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I am new to blacksmithing, and I just started to make my second forge. This one will be a significant upgrade from my last one; it was cheap and started to break down after a few uses. I am in the process of claying it, but I have no idea how deep to make my firepot. It is a bottom blast forge, has a 2 inch pipe for air supply, and uses charcoal as its fuel source. Any help will be appreciated.

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Welcome aboard Randy, glad to have you. If you'll put your general location in the header you might be surprised how many of the gang live within visiting distance. 

Bottom blast isn't the best for charcoal but it CAN be made to work. There are measurements I don't know in the "Solid fuel forge" section of Iforge. If you're scratch building a forge I highly recommend you take a look at side blast trench forges. They work much better for charcoal and work just fine for coal as well. The JABOD thread is good information and that particular forge is a proven winner. However you can just pile dirt on a table, scoop a trench and go to work. It's really dirt simple. (Sorry I just couldn't resist. I'm bad I know. :P )

Frosty The Lucky.

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I would suggest you go to the solid fuel forge section and read Charles   Stevens thread, "Just a box of dirt"  and start from there. It has been very helpful to me.  Here is the link to that thread:

Also others will chime in and likely start...well nevermind.  Just the more info you can give about the type of forge you have, and it's intended use will be helpful.

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4 inches is good, no less than 3. 4 inches is the depth of mine, mine is also a bottom blast.  I started with charcoal and it worked well, still use it from time to time when coke is in short supply. Put an easy to use air control on it, a slide a or similar, charcoal burns up quick if you don't switch off the air flow between heats and it doesn't need a lot of air.

good luck.

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Also look up the "Tim Lively washtub forge" on the net for a good example of one that is easily home built.  

We can't tell you anything much without knowing a whole lot more about how your forge is built and how you plan to use it.  What are you using as a blower? A picture would help. Measurements could vary by feet given the information provided.  I like charcoal forges to have deep steeply sloping walls to funnel the charcoal into the hot zone and provide a reducing area to heat metal in.  I often stack firebrick into side walls when I use charcoal in a bottom blast forge designed for coal. If you need a wide hot spot a deep firepot helps with a flat forge table and walls far enough apart to take the work piece. You run through a LOT of fuel doing it that way though as pretty much all charcoal on the table will be burning.

 

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TP is the man for making charcoal and bottom blasts play well together, we're 3 1/3-4" from steel ( table top) to top of tuyere work well for sideblast forges with 3/4" schedual 40 pipe tuyere, I understand from TP you may have to go 6-8" with a bottom blast. You still need about 4" of fuel on top of the steel. 

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And Charles is the side blast spokesperson, (almost said "poster child").  So either way we've got you covered!

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Poster child is probably correct

But we have members across the pond that use cosmetically built sideblast forges on any given day. 

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I considered going side blast. Unfortunately, at this point I am committed to bottom blast. So what I understand is that I need to go a bit deeper than a coal forge firepot; I do remember reading this somewhere. I plan on using it to make tools, hooks, etc. and possibly knifes down the road. I am using a 24" charcoal dome bbq. My air source is a blowdryer. I kind of had to work with minimal spending (hard to justify spending money on a forge to my wife. I'm using a 2 inch diameter pipe for my air supply. I read that high air volume with low pressure was the goal. I dont know if these detauls help any.

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Its not so much you need to go deeper, but you need to be able to pile the fuel higher if you need to. My pot is 4 inches deep, I sometimes struggle to get metal into it because it is to deep, you don't need a big fire if your working a long bit of 1/4 inch round, or a knife blade, but sometimes I have to make my fire bigger just to be able to get the but of metal into it I want to work. Some people just have a couple of fire bricks or bits of RHS metal they can put on the sides of the pot to get more depth when needed without build a big fire spilling across your wider table.

But its not hard to modify whatever you do build. It really is a suck it and see exercise for what you are doing.

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With charcoal it's just a gental breeze. You will need to either vent extra air or install a valve of some kind. Also you only need about 6" of fire ball, so about 8" of fuel pile. Anything bigger and your waisting fuel.  

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2 hours ago, Charles R. Stevens said:

With charcoal it's just a gental breeze. You will need to either vent extra air or install a valve of some kind. Also you only need about 6" of fire ball, so about 8" of fuel pile. Anything bigger and your waisting fuel.  

I installed a ball valve to throttle my air supply. Had to use a pvc one or spend $90+ (that would have gotten me into a fair amount of trouble). I think that it will be far enough away to prevent damage. when you say 8" pile is that including the firepot. After reading these posts I was thinking about around 5" on the depth. I hadnt thought about using firebrick to increase depth if needed. On the other hand, if I need it shallower I still have some extra refractory mix.

Thanks for the help so far everyone.

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8" is total depth of the pile measuring from the air grate up. Put your PVC valve by the blow drier it'll be fine, the air blowing through will keep both cool and without air the fire will die down.

