Thread: This forge, or that forge....

I'm actually not really sure. But I'll tell you what. I just got a new one and I'll put a timer on for that one. I'll be able to tell you after. I don't forge/heat treat much though so it might take a while for me to find out.

This is a problem that has plagued smiths for years. It will come down to personal preference and that will be based on the job at hand. All the feedback so far is spot on. Maybe the best way to look at this question is to consider what job is being done. Shaping the fire to a specific piece of work gives the advantage to coal/charcoal. Forge welding patterned steels the advantage is gas. The steel does not really care what gets it hot and they will all work to do that job.

But, the smith is obligated to learn how to run the fire, to control the heat in a manner that helps get the work done and does not waste the resource. It is possible to burn steel in coal or charcoal and that means constant attention to the fire and the workpiece. It's been a long time since I've burned steel in a gas fire. But then, the gas fire is controlled to avoid overheating.

One process not mentioned is coking. I was trained in fire operations first when I was a new smith. One job the apprentice did was to make coke for the next day's work. This is a process to take raw coal and burn off the smoky waste products and leave a purer form of carbon. Raw coal stinks and smokes and makes for a bad day working and the contaminants do not help the job get done. There is time and work lost making this transition. Coke is a little hotter and does help in the welding process if done in a coal based fire.

Either way the fuel is a consumed item, the cost of doing business. If the fire is inefficient or the worker ineffective that cost affects the margin of profit. YOu have to treat such things as if they are free, otherwise you will be tempted to do things with too little heat or too little control and the work will suffer eventually.

With the venturi burners I use, a 20 lb bottle typically used for barbecues, doing general forging will last up to three days plus or minus. If I am forge welding maybe a day and a half, but the burner arrangement is more generous and uses more fuel at higher temperatures. Another problem with the small bottles is that the surface area for evaporation is small too. You can't "pull" gas from the bottle and running a small bottle will cool the fuel and reduce evaporation capacity over time. This can be addressed by putting the bottle in some water to prevent the bottle from freezing up and causing an output problem. Buying small bottles is more expensive than buying in bulk.

With the forced air burners, varying degrees of efficiency are present and there are multiple types each with advantages and disadvantages. But now we're back to personal preference or the type of forge you learned on. My recommendation is to use them all and get comfortable with the one that produces the most confidence in getting work done for the type of work you intend. But I think a good smith will be able to use any fire set in front of them (generalist vs. specialist).

For my personal tastes, I am leaning heavily toward gas forging.

The teachers at the New England school seem to lean toward blowers for welding and larger pieces, and plain gas input for the smaller work. If I am going to build my own, I would be using propane, (no NatGas in my area) so I would want as efficient a use of my dollars per gallon as possible.

On the forced air set ups, I have only ever seen single speed blowers. Can they use a variable speed blower to gain more control?

Don't know about gas, but with charcoal, air speed controls the fire.

Mike is indeed spot on about needing to put mind to controlling the fire with coal and charcoal.
A couple of weeks ago I had a bar of O1 in the fire, and got distracted for a minute.
When I pulled it out, it was burning like one of those sparkling fireworks sticks for kids.
when I beat it with a hammer, it just pulverized like a cookie.

Originally Posted by Magpie

...On the forced air set ups, I have only ever seen single speed blowers. Can they use a variable speed blower to gain more control?

Put some sort of valve in the air side of the system, then you can balance air input against gas.

One thing about charcoal - make sure you use "all natural" charcoal - the stuff with the chemical binder doesn't work. I've seen all natural at Target. Back in colonial times, most all smithing was charcoal. The story is, that's where all the trees in the eastern US went - made into charcoal for the village smithy. Can't confirm, but a good story. I use mostly propane, because I haven't developed my fire management skills to a degree that I can do what I want with coal or charcoal. Definitely can be done, and I agree that you can easily build the fire to suit a specific sized project. This has been an interesting thread.

What about nozzle placement?

I have seen forges with the gas being input from above, and with the input from the sides/rear. But I have not seen any with input from the bottom.

Doe the placements have any correlation to size and placement of the opening? (I have seen open front and open front and back) not to mention doors on the front, open fronts, and fronts with "restrictor" doors that shrink the size of the opening, but do not close it completely.

Most coal forges the air intake is from the bottom (the tuyere) through a cast iron artifice with or without a clinker grate. But coal forges and most charcoal forges have been built using a side tuyere. This is not a formal or permanent issue as forge designs can be easily modified to suit the work.

Gas forges have been built in as many different ways as there are sides to them. The "best" way is to bring the burner flame into the forge at a tanget to a circular body so the flame front swirls around the circumference and avoids both hot spots on the side walls of the forge and that the flame front does not directly impinge on the work being heated to avoid scaling away unnecessary material. Once the forge walls heat up, most of the work is done by radiation not direct flame.

I don't think it matters much for coal and charcoal. My air inlet is in the bottom, through a 1/8 metal plate with holes drilled in. The one thing I do think is that having it in the bottom is that the fireflies are blown up instead of swirling around.

Something that I read that made since to me in regards to gas forges & hotspots was to protect your piece (like a razor or knife) with a thin walled pipe that it would fit into. Supposedly the pipe keeps you from burning your piece, would this be true in your opinions?