find reliable info online. 

Charles, you've saved me a lot of head scratching and frustration. Thank you. I am going to follow your suggestions(as well as Frosty) and find a bag of cat litter, some sand and quit making things more complicated than a hole in the ground. Me, try to re-invent the wheel? Never heard of such a thing...

[Charles R. Stevens]

Remember, what I showed is one way to do it, not the only way, use what materials Are at hand. 

[TimeToWaste]

Tried it my way, didn't turn out so good, going to take a stab at it your way, hopefully be forging in a couple of days.