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Steel plate thickness for a fire pot?


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Hey guys, I have made a 3d model for a fire pot I plan to build, but I was wondering, would the thickness of 1cm (0.393700787)be enough?
At first I thought it would be enough, but now when I think about it, it does seem a bit on the thin side.
I will be burning mostly coke, pet-coke specifically so any info would be appreciated.
I wanted to upload a model, but the forum wouldn't let me attach a .skp file .)

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I`m going to go out on a limb here and say there`s 2 approaches to this.

1-Build to last.
Make it as strong and thick as you can,use appropriate material(like cast iron) and learn how to use it properly.Abusing anything greatly shortens it`s life.
All the old large forges I`ve seen that are in good shape had cast iron fire pots either bolted or carefully fitted and free floating on a steel table plate.
The smaller steel ones were lined with either firebrick or clay and still they didn`t fare near as well.The brick or clay held the moisture and rusted the steel.The throat of these small forges that survived was still cast iron,just the body of the fire pot was steel.

2-Build it for ease of maintenance.
Cast is king for this type of work.If you must make it out of steel plate then line it with something(think farrier`s or rivet forge) or at least build it so that you can replace the firepot instead of trashing the entire forge.
Steel+ direct,intense heat=eventual burn thru and distortion and cracked welds.Plan for this,if you make your welds in the fire pot killer strong and then weld the pot to the table plate with killer strong welds then that distortion has to go somewhere.Guess which formerly flat plate will distort making high and low spots in the formerly flat table.You`ll be replacing the fire pot when it burns out so plan to let it move without taking the table with it.

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Hard to say how long it will last.
That depends on the fuel being used,the type of work(large,heavy forgings require more heat as does forge welding).Do you plan on using this 8-10 hours a day 5-6 days a week or just once a month for about 4-5 hours at a time?Will it be inside a building or left outside with a tarp thrown over it?

Let`s start with what type of work do you plan to do and how often would you be doing it?
Do you plan on using charcoal,coal or coke for fuel?The more you say about where you are headed work wise and what`s available locally for fuel or material the more we can help.

It would be a shame for you to put alot of work into a nice coal forge only to find coal is a problem to get in your area and a nice natural gas forge would be a better fit or that you can get barrels of waste oil for nothing so that might have been where we should have steered you from the start.

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hello aral,

i have made fire pots out of 3/16 steel plate (on the small side for a travel forge) but for a shop
forge it would be better to use 1/4 to 3/8 inch plate. if you need more ideas go to www.blksmth.com then to
his "how to" page. he has plans for welded steel fire pots. i don't weld or fasten my pots to the forge table i
let them "float" helps to save the thinner material of the forge table. my shop forge has a 5/16 plate fire pot and
still looks new after 2 years daily forging.

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Everything`s debatable.
When I said cast was king I was speaking of it`s stability and durability when exposed to heat.I also took into account it`s resistance to oxidation and/or corrosion relative to steel.
Steel might be a better choice if your concerns are ease of fabrication and welding and you intended to line the fire pot and keep the forge under cover.
There are very good and sound reasons for not restricting yourself to only one material but use both where they each excell.
After burning out both steel and stainless grates in one of my forges I went with a cast iron drain grate and had no further trouble.
My intention was to illustrate that there were choices and to extract further information so we could move from generalizations into more constructive advise.To truly give the best suggestions to solve things for Aral in the best way possible for him I,and I assumed others needed more information.

I`d like to hear your side of the debate.I`m always willing to keep an open mind and aspire to never stop learning.I`m sure others would benefit from reading an objective view of both sides too.

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What is your basis for asuming cast iron would work better? When I built my coal forge decades ago, I used mild steel for the clinker breaker even though it was supposed to be cast iron. It is still there. Cast iron melts at a much lower temp than steel (almost a third lower). It is also brittle, hot or cold. Steel is not brittle cold and gets even more ductile when hot. Do you have any empirical evidence that cast iron makes a better firepot?

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Well, I would use the forge lightly, no large and heavy work, and not so often, a week or 2 of a few hours work every few months for now.
And I would be using pet coke, it is the fuel I can get most easily, and it costs me nothing.

