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1 Burner forge build advice


Ryanw

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I'm trying to design a new forge since my first one is a pile of bricks from menards that barely heats to 2200 degrees F. After reading this forum for hours, I'm coming close to my design.  Hoping to get some advice before I build anything. Plus maybe someone else can use what I do wrong in the future.  

 

The shape kind of takes after video removed dur to advertising by alec steele, but with 1 burner and significantly smaller. 

The burner is a Mikey style 3/4 Venturi Burner from his book. Its as advanced and tuned as we were able to get it. 

I planned on having it pointing at one of the sides of the inside of the dome to get the swirl. I know where to find the post about how deep to put it. 

 

The forge is a bottom with a dome shape on top, with 12 gauge steel. It would have 2, 1" ceramic blanket layers (with the rigidizer), followed up by 1/2in Kastolite 30 (With kiln wash). All with a kiln shelf floor. 

I was thinking to build it in 2 parts, the top and bottom. Then have the arch sitting on either kastolite or blanket to seal the gaps. For ease of construction.

The limiting factors I've found are that I only have 1 burner, and I've already purchased 10lbs of kastolite so I'm trying not to need more

 

Is there anything wrong with my design?

Do you have any advice with the way im building it?

Should I make it longer? Its at 261 In^3 with 10 inches length. So according to the 300in^3 per burner I could add a little. 

I haven't thought about what I should do for any sort of forge doors. We have firebrick but I've read that it sucks in heat. 

 

Will it provide enough heat with this setup?

I want to make this forge as nice as I can, so it can last a long time and provide what I need. 

 

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Good point. This is going to be used for mostly introduction forging with smaller projects or hobby projects probably a knife here and there. I read that alot of people use their small forge even after building larger ones because its more efficient for small projects

Id like this one to be a solid small forge for projects around its size. 

Edited by Mod30
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Right now its setup so it has an even opening on both sides.

Should I make the back opening smaller?

so it has space to pass through if needed but its more closed off to keep heat in?

Edited by Mod30
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My forge has swinging metal doors that are insulated with kaowool and have a hard refractory lining, and they do a fine job. However, they were kind of overkill and a lot of work. You'd probably do well to get some insulating firebricks that can be stacked as needed to close off the front and back openings.

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Ryan: The only thing lacking in your design are heat baffles. (doors) Mike does a great job of explaining them, how and why in the "Forges 101" section. 

To operate a gas forge MUST have a way for burnt gasses to escape but you want to keep the heat inside as much as possible. Mike's basic method is to close the openings with high temp fire brick, Morgan ceramics K26 by preference but others do as well. They aren't there to insulate or stop exhaust from escaping. 

What the baffles do is limit exhaust to almost inhibiting the burner's operation from back pressure. The face of the baffle facing the fire super heats like the rest of the forge liner and radiates IR in the only direction available. BACK into the forge and your work. exhaust gasses escape through the gap between the baffles and forge. Yes?

So far the best in MY opinion, method is to make a porch on the forge in front of the openings. It needs to be smooth and flat enough you can stand IFBs on them on edge and move them. Some guys are having good luck making angle iron tracks to hold the IFB baffles. 

I've been thinking about making my next forge with a lid that can be moved or removed as needed. I spent a lot of time thinking about sealing the contact points so flame couldn't pass through. I thought about and did mental testing regarding shaped contact points. Think a tongue and groove sort of thing. Finally I rejected the idea for just making the contact areas as smooth and flat as possible. Basically I figured out how to make cast refractory with a smooth finish or one that matches another. 

It turned out to be really easy and a real head slapper for me, I'd already known the technique I just hadn't applied it to casting refractory. 

Say you have the walls of your forge made and want the tops to match the lid. Yes? If you plaster the top edge with Kastolite (or whatever you use) cover it with Saran Wrap and lay a piece of SMOOTH plywood or lumber on it and put weight on it evenly. When the refractory sets up in say an hour or two you can lift the weight and lumber off. So the same thing to the lid when you make it. The contact areas will be matched close enough little or no flame can pass. 

