How deep a fire must be?

[LeMarechal]

Hi to all the blacksmiths out there,

is there a rule of thumb how deep a firepot or a fire(coal) should be to get the three zones in a fire? With the three zones I mean, oxydizing, neutral and reducing zone...

 

Greetings

Sascha

[Glenn]

How large is your fire pot?  What size stock and what length stock are you trying to get hot? 

[Irondragon Forge ClayWorks]

For most work we do this firepot works very well.

Bob Patrick Firepot

[Donal Harris]

What about clinker?  That slit looks like it would plug up easily. 

[Irondragon Forge ClayWorks]

Depends upon the coal. Our coal comes from your neighborhood (Vinita) and is fairly clinker free. When a clinker does form (after about 6 hours of forging) we just pull it out with a coal rake & pick up tongs then rebuild the fire. No problem.

[anvil]

A good general rule of thumb is 4" of coke underneath your work and 2" above. 

This will consume the o2 from below and from above and make a good neutral heat wirhin the firepot.

I much prefer a clinker ball to a grate. Then you can remove clinker and ash and not have to rebuild your fire.

[LeMarechal]

Thank you all for your responses,

 

my firepot is about 8" wide and 11" long, but only 2" deep. Lenght and width seems to be ok for my projects. i`m usually working with stocks 1" to 1,5".

2" in thickness is a seldom thing. I´m not thinking about working with heavyer stock in the next time because:

The products I want to produce for the moment must all be portable by hand, hope this describtion make sense. I want to sell this things on christmas markets. So everything must not be to big and heavy.

That´s what I need my firepot for...

 

Well, my coalfire is working well i.e. get all stuff heated up in an adequately time. But I´m just wondering if I can improve it...

BTW... what do you think are the marks for a not deep enough fire?

Greetings Sascha

[ThomasPowers]

Too much oxidation, too easy to burn your steel.

[anvil]

On 5/12/2019 at 12:00 PM, LeMarechal said:

With the three zones I mean, oxydizing, neutral and reducing zone...

Again, you need about 4" of coke under your iron and 2" above to consume the ox and get a neutral fire. 

With proper fire control, and maxing out your firepot, your firepot will only be neutral. 

with good fire control, you can get a smaller fire and then you will have more than one heat "zone" in your firepot.

I have a flat bottomed portable riveting forge, and i can still get my 4" of coke between grate and my iron. and 2" of coke on the top. It has about 4" sides.

[Charles R. Stevens]

Depends on forge design, fuel type, tuyere size and air pressure/volume 

[Cedar Crest Forge]

..proper depth also depends on whether or not you are forge welding.

[pnut]

Can you increase your firepot depth by using some bricks on the left and right sides. 

Pnut (Mike)

[rockstar.esq]

To the OP, be advised that the responses are measured in depths of packed, burning coke.  That's a bigger distinction than it may seem, especially if you're using coke fuel.  

A lot of recommendations to learn "fire maintenance" don't go into specifics.  For example, lots of dry coal will pretty much catch fire wherever it's got airflow near the burning coke.  This is why some smiths wet their coal around the fire's perimeter to keep the fire centralized.  

Burning coke will develop hollows, especially where heated stock and clinkers are removed from above.  If you don't pack burning coke together, air passages will form which makes a fire where stock takes forever to heat up, then suddenly burns in half.  The airflow through the coke acts like a cutting torch.  

There is a pervasive assumption that "hot enough to throw sparks" means the fire will be able to forge weld. Sometimes, stock is sparking because the oxidizing fire is burning through the stock so quickly that the adjacent material can't get to forge welding temperatures before the material is burnt through.