Is it safe to assume, (like for non-blown autos, and house fu\rnaces), that
one loses 3 percent efficiency per 1000 foot of elevation?
So one at 5300 feet above sea level, would have to scale back the rule of
thumb that a 3/4" burner will serve 350 cubic inches of forge? So at that
elevation, a 3/4" burner would be good for about 294 cubic inches?
One of those 5 gallon paint can forges reduced to 5" dia. X 15" long=294.
Should work????? right?
. . . .Also, if one built a forge slighly oversize, and then placed a
firebrick (say, 2X4X6 ) inside the cavity, to reduce the volume by 48 cubic
inches, would that work? IAT. . .
Looks like that at this altitude (5300') I'm limited to a coal forge.
Or spending much $$$$ for propane everyday. Like $20/day for for an
atmospheric forge.. . .(blown forges are too noisy for a city)....
I have to look into a real small propane forge...2.5" diameter by 12 inches
(60 cubic inches)...and well insulated...maybe a 1/2" burner.
I have coal available, but I have never tended a forge fire. So I imagine
I would be doing more fire tending, than metal forming. If I'm lucky enough
to even get the coke formed..
Blown forges are too noisy??? Huh???
Dunno where that tidbit comes from, but the ones I have built and been
around were still quieter than a handcrank blower on a coal forge.
If you use a gas powered leafblower to push the air, maybe, but you
really gotta do some more research. Get out to more hammer-ins or
something like that.
Any smithing or knifemaking groups near you?
Aside from that, if you think that the neighbors are gonna get wierd
on your ass fo a little noise coming from the shop (and it will be the
hammering that they will hear, then), they will get RIGHT bent when they
see the plumes of snotty yellow smoke from the coal coking off!
Tending a coal fire is nothing really, once you get it figured out.
Good coal will make a heck of a difference, too. Find some decent
metalurgical coal if you can.
Say I made a forge from a 5 gallon bucket, and used a 3/4" burner.
Then at this altitude of 5300 feet, with a blower on the burner, I could get
enough 'quiet' heat to do (try) some smithing.
I could even capture waste heat off the forge with a shroud, and 'pump that
to the burner. Then with a 3/4" burner, at this altitude I could have the
350 cubic inch forge.
I read where one man used a solenoid valve on his gas line, so if the fan
lost power, the fuel would shut off... sounds safe.
As you can tell, I'm a newbie. No smithy near me that I know of. There may
be one 35 miles away that I plan to check on when the snow gets below my
Admittedly, this was a few years ago (well, alright, ten). I was living
at 5000 feet and measured how much propane my two burner forge (8" dia.
x 18" long) consumed. It came to $1 per hour. So your estimate doesn't
I'm not sure what altitude has to do with it--for a well tuned forge, it
takes the same amount of propane whatever altitude you're at.
I'm using a 5 gallon bucket with 2" insulation and a single 3/4" Reil
burner (atmospheric). When I lived in Colorado at 5000', it worked just
I wouldn't use a single burner with any larger interior volume though.
No solenoid either.
I generally don't leave my forge running if I'm not in the shop.
The snow was fine in Maine until our tractor broke last week....
You really need to check your math there. You are way off. I don't know
how well a venturi
burner works at that kind of altitude but I would think a 3/4" burner would
work fine on that size of a forge chamber. What you really need to look at
is how well it's insulated. Folks do heat treating in 50 gallon barrels
with a single burner of the size you are talking about. How good is your
burner and how good is your insulation? Those are the things you should
concern yourself with. My forge is about 8x24 inch inside with a T-Rex 3/4"
burner and I don't even have to try hard to pull 2000F. Noise is not even a
If you weld, these are pretty simple.
The burner jet mounting is put in place with a mandril I made. The
mandril is a 3/4" piece of pipe with a rod sticking out one end that is
the same OD as the 1/8" brass pipe I use for gas. There is a larger
diameter stop on it. I screw on a 1-1/2" to 3/4" bell fitting, drop the
jet mounting over the rod and weld on the supports. This way I don't
have to worry about alignment. A lathe helps making this stuff too.
To mount the burner to the forge body, I run a piece of 1" x 3/16" up
the side of the forge, welded in place. The last 4" or so is bent at an
angle so that the burner will point at the center of the forge floor
(you can eyeball this and bend it cold to fit). You may have to tweak
the angle, don't use 1/4" thick stock. Use U bolts to mount the burner
(buy the right size (measure!)).
Be sure to make the tables outside each end of the forge large enough. I
like them about 20" long and 6" wide. You can also run tubing along the
sides of the forge. If you mount two tubes carefully parallel you can
then make a sliding support for longer pieces.
If your insulation on the forge is good enough you can heat it with mapp
gas. besides you're math sucks. or mine does. whatever. IF... you are
serious - build a heat chamber. Start with (ins/kao/whatever)wool, two
inches thick, since you are worried about your torch having the required
balls and if you really want to conserve the heat, coat the inside with ITC.
Keep the access opening small - but not air tight. the exhaust resistance
should be less than the pressure of the gas and air going in. Get a torch
that kicks out a blue or green flame going into it and fire it up. All
that flame and heat soulds so intimidating and complex to folks when they
don't have the experience of it. After first blush it's so simple and
uncomplicated you will wonder what the problems were.
A 5 gallon bucket is HUGE for a forge. A guy could go broke stuffing
enough refractory into it to get the inside space down to a decent size.
To the plus side of that, one could use a couple different types of
refractory and end up with a small enough working area, and have a
minimum of heat escaping through the sides. Of course, with the right
refractory, you could get the same results in a forge that was far
smaller, too. EG using some ceramic foam and ceramic fiber with a
liberal coat of ITC-100, would put you a bit ahead of a firebrick or
castable refractory liner, but at far higher cost.
My forge is mostly plumbed with salvaged BBQ fittings and line. The
reg has been butchered in order to adjust the flow, and there are no
safety features other than a ball valve shut-off and the valve on the
propane tank. It does not get left running unattended. It does not worry
me to be without the safety stuff, but your mileage may vary somewhat on
If you want to try a blown burner, get it out of your head that you
should be comparing same size burners. A naturally aspirated burner will
be much smaller to get similar flows. The blown burner on mine is made
of 2 inch pipe fittings and nipples from the hardware store, and it
works very well. I made no efforts at theoretical perfection when I made
mine, and built a set of nested pipe sections into the hot end of the
assembly as a flame spreader and keeper. Works great. The naturally
aspirated burner that i made for it was of 1 inch pipe and worked OK as
well but I found that the blown one met my needs and have not
reinstalled the other one.
I made my forge too large, and it is all castable except the floor
liner which is a half-split hard firebrick. When I get around to making
another, it will be far smaller, and I will not bother to put a hole in
the back for long peices, as I can lay them across the front of the
forge and get the same heat. I have not welded with this forge, but have
burnt a few peices badly enough that I have no worries about it's
Picture and text explanation at
I used his design at 400 feet on the western side of the Santa Cruz Mountains.
Very nice and hot.
I suspect their is another issue. He has some monster sized ones...
But I don't use them.
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.