However, if there is an area where flame passes through the seam lift the lid after it's cool OF COURSE and you'll be able to see where it's passing. Saran Wrap both walls and lid and apply a coat of kiln wash to the walls or lid. Both will show signs of the flame so do the other after the first is set hard. 

The Saran Wrap release agent makes it possible to match surfaces this way. I tried sanding, painting, and waxing or greasing to release the Kastolite but that stuff sticks to everything. Letting it stick to something that doesn't matter is the secret.

Frosty The Lucky.

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I will definitely look into that more before starting. I completely spaced the porch (I wouldve realized eventually). 

1 hour ago, Frosty said:

I've been thinking about making my next forge with a lid that can be moved or removed as needed. I spent a lot of time thinking about sealing the contact points so flame couldn't pass through. I thought about and did mental testing regarding shaped contact points. Think a tongue and groove sort of thing. Finally I rejected the idea for just making the contact areas as smooth and flat as possible. Basically I figured out how to make cast refractory with a smooth finish or one that matches another. 

My thought process behind it (Outside of doing what you said and just making it as smooth as possible) was to make the top slightly smaller so it slots into the base a little.

Or using kwool/kastolite in a fashion where it seals the gaps. Like gum over a leaky pipe 

I dont think Ill ever need to take it apart so I could just kastolite the crack between the tops wall and the kiln brick couldn't I? Then kiln wash over it all and tac weld the corners together?

Is it that easy for flame to escape through cracks?

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I considered the slot idea but there has to be a step of some sort. I figured I'd simply use a 1/4" slice of 1"x4" as a "core" on both wall and lid so they fit together. Once again Kastolite is just so sticky I never got a clean casting so gave it up.

If you're not going to take the lid off just cement them together. Make the lid first and when you have the walls ready lay a layer of Kastolite on top and tap the lid down until some squeezes from the joint. 

Use a colander to sift the larger aggregate from the Kastolite or it won't squeeze down it just doesn't move smoothly that way. 

Or use the kiln wash mixed a little stiffer than you would to brush it on, say tooth paste consistency, trowel a layer on and set the lid on it. Tap it down to drive out air bubbles and cause the kiln wash to flow into all the nooks and crannies. 

Remember to butter the tops of the walls and joint surface of the lid so whatever you're cementing them together with, bonds properly. I've explained Buttering masonry joints and such in depth already, a search should turn it up and I've already gotten too rambly. No need to write another few hundred words today.

Frosty The Lucky.

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What I did where the "dome" meets the floor on my D shaped forge is use a couple strips of fiber blanket which were sprayed with rigidizer to make a gasket of sorts.  This makes removal of the top portion easy when needed but also provides a "flame tight" connection between the two slightly irregular surfaces.

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My thought exactly Mike but better expressed.

With an adequate work opening, the joints in walls and lids would have to be pretty large for flame to pass. Mine shoots flames in a number of unexpected places if the doorway is blocked completely.

Frosty The Lucky.

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Thank you for everyones responses sofar. Im glad my overall design hasn't been completely torn apart. I just need to tweak a few things like the door situation. 

 

A question I didnt include as much in detail was the forge length. Currently with the 10 inch length I get 261 in^3. If I raise it to 11 in Its only 287 in^3 or even 12 inches. 

I know from previous posts that 1 well tuned burner is about 300-350 cu^3. Assuming my burner IS well tuned and made properly, I could add more. 

Is there any pro or con to making it slightly longer? Does the extra material act like a heat sink or does it just hold in more heat?

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Keep your forge as small as will serve your purposes. As Thomas says larger costs more in fuel, provides more material to wear out and takes longer to heat up and cool down. 

You only want enough extra room to manipulate your work without poking and scuffing the liner more than necessary.

Frosty The Lucky.

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17 hours ago, Mikey98118 said:

Flame tight is an admirable goal, but flame restrictive may be all you actually need.

This was just for the 2 places where the half cylinder meets the flat floor.  There's no shortage of space for exhaust gases to escape because of the front opening and the rear pass-through.

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