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Cast iron will burn out. I have had a few exhaust manifolds brought into my shop for repairs. Some were so burned out after only 5 years that there wasn't anything to weld to. They were all puffed up, and cracked where the majority of the heat was concentrated. Kind of like hard ash, no sparks from the grinder, just dust. My Dad also mentioned how the cast iron grate in their coal furnace at home would get noticeably lighter, and eventually need to be replaced due to burning out.

Does the fire pot in a forge actually get red hot? Never looked at mine while it was going, but I do not think that it ever does, as the fire is well above it. I have 3 factory forges, and all of them are pretty thin 5/16", or so max. The Buffalo is a sheet metal pan with a cast iron pot.

Aral, 1CM is more than sufficient in my estimation. 5MM/6MM would probably be fine.

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The only empirical evidence I have is that all the old cast fire pots I`ve seen have held up far better than the steel ones over time.I realize that many things can contribute to that but the results seem to speak for themselves.
The steel wood stoves I`ve owned,repaired and seen are more prone to weld cracking and distortion if they`re not lined than the unlined CI stoves both old and new especially if the fire gets out of hand.The steel stoves even have cast iron doors because they`re less prone to warp under heat.
When building a poorboy rivet forge most folks will go looking for a CI brake drum or rotor as opposed to grabbing steel from the scrap yard.
If welded steel fire pots are better then why are the bulk of manufactured fire pots still made from cast iron?Seems like a CI pot would be more costly to produce as opposed to a fabbed or drop forged steel one,especially with off shore labor.

As far as exhaust manifolds go.I have no idea why a CI manifold would burn out in 5 years perhaps it came off an import or was made offshore.Following that train of thought wouldn`t the CI heads burn out too.I can`t imagine the manifolds came off a motor with aluminum heads as I know aluminum melts or burns far sooner than cast does.(yes,I know they`re water cooled)
I can tell you that there are cars out of Detroit still sporting the stock CI manifolds going on 40+ years with no burn out.I myself have reworked fishing and work boats that are older than that and the CI manifolds last alot longer than the steel stacks they`re hooked up to.Before you blame it on corrosion,remember that most of these CI manifolds have salt water running thru them to help cool them.Most times they`re replaced because of salt and mineral build up in the jackets.
I have yet to see a set of welded steel headers last as long as a set of stock cast manifolds on any car either I or my buddies have hotrodded.We replaced the cast manifolds with headers for performance,not durability.

I know cast burns out,I`ve had to replace the cast burner on my grill after 10 years.I replaced it with a stainless burner and if that lasts 5 years I`ll be happy.We BBQ alot,My wife shovels snow in order to cook on the grill this time of year.To be fair,the new burner is made from what most would consider sheet metal but it still cost 75% of what I paid for the whole grill.If I could have bought a direct replacement cast burner I would have.

One of the reasons we have so many different materials available is because no single material does all things well.It`s always a compromise.There are reasons that exhaust manifolds are made from cast iron and then hooked up to welded steel tubing and not the other way round.Each has it`s own best application but it takes both to get the job done.
The forge I`m building for my son will have a free floating cast brake drum for a fire pot,steel pipe to the bottom and a steel clinker breaker and ash dump.The grate will be the spare CI drain grate I picked up as a replacement for my forge.These are the things that have proven to work best for me and I hope they hold true for my son.We`ll see.

On to Aral`s questions.Now that we know he will be using coke because it`s plentiful and free and doing only lite to medium work on a limited basis every few months I personally see no reason why he can`t do just fine with what he has planned to do.I would still caution against doing more than bolting the welded fire pot to the table and say that lining will increase the life of the pot.If his work habits change and he outgrows this forge I`m sure he`ll come back here for advice on building an upgraded one.
Good luck Aral,shout if you need more help.
Oh yeah,we expect pictures of the forge and your work.Once you figure that out then maybe you can help me figure out how to post my own.Without my youngest son around to help I`m lost in that regard.My wife wanted to be cropped out of the profile pic but I couldn`t figure how to do that either. :huh:

