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Fire pot dimensions for coal forge

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I used 1/2” which equates to something like 12.7 mm.  There appear to be several steel fabrication shops in São Paulo. Call them all until you find one willing to let you pick from their scrap pile. If they won’t, remind them you were planning to pay 4-5 x the current scrap price. If that won’t work, see if they will let you pick through their pile for free if you sweep out their shop. 

Actually if you tell them you are looking for steel plate to make an forge so you can begin blacksmithing, they may just let you have anything you want. 

As for how thick?  3/8” is about as low as I would go. But I really don’t know the thinnest which will hold up. I went with 1/2” because it was just what I had. At first I thought it was 3/8” by eyeballing it, but this afternoon I took a tape to some of the left over bits and it is 1/2”. 

Maybe some of the others might know the minimum thickness or optimum thickness. 

While it will not melt, it does rust quickly and flake away. 


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I do have a nearby steel store and they already let me have a lot of scrap they had no use for. Besides the table on my first forge (please don't judge my welding =P), everything else is scrap, including the brake rotor and the smaller plates I used. 

I wanted to know because now that I have a tuyere and a blower, I want to make a better firepot. I'll ask around for 12mm plates, but IDK if'll be able to cut everything with a 4 1/2" angle grinder. Might be cheaper to have them cut it for me and take some scrap along.

The plate I have made my forge from is 6mm and it bends A LOT when I heat the whole think with coke. 


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When I'm buying stock for general use I always as the dealer about: rusty, bent, shorts, off size or damaged stock; as I can almost certainly use it and the price cut can be substantial!  Las time I was buying 1/4" sq stock---my general teaching stock---I ended up cleaning the bin out for the dealer of a lot of "unsaleable" stuff for 1/2 price and every inch of it was usable for me!

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So I was looking into some designs and I settled with Bob's, then I took a second look at my tuyere and the think is large...

The top opening (where the clinker breaker is located) is 4 3/4". And from the distance between the fixing hole (diagonal) is 6 1/2". I think that if I leave it like that, most coke will fall through without even getting a heat... :P

This a really big opening, isn't it? I don't want to leave this tuyere aside. What can I do to adapt it to a firepot design like Bob's?

I thought about having a plate that would fit between the tuyere and the bottom of the firepot, to get rid of the distance without stressing the parts and then have the bottom of the firepot have a smaller hole; We'd only be able to see a small part of the clinker breaker.



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2 hours ago, anvil said:

Check the size of a clinker ball from centaur forge.

they say commercial link removed that it is 2-1/2" long with a 2" wide flat face. 

Following those measurements, mine is 2 3/4" long but has no flat face. The shape is different.

I'm not sure what I should understand from looking at theirs.


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If your twyre is too big for your clinker ball, then a larger ball might be better. It appears that your ball is bigger than centaur forge, so its smaller than yours. .  ;)

I'd try yours and see how it works. It will probably be fine.

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I'm more concerned about the space between the ball and the tubing. Seems a bit too large...

When looking at other examples, I can see that the distance is smaller, avoiding coal/coke falling through.

Some examples I found on Google:

Mild Steel Firepot | Shady Grove Blacksmith

clinker breaker - Google Search | Clinker, Blacksmithing ...

Blacksmith's Blog PostsOld/New, Compact, "Convertible" Solid-Fuel Forge (photo heavy ...


Does it make sense what I'm thinking?

I'm honestly asking because I really don't know much about firepots.


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Depends a lot on the fuel too.  When I use the "local" coal it comes the size of very coarse sand, smaller than pea sized, yet I use it with an open grate as it cokes up into chunks big enough to not fall through.  It does mean I have to be careful to leave enough coked up to start the next fire and start the coking into chunks cycle all over again.

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Unfortunately the coke that I buy here varies a lot of size. Sometimes is small, like 4-5 mm, other times it's quite large like 20-30 mm... 

Would you mind sharing some pictures of your firepot + clinker breaker?

I guess I'd have to go with trial and error... :)


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The air grate on my rivet forge is a slightly domed cast piece with holes. The air grate I prefer on the old too large forge is a simple bar grate, I welded that one up from 1/2" hot rolled round stock with between 3/8" and 1/4" spaces between bars. It replaced my first couple experimental ones and it works much better. It's easy to make smaller or shape the air blast by dropping pieces of 1/2" round stock in the spaces or small pieces of flat stock to block air flow. Cleaning it is as easy as rubbing it with a fire tool in the same direction as the bars. At worst I used the point on the end of the coal rake to pick hard or stuck bits like clinker, stones, etc. out of the gaps.

I don't have a fire pot on my forges, I much prefer a "Duck's nest". It's a shallow, around 4" diameter,  depression, in the clay I ram in the pan. The depression is a little thinner than the thickness of the clay maybe 1" - 1 1/2", like the depression's diameter I don't measure the clay's thickness it's just an eyeball estimate. If I gauge the diameter with a brick if I think it's a little too large. I don't want it more than a brick's width.