You don't need refractory mix for a charcoal or coal fire, fire resistant is fine. You can simply ram damp clay with a wood mallet for the fire pot and table. I run a "duck's nest" rivet forge. It's a shallow cast iron or sheet steel pan with an air port in the center covered by an air grate. You can build the fire directly on the sheet steel pans but many of the cast iron pans say "clay before using." Ram a layer of damp dirt or clay in the pan. Cast iron doesn't like a lot of localized heat, it isn't flexible enough to have the center expand much without cracking the pan. Mine is cracked from the tuyere to one edge but it could've been dropped.

You don't need a lot of clay, enough to make your trench or duck's nest is all. The duck's nest is a spot at the air grate where the clay shallows down to nothing to let the air blast through. I shape and size my fire with fire bricks anywhere from coffee mug size to a raging bonfire say a beehive of coal 18" across and 10" high. Or long and narrow for bending and twisting bar stock. I have full and half bricks handy, my typical fire is between two bricks with a half brick in back call it about 5" wide by 9" long 5" deep. It's a very versatile forge, my favorite for that. 

I'm a gas forge guy though, until just recently good smithing coal was really hard to come by here so I worked out of a gas forge. Over the years though, I've worked out of any kind of fire I could, you don't need anything fancy a fire and a blast is it.

Frosty The Lucky.

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Thanks for the clarification Frosty. I was pretty sure thats what 8" meant, but I wanted to be sure. As for not needing a refactory mix, I allready got the ingredients (perlite, silica sand, and fire clay). So, I might as well us it.

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7 minutes ago, RandyJ said:

Thanks for the clarification Frosty. I was pretty sure thats what 8" meant, but I wanted to be sure. As for not needing a refactory mix, I allready got the ingredients (perlite, silica sand, and fire clay). So, I might as well us it.

You're welcome, my pleasure. Forget the perlite it won't help in a solid fuel forge liner, it'll do more good in the garden. I started to say it couldn't hurt but on second thought it holds water and you don't want your liner holding more water than necessary. I use fire clay and sand to clay mine because I've had this sack of fire clay for probably 30 years now. 

Frosty The Lucky.

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My experiance is a 8" wide fire makes a 6" length to forging heat. How deap, with a bottom blast is a different matter, at least 6" from tuyere to the table. A couple bricks on the sides keep the hot coals from getting away.

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Thanks for the clarification Charles. Thanks again everyone. I will feel alot better when I clay my forge.

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Nice thing about dirt is you can easaly remodel it untile it works for you, and the job at hand

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Randy, your ball valve probably cost more than 10 forges I have built.  You didn't need a ball valve;  just cutting a slot in a piece of PVC pipe and sliding a tapered piece of scrap sheet metal would have worked fine and cost US$0

So if money is an issue STOP SPENDING IT and ask how to do something first! Doing stuff when you don't know what you are doing is not the way to get a good working system on the cheap!  (Too much trial and error involved...)

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I will admit to buying a 3/4" ball valve and black pipe for the JABOD mark II forge...

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I bought a PVC ball valve too.  The fan sucked in dirty shop air and it gunked up so that I had to start lifting weights again to open or close it.  I should have built the awesome gate JHCC made (or the one Denis Frechette showed on YouTube) but I found a 2" aluminum gate valve on Amazon for $7 and the lazy won out.

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Lazy is not always a bad thing, I like once and done solutions. 

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1 hour ago, ThomasPowers said:

Randy, your ball valve probably cost more than 10 forges I have built.  You didn't need a ball valve;  just cutting a slot in a piece of PVC pipe and sliding a tapered piece of scrap sheet metal would have worked fine and cost US$0

So if money is an issue STOP SPENDING IT and ask how to do something first! Doing stuff when you don't know what you are doing is not the way to get a good working system on the cheap!  (Too much trial and error involved...)

oh no man. I did not buy the $90 one. That would have been crazy for what I am building. I bought a $9 dollar pvc one.

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Which is crazy vs the $0 one if your budget is tight.

I get an allowance from my wife for all my vices: coal, scrapmetal, books,vises, beer, steel, tools, fleamarket money, etc. I get it in cash the start of each month and as long as I stay within it I do not have to provide an accounting to SWMBO.  She gets an equal allowance for her Vices: fiber, books, spinning wheels, antique fiber working tools, etc.   When we were first married it was US$5 a week, after 33 years it's up to $25. As we stay within our budget there is always money in savings for "once in a lifetime" deals .

So if I come across as a tightwad; its 3 decades practice of smithing on the cheap and can be a lot of fun figuring out how to do things not spending a lot of money on them. My wife has not worked much during our marriage; but by holding the household budget tightly we have paid off our house and do not have a car payment and can afford for her to fly up to help out with the birth of our 8th grandchild.

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