firepot depth

[ksb]

In case you don't figure I'm just a wanabe blacksmith. Try to do a little blade work. (use my propane forge for that). Trashed my old brake drum firepot. Just didn't seem to do right. Built a new one outa 1/2 " plate. Appx 10" x 12" at top tapering down to appx 2 1/2 - 3 sq. at bottom , 4 1/2 " deep. More than enough blower. Question is - is that deep enough or too deep for general work. I don't have much experience with coal forges but I like to do some things I can't get in my gas forge. Tried to work some leaf spring the other day and even with it laying flat on the table the 'heat' was below it. Maybe I should pile the coal up higher and turn up the air. Any advice/ideas would be much appreciated. Thanks.

Ken

[Ed Thomas]

Ken:

A friend of mine told me: "A firepot is to fire as a soup pot is to soup." His point, of course, was that the fire should be contained within the firepot, and the firepot should be deep enough to sustain an adequate fire. Your firepot is deep enough, but I'm not sure I've ever seen one with a slope like yours. Good rectangular pots have sloped sides, but seem to have a bit wider bottom... maybe 1/2 the area of the top? However, yours should still work.

My suspicion is that with your configuration, you won't be consuming oxygen as low in the fuel heap as other firepots, so you might want to compensate by mounding the fire higher. Regardless the shape of the firepot, a well-built fire is domed over the firepot, so that the piece of iron to be heated lays flat into the heap with about 2/3 of the fuel below it and 1/3 above it.

If attention to the coal doesn't fix things, then you might have other fire management issues. Coal itself, for instance, isn't directly all that great a fuel for blacksmithing. It should first be converted to coke. Your first fires will do that for you, but if you have lots of flame and smoke, you might have more coal than coke and it will be hard to heat the steel.

You said you have more than enough blower. Do you have specs? A good blower should probably be above 300 scfm. Hollis posted a terrific note on this awhile back but I don't know where. I hope he chimes in shortly.

So... your firepot shape is probably adequate and you have other issues. :)

[irnsrgn]

[ksb]

Ed - the fire had coked down ok. From what you say seem I just don't have coal mounded up enough ( thats what i was woundering about myself) . There wasn't much coal over work piece. Blower is a centrifugal type powered by an electric motor. It appears to have been made for a forge. Wide open it'll just about below the coal out of the pot. It has a damper plus I also have a sliding valve from the other blower on it. I think I just need to adjust coal and air.

Irnsrgn - Good info.. Like 'they' say - a picture is worth a thousand words.

Thanks 'both 'yall.

Ken

[Ed Thomas]

Ken:

It sounds like you got a pretty good handle on it, then. You might want to mound up a bunch of coal,coke and let the blower go at it once the fire is going. If the air is strong and the fuel is good, the fire has a distinctive healthy roar to it. Try all the extremes... what you think is TOO much coal, or TOO much air, and so on. Get a feel for the behavior of your particular forge. They really can be very different sometimes. Sometimes it takes a little effort to find the sweet spots and the fuel/air balance for different heats.

[HWooldridge]

Ken,

I made a pot very similar to yours that worked just fine. I sold it at some point but not because it didn't function.

A good design for a homemade pot built from plate is to have a simple slot in the bottom piece - with no clinker breaker. The slot can be 1/2x3 or so, exact dimensions are not important but small enough that most of your coke won't fall through with the blast turned off.

A good centrifugal blower will often blow the coke out of the pot but only if there is no extra fuel on top. Jr's pictures tell the story better than any words can...although I disagree with the original author's recommendation on a hollow fire - I don't think it's good for much of anything, much less forge welding.