How thick should my fire pot be?

[Vithonil]

Hello guys,

I am new to this whole thing and wanted to start by welding my own forge together. I have bought 5mm thick steel to make my firepot out of and after my initial research, that seemed to be fine, but after stumbling across more videos (which all appeared after I ordered, of course) I am not so sure about it.

What do you guys think?

Best wishes!

[Irondragon Forge ClayWorks]

To me 5mm (3/16 in) would be a little too thin, 8mm (5/16 in) or 10mm (3/8 in) would be better.

[ThomasPowers]

A lot of it will be longevity, I've used thin firepots before and burnt them out fairly rapidly.

[Vithonil]

What if I insulated the inside of it with some plaster of Paris and sand mixture? I would reduce the size of the fire pot, but would it help with longetivity? 

 

[JHCC]

No, no, NO! Plaster of Paris and sand is a LOUSY forge material: the plaster degrades before it even gets to forging heat, and the resulting spalling can send hot debris in unfortunate directions.

You could in theory add a lining of rammed clay to the inside of the firepot, but it would be such a thin layer that it would break apart pretty easily. You would be much better served by getting some thicker plate for the firepot itself and using the 5mm for the forge pan.

All that said, welcome to IFI! If you haven't yet, please READ THIS FIRST!!

[ThomasPowers]

Any suggestion of using Plaster of Paris in a forge is a massive indicator that the person doesn't know SQUAT about forges and forging and you can probably disregard anything else they say about them.

[JHCC]

Also, check out the JABOD forge threads for ways to make an inexpensive, durable, and adaptable forge for practically nothing.

[Jobtiel1]

Hi, I fabricated my own fire pot as well, I used 2 cm thick plate for the bottom of the firepot, and roughly 7-8 mm plate for the sides of the firepot. I have been practicing forge welding a lot, and my blower is as of currently constantly on while forging. I have noticed no degradation as of yet.

I followed this design: http://www.bamsite.org/firepot.html

Hope this helps.

~Jobtiel

 

[Vithonil]

Thank you guys for all the answers, I got the plaster idea off Youtube where people built a forge out of a BBQ Grill  I didn't want to start out all expensive but after reading what you guys have replied here I did order 10mm thick steel to make my firepot from, I'm not going to touch any plaster or sand!  

Thank you all, I might post a picture of my forge on here once I'm done  Have a good one guys!

[JHCC]

Please do; we love photos. 

Also, nothing wrong with sand; it's the plaster that's the problem. Plaster of Paris is a hydrated form of calcium sulfate, and when it gets heated above about 300°F/150°C, the water trapped in its crystal lattice escapes as steam, with results as described above. Sand, on the other hand, is often used as a component of the filler in traditional side-blast forges; it may melt, but it won't explode.

Interestingly, plaster of Paris has sometimes been used as a fireproofing material in buildings precisely because of how it reacts to heat: the escaping steam can help slow down the fire, and the nonflammable calcium sulfate can help block fire transmission within a structure. However, "fireproof" and "refractory" are NOT the same thing!

[bluerooster]

My fire pot is 3/16" thick because it's what I had on hand when I built it. Actually I built two of them. One deeper than the other.  I used the shallow one for a year or more, before I decided to make the deeper one.   I just let the coal ash fill the corners, and leave it there. It acts as an insulating layer.  The only time I had one glowing hot was when I tried to make the deeper pot shallower by raising the grate, leaving a void between the grate and bottom of the pot.Which filled up with burning coke, and got quite warm when air was introduced.Other than that one time, they both run pretty cool. Even the paint is still on the shallow one.

  When this one burns out, I'll use 3/8" for the next one.

[Yanni Rockitz]

I made my coal forge firepot out of 1/2" plate, 10"x12" and 5" deep -- probably overkill, but that lets me forge big stuff like axes and hammers with a big enough fire and that's why you my eventually just want to make two -- a deep one and a shallow one -- preferably able to pop into and out of the same table, as needed. (Shallow one's next for me -- probably just 8"x10", 3" deep, with some wider flanges around the top to fit the bigger hole in the table -- use that one when I'm heating smaller material -- or just use the propane forge. Options are good!

My big Bertha 5" deep firepot runs the risk of wasting some coal just with its size, so I opted for the more coal-conserving "straight grate" at the bottom rather than a clinker breaker, as clinker breakers tend to also drop good coal through, a bit more. With this grate style, you just have to dig the clinker out with a poker, but it's easy to clear with the poker because the vents are straight, as opposed to drilled holes like in shower drains. Curious to hear anyones' experiences with the different sizes of firepots and grates vs clinker breakers. Thickness of plate is a no brainer -- get the thickest stuff you can swing -- it'll last longer. I can't think of any reason you'd need to go thicker then half an inch or ~12 mil...