Hello everyone,

After a good time lurking this forum I decided to finally to build my very own box of dirt! I will follow Charles Stevens' design: 60cm (~24") square box that is 20cm (8") high. The bowl being 15cm(6") at the top and 5cm (2") at the bottom. The tuyere has diameter of 4.5cm (1 3/4") and will sit 3cm (1 1/4") above the bottom of the bowl. And will use charcoal as the fuel.

I will be making two 30x50cm (11"x20") bellows as I cannot find a manual blower at a reasonable price.

As for the dirt I was thinking of using some fire bricks that I have laying around and a 50/50 mixture of plaster of paris and sand to but, I see some people saying it's not a good option for a forge. I thought that a forge fire will not get that much hotter in the outside of the charcoal pile, because I see some people using it for a casting furnace, and so I thought it is a good option for lining the forge. And I do not want to use just sand, because the neighborhood cats will end up using it as a toilet. Unfortunately, other kinds of dirt are not a option at the moment. And thankfully plaster of paris is relatively cheap, the price of a cup of coffee for a bag of 1kg (2.2lbs).

I will be making woodworking related tools and hardware: Chisels, plane irons, hinges, pulls and so on. A hatched and holdfast being the biggest things a can think of I making on this forge.

Taking all of this in consideration, is my forge plan ok? Or is too big/small? Also, can someone say how much charcoal it will use per hour, so I know if a need to order a larger quantity instead of picking a few 5kg bags at the grocery store.

 

Thank you for your attention.

Dimensions look okay, with the exception of the tuyere, which is much too big. 190mm (3/4") is a better bet. Remember that charcoal uses less air than you think. 

Don't use plaster of Paris. If you want to add something to make the sand hold together better, get a bag of cheap, unscented clay cat litter. Pound it up, mix it into the sand, add just barely enough water to moisten it and help it hold its shape, and fill up the box.

If you're worried about cats, make a cover for when the forge is not in use. A tarp or a wooden lid would be fine, as long as you're sure that the fire is completely out before you put on the cover. 

 The thing to remember about both plaster of Paris and Portland cement is that they cure by absorbing water and turning into hydrates. Above a certain temperature, those hydrates break down, the water is released and flashes into steam (sometimes explosively),  and the remaining solids crumble. 

Brazil is rather famous for it's kaolinite and red clays that would work very very much better than plaster of paris which degrades in just campfire conditions. (There is a large expanse of gypsum sands in New Mexico and one way of finding archaeological sites of  indigenous peoples is that their campfires would turn the gypsum sands to plaster of paris and so a later rainstorm would then set the plaster and winds would blow away surround sands leaving a mushroom shaped plaster of paris marker for the site.)

3 hours ago, JHCC said:

Dimensions look okay, with the exception of the tuyere, which is much too big. 190mm (3/4") is a better bet. Remember that charcoal uses less air than you think. 

Don't use plaster of Paris. If you want to add something to make the sand hold together better, get a bag of cheap, unscented clay cat litter. Pound it up, mix it into the sand, add just barely enough water to moisten it and help it hold its shape, and fill up the box.

If you're worried about cats, make a cover for when the forge is not in use. A tarp or a wooden lid would be fine, as long as you're sure that the fire is completely out before you put on the cover. 

I decided to go with a bigger tuyere because it's less work to make it smaller than is to make it bigger afterwards, but since charcoal uses less air, I will go with 3/4".

Oh, now it makes sense on why not use plaster of paris, thank you for the answer!

Yeah, I will have to deal with the cats every now and then (I know I will forget to cover the forge).

Thank you again!

1 hour ago, ThomasPowers said:

Brazil is rather famous for it's kaolinite and red clays that would work very very much better than plaster of paris which degrades in just campfire conditions.

One more for the series "things that my country are quite famous about and I didn't know"! I have to do some digging to see if I can get some clayish material. I will be right thinking that it's ok to mix up some sand with the clay?

Sand or I used to mix wood ashes in with the clay, (and my first degree was geology and so I remember little things like that...)

On 4/17/2017 at 2:12 PM, ThomasPowers said:

Sand or I used to mix wood ashes in with the clay, (and my first degree was geology and so I remember little things like that...)

Well, I don't have any wood ashes in hand (haven't made a barbecue in quite a while, have to fix that soon!) so I will use some construction sand that I have.

And you were right, I dig up a small hole and after the top layer I see something that looks like red clay, looks like I have whole lot of digging in my feature...

Thank you!

You're burning charcoal, right? If you're using coal, use just enough clay to make the sand hold together; more tends to melt and stick to the clinker. This isn't so much of a problem with charcoal, which mostly just makes ash.

1 minute ago, JHCC said:

You're burning charcoal, right? If you're using coal, use just enough clay to make the sand hold together; more tends to melt and stick to the clinker. This isn't so much of a problem with charcoal, which mostly just makes ash.

yep, I'll be burning charcoal.

Okay, good.