A duck's nest allows me to shape the fire in real time, usually I have a brick on edge on each side to form a trough and one laying flat as a porch to rest work on and position it in the fire, placing it from 3 1/2" to maybe 4" above the air grate. Sometimes I block the far end of the trench with a brick, laying flat to support long pieces or on edge to contain the coal / fire. 

If I need a larger fire I can move the bricks outwards to form a wider trench, square or round. Making it deeper is as easy as laying bricks flat and placing bricks on edge making the fire 2 1/4" deeper. 

I can make changes while the fire is lit, sometimes while I'm heating a piece of steel in preparation for the next heat. I rarely work in a fire much larger than about 4" - 6" across but can build it up to the size of the forge pan if I need to.

Frosty The Lucky.

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Thanks a lot for all the inputs guys.

Because of the language barrier I face some difficulty visualizing everything you guys describe, so if you're able to and it's not much work, I'd really appreciate whatever pictures you guys think would be nice to share.

The first thing I though before your post was putting a plate over the opening to reduce the hole diameter. Something along these lines:


But now I'll give some more thought to what you guys shared.

Once again, thanks a lot!

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Hey, guys.

So, two thing.

First, this is the solution I found to avoid the large gap between the ball and the side of the pipe:

What you think?

Also, the model I made looks like this:






It's about 2 1/2" deep. What you guys think?

The steel plate the seller has available is 1010, 1020 and A36. Which one should I go for?

Cheers all!

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21 hours ago, DHarris said:

Is the problem on my end. 

Nope, after I posted the images were gone for me too... 

21 hours ago, DHarris said:

Bolts in a pot, how do they not get permanently fused?

Yeah, that's what I'm currently thinking about. I could go and remove that small "pipe bevel" (IDK how to call it) and make the whole thing touch the bottom plate, or I can weld four big hex headed screws on the under side of the bottom plate - thus not needing to remove the bevel on the tuyere and making the screws head's act as an spacer. IDK which approach would be better, but the former sounds safer.

Also, I went ahead and made another model a bit more like Bob's design: 3 1/2" deep but with sizes adjusted to my tuyere. Here's how the model looks: 


I had a company cut the whole thing down on 1/2" plates for me: 




Don't judge my welding :P

I'm still figuring out how I'm going to cut that square hole on the bottom plate. I'll probably try with my angle grinder, but it might turn out bad. The alternative is having another nearby company plasma cut the piece with the hole for me.

I'm pretty happy with the result. Seems very sturdy even though I eyeballed most of it (as I have almost no tool to weld stuff).


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Why do you want a square hole?  If you are having it plasma cut, they could cut a perfect circle of any size you ask them to. If cutting it with an angle grinder, square would be easier than a circle. 

As for how you connect the tuyere to the pot, I will leave that for someone who actually knows what they are talking about. :D

I think you are going to like the pot. 

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15 hours ago, DHarris said:

Why do you want a square hole?  

Because of the gap between the tuyere's pipe and the clinker ball... stuff will easily fall through, I guess. But maybe that's just something that I'm afraid will happen and, as Thomas said:

On 6/10/2020 at 11:11 AM, ThomasPowers said:

I use it with an open grate as it cokes up into chunks big enough to not fall through

This might be the simpler solution. 

And yes, I'd really some input from the guys who know what they're doing, unlike me, regarding connecting the tuyere to the pot...

I Have No Idea What I'm Doing | Know Your Meme

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I welded short bolts to the bottom of the forge table and drilled matching holes in the flange with the opening for the tuyere. Slip the flange over the bolts and secure them with wing nuts. 

I made the tuyere for that forge from truck exhaust tubing 3" dia for the vertical and 2" for the horizontal that connects to the blower. The flange was 14ga. sheet steel. The air grate just laid over the tuyere, held in place by the rammed clayey soil on the table.

Frosty The Lucky.

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My previous fire pot began life with a grate made of welded sucker rod. It took a long time, maybe two years, but eventually it burnt to the point it wasn’t usable. Rather than weld up another I began to just take bits of failed practice pieces and lay them over the hole as you can see below. I could get several sessions out of them before they needed to be replaced. In the photo, one piece is a terrible bottle opener I never wanted to see again and the other a chain link I had attempted to make. 


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Thanks for the earworm. :blink::lol:

Fired up the forge for the first time this evening. Too wide. It takes an awful lot of fuel to fill it up. Coal is fairly cheap, but hauling my barrels up to Norman to get more and then muscling them down out of the trailer isn’t fun. I will probably buy a third or fourth barrel. I may also make another pot at some point and just use this one for the times I work on thicker stock. That is one of the pluses of having a pot that just drops into the table. 

After almost a year without forging, I seem to have forgotten everything I had learned about how to move metal. That I hadn’t expected. 

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On 6/24/2020 at 11:27 PM, DHarris said:

It takes an awful lot of fuel to fill it up.

I think your dimensions are correct. You control how much coal gets burned by maxing your fire control. This is the purpose of water. Use water to control the size(width) of your fire. With practice you should easily be able to maintain a very narrow slit for heat treating tools and keeping a bunch of say rivits hot when kept in a 1"-1-1/2" length of channel iron, all the way up to max width, and everything in-between. 

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