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My wood stove (sole source of heat) is 32 years old, all steel including the door, and I removed the firebrick years ago for a larger firebox. It has no cracks and has never been welded. It is quite tight and capable of routine overnight burns. The cast iron stove it replaced had been welded numerous times and was so far from airtight that an overnight burn was impossible.
Begining enthusiasts are often advised to use a free brake drum to build their first forge since it is fast, easy, cheap, and requires few tools or skills. They do not work well however, being too large in diameter for most applications, and having vertical sides as opposed to the time proven sixty degree angle. In fact, a brake rotor would make a better, though still not great forge for most beginers.
In the U.S., where the vast majority of foundrys have disapeared, due to OSHA and the EPA, casting is very expensive. "Offshore", it is far cheaper than fabricating, as the equipment costs are lower and workers health and safety and the enviroment are not big concerns. The same was true of items made in this country before the advent of OSHA and the EPA, hence the preponderence of old cast forges and other items.

On to Aral's question. The only question he asked was whether 1 cm thick steel is thick enough for a firepot. It is.

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The manifolds that were burned out in 5 years were off of a Chevrolet Suburban with a small block in it. Had to be before 1993, as that is the year we closed the shop. The customer heard a leak, and when we popped off the stainless heat shields we found the problem. I have sold many exhaust manifolds that went back to the 50's that were still perfect.

Like you said we have different materials available. All cast iron is not the same. There are white, gray, malleable,nodular, etc. grades of cast iron. Some work better for different applications. My guess is an improper grade was used, probably to save money, and it failed. Chevy had a problem with the small block manifolds warping during a time, and had to reinforce the manifolds with a brace between the runners to keep them in place. They were a real PITA to put back on after removing them, as they pulled in so much between the two runners.It usually took a taper on the manifold bolt threads and starting them with the manifold held off of the head in order to get them to line up close enough with the holes. Again poor design for the application. Datsun had a problem with a "Y" shaped 4 cyl manifold that would crack down the middle from warping. Again, poor design/material choice. New stainless headers may outlast the cars nowadays.

My Dad grew up in Detroit during the 20's-30's and told me how the auto companies would take a rough cut on the engine blocks then pile them up outside of the factory to let then season for some time. They did this because a green casting moved too much after it was fully machined. Drag racers would heat cycle new engine castings in an oven to get them fully settled before machining, and assembly.

As to cast iron fire pots, it probably is the cheapest/quickest way to make them, at least overseas. Mold it, cast it, trim it. The reason that bake drums, and rotors get used a lot is that they have the shape, and you can get them for free most of the time. I have a few laying around my place.

Anyhoo this thread has taken a left turn, so to speak. Each material has it's advantages, and disadvantages. Poor design can make a good material fail, and poor material choice can make a good design fail.

Aral, build it, and get forging. As Larry the Cable Guy would say-- Git r done :P

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Hey guys, no worries about the thread going in another direction, it's fine by me, and I like reading all the stuff you posted :)I'll try to model a different design with removable grill and a different way of attaching the fire pot, other than welding it.

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Glad your stove is working so well for you,I hope it continues to give you great service.

You are correct that sealing the cast stoves is a problem.That`s one of the drawbacks of cast components.As a single piece they`re great,try and join them to another and don`t allow for flex or movement and you run into problems.I suspect it`s ridgidity makes it difficult to play well with others even those of the same material.The trick is getting them to assemble properly and work together with no gaps,as with all things.
My father bought a top of the line Vermont Castings wood stove for the sole heating source for their home.He insisted on getting it roaring every morning and frequently had the sides glowing due to inattention.I was not surprised that the gaskets wore out and it leaked air everywhere.Niether was I surprised that the rear baffle plate was burned and cracked when I rebuilt it.That rebuilt stove is still going strong in a neighbor`s shop.Unlike my father Adriano listens to advise about how not to abuse fire related tools.The stove model is a Defiant,I thought it fit my father pretty well.Abuse will kill most anything no matter what it`s made of.
I replaced the Defiant with a new,more efficient steel stove that burns much cleaner and is easier for my wife to manage.She picked it out because it has a window in the front to see the flames.The new stove has an all steel welded body and only 2 cast parts,a floating plate in the bottom and the frame of the door is cast too.Me and the new stove get along fine and I have to admit it was a big improvement over the Defiant.

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